[PATCH 00/12] Introduce `refStorage` extension

[PATCH 00/12] Introduce `refStorage` extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4087 bytes --]

Hi,

this patch series introduces a new `refStorage` extension and related
tooling. While there is only a single user-visible ref backend for now,
this extension will eventually allow us to determine which backend shall
be used for a repository. Furthermore, the series introduces tooling so
that the ref storage format becomes more accessible.

The series is structured as follows:

  - Patches 1 - 3: preliminary refactorings that prepare for the
    introduction of the ref storage format.

  - Patches 4 - 6: wire up the ref format when setting up the repository
    and creating a new one.

  - Patches 7 - 8: introduction of envvars to control the ref format
    globally.

  - Patches 9 - 11: amend our tooling to know how to access and set the
    ref storage format.

  - Patch 12: small patch for t9500 to make it handle ref storage
    extensions in the future.

I've been kind of torn regarding how to name this in the user-facing
parts. Even though the extension is called "refStorage", I rather opted
to use "ref format" in the user-facing parts, which is similar in nature
to the "object format". Changing the extension to be called "refFormat"
would cause issues for JGit though, so it's likely not an option to
change it now.

Anyway, I'd appreciate your thoughts and proposals and am happy to
rename the user-facing parts if we get to a preferable agreement.

This series depends on 18c9cb7524 (builtin/clone: create the refdb with
the correct object format, 2023-12-12) because it relies on the more
careful setup of the repository's refdb during clones.

Thanks!

Patrick

Patrick Steinhardt (12):
  t: introduce DEFAULT_REPO_FORMAT prereq
  worktree: skip reading HEAD when repairing worktrees
  refs: refactor logic to look up storage backends
  setup: start tracking ref storage format when
  setup: set repository's formats on init
  setup: introduce "extensions.refStorage" extension
  setup: introduce GIT_DEFAULT_REF_FORMAT envvar
  t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
  builtin/rev-parse: introduce `--show-ref-format` flag
  builtin/init: introduce `--ref-format=` value flag
  builtin/clone: introduce `--ref-format=` value flag
  t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  4 ++
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  1 +
 repository.h                                  |  6 ++
 setup.c                                       | 63 +++++++++++++++--
 setup.h                                       |  9 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 24 ++++---
 29 files changed, 318 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 01/12] t: introduce DEFAULT_REPO_FORMAT prereq

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1588 bytes --]

A limited number of tests require repositories to have the default
repository format or otherwise they would fail to run, e.g. because they
fail to detect the correct hash function. While the hash function is the
only extension right now that creates problems like this, we are about
to add a second extensions for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended
whenever we add new format extensions. Next to making any such changes
easier on us, the prerequisite's name should also help to clarify the
intent better.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 6a316f081e..de7d3014e4 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 876b99562a..dc03f06b8e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 02/12] worktree: skip reading HEAD when repairing worktrees

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4307 bytes --]

When calling `git init --separate-git-dir=<new-path>` on a preexisting
repository, then we move the Git directory of that repository to the new
path specified by the user. If there are worktrees present in the Git
repository, we need to repair the worktrees so that their gitlinks point
to the new location of the repository.

This repair logic will load repositories via `get_worktrees()`, which
will enumerate up and initialize all worktrees. Part of initialization
is logic that we resolve their respective worktree HEADs, even though
that information may not actually be needed in the end by all callers.

In the context of git-init(1) this is about to become a problem, because
we do not have a repository that was set up via `setup_git_directory()`
or friends. Consequentially, it is not yet fully initialized at the time
of calling `repair_worktrees()`, and properly setting up all parts of
the repository in `init_db()` before we repair worktrees is not an easy
thing to do. While this is okay right now where we only have a single
reference backend in Git, once we gain a second one we would be trying
to look up the worktree HEADs before we have figured out the reference
format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So
let's fix issue this by skipping over the step that reads them.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 worktree.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/worktree.c b/worktree.c
index a56a6c2a3d..9702ed0308 100644
--- a/worktree.c
+++ b/worktree.c
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;
@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);
@@ -118,7 +121,7 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -128,7 +131,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);
@@ -137,7 +140,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}
@@ -151,6 +154,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)
@@ -591,7 +599,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 03/12] refs: refactor logic to look up storage backends

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5190 bytes --]

In order to look up ref storage backends, we're currently using a linked
list of backends, where each backend is expected to set up its `next`
pointer to the next ref storage backend. This is kind of a weird setup
as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in
"refs.c", where each backend is now identified by an integer constant.
Expose functions to translate from those integer constants to the name
and vice versa, which will be required by subsequent patches.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/refs.c b/refs.c
index 16bfa21df7..e87c85897d 100644
--- a/refs.c
+++ b/refs.c
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format && ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+int ref_storage_format_by_name(const char *name)
+{
+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs
@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;
diff --git a/refs.h b/refs.h
index 23211a5ea1..c6571bcf6c 100644
--- a/refs.h
+++ b/refs.h
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *
diff --git a/refs/debug.c b/refs/debug.c
index 83b7a0ba65..b9775f2c37 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ad8b1d143f..43fd0ac760 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index b9fa097a29..8d1090e284 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 4af83bf9a5..8e9f04cc67 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;
diff --git a/repository.h b/repository.h
index 5f18486f64..ea4c488b81 100644
--- a/repository.h
+++ b/repository.h
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 04/12] setup: start tracking ref storage format when

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 9599 bytes --]

In order to discern which ref storage format a repository is supposed to
use we need to start setting up and/or discovering the format. This
needs to happen in two separate code paths.

  - The first path is when we create a repository via `init_db()`. When
    we are re-initializing a preexisting repository we need to retain
    the previously used ref storage format -- if the user asked for a
    different format then this indicates an erorr and we error out.
    Otherwise we either initialize the repository with the format asked
    for by the user or the default format, which currently is the
    "files" backend.

  - The second path is when discovering repositories, where we need to
    read the config of that repository. There is not yet any way to
    configure something other than the "files" backend, so we can just
    blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily
available when needed. As there is only a single backend and because it
is not configurable we cannot yet verify that this tracking works as
expected via tests, but tests will be added in subsequent commits. To
countermand this ommission now though, raise a BUG() in case the ref
storage format is not set up properly in `ref_store_init()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  6 +++---
 refs.h            |  1 +
 repository.c      |  1 +
 repository.h      |  3 +++
 setup.c           | 26 +++++++++++++++++++++++---
 setup.h           |  6 +++++-
 8 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 339af10c10..6840064b59 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1105,7 +1105,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
@@ -1290,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle
diff --git a/builtin/init-db.c b/builtin/init-db.c
index cb727c826f..b6e80feab6 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 
@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }
diff --git a/refs.c b/refs.c
index e87c85897d..d289a5e175 100644
--- a/refs.c
+++ b/refs.c
@@ -2045,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
-		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;
diff --git a/refs.h b/refs.h
index c6571bcf6c..944a67ac1b 100644
--- a/refs.h
+++ b/refs.h
@@ -11,6 +11,7 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int default_ref_storage_format(void);
 int ref_storage_format_by_name(const char *name);
 const char *ref_storage_format_to_name(int ref_storage_format);
 
diff --git a/repository.c b/repository.c
index a7679ceeaa..a75c1598b0 100644
--- a/repository.c
+++ b/repository.c
@@ -184,6 +184,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo->ref_storage_format = format.ref_storage_format;
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */
diff --git a/repository.h b/repository.h
index ea4c488b81..22c30cdbc9 100644
--- a/repository.h
+++ b/repository.h
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 
diff --git a/setup.c b/setup.c
index 155fe13f70..c1bf106379 100644
--- a/setup.c
+++ b/setup.c
@@ -1564,6 +1564,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			the_repository->ref_storage_format =
+				repo_fmt.ref_storage_format;
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */
@@ -1657,6 +1659,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	the_repository->ref_storage_format =
+		fmt->ref_storage_format;
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =
@@ -1897,7 +1901,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();
@@ -1917,6 +1922,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	the_repository->ref_storage_format = ref_storage_format;
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 
@@ -2135,8 +2141,20 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    int ref_storage_format, const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;
@@ -2179,13 +2197,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {
diff --git a/setup.h b/setup.h
index 3f0f17c351..4927abf2cf 100644
--- a/setup.h
+++ b/setup.h
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;
@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }
@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 05/12] setup: set repository's formats on init

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2228 bytes --]

The proper hash algorithm and ref storage format that will be used for a
newly initialized repository will be figured out in `init_db()` via
`validate_hash_algorithm()` and `validate_ref_storage_format()`. Until
now though, we never set up the hash algorithm or ref storage format of
`the_repository` accordingly.

There are only two callsites of `init_db()`, one in git-init(1) and one
in git-clone(1). The former function doesn't care for the formats to be
set up properly because it never access the repository after calling the
function in the first place.

For git-clone(1) it's a different story though, as we call `init_db()`
before listing remote refs. While we do indeed have the wrong hash
function in `the_repository` when `init_db()` sets up a non-default
object format for the repository, it never mattered because we adjust
the hash after learning about the remote's hash function via the listed
refs.

So the current state is correct for the hash algo, but it's not for the
ref storage format because git-clone(1) wouldn't know to set it up
properly. But instead of adjusting only the `ref_storage_format`, set
both the hash algo and the ref storage format so that `the_repository`
is in the correct state when `init_db()` exits. This is fine as we will
adjust the hash later on anyway and makes it easier to reason about the
end state of `the_repository`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/setup.c b/setup.c
index c1bf106379..5dffea6e2f 100644
--- a/setup.c
+++ b/setup.c
@@ -2203,6 +2203,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	the_repository->hash_algo = &hash_algos[repo_fmt.hash_algo];
+	the_repository->ref_storage_format = repo_fmt.ref_storage_format;
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 06/12] setup: introduce "extensions.refStorage" extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 9372 bytes --]

Introduce a new "extensions.refStorage" extension that allows us to
specify the ref storage format used by a repository. For now, the only
supported format is the "files" format, but this list will likely soon
be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around
how exactly this extension should look like. One alternative [1] that
was discussed was whether it would make sense to model the extension in
such a way that backends are arbitrarily stackable. This would allow for
a combined value of e.g. "loose,packed-refs" or "loose,reftable", which
indicates that new refs would be written via "loose" files backend and
compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that
it brings with it is really required for now. It is not foreseeable that
there will be a proliferation of backends in the near-term future, and
the current set of existing formats and formats which are on the horizon
can easily be configured with the much simpler proposal where we have a
single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to
arbitrarily stack the ref formats, then we can adapt the current
extension rather easily. Given that Git clients will refuse any unknown
value for the "extensions.refStorage" extension they would also know to
ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the
extension.

[1]: <pull.1408.git.1667846164.gitgitgadget@gmail.com>

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 23 +++++++++++++---
 setup.h                                       |  3 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 67 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
index bccaec7a96..66db0e15da 100644
--- a/Documentation/config/extensions.txt
+++ b/Documentation/config/extensions.txt
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
diff --git a/Documentation/ref-storage-format.txt b/Documentation/ref-storage-format.txt
new file mode 100644
index 0000000000..1a65cac468
--- /dev/null
+++ b/Documentation/ref-storage-format.txt
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.
diff --git a/Documentation/technical/repository-version.txt b/Documentation/technical/repository-version.txt
index 045a76756f..27be3741e6 100644
--- a/Documentation/technical/repository-version.txt
+++ b/Documentation/technical/repository-version.txt
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).
diff --git a/builtin/clone.c b/builtin/clone.c
index 6840064b59..20c161e94a 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1289,7 +1289,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
diff --git a/setup.c b/setup.c
index 5dffea6e2f..7eb4ae8ea0 100644
--- a/setup.c
+++ b/setup.c
@@ -590,6 +590,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }
@@ -1869,12 +1880,14 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */
@@ -1887,6 +1900,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)
@@ -2028,7 +2045,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");
diff --git a/setup.h b/setup.h
index 4927abf2cf..89033ae1d9 100644
--- a/setup.h
+++ b/setup.h
@@ -180,7 +180,8 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit);
 void create_reference_database(int ref_storage_format,
 			       const char *initial_branch, int quiet);
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 2b78e3be47..38b3e4c39e 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -532,6 +532,32 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
diff --git a/t/test-lib.sh b/t/test-lib.sh
index dc03f06b8e..4685cc3d48 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1937,7 +1937,7 @@ test_lazy_prereq SHA1 '
 '
 
 test_lazy_prereq DEFAULT_REPO_FORMAT '
-	test_have_prereq SHA1
+	test_have_prereq SHA1,REFFILES
 '
 
 # Ensure that no test accidentally triggers a Git command
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 07/12] setup: introduce GIT_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3130 bytes --]

Introduce a new GIT_DEFAULT_REF_FORMAT environment variable that lets
users control the default ref format used by both git-init(1) and
git-clone(1). This is modeled after GIT_DEFAULT_OBJECT_FORMAT, which
does the same thing for the repository's object format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git.txt |  5 +++++
 setup.c               |  7 +++++++
 t/t0001-init.sh       | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 4698d7a42b..0ab19eef3b 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::
diff --git a/setup.c b/setup.c
index 7eb4ae8ea0..8913e30974 100644
--- a/setup.c
+++ b/setup.c
@@ -2160,12 +2160,19 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 
 static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
 {
+	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+
 	if (repo_fmt->version >= 0 &&
 	    format != REF_STORAGE_FORMAT_UNKNOWN &&
 	    format != repo_fmt->ref_storage_format) {
 		die(_("attempt to reinitialize repository with different reference storage format"));
 	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
 		repo_fmt->ref_storage_format = format;
+	} else if (name) {
+		format = ref_storage_format_by_name(name);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), name);
+		repo_fmt->ref_storage_format = format;
 	}
 }
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 38b3e4c39e..30ce752cc1 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -558,6 +558,24 @@ test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown back
 	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 08/12] t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2531 bytes --]

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that
lets developers run the test suite with a different default ref format
without impacting the ref format used by non-test Git invocations. This
is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same
thing for the repository's object format.

