[PATCH] attr: teach "--attr-source=<tree>" global option to "git"

[PATCH] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: John Cai <johncai86@gmail.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish.  Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs internally.

Add an environment variable GIT_ATTR_SOURCE that is set when
--attr-source is passed in, so that subprocesses use the same value for
the attributes source tree.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: John Cai <johncai86@gmail.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v1
Pull-Request: https://github.com/git/git/pull/1470

 Documentation/git.txt     |  3 +++
 archive.c                 |  2 +-
 attr.c                    | 37 +++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++++----
 builtin/check-attr.c      | 17 ++++++++---------
 builtin/pack-objects.c    |  2 +-
 cache.h                   |  1 +
 convert.c                 |  2 +-
 git.c                     |  4 ++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 ++++++++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 ++++++++++-
 t/t4018-diff-funcname.sh  | 19 +++++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 123 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..8be4b66cc62 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,9 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree.
+
 GIT COMMANDS
 ------------
 
diff --git a/archive.c b/archive.c
index 1c2ca78e52a..675e94633a3 100644
--- a/archive.c
+++ b/archive.c
@@ -122,7 +122,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 657ee52229e..2539309b92f 100644
--- a/attr.c
+++ b/attr.c
@@ -1166,11 +1166,43 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	if (!default_attr_source_tree_object_name)
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (get_oid_treeish(default_attr_source_tree_object_name, attr_source))
+		die(_("bad --attr-source object"));
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1183,10 +1215,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index d7a40e674ca..1a7929c980b 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -58,7 +58,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -66,9 +66,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -76,7 +76,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -90,7 +90,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -106,7 +106,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -182,14 +181,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 545b8bddc8e..b6445541954 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1322,7 +1322,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/cache.h b/cache.h
index 0221bc6d5c9..5e219c978d4 100644
--- a/cache.h
+++ b/cache.h
@@ -489,6 +489,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/convert.c b/convert.c
index 349c7e4af15..f770c26f3f6 100644
--- a/convert.c
+++ b/convert.c
@@ -1309,7 +1309,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/git.c b/git.c
index ae2134f29a8..fd253316d9b 100644
--- a/git.c
+++ b/git.c
@@ -5,6 +5,7 @@
 #include "run-command.h"
 #include "alias.h"
 #include "replace-object.h"
+#include "attr.h"
 #include "shallow.h"
 
 #define RUN_SETUP		(1<<0)
@@ -308,6 +309,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 130d26501c6..22a603e8af4 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -391,7 +391,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -419,7 +419,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index ab70fcbe613..74e02c75fc1 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -730,7 +730,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index 09203fbc354..71e3f715b6e 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -417,7 +417,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: 950264636c68591989456e3ba0a5442f93152c1a
-- 
gitgitgadget

[PATCH v2] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: Junio C Hamano <gitster@pobox.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish.  Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs internally.

Additionally, add an environment variable GIT_ATTR_SOURCE that is set
when --attr-source is passed in, so that subprocesses use the same value
for the attributes source tree.

Signed-off-by: John Cai <johncai86@gmail.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
    This version is the same as v1. Just changed the author to Junio as he
    contributed most of the code.
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v2
Pull-Request: https://github.com/git/git/pull/1470

Range-diff vs v1:

 1:  ec04719b81a ! 1:  0667b473e17 attr: teach "--attr-source=<tree>" global option to "git"
     @@
       ## Metadata ##
     -Author: John Cai <johncai86@gmail.com>
     +Author: Junio C Hamano <gitster@pobox.com>
      
       ## Commit message ##
          attr: teach "--attr-source=<tree>" global option to "git"
     @@ Commit message
          given to "git", so that it can be used with any git command that
          runs internally.
      
     -    Add an environment variable GIT_ATTR_SOURCE that is set when
     -    --attr-source is passed in, so that subprocesses use the same value for
     -    the attributes source tree.
     +    Additionally, add an environment variable GIT_ATTR_SOURCE that is set
     +    when --attr-source is passed in, so that subprocesses use the same value
     +    for the attributes source tree.
      
     -    Signed-off-by: Junio C Hamano <gitster@pobox.com>
          Signed-off-by: John Cai <johncai86@gmail.com>
      
       ## Documentation/git.txt ##


 Documentation/git.txt     |  3 +++
 archive.c                 |  2 +-
 attr.c                    | 37 +++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++++----
 builtin/check-attr.c      | 17 ++++++++---------
 builtin/pack-objects.c    |  2 +-
 cache.h                   |  1 +
 convert.c                 |  2 +-
 git.c                     |  4 ++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 ++++++++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 ++++++++++-
 t/t4018-diff-funcname.sh  | 19 +++++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 123 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..8be4b66cc62 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,9 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree.
+
 GIT COMMANDS
 ------------
 
