[PATCH 7/8] repository: adjust repo paths when $CWD moves

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

From: Duy Nguyen <pclouds@gmail.com>

As noted in previous and previous patches, when setup_work_tree()
moves $CWD, it calls set_git_dir() with a new path to make sure
relative $GIT_DIR is still correct.

The same problem from the previous patch applies here: if
$GIT_ALTERNATE_OBJECT_DIRECTORIES or $GIT_OBJECT_DIRECTORY are also
relative, the user is screwed.

Fortuntely the previous patch indirectly fixes this as well:
update_path_envs() in environment.c is actually called before
setup_git_env() is indirectly called by setup_work_tree() via
set_git_dir(). At that point, it correctly gets the updated paths from
env and pass them down. This patch is here for another reason.

From the design perspective, calling set_git_dir() the second time [1]
is just bad because it could potentially be used to point repo code to
_another_ repository. The promise that "the new path actually points
to the same place as the old one" is not guaranteed and also hard to
see unless you know setup code well.

This patch avoids this. The second set_git_dir() call is just a
workaround to adjust paths. We can now do it directly from repo code
by subscribing to the "$CWD updated" event and do everything needed by
the repo. After this we could die() on subsequent repo_set_gitdir()
calls because we do not support it (we never did).

[1] The first time is done by setup_git_directory() code, which is
correct: we have just found a repo and we want to initialize our code
to read from that repo.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 object-store.h |  3 +++
 object.c       | 15 +++++++++++++++
 repository.c   | 28 ++++++++++++++++++++++++++++
 setup.c        |  6 +-----
 4 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/object-store.h b/object-store.h
index fef33f345f..4af2c53bca 100644
--- a/object-store.h
+++ b/object-store.h
@@ -119,6 +119,9 @@ struct raw_object_store {
 };
 
 struct raw_object_store *raw_object_store_new(void);
+void raw_object_store_adjust_paths(struct raw_object_store *o,
+				   const char *old_cwd,
+				   const char *new_cwd);
 void raw_object_store_clear(struct raw_object_store *o);
 
 /*
diff --git a/object.c b/object.c
index a0a756f24f..5318922efd 100644
--- a/object.c
+++ b/object.c
@@ -457,6 +457,21 @@ struct raw_object_store *raw_object_store_new(void)
 	return o;
 }
 
+void raw_object_store_adjust_paths(struct raw_object_store *o,
+				   const char *old_cwd,
+				   const char *new_cwd)
+{
+	/*
+	 * "main repo" is technically wrong because we don't know that
+	 * from here. But it's the only repo that will execute this
+	 * function for now.
+	 */
+	setup_adjust_path("main repo's object dir",
+			  &o->objectdir, old_cwd, new_cwd);
+	setup_adjust_path("main repo's alt dir",
+			  &o->alternate_db, old_cwd, new_cwd);
+}
+
 static void free_alt_odb(struct alternate_object_database *alt)
 {
 	strbuf_release(&alt->scratch);
diff --git a/repository.c b/repository.c
index a4848c1bd0..c2edf227fe 100644
--- a/repository.c
+++ b/repository.c
@@ -8,6 +8,10 @@
 static struct repository the_repo;
 struct repository *the_repository;
 
+static void repo_adjust_paths(const char *old_cwd,
+			      const char *new_cwd,
+			      void *cb_data);
+
 void initialize_the_repository(void)
 {
 	the_repository = &the_repo;
@@ -15,6 +19,11 @@ void initialize_the_repository(void)
 	the_repo.index = &the_index;
 	the_repo.objects = raw_object_store_new();
 	repo_set_hash_algo(&the_repo, GIT_HASH_SHA1);
+	/*
+	 * non-main repos probably does not need this since $CWD should
+	 * never change again by the time they are created.
+	 */
+	add_cwd_update_callback(repo_adjust_paths, the_repository);
 }
 
 static void expand_base_dir(char **out, const char *in,
@@ -70,6 +79,25 @@ void repo_set_gitdir(struct repository *repo,
 			repo->gitdir, "index");
 }
 
+static void repo_adjust_paths(const char *old_cwd, const char *new_cwd,
+			      void *cb_data)
+{
+	struct repository *repo = cb_data;
+
+	if (repo != the_repository)
+		die("BUG: this is supposed to happen to main repo only");
+
+	setup_adjust_path("main repo's gitdir",
+			  &repo->gitdir, old_cwd, new_cwd);
+	setup_adjust_path("main repo's commondir",
+			  &repo->commondir, old_cwd, new_cwd);
+	setup_adjust_path("main repo's graft file",
+			  &repo->graft_file, old_cwd, new_cwd);
+	setup_adjust_path("main repo's index file",
+			  &repo->index_file, old_cwd, new_cwd);
+	raw_object_store_adjust_paths(repo->objects, old_cwd, new_cwd);
+}
+
 void repo_set_hash_algo(struct repository *repo, int hash_algo)
 {
 	repo->hash_algo = &hash_algos[hash_algo];
diff --git a/setup.c b/setup.c
index 23b8f89ce2..e364aea7e5 100644
--- a/setup.c
+++ b/setup.c
@@ -417,7 +417,7 @@ void setup_adjust_path(const char *name, char **path,
 void setup_work_tree(void)
 {
 	static int initialized = 0;
-	const char *work_tree, *git_dir;
+	const char *work_tree;
 	struct strbuf old_cwd = STRBUF_INIT;
 	int i;
 
@@ -428,9 +428,6 @@ void setup_work_tree(void)
 		die(_("unable to set up work tree using invalid config"));
 
 	work_tree = get_git_work_tree();
-	git_dir = get_git_dir();
-	if (!is_absolute_path(git_dir))
-		git_dir = real_path(get_git_dir());
 	strbuf_get_pwd_cwd(&old_cwd);
 	if (!work_tree || chdir(work_tree))
 		die(_("this operation must be run in a work tree"));
@@ -439,7 +436,6 @@ void setup_work_tree(void)
 		cwd_callbacks[i].fn(old_cwd.buf, work_tree,
 				    cwd_callbacks[i].cb_data);
 	strbuf_release(&old_cwd);
-	set_git_dir(remove_leading_path(git_dir, work_tree));
 	initialized = 1;
 }
 
-- 
2.17.0.rc1.439.gca064e2955