Adapt the setup of the `REFFILES` test prerequisite to be conditionally
set based on the default ref format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/README                |  3 +++
 t/test-lib-functions.sh |  5 +++++
 t/test-lib.sh           | 11 ++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/t/README b/t/README
index 36463d0742..621d3b8c09 100644
--- a/t/README
+++ b/t/README
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 03292602fb..61871b2a3b 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 4685cc3d48..fc93aa57e6 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 
@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 09/12] builtin/rev-parse: introduce `--show-ref-format` flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2428 bytes --]

Introduce a new `--show-ref-format` to git-rev-parse(1) that causes it
to print the ref format used by a repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-rev-parse.txt |  3 +++
 builtin/rev-parse.c             |  4 ++++
 t/t1500-rev-parse.sh            | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 912fab9f5e..546faf9017 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index fde8861ca4..99725a6ff1 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -1059,6 +1059,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--show-ref-format")) {
+				puts(ref_storage_format_to_name(the_repository->ref_storage_format));
+				continue;
+			}
 			if (!strcmp(arg, "--end-of-options")) {
 				seen_end_of_options = 1;
 				if (filter & (DO_FLAGS | DO_REVS))
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 3f9e7f62e4..a669e592f1 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 10/12] builtin/init: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4852 bytes --]

Introduce a new `--ref-format` value flag for git-init(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-init.txt |  7 +++++++
 builtin/init-db.c          | 13 ++++++++++++-
 t/t0001-init.sh            | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-init.txt b/Documentation/git-init.txt
index 6f0d2973bf..e8dc645bb5 100644
--- a/Documentation/git-init.txt
+++ b/Documentation/git-init.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 
@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE
diff --git a/builtin/init-db.c b/builtin/init-db.c
index b6e80feab6..770b2822fe 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -58,6 +58,7 @@ static int shared_callback(const struct option *opt, const char *arg, int unset)
 static const char *const init_db_usage[] = {
 	N_("git init [-q | --quiet] [--bare] [--template=<template-directory>]\n"
 	   "         [--separate-git-dir <git-dir>] [--object-format=<format>]\n"
+	   "         [--ref-format=<format>]\n"
 	   "         [-b <branch-name> | --initial-branch=<branch-name>]\n"
 	   "         [--shared[=<permissions>]] [<directory>]"),
 	NULL
@@ -77,8 +78,10 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *ref_format = NULL;
 	const char *initial_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	int init_shared_repository = -1;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
@@ -96,6 +99,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			   N_("override the name of the initial branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
+		OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+			   N_("specify the reference format to use")),
 		OPT_END()
 	};
 
@@ -159,6 +164,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			die(_("unknown hash algorithm '%s'"), object_format);
 	}
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (init_shared_repository != -1)
 		set_shared_repository(init_shared_repository);
 
@@ -237,6 +248,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       ref_storage_format, initial_branch,
 		       init_shared_repository, flags);
 }
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 30ce752cc1..b131d665db 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -576,6 +576,32 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 11/12] builtin/clone: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3995 bytes --]

Introduce a new `--ref-format` value flag for git-clone(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-clone.txt |  6 ++++++
 builtin/clone.c             | 12 +++++++++++-
 t/t5601-clone.sh            | 17 +++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index c37c4a37f7..6e43eb9c20 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.
diff --git a/builtin/clone.c b/builtin/clone.c
index 20c161e94a..b635bbcb43 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -72,6 +72,7 @@ static char *remote_name = NULL;
 static char *option_branch = NULL;
 static struct string_list option_not = STRING_LIST_INIT_NODUP;
 static const char *real_git_dir;
+static const char *ref_format;
 static char *option_upload_pack = "git-upload-pack";
 static int option_verbosity;
 static int option_progress = -1;
@@ -157,6 +158,8 @@ static struct option builtin_clone_options[] = {
 		    N_("any cloned submodules will be shallow")),
 	OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 		   N_("separate git dir from working tree")),
+	OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+		   N_("specify the reference format to use")),
 	OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
 			N_("set config inside the new repository")),
 	OPT_STRING_LIST(0, "server-option", &server_options,
@@ -930,6 +933,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int submodule_progress;
 	int filter_submodules = 0;
 	int hash_algo;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
 
 	struct transport_ls_refs_options transport_ls_refs_options =
@@ -955,6 +959,12 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (option_single_branch == -1)
 		option_single_branch = deepen ? 1 : 0;
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (option_mirror)
 		option_bare = 1;
 
@@ -1106,7 +1116,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * their on-disk data structures.
 	 */
 	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
-		REF_STORAGE_FORMAT_UNKNOWN, NULL,
+		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 47eae641f0..fb1b9c686d 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH 12/12] t9500: write "extensions.refstorage" into config

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1309 bytes --]

In t9500 we're writing a custom configuration that sets up gitweb. This
requires us manually ensure that the repository format is configured as
required, including both the repository format version and extensions.
With the introduction of the "extensions.refStorage" extension we need
to update the test to also write this new one.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t9500-gitweb-standalone-no-errors.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index 0333065d4d..7679780fb8 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]
@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Junio C Hamano]

There is a topic in-flight that introduces the .compat_hash_algo
member to the repo_fmt structure.  Seeing a conflict resolution like
the attached (there are many others that are similar in spirit), I
have to wonder if we want to add repo_set_ref_storage_format()
helper function.  There are many assignments to .ref_storage_format
member after this series is applied.

Note that I haven't read the series in full, so take the above with
a grain of salt---it might turn out to be that direct assignment is
more desirable, I dunno.

Thanks.

diff --cc setup.c
index 2f4571c12a,5038e78cdd..0000000000
--- i/setup.c
+++ w/setup.c
@@@ ...
@@@ -1584,8 -1577,8 +1595,10 @@@ const char *setup_git_directory_gently(
  		}
  		if (startup_info->have_repository) {
  			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
 +			repo_set_compat_hash_algo(the_repository,
 +						  repo_fmt.compat_hash_algo);
+ 			the_repository->ref_storage_format =
+ 				repo_fmt.ref_storage_format;
  			the_repository->repository_format_worktree_config =
  				repo_fmt.worktree_config;
  			/* take ownership of repo_fmt.partial_clone */

Re: [PATCH 01/12] t: introduce DEFAULT_REPO_FORMAT prereq

[Karthik Nayak]

Patrick Steinhardt <ps@pks.im> writes:

> A limited number of tests require repositories to have the default
> repository format or otherwise they would fail to run, e.g. because they
> fail to detect the correct hash function. While the hash function is the
> only extension right now that creates problems like this, we are about
> to add a second extensions for the ref format.
>

Nit: s/extensions/extension

> -test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
> +test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
>  	git branch -m q q2 &&
>  	git branch -m q2 q
>  '

My only concern is whether we'll end up blindly adding
DEFAULT_REPO_FORMAT for tests where only SHA1 is a prereq or only where
the new format extension is a prereq.

Re: [PATCH 02/12] worktree: skip reading HEAD when repairing worktrees

[Karthik Nayak]

Patrick Steinhardt <ps@pks.im> writes:

> When calling `git init --separate-git-dir=<new-path>` on a preexisting
> repository, then we move the Git directory of that repository to the new
> path specified by the user. If there are worktrees present in the Git
> repository, we need to repair the worktrees so that their gitlinks point
> to the new location of the repository.
>

Nit: s/then we/we

Re: [PATCH 03/12] refs: refactor logic to look up storage backends

[Karthik Nayak]

Patrick Steinhardt <ps@pks.im> writes:

> +
> +const char *ref_storage_format_to_name(int ref_storage_format)
> +{
> +	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
> +	if (!be)
> +		return "unknown";
> +	return be->name;
> +}
>

Would it make more sense to return NULL here?

> +
>  /*
>   * How to handle various characters in refnames:
>   * 0: An acceptable character for refs
> @@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
>  					const char *gitdir,
>  					unsigned int flags)
>  {
> -	const char *be_name = "files";
> -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
> +	int format = REF_STORAGE_FORMAT_FILES;
> +	const struct ref_storage_be *be = find_ref_storage_backend(format);
>  	struct ref_store *refs;
>
>  	if (!be)
> -		BUG("reference backend %s is unknown", be_name);
> +		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
>

This doesn't really get us more information, since be == NULL, calling
`ref_storage_format_to_name` will again call `find_ref_storage_backend`,
which will be NULL. I wonder if its better to:

@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct
repository *repo,
                     const char *gitdir,
                     unsigned int flags)
  {
 -	const char *be_name = "files";
 -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
 +	int format = REF_STORAGE_FORMAT_FILES;
 +	const struct ref_storage_be *be = find_ref_storage_backend(format);
     struct ref_store *refs;

     if (!be)
 -		BUG("reference backend %s is unknown", be_name);
 +		BUG("reference backend is unknown");

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Karthik Nayak]

Patrick Steinhardt <ps@pks.im> writes:

> In order to discern which ref storage format a repository is supposed to
> use we need to start setting up and/or discovering the format. This
> needs to happen in two separate code paths.
>
>   - The first path is when we create a repository via `init_db()`. When
>     we are re-initializing a preexisting repository we need to retain
>     the previously used ref storage format -- if the user asked for a
>     different format then this indicates an erorr and we error out.

Nit: s/erorr/error

> diff --git a/refs.c b/refs.c
> index e87c85897d..d289a5e175 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -2045,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
>  					const char *gitdir,
>  					unsigned int flags)
>  {
> -	int format = REF_STORAGE_FORMAT_FILES;
> -	const struct ref_storage_be *be = find_ref_storage_backend(format);
> +	const struct ref_storage_be *be;
>  	struct ref_store *refs;
>
> +	be = find_ref_storage_backend(repo->ref_storage_format);
>  	if (!be)
> -		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
> +		BUG("reference backend is unknown");
>
>  	refs = be->init(repo, gitdir, flags);
>  	return refs;
> diff --git a/refs.h b/refs.h
> index c6571bcf6c..944a67ac1b 100644
> --- a/refs.h
> +++ b/refs.h
> @@ -11,6 +11,7 @@ struct string_list;
>  struct string_list_item;
>  struct worktree;
>
> +int default_ref_storage_format(void);
>

Is this used/defined somewhere?

Re: [PATCH 12/12] t9500: write "extensions.refstorage" into config

[Karthik Nayak]

Patrick Steinhardt <ps@pks.im> writes:

> In t9500 we're writing a custom configuration that sets up gitweb. This
> requires us manually ensure that the repository format is configured as
>

Nit: s/requires us/requires us to/

Re: [PATCH 00/12] Introduce `refStorage` extension

[Karthik Nayak]

Hello,

Patrick Steinhardt <ps@pks.im> writes:
> Hi,
>
> this patch series introduces a new `refStorage` extension and related
> tooling. While there is only a single user-visible ref backend for now,
> this extension will eventually allow us to determine which backend shall
> be used for a repository. Furthermore, the series introduces tooling so
> that the ref storage format becomes more accessible.

Apart from small nits, the series looks good to me, thanks!

Re: [PATCH 00/12] Introduce `refStorage` extension

[Junio C Hamano]

Karthik Nayak <karthik.188@gmail.com> writes:

> Hello,
>
> Patrick Steinhardt <ps@pks.im> writes:
>> Hi,
>>
>> this patch series introduces a new `refStorage` extension and related
>> tooling. While there is only a single user-visible ref backend for now,
>> this extension will eventually allow us to determine which backend shall
>> be used for a repository. Furthermore, the series introduces tooling so
>> that the ref storage format becomes more accessible.
>
> Apart from small nits, the series looks good to me, thanks!