diff --git a/archive.c b/archive.c
index 1c2ca78e52a..675e94633a3 100644
--- a/archive.c
+++ b/archive.c
@@ -122,7 +122,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 657ee52229e..2539309b92f 100644
--- a/attr.c
+++ b/attr.c
@@ -1166,11 +1166,43 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	if (!default_attr_source_tree_object_name)
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (get_oid_treeish(default_attr_source_tree_object_name, attr_source))
+		die(_("bad --attr-source object"));
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1183,10 +1215,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index d7a40e674ca..1a7929c980b 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -58,7 +58,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -66,9 +66,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -76,7 +76,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -90,7 +90,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -106,7 +106,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -182,14 +181,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 545b8bddc8e..b6445541954 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1322,7 +1322,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/cache.h b/cache.h
index 0221bc6d5c9..5e219c978d4 100644
--- a/cache.h
+++ b/cache.h
@@ -489,6 +489,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/convert.c b/convert.c
index 349c7e4af15..f770c26f3f6 100644
--- a/convert.c
+++ b/convert.c
@@ -1309,7 +1309,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/git.c b/git.c
index ae2134f29a8..fd253316d9b 100644
--- a/git.c
+++ b/git.c
@@ -5,6 +5,7 @@
 #include "run-command.h"
 #include "alias.h"
 #include "replace-object.h"
+#include "attr.h"
 #include "shallow.h"
 
 #define RUN_SETUP		(1<<0)
@@ -308,6 +309,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 130d26501c6..22a603e8af4 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -391,7 +391,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -419,7 +419,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index ab70fcbe613..74e02c75fc1 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -730,7 +730,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index 09203fbc354..71e3f715b6e 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -417,7 +417,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: 950264636c68591989456e3ba0a5442f93152c1a
-- 
gitgitgadget

Re: [PATCH v2] attr: teach "--attr-source=<tree>" global option to "git"

[Junio C Hamano]

"John Cai via GitGitGadget" <gitgitgadget@gmail.com> writes:

>     This version is the same as v1. Just changed the author to Junio as he
>     contributed most of the code.

Heh, I do not need an extra credit.  The most important missing
piece I punted (i.e. the environment passing and receiving) was done
by you that is a larger contribution anyway ;-)

I am kind-a surprised that we haven't queued the earlier one.  Is
this ready to ship?

Thanks.

Re: [PATCH v2] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai]

Hi Junio,

On 27 Mar 2023, at 14:29, Junio C Hamano wrote:

> "John Cai via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>>     This version is the same as v1. Just changed the author to Junio as he
>>     contributed most of the code.
>
> Heh, I do not need an extra credit.  The most important missing
> piece I punted (i.e. the environment passing and receiving) was done
> by you that is a larger contribution anyway ;-)

Given that the main idea was yours and most of the code minus the test was as well, I
thought it made the most sense.

>
> I am kind-a surprised that we haven't queued the earlier one.  Is
> this ready to ship?

I believe so, though a review wouldn't hurt--especially on the environment
variable passing and receiving piece.

>
> Thanks.

thanks!
John

Re: [PATCH v2] attr: teach "--attr-source=<tree>" global option to "git"

[Christian Couder]

On Mon, Mar 27, 2023 at 7:44 PM John Cai via GitGitGadget
<gitgitgadget@gmail.com> wrote:

> Undo most of the UI change the commit made, while keeping the
> internal logic to read attributes from a given tree-ish.  Expose the
> internal logic via a new "--attr-source=<tree>" command line option
> given to "git", so that it can be used with any git command that
> runs internally.

I am not sure what are the git commands that run internally. You mean
any builtin command? Actually from the sentence below it looks like it
means any command running as part of the main git process.

> Additionally, add an environment variable GIT_ATTR_SOURCE that is set
> when --attr-source is passed in, so that subprocesses use the same value
> for the attributes source tree.
>
> Signed-off-by: John Cai <johncai86@gmail.com>
> ---
>     attr: teach "--attr-source=" global option to "git"

Not sure you can do something about it but it looks like "<tree>" has
been removed after "--attr-source=" in the above sentence. It might be
that the commit subject wasn't properly quoted in the tool chain and
mistaken for an HTML or XML tag.

>     [1] aimed to allow gitattributes to be read from bare repositories when
>     running git-diff(1). Through discussion, a more general solution emerged
>     (represented by this patch), which allows the attribute machinery to
>     read attributes from a source passed in through a git flag.
>
>     This version is the same as v1. Just changed the author to Junio as he
>     contributed most of the code.
>
>      1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v2
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v2
> Pull-Request: https://github.com/git/git/pull/1470
>
> Range-diff vs v1:

>      -    Add an environment variable GIT_ATTR_SOURCE that is set when
>      -    --attr-source is passed in, so that subprocesses use the same value for
>      -    the attributes source tree.
>      +    Additionally, add an environment variable GIT_ATTR_SOURCE that is set
>      +    when --attr-source is passed in, so that subprocesses use the same value
>      +    for the attributes source tree.
>
>      -    Signed-off-by: Junio C Hamano <gitster@pobox.com>
>           Signed-off-by: John Cai <johncai86@gmail.com>

If the patch is from Junio, I think you should keep his Signed-off-by. If you

> --- a/Documentation/git.txt
> +++ b/Documentation/git.txt
> @@ -212,6 +212,9 @@ If you just want to run git as if it was started in `<path>` then use
>         nohelpers (exclude helper commands), alias and config
>         (retrieve command list from config variable completion.commands)
>
> +--attr-source=<tree-ish>::
> +       Read gitattributes from <tree-ish> instead of the worktree.