Thanks.  Hopefully we can merge it down after a quick, small, and
final reroll?

Re: [PATCH 01/12] t: introduce DEFAULT_REPO_FORMAT prereq

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 724 bytes --]

On Fri, Dec 22, 2023 at 03:41:10AM -0800, Karthik Nayak wrote:
> Patrick Steinhardt <ps@pks.im> writes:
[snip]
> > -test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
> > +test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
> >  	git branch -m q q2 &&
> >  	git branch -m q2 q
> >  '
> 
> My only concern is whether we'll end up blindly adding
> DEFAULT_REPO_FORMAT for tests where only SHA1 is a prereq or only where
> the new format extension is a prereq.

Yeah, this is of course a possibility with this new prereq. I don't
really know what to do about it though, and think that it does serve a
sensible purpose. So... dunno.

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 03/12] refs: refactor logic to look up storage backends

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2044 bytes --]

On Fri, Dec 22, 2023 at 04:38:30AM -0800, Karthik Nayak wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > +
> > +const char *ref_storage_format_to_name(int ref_storage_format)
> > +{
> > +	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
> > +	if (!be)
> > +		return "unknown";
> > +	return be->name;
> > +}
> >
> 
> Would it make more sense to return NULL here?

The only purpose of this function will be to print error messages, so
"unknown" seems like the better choice.

> >  /*
> >   * How to handle various characters in refnames:
> >   * 0: An acceptable character for refs
> > @@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
> >  					const char *gitdir,
> >  					unsigned int flags)
> >  {
> > -	const char *be_name = "files";
> > -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
> > +	int format = REF_STORAGE_FORMAT_FILES;
> > +	const struct ref_storage_be *be = find_ref_storage_backend(format);
> >  	struct ref_store *refs;
> >
> >  	if (!be)
> > -		BUG("reference backend %s is unknown", be_name);
> > +		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
> >
> 
> This doesn't really get us more information, since be == NULL, calling
> `ref_storage_format_to_name` will again call `find_ref_storage_backend`,
> which will be NULL. I wonder if its better to:
> 
> @@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct
> repository *repo,
>                      const char *gitdir,
>                      unsigned int flags)
>   {
>  -	const char *be_name = "files";
>  -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
>  +	int format = REF_STORAGE_FORMAT_FILES;
>  +	const struct ref_storage_be *be = find_ref_storage_backend(format);
>      struct ref_store *refs;
> 
>      if (!be)
>  -		BUG("reference backend %s is unknown", be_name);
>  +		BUG("reference backend is unknown");

Good point, will change.

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1230 bytes --]

On Fri, Dec 22, 2023 at 05:09:37AM -0800, Karthik Nayak wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> > diff --git a/refs.c b/refs.c
> > index e87c85897d..d289a5e175 100644
> > --- a/refs.c
> > +++ b/refs.c
> > @@ -2045,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
> >  					const char *gitdir,
> >  					unsigned int flags)
> >  {
> > -	int format = REF_STORAGE_FORMAT_FILES;
> > -	const struct ref_storage_be *be = find_ref_storage_backend(format);
> > +	const struct ref_storage_be *be;
> >  	struct ref_store *refs;
> >
> > +	be = find_ref_storage_backend(repo->ref_storage_format);
> >  	if (!be)
> > -		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
> > +		BUG("reference backend is unknown");
> >
> >  	refs = be->init(repo, gitdir, flags);
> >  	return refs;
> > diff --git a/refs.h b/refs.h
> > index c6571bcf6c..944a67ac1b 100644
> > --- a/refs.h
> > +++ b/refs.h
> > @@ -11,6 +11,7 @@ struct string_list;
> >  struct string_list_item;
> >  struct worktree;
> >
> > +int default_ref_storage_format(void);
> >
> 
> Is this used/defined somewhere?

No, it's a leftover from a previous iteration. Will drop.

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1629 bytes --]

On Wed, Dec 20, 2023 at 10:30:28AM -0800, Junio C Hamano wrote:
> There is a topic in-flight that introduces the .compat_hash_algo
> member to the repo_fmt structure.  Seeing a conflict resolution like
> the attached (there are many others that are similar in spirit), I
> have to wonder if we want to add repo_set_ref_storage_format()
> helper function.  There are many assignments to .ref_storage_format
> member after this series is applied.
> 
> Note that I haven't read the series in full, so take the above with
> a grain of salt---it might turn out to be that direct assignment is
> more desirable, I dunno.
> 
> Thanks.

Wrapping this in a `repo_set_ref_storage_format()` doesn't add much for
now, but on the other hand it also doesn't hurt and is more in line with
how we set the other formats. This could also be useful in the future to
have a central place for additional sanity checks, if required. So yeah,
let's do it.

Makes me wonder whether we should then also add the following diff to
"setup: set repository's format on init" when both topics are being
merged together:

diff --git a/setup.c b/setup.c
index 3d980814bc..3d35c78c68 100644
--- a/setup.c
+++ b/setup.c
@@ -2210,6 +2210,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	 * format we can update the repository's settings accordingly.
 	 */
 	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_compat_hash_algo(the_repository, repo_fmt.compat_hash_algo);
 	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 00/12] Introduce `refStorage` extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 12827 bytes --]

Hi,

this is the second version of my patch series that introduces the new
`refStorage` extension. This extension will be used for the upcoming
reftable backend.

Changes compared to v2:

  - Fixed various typos in commit messages.

  - Fixed redundant information when the refstorage extension's value
    isn't understood.

  - Introduced `repo_set_ref_storage_format()`.

Thanks for the feedback so far!

Patrick

Patrick Steinhardt (12):
  t: introduce DEFAULT_REPO_FORMAT prereq
  worktree: skip reading HEAD when repairing worktrees
  refs: refactor logic to look up storage backends
  setup: start tracking ref storage format
  setup: set repository's formats on init
  setup: introduce "extensions.refStorage" extension
  setup: introduce GIT_DEFAULT_REF_FORMAT envvar
  t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
  builtin/rev-parse: introduce `--show-ref-format` flag
  builtin/init: introduce `--ref-format=` value flag
  builtin/clone: introduce `--ref-format=` value flag
  t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  3 +
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  6 ++
 repository.h                                  |  7 ++
 setup.c                                       | 63 +++++++++++++++--
 setup.h                                       |  9 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 24 ++++---
 29 files changed, 323 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

Range-diff against v1:
 1:  239ca38efd !  1:  3613439cb7 t: introduce DEFAULT_REPO_FORMAT prereq
    @@ Commit message
         repository format or otherwise they would fail to run, e.g. because they
         fail to detect the correct hash function. While the hash function is the
         only extension right now that creates problems like this, we are about
    -    to add a second extensions for the ref format.
    +    to add a second extension for the ref format.
     
         Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended
         whenever we add new format extensions. Next to making any such changes
 2:  e895091025 !  2:  ecf4f1ddee worktree: skip reading HEAD when repairing worktrees
    @@ Commit message
         worktree: skip reading HEAD when repairing worktrees
     
         When calling `git init --separate-git-dir=<new-path>` on a preexisting
    -    repository, then we move the Git directory of that repository to the new
    -    path specified by the user. If there are worktrees present in the Git
    -    repository, we need to repair the worktrees so that their gitlinks point
    -    to the new location of the repository.
    +    repository, we move the Git directory of that repository to the new path
    +    specified by the user. If there are worktrees present in the repository,
    +    we need to repair the worktrees so that their gitlinks point to the new
    +    location of the repository.
     
         This repair logic will load repositories via `get_worktrees()`, which
         will enumerate up and initialize all worktrees. Part of initialization
    @@ Commit message
         format, which does not work.
     
         We do not require the worktree HEADs at all to repair worktrees. So
    -    let's fix issue this by skipping over the step that reads them.
    +    let's fix this issue by skipping over the step that reads them.
     
         Signed-off-by: Patrick Steinhardt <ps@pks.im>
     
 3:  f712d5ef5b !  3:  12329b99b7 refs: refactor logic to look up storage backends
    @@ refs.c
     -	for (be = refs_backends; be; be = be->next)
     -		if (!strcmp(be->name, name))
     -			return be;
    -+	if (ref_storage_format && ref_storage_format < ARRAY_SIZE(refs_backends))
    ++	if (ref_storage_format < ARRAY_SIZE(refs_backends))
     +		return refs_backends[ref_storage_format];
      	return NULL;
      }
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      
      	if (!be)
     -		BUG("reference backend %s is unknown", be_name);
    -+		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
    ++		BUG("reference backend is unknown");
      
      	refs = be->init(repo, gitdir, flags);
      	return refs;
 4:  6564659d40 !  4:  ddd099fbaf setup: start tracking ref storage format when
    @@ Metadata
     Author: Patrick Steinhardt <ps@pks.im>
     
      ## Commit message ##
    -    setup: start tracking ref storage format when
    +    setup: start tracking ref storage format
     
         In order to discern which ref storage format a repository is supposed to
         use we need to start setting up and/or discovering the format. This
    @@ Commit message
           - The first path is when we create a repository via `init_db()`. When
             we are re-initializing a preexisting repository we need to retain
             the previously used ref storage format -- if the user asked for a
    -        different format then this indicates an erorr and we error out.
    +        different format then this indicates an error and we error out.
             Otherwise we either initialize the repository with the format asked
             for by the user or the default format, which currently is the
             "files" backend.
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      
     +	be = find_ref_storage_backend(repo->ref_storage_format);
      	if (!be)
    --		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
    -+		BUG("reference backend is unknown");
    - 
    - 	refs = be->init(repo, gitdir, flags);
    - 	return refs;
    -
    - ## refs.h ##
    -@@ refs.h: struct string_list;
    - struct string_list_item;
    - struct worktree;
    - 
    -+int default_ref_storage_format(void);
    - int ref_storage_format_by_name(const char *name);
    - const char *ref_storage_format_to_name(int ref_storage_format);
    + 		BUG("reference backend is unknown");
      
     
      ## repository.c ##
    +@@ repository.c: void repo_set_hash_algo(struct repository *repo, int hash_algo)
    + 	repo->hash_algo = &hash_algos[hash_algo];
    + }
    + 
    ++void repo_set_ref_storage_format(struct repository *repo, int format)
    ++{
    ++	repo->ref_storage_format = format;
    ++}
    ++
    + /*
    +  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
    +  * Return 0 upon success and a non-zero value upon failure.
     @@ repository.c: int repo_init(struct repository *repo,
      		goto error;
      
      	repo_set_hash_algo(repo, format.hash_algo);
    -+	repo->ref_storage_format = format.ref_storage_format;
    ++	repo_set_ref_storage_format(repo, format.ref_storage_format);
      	repo->repository_format_worktree_config = format.worktree_config;
      
      	/* take ownership of format.partial_clone */
    @@ repository.h: struct repository {
      	/* A unique-id for tracing purposes. */
      	int trace2_repo_id;
      
    +@@ repository.h: void repo_set_gitdir(struct repository *repo, const char *root,
    + 		     const struct set_gitdir_args *extra_args);
    + void repo_set_worktree(struct repository *repo, const char *path);
    + void repo_set_hash_algo(struct repository *repo, int algo);
    ++void repo_set_ref_storage_format(struct repository *repo, int format);
    + void initialize_the_repository(void);
    + RESULT_MUST_BE_USED
    + int repo_init(struct repository *r, const char *gitdir, const char *worktree);
     
      ## setup.c ##
     @@ setup.c: const char *setup_git_directory_gently(int *nongit_ok)
      		}
      		if (startup_info->have_repository) {
      			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
    -+			the_repository->ref_storage_format =
    -+				repo_fmt.ref_storage_format;
    ++			repo_set_ref_storage_format(the_repository,
    ++						    repo_fmt.ref_storage_format);
      			the_repository->repository_format_worktree_config =
      				repo_fmt.worktree_config;
      			/* take ownership of repo_fmt.partial_clone */
    @@ setup.c: void check_repository_format(struct repository_format *fmt)
      	check_repository_format_gently(get_git_dir(), fmt, NULL);
      	startup_info->have_repository = 1;
      	repo_set_hash_algo(the_repository, fmt->hash_algo);
    -+	the_repository->ref_storage_format =
    -+		fmt->ref_storage_format;
    ++	repo_set_ref_storage_format(the_repository,
    ++				    fmt->ref_storage_format);
      	the_repository->repository_format_worktree_config =
      		fmt->worktree_config;
      	the_repository->repository_format_partial_clone =
    @@ setup.c: void create_reference_database(const char *initial_branch, int quiet)
      	safe_create_dir(git_path("refs"), 1);
      	adjust_shared_perm(git_path("refs"));
      