Nit: maybe something like "See gitattributes(5)." could help beginners here.

> diff --git a/attr.c b/attr.c
> index 657ee52229e..2539309b92f 100644
> --- a/attr.c
> +++ b/attr.c
> @@ -1166,11 +1166,43 @@ static void collect_some_attrs(struct index_state *istate,
>         fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
>  }
>
> +static const char *default_attr_source_tree_object_name;

I think we are trying to avoid global variables, but I guess there is
no infrastructure yet to put these kinds of variables into a global
struct.

> +static void compute_default_attr_source(struct object_id *attr_source)
> +{
> +       if (!default_attr_source_tree_object_name)
> +               default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);

I wonder what happens if the env variable is set to an empty string,
instead of unset...

> +       if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
> +               return;
> +
> +       if (get_oid_treeish(default_attr_source_tree_object_name, attr_source))
> +               die(_("bad --attr-source object"));

... so it seems that in the case of an empty string, we will just die
with "bad --attr-source object". That doesn't seem very user friendly
to me as users might not know or remember about the GIT_ATTR_SOURCE
variable when they get the error.

> +}
> +
> +static struct object_id *default_attr_source(void)
> +{
> +       static struct object_id attr_source;
> +
> +       if (is_null_oid(&attr_source))
> +               compute_default_attr_source(&attr_source);
> +       if (is_null_oid(&attr_source))
> +               return NULL;

It looks like is_null_oid(&attr_source) can happen when
default_attr_source_tree_object_name is NULL, Ok.

> +       return &attr_source;
> +}
> +


> --- a/git.c
> +++ b/git.c
> @@ -5,6 +5,7 @@
>  #include "run-command.h"
>  #include "alias.h"
>  #include "replace-object.h"
> +#include "attr.h"
>  #include "shallow.h"
>
>  #define RUN_SETUP              (1<<0)
> @@ -308,6 +309,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
>                         } else {
>                                 exit(list_cmds(cmd));
>                         }
> +               } else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
> +                       set_git_attr_source(cmd);
> +                       setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);

This seems a strange to me as it looks like other similar options
require code like the following:

               } else if (!strcmp(cmd, "--super-prefix")) {
                       if (*argc < 2) {
                               fprintf(stderr, _("no prefix given for
--super-prefix\n" ));
                               usage(git_usage_string);
                       }
                       setenv(GIT_SUPER_PREFIX_ENVIRONMENT, (*argv)[1], 1);
                       if (envchanged)
                               *envchanged = 1;
                       (*argv)++;
                       (*argc)--;
               } else if (skip_prefix(cmd, "--super-prefix=", &cmd)) {
                       setenv(GIT_SUPER_PREFIX_ENVIRONMENT, cmd, 1);
                       if (envchanged)
                               *envchanged = 1;

>                 } else {
>                         fprintf(stderr, _("unknown option: %s\n"), cmd);
>                         usage(git_usage_string);

I haven't taken a look at the tests but the rest of the code looks good to me.

Thanks!

Re: [PATCH v2] attr: teach "--attr-source=<tree>" global option to "git"

[Christian Couder]

On Thu, Apr 27, 2023 at 4:02 PM Christian Couder
<christian.couder@gmail.com> wrote:

> >      -    Add an environment variable GIT_ATTR_SOURCE that is set when
> >      -    --attr-source is passed in, so that subprocesses use the same value for
> >      -    the attributes source tree.
> >      +    Additionally, add an environment variable GIT_ATTR_SOURCE that is set
> >      +    when --attr-source is passed in, so that subprocesses use the same value
> >      +    for the attributes source tree.
> >
> >      -    Signed-off-by: Junio C Hamano <gitster@pobox.com>
> >           Signed-off-by: John Cai <johncai86@gmail.com>
>
> If the patch is from Junio, I think you should keep his Signed-off-by. If you

I wanted to say that if you take ownership of the patch as Junio
suggested, I think it should be Ok either way.

[PATCH v3] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: John Cai <johncai86@gmail.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish. Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs as part of the main git process.

Additionally, add an environment variable GIT_ATTR_SOURCE that is set
when --attr-source is passed in, so that subprocesses use the same value
for the attributes source tree.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
    Changes since v3:
    
     * allow --attr-source= and --attr-source
     * fixes to commit message
     * fix error message to distinguish between --attr-source and
       GIT_ATTR_SOURCE
    
    Changes since v2:
    
     * This version is the same as v1. Just changed the author to Junio as
       he contributed most of the code.
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v3
Pull-Request: https://github.com/git/git/pull/1470

Range-diff vs v2:

 1:  0667b473e17 ! 1:  ff8d3a0e780 attr: teach "--attr-source=<tree>" global option to "git"
     @@
       ## Metadata ##
     -Author: Junio C Hamano <gitster@pobox.com>
     +Author: John Cai <johncai86@gmail.com>
      
       ## Commit message ##
          attr: teach "--attr-source=<tree>" global option to "git"
     @@ Commit message
          same.
      
          Undo most of the UI change the commit made, while keeping the
     -    internal logic to read attributes from a given tree-ish.  Expose the
     +    internal logic to read attributes from a given tree-ish. Expose the
          internal logic via a new "--attr-source=<tree>" command line option
          given to "git", so that it can be used with any git command that
     -    runs internally.
     +    runs as part of the main git process.
      
          Additionally, add an environment variable GIT_ATTR_SOURCE that is set
          when --attr-source is passed in, so that subprocesses use the same value
          for the attributes source tree.
      
          Signed-off-by: John Cai <johncai86@gmail.com>
     +    Signed-off-by: Junio C Hamano <gitster@pobox.com>
      
       ## Documentation/git.txt ##
      @@ Documentation/git.txt: If you just want to run git as if it was started in `<path>` then use
     @@ Documentation/git.txt: If you just want to run git as if it was started in `<pat
       	(retrieve command list from config variable completion.commands)
       
      +--attr-source=<tree-ish>::
     -+	Read gitattributes from <tree-ish> instead of the worktree.
     ++	Read gitattributes from <tree-ish> instead of the worktree. See
     ++	linkgit:gitrevisions[7].
      +
       GIT COMMANDS
       ------------
     @@ archive.c: static const struct attr_check *get_archive_attrs(struct index_state
       
      
       ## attr.c ##
     +@@
     + #include "object-store.h"
     + #include "setup.h"
     + #include "thread-utils.h"
     ++#include "object-name.h"
     + 
     + const char git_attr__true[] = "(builtin)true";
     + const char git_attr__false[] = "\0(builtin)false";
      @@ attr.c: static void collect_some_attrs(struct index_state *istate,
       	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
       }
     @@ attr.c: static void collect_some_attrs(struct index_state *istate,
      +
      +static void compute_default_attr_source(struct object_id *attr_source)
      +{
     -+	if (!default_attr_source_tree_object_name)
     ++	int from_env = 0;
     ++
     ++	if (!default_attr_source_tree_object_name) {
      +		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
     ++		from_env = 1;
     ++	}
      +
      +	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
      +		return;
      +
     -+	if (get_oid_treeish(default_attr_source_tree_object_name, attr_source))
     -+		die(_("bad --attr-source object"));
     ++	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source)) {
     ++		if (from_env)
     ++			die(_("bad --attr-source object"));
     ++		else
     ++			die(_("bad GIT_ATTR_SOURCE"));
     ++	}
      +}
      +
      +static struct object_id *default_attr_source(void)
     @@ builtin/pack-objects.c: static int no_try_delta(const char *path)
       		return 1;
       	return 0;
      
     - ## cache.h ##
     -@@ cache.h: static inline enum object_type object_type(unsigned int mode)
     - #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
     - #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
     - #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
     -+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
     - 
     - /*
     -  * Environment variable used in handshaking the wire protocol.
     -
       ## convert.c ##
      @@ convert.c: void convert_attrs(struct index_state *istate,
       		git_config(read_convert_config, NULL);
     @@ convert.c: void convert_attrs(struct index_state *istate,
       	ca->crlf_action = git_path_check_crlf(ccheck + 4);
       	if (ca->crlf_action == CRLF_UNDEFINED)
      
     + ## environment.h ##
     +@@ environment.h: const char *getenv_safe(struct strvec *argv, const char *name);
     + #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
     + #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
     + #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
     ++#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
     + 
     + /*
     +  * Environment variable used in handshaking the wire protocol.
     +
       ## git.c ##
      @@
     - #include "run-command.h"
       #include "alias.h"
       #include "replace-object.h"
     + #include "setup.h"
      +#include "attr.h"
       #include "shallow.h"
     - 
     - #define RUN_SETUP		(1<<0)
     + #include "trace.h"
     + #include "trace2.h"
      @@ git.c: static int handle_options(const char ***argv, int *argc, int *envchanged)
       			} else {
       				exit(list_cmds(cmd));
       			}
     ++		} else if (!strcmp(cmd, "--attr-source")) {
     ++			if (*argc < 2) {
     ++				fprintf(stderr, _("no prefix given for --attr-source\n" ));
     ++				usage(git_usage_string);
     ++			}
     ++			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
     ++			if (envchanged)
     ++				*envchanged = 1;
     ++			(*argv)++;
     ++			(*argc)--;
      +		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
      +			set_git_attr_source(cmd);
      +			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
     ++			if (envchanged)
     ++				*envchanged = 1;
       		} else {
       			fprintf(stderr, _("unknown option: %s\n"), cmd);
       			usage(git_usage_string);