    -+	the_repository->ref_storage_format = ref_storage_format;
    ++	repo_set_ref_storage_format(the_repository, ref_storage_format);
      	if (refs_init_db(&err))
      		die("failed to set up refs db: %s", err.buf);
      
 5:  f90a63d63c !  5:  01a1e58a97 setup: set repository's formats on init
    @@ setup.c: int init_db(const char *git_dir, const char *real_git_dir,
     +	 * Now that we have set up both the hash algorithm and the ref storage
     +	 * format we can update the repository's settings accordingly.
     +	 */
    -+	the_repository->hash_algo = &hash_algos[repo_fmt.hash_algo];
    -+	the_repository->ref_storage_format = repo_fmt.ref_storage_format;
    ++	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
    ++	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
     +
      	if (!(flags & INIT_DB_SKIP_REFDB))
      		create_reference_database(repo_fmt.ref_storage_format,
 6:  beeb182f28 =  6:  0a586fa648 setup: introduce "extensions.refStorage" extension
 7:  dd91a75da4 =  7:  6d8754f73a setup: introduce GIT_DEFAULT_REF_FORMAT envvar
 8:  ed3bf008cd =  8:  c645932f3d t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
 9:  8a3d950d69 =  9:  761d647770 builtin/rev-parse: introduce `--show-ref-format` flag
10:  4d98b53553 = 10:  e382b5bf08 builtin/init: introduce `--ref-format=` value flag
11:  71cf0ce827 = 11:  257233658d builtin/clone: introduce `--ref-format=` value flag
12:  bbe2fbb154 ! 12:  b8cd06ec53 t9500: write "extensions.refstorage" into config
    @@ Commit message
         t9500: write "extensions.refstorage" into config
     
         In t9500 we're writing a custom configuration that sets up gitweb. This
    -    requires us manually ensure that the repository format is configured as
    -    required, including both the repository format version and extensions.
    -    With the introduction of the "extensions.refStorage" extension we need
    -    to update the test to also write this new one.
    +    requires us to manually ensure that the repository format is configured
    +    as required, including both the repository format version and
    +    extensions. With the introduction of the "extensions.refStorage"
    +    extension we need to update the test to also write this new one.
     
         Signed-off-by: Patrick Steinhardt <ps@pks.im>
     

base-commit: e79552d19784ee7f4bbce278fe25f93fbda196fa
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 01/12] t: introduce DEFAULT_REPO_FORMAT prereq

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1587 bytes --]

A limited number of tests require repositories to have the default
repository format or otherwise they would fail to run, e.g. because they
fail to detect the correct hash function. While the hash function is the
only extension right now that creates problems like this, we are about
to add a second extension for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended
whenever we add new format extensions. Next to making any such changes
easier on us, the prerequisite's name should also help to clarify the
intent better.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 6a316f081e..de7d3014e4 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 876b99562a..dc03f06b8e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 02/12] worktree: skip reading HEAD when repairing worktrees

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4298 bytes --]

When calling `git init --separate-git-dir=<new-path>` on a preexisting
repository, we move the Git directory of that repository to the new path
specified by the user. If there are worktrees present in the repository,
we need to repair the worktrees so that their gitlinks point to the new
location of the repository.

This repair logic will load repositories via `get_worktrees()`, which
will enumerate up and initialize all worktrees. Part of initialization
is logic that we resolve their respective worktree HEADs, even though
that information may not actually be needed in the end by all callers.

In the context of git-init(1) this is about to become a problem, because
we do not have a repository that was set up via `setup_git_directory()`
or friends. Consequentially, it is not yet fully initialized at the time
of calling `repair_worktrees()`, and properly setting up all parts of
the repository in `init_db()` before we repair worktrees is not an easy
thing to do. While this is okay right now where we only have a single
reference backend in Git, once we gain a second one we would be trying
to look up the worktree HEADs before we have figured out the reference
format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So
let's fix this issue by skipping over the step that reads them.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 worktree.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/worktree.c b/worktree.c
index a56a6c2a3d..9702ed0308 100644
--- a/worktree.c
+++ b/worktree.c
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;
@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);
@@ -118,7 +121,7 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -128,7 +131,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);
@@ -137,7 +140,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}
@@ -151,6 +154,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)
@@ -591,7 +599,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 03/12] refs: refactor logic to look up storage backends

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5129 bytes --]

In order to look up ref storage backends, we're currently using a linked
list of backends, where each backend is expected to set up its `next`
pointer to the next ref storage backend. This is kind of a weird setup
as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in
"refs.c", where each backend is now identified by an integer constant.
Expose functions to translate from those integer constants to the name
and vice versa, which will be required by subsequent patches.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/refs.c b/refs.c
index 16bfa21df7..ab14634731 100644
--- a/refs.c
+++ b/refs.c
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+int ref_storage_format_by_name(const char *name)
+{
+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs
@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;
diff --git a/refs.h b/refs.h
index ff113bb12a..e2098ea51b 100644
--- a/refs.h
+++ b/refs.h
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *
diff --git a/refs/debug.c b/refs/debug.c
index 83b7a0ba65..b9775f2c37 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ad8b1d143f..43fd0ac760 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index b9fa097a29..8d1090e284 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 4af83bf9a5..8e9f04cc67 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;
diff --git a/repository.h b/repository.h
index 5f18486f64..ea4c488b81 100644
--- a/repository.h
+++ b/repository.h
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 04/12] setup: start tracking ref storage format

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 10025 bytes --]

In order to discern which ref storage format a repository is supposed to
use we need to start setting up and/or discovering the format. This
needs to happen in two separate code paths.

  - The first path is when we create a repository via `init_db()`. When
    we are re-initializing a preexisting repository we need to retain
    the previously used ref storage format -- if the user asked for a
    different format then this indicates an error and we error out.
    Otherwise we either initialize the repository with the format asked
    for by the user or the default format, which currently is the
    "files" backend.

  - The second path is when discovering repositories, where we need to
    read the config of that repository. There is not yet any way to
    configure something other than the "files" backend, so we can just
    blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily
available when needed. As there is only a single backend and because it
is not configurable we cannot yet verify that this tracking works as
expected via tests, but tests will be added in subsequent commits. To
countermand this ommission now though, raise a BUG() in case the ref
storage format is not set up properly in `ref_store_init()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  4 ++--
 repository.c      |  6 ++++++
 repository.h      |  4 ++++
 setup.c           | 26 +++++++++++++++++++++++---
 setup.h           |  6 +++++-
 7 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 343f536cf8..48aeb1b90b 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1107,7 +1107,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
@@ -1292,7 +1293,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle
diff --git a/builtin/init-db.c b/builtin/init-db.c
index cb727c826f..b6e80feab6 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 
@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }
diff --git a/refs.c b/refs.c
index ab14634731..be8fcabde0 100644
--- a/refs.c
+++ b/refs.c
@@ -2045,10 +2045,10 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
 		BUG("reference backend is unknown");
 
diff --git a/repository.c b/repository.c
index a7679ceeaa..691cabf45b 100644
--- a/repository.c
+++ b/repository.c
@@ -104,6 +104,11 @@ void repo_set_hash_algo(struct repository *repo, int hash_algo)
 	repo->hash_algo = &hash_algos[hash_algo];
 }
 
+void repo_set_ref_storage_format(struct repository *repo, int format)
+{
+	repo->ref_storage_format = format;
+}
+
 /*
  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
  * Return 0 upon success and a non-zero value upon failure.
@@ -184,6 +189,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */
diff --git a/repository.h b/repository.h
index ea4c488b81..d3a24da4d6 100644
--- a/repository.h
+++ b/repository.h
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 
@@ -202,6 +205,7 @@ void repo_set_gitdir(struct repository *repo, const char *root,
 		     const struct set_gitdir_args *extra_args);
 void repo_set_worktree(struct repository *repo, const char *path);
 void repo_set_hash_algo(struct repository *repo, int algo);
+void repo_set_ref_storage_format(struct repository *repo, int format);
 void initialize_the_repository(void);
 RESULT_MUST_BE_USED
 int repo_init(struct repository *r, const char *gitdir, const char *worktree);
diff --git a/setup.c b/setup.c
index bc90bbd033..e58ab7e786 100644
--- a/setup.c
+++ b/setup.c
@@ -1566,6 +1566,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			repo_set_ref_storage_format(the_repository,
+						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */
@@ -1659,6 +1661,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	repo_set_ref_storage_format(the_repository,
+				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =
@@ -1899,7 +1903,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();
@@ -1919,6 +1924,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	repo_set_ref_storage_format(the_repository, ref_storage_format);
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 
@@ -2137,8 +2143,20 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    int ref_storage_format, const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;
@@ -2181,13 +2199,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {
diff --git a/setup.h b/setup.h
index 3f0f17c351..4927abf2cf 100644
--- a/setup.h
+++ b/setup.h
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;
@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }
@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 05/12] setup: set repository's formats on init

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2231 bytes --]

The proper hash algorithm and ref storage format that will be used for a
newly initialized repository will be figured out in `init_db()` via
`validate_hash_algorithm()` and `validate_ref_storage_format()`. Until
now though, we never set up the hash algorithm or ref storage format of
`the_repository` accordingly.

There are only two callsites of `init_db()`, one in git-init(1) and one
in git-clone(1). The former function doesn't care for the formats to be
set up properly because it never access the repository after calling the
function in the first place.

For git-clone(1) it's a different story though, as we call `init_db()`
before listing remote refs. While we do indeed have the wrong hash
function in `the_repository` when `init_db()` sets up a non-default
object format for the repository, it never mattered because we adjust
the hash after learning about the remote's hash function via the listed
refs.

So the current state is correct for the hash algo, but it's not for the
ref storage format because git-clone(1) wouldn't know to set it up
properly. But instead of adjusting only the `ref_storage_format`, set
both the hash algo and the ref storage format so that `the_repository`
is in the correct state when `init_db()` exits. This is fine as we will
adjust the hash later on anyway and makes it easier to reason about the
end state of `the_repository`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/setup.c b/setup.c
index e58ab7e786..3d980814bc 100644
--- a/setup.c
+++ b/setup.c
@@ -2205,6 +2205,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 06/12] setup: introduce "extensions.refStorage" extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 9372 bytes --]

Introduce a new "extensions.refStorage" extension that allows us to
specify the ref storage format used by a repository. For now, the only
supported format is the "files" format, but this list will likely soon
be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around
how exactly this extension should look like. One alternative [1] that
was discussed was whether it would make sense to model the extension in
such a way that backends are arbitrarily stackable. This would allow for
a combined value of e.g. "loose,packed-refs" or "loose,reftable", which
indicates that new refs would be written via "loose" files backend and
compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that
it brings with it is really required for now. It is not foreseeable that
there will be a proliferation of backends in the near-term future, and
the current set of existing formats and formats which are on the horizon
can easily be configured with the much simpler proposal where we have a
single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to
arbitrarily stack the ref formats, then we can adapt the current
extension rather easily. Given that Git clients will refuse any unknown
value for the "extensions.refStorage" extension they would also know to
ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the
extension.

[1]: <pull.1408.git.1667846164.gitgitgadget@gmail.com>

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 23 +++++++++++++---
 setup.h                                       |  3 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 67 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
index bccaec7a96..66db0e15da 100644
--- a/Documentation/config/extensions.txt
+++ b/Documentation/config/extensions.txt
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
diff --git a/Documentation/ref-storage-format.txt b/Documentation/ref-storage-format.txt
new file mode 100644
index 0000000000..1a65cac468
--- /dev/null
+++ b/Documentation/ref-storage-format.txt
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.
diff --git a/Documentation/technical/repository-version.txt b/Documentation/technical/repository-version.txt
index 045a76756f..27be3741e6 100644
--- a/Documentation/technical/repository-version.txt
+++ b/Documentation/technical/repository-version.txt
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).
diff --git a/builtin/clone.c b/builtin/clone.c
index 48aeb1b90b..0fb3816d0c 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1291,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
diff --git a/setup.c b/setup.c
index 3d980814bc..3aac8c01cd 100644
--- a/setup.c
+++ b/setup.c
@@ -592,6 +592,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }
@@ -1871,12 +1882,14 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */
@@ -1889,6 +1902,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)
@@ -2030,7 +2047,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");
diff --git a/setup.h b/setup.h
index 4927abf2cf..89033ae1d9 100644
--- a/setup.h
+++ b/setup.h
@@ -180,7 +180,8 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit);
 void create_reference_database(int ref_storage_format,
 			       const char *initial_branch, int quiet);
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 2b78e3be47..38b3e4c39e 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -532,6 +532,32 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
diff --git a/t/test-lib.sh b/t/test-lib.sh
index dc03f06b8e..4685cc3d48 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1937,7 +1937,7 @@ test_lazy_prereq SHA1 '
 '
 
 test_lazy_prereq DEFAULT_REPO_FORMAT '
-	test_have_prereq SHA1
+	test_have_prereq SHA1,REFFILES
 '
 
 # Ensure that no test accidentally triggers a Git command
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 07/12] setup: introduce GIT_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3130 bytes --]

Introduce a new GIT_DEFAULT_REF_FORMAT environment variable that lets
users control the default ref format used by both git-init(1) and
git-clone(1). This is modeled after GIT_DEFAULT_OBJECT_FORMAT, which
does the same thing for the repository's object format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git.txt |  5 +++++
 setup.c               |  7 +++++++
 t/t0001-init.sh       | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index bf9e6af695..88e4ed4bd6 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::
diff --git a/setup.c b/setup.c
index 3aac8c01cd..4712bba6f8 100644
--- a/setup.c
+++ b/setup.c
@@ -2162,12 +2162,19 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 
 static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
 {
+	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+
 	if (repo_fmt->version >= 0 &&
 	    format != REF_STORAGE_FORMAT_UNKNOWN &&
 	    format != repo_fmt->ref_storage_format) {
 		die(_("attempt to reinitialize repository with different reference storage format"));
 	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
 		repo_fmt->ref_storage_format = format;
+	} else if (name) {
+		format = ref_storage_format_by_name(name);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), name);
+		repo_fmt->ref_storage_format = format;
 	}
 }
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 38b3e4c39e..30ce752cc1 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -558,6 +558,24 @@ test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown back
 	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 08/12] t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2531 bytes --]

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that
lets developers run the test suite with a different default ref format
without impacting the ref format used by non-test Git invocations. This
is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same
thing for the repository's object format.