 Documentation/git.txt     |  4 ++++
 archive.c                 |  2 +-
 attr.c                    | 46 +++++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++----
 builtin/check-attr.c      | 17 +++++++--------
 builtin/pack-objects.c    |  2 +-
 convert.c                 |  2 +-
 environment.h             |  1 +
 git.c                     | 16 ++++++++++++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 +++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 +++++++++-
 t/t4018-diff-funcname.sh  | 19 ++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 145 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..4fe226b2135 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,10 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree. See
+	linkgit:gitrevisions[7].
+
 GIT COMMANDS
 ------------
 
diff --git a/archive.c b/archive.c
index 8570cf37ff7..e809514fe70 100644
--- a/archive.c
+++ b/archive.c
@@ -128,7 +128,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 2d8aeb8b58c..04c75f948ab 100644
--- a/attr.c
+++ b/attr.c
@@ -20,6 +20,7 @@
 #include "object-store.h"
 #include "setup.h"
 #include "thread-utils.h"
+#include "object-name.h"
 
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
@@ -1169,11 +1170,51 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	int from_env = 0;
+
+	if (!default_attr_source_tree_object_name) {
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
+		from_env = 1;
+	}
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source)) {
+		if (from_env)
+			die(_("bad --attr-source object"));
+		else
+			die(_("bad GIT_ATTR_SOURCE"));
+	}
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1186,10 +1227,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index 037bf1aaa2a..748f3578b2a 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -63,7 +63,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -71,9 +71,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -81,7 +81,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -95,7 +95,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -111,7 +111,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -187,14 +186,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index a5b466839ba..9cfc8801f9b 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1331,7 +1331,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/convert.c b/convert.c
index 5a2ea5308d6..e65938bb1a8 100644
--- a/convert.c
+++ b/convert.c
@@ -1314,7 +1314,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/environment.h b/environment.h
index a63f0c6a24f..758927a689c 100644
--- a/environment.h
+++ b/environment.h
@@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/git.c b/git.c
index 45899be8265..106c4ab639a 100644
--- a/git.c
+++ b/git.c
@@ -9,6 +9,7 @@
 #include "alias.h"
 #include "replace-object.h"
 #include "setup.h"
+#include "attr.h"
 #include "shallow.h"
 #include "trace.h"
 #include "trace2.h"
@@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (!strcmp(cmd, "--attr-source")) {
+			if (*argc < 2) {
+				fprintf(stderr, _("no prefix given for --attr-source\n" ));
+				usage(git_usage_string);
+			}
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 28bc94c45d6..6580970a670 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -393,7 +393,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -421,7 +421,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index 6972d515f0c..09103a137ef 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -734,7 +734,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index eaec6ebb5e9..664c7c14025 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -444,7 +444,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: f85cd430b12b0d3e4f1a30ef3239a1b73d5f6331
-- 
gitgitgadget

Re: [PATCH v3] attr: teach "--attr-source=<tree>" global option to "git"

[Christian Couder]

>       +--attr-source=<tree-ish>::
>      -+ Read gitattributes from <tree-ish> instead of the worktree.
>      ++ Read gitattributes from <tree-ish> instead of the worktree. See
>      ++ linkgit:gitrevisions[7].

I think it's more sensible to link to gitattributes(5) instead of
gitrevisions(7)

> +static const char *default_attr_source_tree_object_name;
> +
> +void set_git_attr_source(const char *tree_object_name)
> +{
> +       default_attr_source_tree_object_name = xstrdup(tree_object_name);
> +}
> +
> +

One empty line is enough here.

> +static void compute_default_attr_source(struct object_id *attr_source)
> +{
> +       int from_env = 0;
> +
> +       if (!default_attr_source_tree_object_name) {
> +               default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
> +               from_env = 1;
> +       }
> +
> +       if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
> +               return;
> +
> +       if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source)) {
> +               if (from_env)
> +                       die(_("bad --attr-source object"));
> +               else
> +                       die(_("bad GIT_ATTR_SOURCE"));

I think it would be better to have just the following instead of the 4
lines above:

die(_("invalid tree object from --attr-source flag or GIT_ATTR_SOURCE
env variable"));

as a bad GIT_ATTR_SOURCE in a subprocess could come from a bad
--attr-source in the main process.

And this way the from_env variable is not needed.

> +       }
> +}

The rest looks good to me, thanks!

Re: [PATCH v3] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai]

Hi Christian

On 28 Apr 2023, at 16:22, Christian Couder wrote:

>>       +--attr-source=<tree-ish>::
>>      -+ Read gitattributes from <tree-ish> instead of the worktree.
>>      ++ Read gitattributes from <tree-ish> instead of the worktree. See
>>      ++ linkgit:gitrevisions[7].
>
> I think it's more sensible to link to gitattributes(5) instead of
> gitrevisions(7)

oops, I forgot to push up the version with this fix. Thanks for catching it.