Adapt the setup of the `REFFILES` test prerequisite to be conditionally
set based on the default ref format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/README                |  3 +++
 t/test-lib-functions.sh |  5 +++++
 t/test-lib.sh           | 11 ++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/t/README b/t/README
index 36463d0742..621d3b8c09 100644
--- a/t/README
+++ b/t/README
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 5eb57914ab..a3a51ea9e8 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 4685cc3d48..fc93aa57e6 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 
@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 09/12] builtin/rev-parse: introduce `--show-ref-format` flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2428 bytes --]

Introduce a new `--show-ref-format` to git-rev-parse(1) that causes it
to print the ref format used by a repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-rev-parse.txt |  3 +++
 builtin/rev-parse.c             |  4 ++++
 t/t1500-rev-parse.sh            | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 912fab9f5e..546faf9017 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 917f122440..d08987646a 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -1062,6 +1062,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--show-ref-format")) {
+				puts(ref_storage_format_to_name(the_repository->ref_storage_format));
+				continue;
+			}
 			if (!strcmp(arg, "--end-of-options")) {
 				seen_end_of_options = 1;
 				if (filter & (DO_FLAGS | DO_REVS))
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 3f9e7f62e4..a669e592f1 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 10/12] builtin/init: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4852 bytes --]

Introduce a new `--ref-format` value flag for git-init(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-init.txt |  7 +++++++
 builtin/init-db.c          | 13 ++++++++++++-
 t/t0001-init.sh            | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-init.txt b/Documentation/git-init.txt
index 6f0d2973bf..e8dc645bb5 100644
--- a/Documentation/git-init.txt
+++ b/Documentation/git-init.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 
@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE
diff --git a/builtin/init-db.c b/builtin/init-db.c
index b6e80feab6..770b2822fe 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -58,6 +58,7 @@ static int shared_callback(const struct option *opt, const char *arg, int unset)
 static const char *const init_db_usage[] = {
 	N_("git init [-q | --quiet] [--bare] [--template=<template-directory>]\n"
 	   "         [--separate-git-dir <git-dir>] [--object-format=<format>]\n"
+	   "         [--ref-format=<format>]\n"
 	   "         [-b <branch-name> | --initial-branch=<branch-name>]\n"
 	   "         [--shared[=<permissions>]] [<directory>]"),
 	NULL
@@ -77,8 +78,10 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *ref_format = NULL;
 	const char *initial_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	int init_shared_repository = -1;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
@@ -96,6 +99,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			   N_("override the name of the initial branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
+		OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+			   N_("specify the reference format to use")),
 		OPT_END()
 	};
 
@@ -159,6 +164,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			die(_("unknown hash algorithm '%s'"), object_format);
 	}
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (init_shared_repository != -1)
 		set_shared_repository(init_shared_repository);
 
@@ -237,6 +248,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       ref_storage_format, initial_branch,
 		       init_shared_repository, flags);
 }
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 30ce752cc1..b131d665db 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -576,6 +576,32 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 11/12] builtin/clone: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3995 bytes --]

Introduce a new `--ref-format` value flag for git-clone(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-clone.txt |  6 ++++++
 builtin/clone.c             | 12 +++++++++++-
 t/t5601-clone.sh            | 17 +++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index c37c4a37f7..6e43eb9c20 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.
diff --git a/builtin/clone.c b/builtin/clone.c
index 0fb3816d0c..18093d5d16 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -72,6 +72,7 @@ static char *remote_name = NULL;
 static char *option_branch = NULL;
 static struct string_list option_not = STRING_LIST_INIT_NODUP;
 static const char *real_git_dir;
+static const char *ref_format;
 static char *option_upload_pack = "git-upload-pack";
 static int option_verbosity;
 static int option_progress = -1;
@@ -157,6 +158,8 @@ static struct option builtin_clone_options[] = {
 		    N_("any cloned submodules will be shallow")),
 	OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 		   N_("separate git dir from working tree")),
+	OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+		   N_("specify the reference format to use")),
 	OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
 			N_("set config inside the new repository")),
 	OPT_STRING_LIST(0, "server-option", &server_options,
@@ -932,6 +935,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int submodule_progress;
 	int filter_submodules = 0;
 	int hash_algo;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
 
 	struct transport_ls_refs_options transport_ls_refs_options =
@@ -957,6 +961,12 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (option_single_branch == -1)
 		option_single_branch = deepen ? 1 : 0;
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (option_mirror)
 		option_bare = 1;
 
@@ -1108,7 +1118,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * their on-disk data structures.
 	 */
 	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
-		REF_STORAGE_FORMAT_UNKNOWN, NULL,
+		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 47eae641f0..fb1b9c686d 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 12/12] t9500: write "extensions.refstorage" into config

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1312 bytes --]

In t9500 we're writing a custom configuration that sets up gitweb. This
requires us to manually ensure that the repository format is configured
as required, including both the repository format version and
extensions. With the introduction of the "extensions.refStorage"
extension we need to update the test to also write this new one.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t9500-gitweb-standalone-no-errors.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index 0333065d4d..7679780fb8 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]
@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> Makes me wonder whether we should then also add the following diff to
> "setup: set repository's format on init" when both topics are being
> merged together:
>
> diff --git a/setup.c b/setup.c
> index 3d980814bc..3d35c78c68 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -2210,6 +2210,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
>  	 * format we can update the repository's settings accordingly.
>  	 */
>  	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
> +	repo_set_compat_hash_algo(the_repository, repo_fmt.compat_hash_algo);
>  	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
>  
>  	if (!(flags & INIT_DB_SKIP_REFDB))

Shouldn't that come from the series that wants .compat_hash_algo in
the repo_fmt structure, whichever it is, not added by an evil merge?

Re: [PATCH v2 03/12] refs: refactor logic to look up storage backends

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> In order to look up ref storage backends, we're currently using a linked
> list of backends, where each backend is expected to set up its `next`
> pointer to the next ref storage backend. This is kind of a weird setup
> as backends need to be aware of other backends without much of a reason.
>
> Refactor the code so that the array of backends is centrally defined in
> "refs.c", where each backend is now identified by an integer constant.
> Expose functions to translate from those integer constants to the name
> and vice versa, which will be required by subsequent patches.

A small question.  Does this have to be "int", or is "unsigned" (or
even an enum, rewrittenfrom the "REF_STORAGE_FORMAT_*" family of CPP
macro constants) good enough?  I am only wondering what happens when
you clal find_ref_storage_backend() with a negative index.

For that matter, how REF_STORAGE_FORMAT_UNKNOWN (whose value is 0)
is handled by the function also gets curious.  The caller may have
to find that the backend hasn't been specified by receiving an
element in the refs_backends[] array that corresponds to it, but the
error behaviour of this function is also to return NULL, so it has
to be prepared to handle both cases?

> +static const struct ref_storage_be *refs_backends[] = {
> +	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
> +};
> ...
> +static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
>  {
> +	if (ref_storage_format < ARRAY_SIZE(refs_backends))
> +		return refs_backends[ref_storage_format];
>  	return NULL;
>  }

Re: [PATCH v2 02/12] worktree: skip reading HEAD when repairing worktrees

[Eric Sunshine]

On Thu, Dec 28, 2023 at 4:57 AM Patrick Steinhardt <ps@pks.im> wrote:
> When calling `git init --separate-git-dir=<new-path>` on a preexisting
> repository, we move the Git directory of that repository to the new path
> specified by the user. If there are worktrees present in the repository,
> we need to repair the worktrees so that their gitlinks point to the new
> location of the repository.
>
> This repair logic will load repositories via `get_worktrees()`, which
> will enumerate up and initialize all worktrees. Part of initialization
> is logic that we resolve their respective worktree HEADs, even though
> that information may not actually be needed in the end by all callers.
>
> In the context of git-init(1) this is about to become a problem, because
> we do not have a repository that was set up via `setup_git_directory()`
> or friends. Consequentially, it is not yet fully initialized at the time
> of calling `repair_worktrees()`, and properly setting up all parts of
> the repository in `init_db()` before we repair worktrees is not an easy
> thing to do. While this is okay right now where we only have a single
> reference backend in Git, once we gain a second one we would be trying
> to look up the worktree HEADs before we have figured out the reference
> format, which does not work.

s/Consequentially/Consequently/

I found it difficult to digest this paragraph with its foreshadowing
phrase "about to become a problem" since it wasn't apparent until the
very final sentence in the paragraph what the actual problem would be.
Perhaps if you mention early on that the reftable backend will have
trouble with the current code, it would be easier to grasp. Maybe
something like this:

    Although not a problem presently with the file-based reference
    backend, it will become a problem with the upcoming reftable
    backend.  In the context of git-init(1) a fully-materialized
    repository set up via `setup_git_directory()` or friends is not
    yet present.  Consequently, it is not yet fully initialized at the
    time `repair_worktrees()` is called, and properly setting up all
    parts of the repository in `init_db()` before we repair worktrees
    is not an easy task.  With introduction of the reftable backend,
    it would try to look up the worktree HEADs before we have figured
    out the reference format, thus would not work.

> We do not require the worktree HEADs at all to repair worktrees. So
> let's fix this issue by skipping over the step that reads them.
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
> diff --git a/worktree.c b/worktree.c
> @@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
> -static struct worktree *get_main_worktree(void)
> +static struct worktree *get_main_worktree(int skip_reading_head)
>  {
> -       add_head_info(worktree);
> +       if (!skip_reading_head)
> +               add_head_info(worktree);

This is so special-case that it feels more than a little dirty.

> @@ -591,7 +599,7 @@ static void repair_noop(int iserr UNUSED,
>  void repair_worktrees(worktree_repair_fn fn, void *cb_data)
>  {
> -       struct worktree **worktrees = get_worktrees();
> +       struct worktree **worktrees = get_worktrees_internal(1);

In an ideal world, a repair function should not be calling
get_worktrees() at all since get_worktrees() is not tolerant of
corruption of the worktree administrative files. (Plus, as you note,
it does more work than necessary for the current set of repairs
performed by `git worktree repair`.)

Even as I was implementing the worktree repair code, I wavered back
and forth multiple times between calling get_worktrees() and writing a
custom corruption-tolerant function to retrieve worktree
administrative information. In the end, I opted for get_worktrees()
for the pragmatic reason that it allowed me to narrow the scope of the
patches to the types of repairs which were the current focus without
getting mired down in the involved details of writing a
corruption-tolerant function for retrieving worktree metadata.
However, that decision was made with the understanding that the
pragmatic choice of the moment would not rule out the possibility of
returning later and implementing the more correct approach of having a
corruption-tolerant function for retrieving worktree metadata.

The special-case ugliness of this patch suggests strongly in favor of
implementing the earlier-envisioned corruption-tolerant function for
retrieving worktree metadata rather than the band-aid approach taken
by this patch. The generic name get_worktrees_internal() isn't helpful
either; it doesn't do a good job of conveying any particular meaning
to the reader.

Having said all that, I'm not overly opposed to this patch, especially
since your main focus is on getting the reftable backend integrated,
and because the changes (and ugliness) introduced by this patch are
entirely self-contained and private to worktree.c, so are not a
show-stopper by any means. Rather, I wanted to get down to writing
what I think would be a better future approach if someone gets around
to tackling it. (There is no pressing need at the moment, and that
someone doesn't have to be you.)