>
>> +static const char *default_attr_source_tree_object_name;
>> +
>> +void set_git_attr_source(const char *tree_object_name)
>> +{
>> +       default_attr_source_tree_object_name = xstrdup(tree_object_name);
>> +}
>> +
>> +
>
> One empty line is enough here.

noted.

>
>> +static void compute_default_attr_source(struct object_id *attr_source)
>> +{
>> +       int from_env = 0;
>> +
>> +       if (!default_attr_source_tree_object_name) {
>> +               default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
>> +               from_env = 1;
>> +       }
>> +
>> +       if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
>> +               return;
>> +
>> +       if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source)) {
>> +               if (from_env)
>> +                       die(_("bad --attr-source object"));
>> +               else
>> +                       die(_("bad GIT_ATTR_SOURCE"));
>
> I think it would be better to have just the following instead of the 4
> lines above:
>
> die(_("invalid tree object from --attr-source flag or GIT_ATTR_SOURCE
> env variable"));
>
> as a bad GIT_ATTR_SOURCE in a subprocess could come from a bad
> --attr-source in the main process.
>
> And this way the from_env variable is not needed.

sounds good
>
>> +       }
>> +}
>
> The rest looks good to me, thanks!

thanks,
John

[PATCH v4] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: John Cai <johncai86@gmail.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish. Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs as part of the main git process.

Additionally, add an environment variable GIT_ATTR_SOURCE that is set
when --attr-source is passed in, so that subprocesses use the same value
for the attributes source tree.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
    Changes since v3:
    
     * fixed documentation link
     * simplified error message handling when --attr-source or
       GIT_ATTR_SOURCE is bad
    
    Changes since v2:
    
     * allow --attr-source= and --attr-source
     * fixes to commit message
     * fix error message to distinguish between --attr-source and
       GIT_ATTR_SOURCE
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v4
Pull-Request: https://github.com/git/git/pull/1470

Range-diff vs v3:

 1:  ff8d3a0e780 ! 1:  e41f931b0ad attr: teach "--attr-source=<tree>" global option to "git"
     @@ Documentation/git.txt: If you just want to run git as if it was started in `<pat
       
      +--attr-source=<tree-ish>::
      +	Read gitattributes from <tree-ish> instead of the worktree. See
     -+	linkgit:gitrevisions[7].
     ++	linkgit:gitattributes[5]. This is equivalent to setting the
     ++	`GIT_ATTR_SOURCE` environment variable.
      +
       GIT COMMANDS
       ------------
     @@ attr.c: static void collect_some_attrs(struct index_state *istate,
      +	default_attr_source_tree_object_name = xstrdup(tree_object_name);
      +}
      +
     -+
      +static void compute_default_attr_source(struct object_id *attr_source)
      +{
     -+	int from_env = 0;
     -+
     -+	if (!default_attr_source_tree_object_name) {
     ++	if (!default_attr_source_tree_object_name)
      +		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
     -+		from_env = 1;
     -+	}
      +
      +	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
      +		return;
      +
     -+	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source)) {
     -+		if (from_env)
     -+			die(_("bad --attr-source object"));
     -+		else
     -+			die(_("bad GIT_ATTR_SOURCE"));
     -+	}
     ++	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source))
     ++		die(_("bad --attr-source or GIT_ATTR_SOURCE"));
      +}
      +
      +static struct object_id *default_attr_source(void)


 Documentation/git.txt     |  5 +++++
 archive.c                 |  2 +-
 attr.c                    | 37 +++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++++----
 builtin/check-attr.c      | 17 ++++++++---------
 builtin/pack-objects.c    |  2 +-
 convert.c                 |  2 +-
 environment.h             |  1 +
 git.c                     | 16 ++++++++++++++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 ++++++++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 ++++++++++-
 t/t4018-diff-funcname.sh  | 19 +++++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 137 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..b8f4f604707 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,11 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree. See
+	linkgit:gitattributes[5]. This is equivalent to setting the
+	`GIT_ATTR_SOURCE` environment variable.
+
 GIT COMMANDS
 ------------
 
diff --git a/archive.c b/archive.c
index 8570cf37ff7..e809514fe70 100644
--- a/archive.c
+++ b/archive.c
@@ -128,7 +128,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 2d8aeb8b58c..27a1d5b9a92 100644
--- a/attr.c
+++ b/attr.c
@@ -20,6 +20,7 @@
 #include "object-store.h"
 #include "setup.h"
 #include "thread-utils.h"
+#include "object-name.h"
 
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
@@ -1169,11 +1170,42 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	if (!default_attr_source_tree_object_name)
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source))
+		die(_("bad --attr-source or GIT_ATTR_SOURCE"));
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1186,10 +1218,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index 037bf1aaa2a..748f3578b2a 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -63,7 +63,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -71,9 +71,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -81,7 +81,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -95,7 +95,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -111,7 +111,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -187,14 +186,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index a5b466839ba..9cfc8801f9b 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1331,7 +1331,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/convert.c b/convert.c
index 5a2ea5308d6..e65938bb1a8 100644
--- a/convert.c
+++ b/convert.c
@@ -1314,7 +1314,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/environment.h b/environment.h
index a63f0c6a24f..758927a689c 100644
--- a/environment.h
+++ b/environment.h
@@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/git.c b/git.c
index 45899be8265..106c4ab639a 100644
--- a/git.c
+++ b/git.c
@@ -9,6 +9,7 @@
 #include "alias.h"
 #include "replace-object.h"
 #include "setup.h"
+#include "attr.h"
 #include "shallow.h"
 #include "trace.h"
 #include "trace2.h"
@@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (!strcmp(cmd, "--attr-source")) {
+			if (*argc < 2) {
+				fprintf(stderr, _("no prefix given for --attr-source\n" ));
+				usage(git_usage_string);
+			}
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 28bc94c45d6..6580970a670 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -393,7 +393,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -421,7 +421,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index 6972d515f0c..09103a137ef 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -734,7 +734,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index eaec6ebb5e9..664c7c14025 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -444,7 +444,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: f85cd430b12b0d3e4f1a30ef3239a1b73d5f6331
-- 
gitgitgadget

Re: [PATCH v4] attr: teach "--attr-source=<tree>" global option to "git"

[Junio C Hamano]

"John Cai via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: John Cai <johncai86@gmail.com>
>
> Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
> 2023-01-14) taught "git check-attr" the "--source=<tree>" option to
> allow it to read attribute files from a tree-ish, but did so only
> for the command.  Just like "check-attr" users wanted a way to use
> attributes from a tree-ish and not from the working tree files,
> users of other commands (like "git diff") would benefit from the
> same.
>
> Undo most of the UI change the commit made, while keeping the
> internal logic to read attributes from a given tree-ish. Expose the
> internal logic via a new "--attr-source=<tree>" command line option
> given to "git", so that it can be used with any git command that
> runs as part of the main git process.
>
> Additionally, add an environment variable GIT_ATTR_SOURCE that is set
> when --attr-source is passed in, so that subprocesses use the same value
> for the attributes source tree.
>
> Signed-off-by: John Cai <johncai86@gmail.com>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>     attr: teach "--attr-source=" global option to "git"
>     
>     [1] aimed to allow gitattributes to be read from bare repositories when
>     running git-diff(1). Through discussion, a more general solution emerged
>     (represented by this patch), which allows the attribute machinery to
>     read attributes from a source passed in through a git flag.
>     
>     Changes since v3:
>     
>      * fixed documentation link
>      * simplified error message handling when --attr-source or
>        GIT_ATTR_SOURCE is bad

Looking good.  Will queue; let's merge it down to 'next' soonish.

Thanks.

Re: [PATCH v4] attr: teach "--attr-source=<tree>" global option to "git"

[Christian Couder]

On Sun, Apr 30, 2023 at 4:39 AM John Cai via GitGitGadget
<gitgitgadget@gmail.com> wrote:

> diff --git a/Documentation/git.txt b/Documentation/git.txt
> index 74973d3cc40..b8f4f604707 100644
> --- a/Documentation/git.txt
> +++ b/Documentation/git.txt
> @@ -212,6 +212,11 @@ If you just want to run git as if it was started in `<path>` then use
>         nohelpers (exclude helper commands), alias and config
>         (retrieve command list from config variable completion.commands)
>
> +--attr-source=<tree-ish>::
> +       Read gitattributes from <tree-ish> instead of the worktree. See
> +       linkgit:gitattributes[5]. This is equivalent to setting the
> +       `GIT_ATTR_SOURCE` environment variable.

As you talk about GIT_ATTR_SOURCE, I wonder if this variable should
also be documented in the "Environment Variables" section of this
Documentation/git.txt doc.

> diff --git a/environment.h b/environment.h
> index a63f0c6a24f..758927a689c 100644
> --- a/environment.h
> +++ b/environment.h
> @@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
>  #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
>  #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
>  #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
> +#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"

To be similar with the definitions that are just above, I think it
actually should be:

#define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"

> @@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
>                         } else {
>                                 exit(list_cmds(cmd));
>                         }
> +               } else if (!strcmp(cmd, "--attr-source")) {
> +                       if (*argc < 2) {
> +                               fprintf(stderr, _("no prefix given for --attr-source\n" ));

The example I sent was about '--super-prefix' so it made sense to say
"no prefix given", but here it makes more sense to say something like
"no attribute source given for --attr-source".