Re: [PATCH v2 02/12] worktree: skip reading HEAD when repairing worktrees

[Eric Sunshine]

On Thu, Dec 28, 2023 at 1:08 PM Eric Sunshine <sunshine@sunshineco.com> wrote:
> Having said all that, I'm not overly opposed to this patch, especially
> since your main focus is on getting the reftable backend integrated,
> and because the changes (and ugliness) introduced by this patch are
> entirely self-contained and private to worktree.c, so are not a
> show-stopper by any means. Rather, I wanted to get down to writing
> what I think would be a better future approach if someone gets around
> to tackling it. (There is no pressing need at the moment, and that
> someone doesn't have to be you.)

I forgot to mention that, if you reroll for some reason, the
get_worktrees()/get_worktrees_internal() dance might deserve an
in-source NEEDSWORK comment explaining that get_worktrees_internal()
exists to work around the shortcoming that a corruption-tolerant
function for retrieving worktree metadata (for use by the "repair"
function) does not yet exist.

Re: [PATCH 04/12] setup: start tracking ref storage format when

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1450 bytes --]

On Thu, Dec 28, 2023 at 09:15:29AM -0800, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > Makes me wonder whether we should then also add the following diff to
> > "setup: set repository's format on init" when both topics are being
> > merged together:
> >
> > diff --git a/setup.c b/setup.c
> > index 3d980814bc..3d35c78c68 100644
> > --- a/setup.c
> > +++ b/setup.c
> > @@ -2210,6 +2210,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
> >  	 * format we can update the repository's settings accordingly.
> >  	 */
> >  	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
> > +	repo_set_compat_hash_algo(the_repository, repo_fmt.compat_hash_algo);
> >  	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
> >  
> >  	if (!(flags & INIT_DB_SKIP_REFDB))
> 
> Shouldn't that come from the series that wants .compat_hash_algo in
> the repo_fmt structure, whichever it is, not added by an evil merge?

Well, the above code is newly added by my series to ensure that
`init_db()` results in a properly initialized repo upon return. So the
compat hash algo series cannot yet call `repo_set_compat_hash_algo()`
because the code site doesn't exist, whereas my series cannot yet add
the call because there is no compat hash algo yet.

So depending on which series lands first we'll either have to adapt the
respective other series or do an evil merge.

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH v2 03/12] refs: refactor logic to look up storage backends

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2650 bytes --]

On Thu, Dec 28, 2023 at 09:25:55AM -0800, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > In order to look up ref storage backends, we're currently using a linked
> > list of backends, where each backend is expected to set up its `next`
> > pointer to the next ref storage backend. This is kind of a weird setup
> > as backends need to be aware of other backends without much of a reason.
> >
> > Refactor the code so that the array of backends is centrally defined in
> > "refs.c", where each backend is now identified by an integer constant.
> > Expose functions to translate from those integer constants to the name
> > and vice versa, which will be required by subsequent patches.
> 
> A small question.  Does this have to be "int", or is "unsigned" (or
> even an enum, rewrittenfrom the "REF_STORAGE_FORMAT_*" family of CPP
> macro constants) good enough?  I am only wondering what happens when
> you clal find_ref_storage_backend() with a negative index.

No, it does not have to be an `int`, and handling a negative index would
be a bug. I tried to stick to what we have with `GIT_HASH_UNKNOWN`,
`GIT_HASH_SHA1` etc, which is exactly similar in spirit. Whether it's
the perfect way to handle this... probably not. Without the context I
would've used an `enum`, but instead I opted for consistency.

> For that matter, how REF_STORAGE_FORMAT_UNKNOWN (whose value is 0)
> is handled by the function also gets curious.  The caller may have
> to find that the backend hasn't been specified by receiving an
> element in the refs_backends[] array that corresponds to it, but the
> error behaviour of this function is also to return NULL, so it has
> to be prepared to handle both cases?

Yeah, we do not really discern those two cases for now and instead just
return `NULL` both for any unknown ref storage format. All callers know
to handle `NULL`, but the error handling will only report a generic
"unknown" backend error.

The easiest way to discern those cases would be to `BUG()` when being
passed an invalid ref storage format smaller than 0 or larger than the
number of known backends. Because ultimately it is just that, a bug that
shouldn't ever occur.

Not sure whether this is worth a reroll?

Patrick

> > +static const struct ref_storage_be *refs_backends[] = {
> > +	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
> > +};
> > ...
> > +static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
> >  {
> > +	if (ref_storage_format < ARRAY_SIZE(refs_backends))
> > +		return refs_backends[ref_storage_format];
> >  	return NULL;
> >  }

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH v2 02/12] worktree: skip reading HEAD when repairing worktrees

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1132 bytes --]

On Thu, Dec 28, 2023 at 01:13:04PM -0500, Eric Sunshine wrote:
> On Thu, Dec 28, 2023 at 1:08 PM Eric Sunshine <sunshine@sunshineco.com> wrote:
> > Having said all that, I'm not overly opposed to this patch, especially
> > since your main focus is on getting the reftable backend integrated,
> > and because the changes (and ugliness) introduced by this patch are
> > entirely self-contained and private to worktree.c, so are not a
> > show-stopper by any means. Rather, I wanted to get down to writing
> > what I think would be a better future approach if someone gets around
> > to tackling it. (There is no pressing need at the moment, and that
> > someone doesn't have to be you.)
> 
> I forgot to mention that, if you reroll for some reason, the
> get_worktrees()/get_worktrees_internal() dance might deserve an
> in-source NEEDSWORK comment explaining that get_worktrees_internal()
> exists to work around the shortcoming that a corruption-tolerant
> function for retrieving worktree metadata (for use by the "repair"
> function) does not yet exist.

Thanks for sharing your thoughts, will do.

Patrick

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH v2 03/12] refs: refactor logic to look up storage backends

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> Yeah, we do not really discern those two cases for now and instead just
> return `NULL` both for any unknown ref storage format. All callers know
> to handle `NULL`, but the error handling will only report a generic
> "unknown" backend error.
>
> The easiest way to discern those cases would be to `BUG()` when being
> passed an invalid ref storage format smaller than 0 or larger than the
> number of known backends. Because ultimately it is just that, a bug that
> shouldn't ever occur.
>
> Not sure whether this is worth a reroll?

By using an unsigned type, you no longer have to worry about getting
handed a negative index, as the "must be smaller than ARRAY_SIZE()"
check will be sufficient to catch anybody who passes "-1" (casted to
unsigned by parameter passing).  So I would say that would be a good
enough reason to reroll, whether we differentiate 0 and an index
that is larger than refs_backends[] (or a negative one) with an
explicit BUG(), or just leave it to the caller by returning NULL.
As to the error handling, I suspect it is sufficient to return NULL
and let the caller handle it.

Thanks.


>
> Patrick
>
>> > +static const struct ref_storage_be *refs_backends[] = {
>> > +	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
>> > +};
>> > ...
>> > +static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
>> >  {
>> > +	if (ref_storage_format < ARRAY_SIZE(refs_backends))
>> > +		return refs_backends[ref_storage_format];
>> >  	return NULL;
>> >  }

[PATCH v3 00/12] Introduce `refStorage` extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 15642 bytes --]

Hi,

this is the third version of my patch series that introduces the new
`refStorage` extension. This extension will be used for the upcoming
reftable backend.

Changes compared to v3:

  - The `ref_storage_format` is now tracked as an `unsigned int`,
    proposed by Junio.

  - Reworded the commit message in patch 2, proposed by Eric.

  - Added a NEEDSWORK comment to `get_worktrees_internal()`, propose by
    Eric.

Thanks for your reviews!

Patrick

Patrick Steinhardt (12):
  t: introduce DEFAULT_REPO_FORMAT prereq
  worktree: skip reading HEAD when repairing worktrees
  refs: refactor logic to look up storage backends
  setup: start tracking ref storage format
  setup: set repository's formats on init
  setup: introduce "extensions.refStorage" extension
  setup: introduce GIT_DEFAULT_REF_FORMAT envvar
  t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
  builtin/rev-parse: introduce `--show-ref-format` flag
  builtin/init: introduce `--ref-format=` value flag
  builtin/clone: introduce `--ref-format=` value flag
  t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  3 +
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  6 ++
 repository.h                                  |  7 ++
 setup.c                                       | 66 +++++++++++++++--
 setup.h                                       | 10 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 31 +++++---
 29 files changed, 334 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

Range-diff against v2:
 1:  3613439cb7 =  1:  578deaabcf t: introduce DEFAULT_REPO_FORMAT prereq
 2:  ecf4f1ddee !  2:  77c7213c66 worktree: skip reading HEAD when repairing worktrees
    @@ Commit message
         is logic that we resolve their respective worktree HEADs, even though
         that information may not actually be needed in the end by all callers.
     
    -    In the context of git-init(1) this is about to become a problem, because
    -    we do not have a repository that was set up via `setup_git_directory()`
    -    or friends. Consequentially, it is not yet fully initialized at the time
    -    of calling `repair_worktrees()`, and properly setting up all parts of
    -    the repository in `init_db()` before we repair worktrees is not an easy
    -    thing to do. While this is okay right now where we only have a single
    -    reference backend in Git, once we gain a second one we would be trying
    -    to look up the worktree HEADs before we have figured out the reference
    -    format, which does not work.
    +    Although not a problem presently with the file-based reference backend,
    +    it will become a problem with the upcoming reftable backend. In the
    +    context of git-init(1) we do not have a fully-initialized repository set
    +    up via `setup_git_directory()` or friends. Consequently, we do not know
    +    about the repository format when `repair_worktrees()` is called, and
    +    properly setting up all parts of the repositroy in `init_db()` before we
    +    try to repair worktrees is not an easy task. With the introduction of
    +    the reftable backend, we would ultimately try to look up the worktree
    +    HEADs before we have figured out the reference format, which does not
    +    work.
     
         We do not require the worktree HEADs at all to repair worktrees. So
         let's fix this issue by skipping over the step that reads them.
    @@ worktree.c: static void mark_current_worktree(struct worktree **worktrees)
      }
      
     -struct worktree **get_worktrees(void)
    ++/*
    ++ * NEEDSWORK: This function exists so that we can look up metadata of a
    ++ * worktree without trying to access any of its internals like the refdb. It
    ++ * would be preferable to instead have a corruption-tolerant function for
    ++ * retrieving worktree metadata that could be used when the worktree is known
    ++ * to not be in a healthy state, e.g. when creating or repairing it.
    ++ */
     +static struct worktree **get_worktrees_internal(int skip_reading_head)
      {
      	struct worktree **list = NULL;
 3:  12329b99b7 !  3:  47649570bf refs: refactor logic to look up storage backends
    @@ refs.c
     +};
      
     -static struct ref_storage_be *find_ref_storage_backend(const char *name)
    -+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
    ++static const struct ref_storage_be *find_ref_storage_backend(unsigned int ref_storage_format)
      {
     -	struct ref_storage_be *be;
     -	for (be = refs_backends; be; be = be->next)
    @@ refs.c
      	return NULL;
      }
      
    -+int ref_storage_format_by_name(const char *name)
    ++unsigned int ref_storage_format_by_name(const char *name)
     +{
    -+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
    ++	for (unsigned int i = 0; i < ARRAY_SIZE(refs_backends); i++)
     +		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
     +			return i;
     +	return REF_STORAGE_FORMAT_UNKNOWN;
     +}
     +
    -+const char *ref_storage_format_to_name(int ref_storage_format)
    ++const char *ref_storage_format_to_name(unsigned int ref_storage_format)
     +{
     +	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
     +	if (!be)
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      {
     -	const char *be_name = "files";
     -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
    -+	int format = REF_STORAGE_FORMAT_FILES;
    ++	unsigned int format = REF_STORAGE_FORMAT_FILES;
     +	const struct ref_storage_be *be = find_ref_storage_backend(format);
      	struct ref_store *refs;
      
    @@ refs.h: struct string_list;
      struct string_list_item;
      struct worktree;
      
    -+int ref_storage_format_by_name(const char *name);
    -+const char *ref_storage_format_to_name(int ref_storage_format);
    ++unsigned int ref_storage_format_by_name(const char *name);
    ++const char *ref_storage_format_to_name(unsigned int ref_storage_format);
     +
      /*
       * Resolve a reference, recursively following symbolic refererences.
 4:  ddd099fbaf !  4:  837764d0b5 setup: start tracking ref storage format
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      					const char *gitdir,
      					unsigned int flags)
      {
    --	int format = REF_STORAGE_FORMAT_FILES;
    +-	unsigned int format = REF_STORAGE_FORMAT_FILES;
     -	const struct ref_storage_be *be = find_ref_storage_backend(format);
     +	const struct ref_storage_be *be;
      	struct ref_store *refs;
    @@ repository.c: void repo_set_hash_algo(struct repository *repo, int hash_algo)
      	repo->hash_algo = &hash_algos[hash_algo];
      }
      
    -+void repo_set_ref_storage_format(struct repository *repo, int format)
    ++void repo_set_ref_storage_format(struct repository *repo, unsigned int format)
     +{
     +	repo->ref_storage_format = format;
     +}
    @@ repository.h: struct repository {
      	const struct git_hash_algo *hash_algo;
      
     +	/* Repository's reference storage format, as serialized on disk. */
    -+	int ref_storage_format;
    ++	unsigned int ref_storage_format;
     +
      	/* A unique-id for tracing purposes. */
      	int trace2_repo_id;
    @@ repository.h: void repo_set_gitdir(struct repository *repo, const char *root,
      		     const struct set_gitdir_args *extra_args);
      void repo_set_worktree(struct repository *repo, const char *path);
      void repo_set_hash_algo(struct repository *repo, int algo);
    -+void repo_set_ref_storage_format(struct repository *repo, int format);
    ++void repo_set_ref_storage_format(struct repository *repo, unsigned int format);
      void initialize_the_repository(void);
      RESULT_MUST_BE_USED
      int repo_init(struct repository *r, const char *gitdir, const char *worktree);
    @@ setup.c: static int is_reinit(void)
      }
      
     -void create_reference_database(const char *initial_branch, int quiet)
    -+void create_reference_database(int ref_storage_format,
    ++void create_reference_database(unsigned int ref_storage_format,
     +			       const char *initial_branch, int quiet)
      {
      	struct strbuf err = STRBUF_INIT;
    @@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt,
      	}
      }
      
    -+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
    ++static void validate_ref_storage_format(struct repository_format *repo_fmt,
    ++					unsigned int format)
     +{
     +	if (repo_fmt->version >= 0 &&
     +	    format != REF_STORAGE_FORMAT_UNKNOWN &&
    @@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt,
      int init_db(const char *git_dir, const char *real_git_dir,
     -	    const char *template_dir, int hash, const char *initial_branch,
     +	    const char *template_dir, int hash,
    -+	    int ref_storage_format, const char *initial_branch,
    ++	    unsigned int ref_storage_format,
    ++	    const char *initial_branch,
      	    int init_shared_repository, unsigned int flags)
      {
      	int reinit;
    @@ setup.h: struct repository_format {
      	int worktree_config;
      	int is_bare;
      	int hash_algo;
    -+	int ref_storage_format;
    ++	unsigned int ref_storage_format;
      	int sparse_index;
      	char *work_tree;
      	struct string_list unknown_extensions;
    @@ setup.h: void check_repository_format(struct repository_format *fmt);
      
      int init_db(const char *git_dir, const char *real_git_dir,
      	    const char *template_dir, int hash_algo,
    -+	    int ref_storage_format,
    ++	    unsigned int ref_storage_format,
      	    const char *initial_branch, int init_shared_repository,
      	    unsigned int flags);
      void initialize_repository_version(int hash_algo, int reinit);
     -void create_reference_database(const char *initial_branch, int quiet);
    -+void create_reference_database(int ref_storage_format,
    ++void create_reference_database(unsigned int ref_storage_format,
     +			       const char *initial_branch, int quiet);
      
      /*
 5:  01a1e58a97 =  5:  a51da56d9b setup: set repository's formats on init
 6:  0a586fa648 !  6:  a1e03e4392 setup: introduce "extensions.refStorage" extension
    @@ setup.c: static enum extension_result handle_extension(const char *var,
      		data->hash_algo = format;
      		return EXTENSION_OK;
     +	} else if (!strcmp(ext, "refstorage")) {
    -+		int format;
    ++		unsigned int format;
     +
     +		if (!value)
     +			return config_error_nonbool(var);
    @@ setup.c: static int needs_work_tree_config(const char *git_dir, const char *work
      }
      
     -void initialize_repository_version(int hash_algo, int reinit)
    -+void initialize_repository_version(int hash_algo, int ref_storage_format,
    ++void initialize_repository_version(int hash_algo,
    ++				   unsigned int ref_storage_format,
     +				   int reinit)
      {
      	char repo_version_string[10];
    @@ setup.c: static int create_default_files(const char *template_path,
     
      ## setup.h ##
     @@ setup.h: int init_db(const char *git_dir, const char *real_git_dir,
    - 	    int ref_storage_format,
    + 	    unsigned int ref_storage_format,
      	    const char *initial_branch, int init_shared_repository,
      	    unsigned int flags);
     -void initialize_repository_version(int hash_algo, int reinit);
    -+void initialize_repository_version(int hash_algo, int ref_storage_format,
    ++void initialize_repository_version(int hash_algo,
    ++				   unsigned int ref_storage_format,
     +				   int reinit);
    - void create_reference_database(int ref_storage_format,
    + void create_reference_database(unsigned int ref_storage_format,
      			       const char *initial_branch, int quiet);
      
     
 7:  6d8754f73a !  7:  5ffc70e9be setup: introduce GIT_DEFAULT_REF_FORMAT envvar
    @@ Documentation/git.txt: double-quotes and respecting backslash escapes. E.g., the
     
      ## setup.c ##
     @@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
    - 
    - static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
    + static void validate_ref_storage_format(struct repository_format *repo_fmt,
    + 					unsigned int format)
      {
     +	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
     +
 8:  c645932f3d =  8:  13c074acdf t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
 9:  761d647770 =  9:  4ee3c9a2d1 builtin/rev-parse: introduce `--show-ref-format` flag
10:  e382b5bf08 ! 10:  25773e3560 builtin/init: introduce `--ref-format=` value flag
    @@ builtin/init-db.c: int cmd_init_db(int argc, const char **argv, const char *pref
     +	const char *ref_format = NULL;
      	const char *initial_branch = NULL;
      	int hash_algo = GIT_HASH_UNKNOWN;
    -+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
    ++	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
      	int init_shared_repository = -1;
      	const struct option init_db_options[] = {
      		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
11:  257233658d ! 11:  3f1cb6b9e5 builtin/clone: introduce `--ref-format=` value flag
    @@ builtin/clone.c: int cmd_clone(int argc, const char **argv, const char *prefix)
      	int submodule_progress;
      	int filter_submodules = 0;
      	int hash_algo;
    -+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
    ++	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
      	const int do_not_override_repo_unix_permissions = -1;
      
      	struct transport_ls_refs_options transport_ls_refs_options =
12:  b8cd06ec53 = 12:  2e7682b2f3 t9500: write "extensions.refstorage" into config

base-commit: e79552d19784ee7f4bbce278fe25f93fbda196fa
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 01/12] t: introduce DEFAULT_REPO_FORMAT prereq

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1587 bytes --]

A limited number of tests require repositories to have the default
repository format or otherwise they would fail to run, e.g. because they
fail to detect the correct hash function. While the hash function is the
only extension right now that creates problems like this, we are about
to add a second extension for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended
whenever we add new format extensions. Next to making any such changes
easier on us, the prerequisite's name should also help to clarify the
intent better.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 6a316f081e..de7d3014e4 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 876b99562a..dc03f06b8e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 02/12] worktree: skip reading HEAD when repairing worktrees

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4740 bytes --]

When calling `git init --separate-git-dir=<new-path>` on a preexisting
repository, we move the Git directory of that repository to the new path
specified by the user. If there are worktrees present in the repository,
we need to repair the worktrees so that their gitlinks point to the new
location of the repository.

This repair logic will load repositories via `get_worktrees()`, which
will enumerate up and initialize all worktrees. Part of initialization
is logic that we resolve their respective worktree HEADs, even though
that information may not actually be needed in the end by all callers.

Although not a problem presently with the file-based reference backend,
it will become a problem with the upcoming reftable backend. In the
context of git-init(1) we do not have a fully-initialized repository set
up via `setup_git_directory()` or friends. Consequently, we do not know
about the repository format when `repair_worktrees()` is called, and
properly setting up all parts of the repositroy in `init_db()` before we
try to repair worktrees is not an easy task. With the introduction of
the reftable backend, we would ultimately try to look up the worktree
HEADs before we have figured out the reference format, which does not
work.

We do not require the worktree HEADs at all to repair worktrees. So
let's fix this issue by skipping over the step that reads them.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 worktree.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/worktree.c b/worktree.c
index a56a6c2a3d..cc34a3419b 100644
--- a/worktree.c
+++ b/worktree.c
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;
@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);
@@ -118,7 +121,14 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+/*
+ * NEEDSWORK: This function exists so that we can look up metadata of a
+ * worktree without trying to access any of its internals like the refdb. It
+ * would be preferable to instead have a corruption-tolerant function for
+ * retrieving worktree metadata that could be used when the worktree is known
+ * to not be in a healthy state, e.g. when creating or repairing it.
+ */
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;
@@ -128,7 +138,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);
@@ -137,7 +147,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}
@@ -151,6 +161,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)
@@ -591,7 +606,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 03/12] refs: refactor logic to look up storage backends

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 5192 bytes --]

In order to look up ref storage backends, we're currently using a linked
list of backends, where each backend is expected to set up its `next`
pointer to the next ref storage backend. This is kind of a weird setup
as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in
"refs.c", where each backend is now identified by an integer constant.
Expose functions to translate from those integer constants to the name
and vice versa, which will be required by subsequent patches.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/refs.c b/refs.c
index 16bfa21df7..dea3d5c9a0 100644
--- a/refs.c
+++ b/refs.c
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(unsigned int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+unsigned int ref_storage_format_by_name(const char *name)
+{
+	for (unsigned int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(unsigned int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs
@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	unsigned int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;
diff --git a/refs.h b/refs.h
index ff113bb12a..11b3b6ccea 100644
--- a/refs.h
+++ b/refs.h
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+unsigned int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(unsigned int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *
diff --git a/refs/debug.c b/refs/debug.c
index 83b7a0ba65..b9775f2c37 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ad8b1d143f..43fd0ac760 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index b9fa097a29..8d1090e284 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 4af83bf9a5..8e9f04cc67 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;
diff --git a/repository.h b/repository.h
index 5f18486f64..ea4c488b81 100644
--- a/repository.h
+++ b/repository.h
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 04/12] setup: start tracking ref storage format

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 10131 bytes --]

In order to discern which ref storage format a repository is supposed to
use we need to start setting up and/or discovering the format. This
needs to happen in two separate code paths.

  - The first path is when we create a repository via `init_db()`. When
    we are re-initializing a preexisting repository we need to retain
    the previously used ref storage format -- if the user asked for a
    different format then this indicates an error and we error out.
    Otherwise we either initialize the repository with the format asked
    for by the user or the default format, which currently is the
    "files" backend.

  - The second path is when discovering repositories, where we need to
    read the config of that repository. There is not yet any way to
    configure something other than the "files" backend, so we can just
    blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily
available when needed. As there is only a single backend and because it
is not configurable we cannot yet verify that this tracking works as
expected via tests, but tests will be added in subsequent commits. To
countermand this ommission now though, raise a BUG() in case the ref
storage format is not set up properly in `ref_store_init()`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  4 ++--
 repository.c      |  6 ++++++
 repository.h      |  4 ++++
 setup.c           | 28 +++++++++++++++++++++++++---
 setup.h           |  6 +++++-
 7 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 343f536cf8..48aeb1b90b 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1107,7 +1107,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
@@ -1292,7 +1293,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle
diff --git a/builtin/init-db.c b/builtin/init-db.c
index cb727c826f..b6e80feab6 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 
@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }
diff --git a/refs.c b/refs.c
index dea3d5c9a0..fdbf5f4cb1 100644
--- a/refs.c
+++ b/refs.c
@@ -2045,10 +2045,10 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	unsigned int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
 		BUG("reference backend is unknown");
 
diff --git a/repository.c b/repository.c
index a7679ceeaa..d7d24d416a 100644
--- a/repository.c
+++ b/repository.c
@@ -104,6 +104,11 @@ void repo_set_hash_algo(struct repository *repo, int hash_algo)
 	repo->hash_algo = &hash_algos[hash_algo];
 }
 
+void repo_set_ref_storage_format(struct repository *repo, unsigned int format)
+{
+	repo->ref_storage_format = format;
+}
+
 /*
  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
  * Return 0 upon success and a non-zero value upon failure.
@@ -184,6 +189,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */
diff --git a/repository.h b/repository.h
index ea4c488b81..f5269b3730 100644
--- a/repository.h
+++ b/repository.h
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	unsigned int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 
@@ -202,6 +205,7 @@ void repo_set_gitdir(struct repository *repo, const char *root,
 		     const struct set_gitdir_args *extra_args);
 void repo_set_worktree(struct repository *repo, const char *path);
 void repo_set_hash_algo(struct repository *repo, int algo);
+void repo_set_ref_storage_format(struct repository *repo, unsigned int format);
 void initialize_the_repository(void);
 RESULT_MUST_BE_USED
 int repo_init(struct repository *r, const char *gitdir, const char *worktree);
diff --git a/setup.c b/setup.c
index bc90bbd033..9c9a167f52 100644
--- a/setup.c
+++ b/setup.c
@@ -1566,6 +1566,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			repo_set_ref_storage_format(the_repository,
+						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */
@@ -1659,6 +1661,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	repo_set_ref_storage_format(the_repository,
+				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =
@@ -1899,7 +1903,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(unsigned int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();
@@ -1919,6 +1924,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	repo_set_ref_storage_format(the_repository, ref_storage_format);
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 
@@ -2137,8 +2143,22 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt,
+					unsigned int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    unsigned int ref_storage_format,
+	    const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;
@@ -2181,13 +2201,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {
diff --git a/setup.h b/setup.h
index 3f0f17c351..3d3eda7967 100644
--- a/setup.h
+++ b/setup.h
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	unsigned int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;
@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }
@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    unsigned int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(unsigned int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 05/12] setup: set repository's formats on init

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2231 bytes --]

The proper hash algorithm and ref storage format that will be used for a
newly initialized repository will be figured out in `init_db()` via
`validate_hash_algorithm()` and `validate_ref_storage_format()`. Until
now though, we never set up the hash algorithm or ref storage format of
`the_repository` accordingly.

There are only two callsites of `init_db()`, one in git-init(1) and one
in git-clone(1). The former function doesn't care for the formats to be
set up properly because it never access the repository after calling the
function in the first place.

For git-clone(1) it's a different story though, as we call `init_db()`
before listing remote refs. While we do indeed have the wrong hash
function in `the_repository` when `init_db()` sets up a non-default
object format for the repository, it never mattered because we adjust
the hash after learning about the remote's hash function via the listed
refs.

So the current state is correct for the hash algo, but it's not for the
ref storage format because git-clone(1) wouldn't know to set it up
properly. But instead of adjusting only the `ref_storage_format`, set
both the hash algo and the ref storage format so that `the_repository`
is in the correct state when `init_db()` exits. This is fine as we will
adjust the hash later on anyway and makes it easier to reason about the
end state of `the_repository`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/setup.c b/setup.c
index 9c9a167f52..49570e6b3a 100644
--- a/setup.c
+++ b/setup.c
@@ -2207,6 +2207,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 06/12] setup: introduce "extensions.refStorage" extension

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 9436 bytes --]

Introduce a new "extensions.refStorage" extension that allows us to
specify the ref storage format used by a repository. For now, the only
supported format is the "files" format, but this list will likely soon
be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around
how exactly this extension should look like. One alternative [1] that
was discussed was whether it would make sense to model the extension in
such a way that backends are arbitrarily stackable. This would allow for
a combined value of e.g. "loose,packed-refs" or "loose,reftable", which
indicates that new refs would be written via "loose" files backend and
compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that
it brings with it is really required for now. It is not foreseeable that
there will be a proliferation of backends in the near-term future, and
the current set of existing formats and formats which are on the horizon
can easily be configured with the much simpler proposal where we have a
single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to
arbitrarily stack the ref formats, then we can adapt the current
extension rather easily. Given that Git clients will refuse any unknown
value for the "extensions.refStorage" extension they would also know to
ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the
extension.

[1]: <pull.1408.git.1667846164.gitgitgadget@gmail.com>

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 24 ++++++++++++++---
 setup.h                                       |  4 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 69 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
index bccaec7a96..66db0e15da 100644
--- a/Documentation/config/extensions.txt
+++ b/Documentation/config/extensions.txt
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
diff --git a/Documentation/ref-storage-format.txt b/Documentation/ref-storage-format.txt
new file mode 100644
index 0000000000..1a65cac468
--- /dev/null
+++ b/Documentation/ref-storage-format.txt
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.
diff --git a/Documentation/technical/repository-version.txt b/Documentation/technical/repository-version.txt
index 045a76756f..27be3741e6 100644
--- a/Documentation/technical/repository-version.txt
+++ b/Documentation/technical/repository-version.txt
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).
diff --git a/builtin/clone.c b/builtin/clone.c
index 48aeb1b90b..0fb3816d0c 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1291,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
diff --git a/setup.c b/setup.c
index 49570e6b3a..fb1413cabd 100644
--- a/setup.c
+++ b/setup.c
@@ -592,6 +592,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		unsigned int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }
@@ -1871,12 +1882,15 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo,
+				   unsigned int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */
@@ -1889,6 +1903,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)
@@ -2030,7 +2048,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");
diff --git a/setup.h b/setup.h
index 3d3eda7967..3599aec93c 100644
--- a/setup.h
+++ b/setup.h
@@ -180,7 +180,9 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    unsigned int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo,
+				   unsigned int ref_storage_format,
+				   int reinit);
 void create_reference_database(unsigned int ref_storage_format,
 			       const char *initial_branch, int quiet);
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 2b78e3be47..38b3e4c39e 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -532,6 +532,32 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
diff --git a/t/test-lib.sh b/t/test-lib.sh
index dc03f06b8e..4685cc3d48 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1937,7 +1937,7 @@ test_lazy_prereq SHA1 '
 '
 
 test_lazy_prereq DEFAULT_REPO_FORMAT '
-	test_have_prereq SHA1
+	test_have_prereq SHA1,REFFILES
 '
 
 # Ensure that no test accidentally triggers a Git command
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 07/12] setup: introduce GIT_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 3143 bytes --]

Introduce a new GIT_DEFAULT_REF_FORMAT environment variable that lets
users control the default ref format used by both git-init(1) and
git-clone(1). This is modeled after GIT_DEFAULT_OBJECT_FORMAT, which
does the same thing for the repository's object format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git.txt |  5 +++++
 setup.c               |  7 +++++++
 t/t0001-init.sh       | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index bf9e6af695..88e4ed4bd6 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::
diff --git a/setup.c b/setup.c
index fb1413cabd..1ab1a66bcb 100644
--- a/setup.c
+++ b/setup.c
@@ -2164,12 +2164,19 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 static void validate_ref_storage_format(struct repository_format *repo_fmt,
 					unsigned int format)
 {
+	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+
 	if (repo_fmt->version >= 0 &&
 	    format != REF_STORAGE_FORMAT_UNKNOWN &&
 	    format != repo_fmt->ref_storage_format) {
 		die(_("attempt to reinitialize repository with different reference storage format"));
 	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
 		repo_fmt->ref_storage_format = format;
+	} else if (name) {
+		format = ref_storage_format_by_name(name);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), name);
+		repo_fmt->ref_storage_format = format;
 	}
 }
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 38b3e4c39e..30ce752cc1 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -558,6 +558,24 @@ test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown back
 	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 08/12] t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2531 bytes --]

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that
lets developers run the test suite with a different default ref format
without impacting the ref format used by non-test Git invocations. This
is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same
thing for the repository's object format.

Adapt the setup of the `REFFILES` test prerequisite to be conditionally
set based on the default ref format.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/README                |  3 +++
 t/test-lib-functions.sh |  5 +++++
 t/test-lib.sh           | 11 ++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/t/README b/t/README
index 36463d0742..621d3b8c09 100644
--- a/t/README
+++ b/t/README
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 5eb57914ab..a3a51ea9e8 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 4685cc3d48..fc93aa57e6 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 
@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 09/12] builtin/rev-parse: introduce `--show-ref-format` flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 2428 bytes --]

Introduce a new `--show-ref-format` to git-rev-parse(1) that causes it
to print the ref format used by a repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-rev-parse.txt |  3 +++
 builtin/rev-parse.c             |  4 ++++
 t/t1500-rev-parse.sh            | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 912fab9f5e..546faf9017 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 917f122440..d08987646a 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -1062,6 +1062,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--show-ref-format")) {
+				puts(ref_storage_format_to_name(the_repository->ref_storage_format));
+				continue;
+			}
 			if (!strcmp(arg, "--end-of-options")) {
 				seen_end_of_options = 1;
 				if (filter & (DO_FLAGS | DO_REVS))
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 3f9e7f62e4..a669e592f1 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 10/12] builtin/init: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4861 bytes --]

Introduce a new `--ref-format` value flag for git-init(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-init.txt |  7 +++++++
 builtin/init-db.c          | 13 ++++++++++++-
 t/t0001-init.sh            | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-init.txt b/Documentation/git-init.txt
index 6f0d2973bf..e8dc645bb5 100644
--- a/Documentation/git-init.txt
+++ b/Documentation/git-init.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 
@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE
diff --git a/builtin/init-db.c b/builtin/init-db.c
index b6e80feab6..a4f81e2af5 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -58,6 +58,7 @@ static int shared_callback(const struct option *opt, const char *arg, int unset)
 static const char *const init_db_usage[] = {
 	N_("git init [-q | --quiet] [--bare] [--template=<template-directory>]\n"
 	   "         [--separate-git-dir <git-dir>] [--object-format=<format>]\n"
+	   "         [--ref-format=<format>]\n"
 	   "         [-b <branch-name> | --initial-branch=<branch-name>]\n"
 	   "         [--shared[=<permissions>]] [<directory>]"),
 	NULL
@@ -77,8 +78,10 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *ref_format = NULL;
 	const char *initial_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
+	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	int init_shared_repository = -1;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
@@ -96,6 +99,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			   N_("override the name of the initial branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
+		OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+			   N_("specify the reference format to use")),
 		OPT_END()
 	};
 
@@ -159,6 +164,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			die(_("unknown hash algorithm '%s'"), object_format);
 	}
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (init_shared_repository != -1)
 		set_shared_repository(init_shared_repository);
 
@@ -237,6 +248,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       ref_storage_format, initial_branch,
 		       init_shared_repository, flags);
 }
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 30ce752cc1..b131d665db 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -576,6 +576,32 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 11/12] builtin/clone: introduce `--ref-format=` value flag

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 4004 bytes --]

Introduce a new `--ref-format` value flag for git-clone(1) that allows
the user to specify the ref format that is to be used for a newly
initialized repository.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-clone.txt |  6 ++++++
 builtin/clone.c             | 12 +++++++++++-
 t/t5601-clone.sh            | 17 +++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index c37c4a37f7..6e43eb9c20 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.
diff --git a/builtin/clone.c b/builtin/clone.c
index 0fb3816d0c..f1635e0e8c 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -72,6 +72,7 @@ static char *remote_name = NULL;
 static char *option_branch = NULL;
 static struct string_list option_not = STRING_LIST_INIT_NODUP;
 static const char *real_git_dir;
+static const char *ref_format;
 static char *option_upload_pack = "git-upload-pack";
 static int option_verbosity;
 static int option_progress = -1;
@@ -157,6 +158,8 @@ static struct option builtin_clone_options[] = {
 		    N_("any cloned submodules will be shallow")),
 	OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 		   N_("separate git dir from working tree")),
+	OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+		   N_("specify the reference format to use")),
 	OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
 			N_("set config inside the new repository")),
 	OPT_STRING_LIST(0, "server-option", &server_options,
@@ -932,6 +935,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int submodule_progress;
 	int filter_submodules = 0;
 	int hash_algo;
+	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
 
 	struct transport_ls_refs_options transport_ls_refs_options =
@@ -957,6 +961,12 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (option_single_branch == -1)
 		option_single_branch = deepen ? 1 : 0;
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (option_mirror)
 		option_bare = 1;
 
@@ -1108,7 +1118,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * their on-disk data structures.
 	 */
 	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
-		REF_STORAGE_FORMAT_UNKNOWN, NULL,
+		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 47eae641f0..fb1b9c686d 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v3 12/12] t9500: write "extensions.refstorage" into config

[Patrick Steinhardt]

[-- Attachment #1: Type: text/plain, Size: 1312 bytes --]

In t9500 we're writing a custom configuration that sets up gitweb. This
requires us to manually ensure that the repository format is configured
as required, including both the repository format version and
extensions. With the introduction of the "extensions.refStorage"
extension we need to update the test to also write this new one.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 t/t9500-gitweb-standalone-no-errors.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index 0333065d4d..7679780fb8 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]
@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 
-- 
2.43.GIT


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH v3 00/12] Introduce `refStorage` extension

[Eric Sunshine]

On Fri, Dec 29, 2023 at 2:26 AM Patrick Steinhardt <ps@pks.im> wrote:
> this is the third version of my patch series that introduces the new
> `refStorage` extension. This extension will be used for the upcoming
> reftable backend.
>
> Changes compared to v3:
>   - Reworded the commit message in patch 2, proposed by Eric.
>   - Added a NEEDSWORK comment to `get_worktrees_internal()`, propose by
>     Eric.

Thanks for addressing my minor review comments.