> +                               usage(git_usage_string);
> +                       }
> +                       setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
> +                       if (envchanged)
> +                               *envchanged = 1;
> +                       (*argv)++;
> +                       (*argc)--;
> +               } else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
> +                       set_git_attr_source(cmd);
> +                       setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
> +                       if (envchanged)
> +                               *envchanged = 1;
>                 } else {
>                         fprintf(stderr, _("unknown option: %s\n"), cmd);
>                         usage(git_usage_string);

Re: [PATCH v4] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai]

Hi Christian,

On 23/05/03 05:10PM, Christian Couder wrote:
> On Sun, Apr 30, 2023 at 4:39 AM John Cai via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> 
> > diff --git a/Documentation/git.txt b/Documentation/git.txt
> > index 74973d3cc40..b8f4f604707 100644
> > --- a/Documentation/git.txt
> > +++ b/Documentation/git.txt
> > @@ -212,6 +212,11 @@ If you just want to run git as if it was started in `<path>` then use
> >         nohelpers (exclude helper commands), alias and config
> >         (retrieve command list from config variable completion.commands)
> >
> > +--attr-source=<tree-ish>::
> > +       Read gitattributes from <tree-ish> instead of the worktree. See
> > +       linkgit:gitattributes[5]. This is equivalent to setting the
> > +       `GIT_ATTR_SOURCE` environment variable.
> 
> As you talk about GIT_ATTR_SOURCE, I wonder if this variable should
> also be documented in the "Environment Variables" section of this
> Documentation/git.txt doc.
> 
> > diff --git a/environment.h b/environment.h
> > index a63f0c6a24f..758927a689c 100644
> > --- a/environment.h
> > +++ b/environment.h
> > @@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
> >  #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
> >  #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
> >  #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
> > +#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
> 
> To be similar with the definitions that are just above, I think it
> actually should be:
> 
> #define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
> 
> > @@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
> >                         } else {
> >                                 exit(list_cmds(cmd));
> >                         }
> > +               } else if (!strcmp(cmd, "--attr-source")) {
> > +                       if (*argc < 2) {
> > +                               fprintf(stderr, _("no prefix given for --attr-source\n" ));
> 
> The example I sent was about '--super-prefix' so it made sense to say
> "no prefix given", but here it makes more sense to say something like
> "no attribute source given for --attr-source".
> 

All good feedback. I'll update the branch with these changes.

> > +                               usage(git_usage_string);
> > +                       }
> > +                       setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
> > +                       if (envchanged)
> > +                               *envchanged = 1;
> > +                       (*argv)++;
> > +                       (*argc)--;
> > +               } else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
> > +                       set_git_attr_source(cmd);
> > +                       setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
> > +                       if (envchanged)
> > +                               *envchanged = 1;
> >                 } else {
> >                         fprintf(stderr, _("unknown option: %s\n"), cmd);
> >                         usage(git_usage_string);

thanks
John

[PATCH v5] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: John Cai <johncai86@gmail.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish. Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs as part of the main git process.

Additionally, add an environment variable GIT_ATTR_SOURCE that is set
when --attr-source is passed in, so that subprocesses use the same value
for the attributes source tree.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
    Changes since v4:
    
     * adjusted env var variable name
     * added documentation for GIT_ATTR_SOURCE env var
     * fixed error message when handling git option
    
    Changes since v3:
    
     * fixed documentation link
     * simplified error message handling when --attr-source or
       GIT_ATTR_SOURCE is bad
    
    Changes since v2:
    
     * allow --attr-source= and --attr-source
     * fixes to commit message
     * fix error message to distinguish between --attr-source and
       GIT_ATTR_SOURCE
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v5
Pull-Request: https://github.com/git/git/pull/1470

Range-diff vs v4:

 1:  e41f931b0ad ! 1:  b3b696bd135 attr: teach "--attr-source=<tree>" global option to "git"
     @@ Documentation/git.txt: If you just want to run git as if it was started in `<pat
       GIT COMMANDS
       ------------
       
     +@@ Documentation/git.txt: for further details.
     + 	tells Git not to verify the SSL certificate when fetching or
     + 	pushing over HTTPS.
     + 
     ++`GIT_ATTR_SOURCE`::
     ++	Sets the treeish that gitattributes will be read from.
     ++
     + `GIT_ASKPASS`::
     + 	If this environment variable is set, then Git commands which need to
     + 	acquire passwords or passphrases (e.g. for HTTP or IMAP authentication)
      
       ## archive.c ##
      @@ archive.c: static const struct attr_check *get_archive_attrs(struct index_state *istate,
     @@ attr.c: static void collect_some_attrs(struct index_state *istate,
      +static void compute_default_attr_source(struct object_id *attr_source)
      +{
      +	if (!default_attr_source_tree_object_name)
     -+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE);
     ++		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE_ENVIRONMENT);
      +
      +	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
      +		return;
     @@ environment.h: const char *getenv_safe(struct strvec *argv, const char *name);
       #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
       #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
       #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
     -+#define GIT_ATTR_SOURCE "GIT_ATTR_SOURCE"
     ++#define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
       
       /*
        * Environment variable used in handshaking the wire protocol.
     @@ git.c: static int handle_options(const char ***argv, int *argc, int *envchanged)
       			}
      +		} else if (!strcmp(cmd, "--attr-source")) {
      +			if (*argc < 2) {
     -+				fprintf(stderr, _("no prefix given for --attr-source\n" ));
     ++				fprintf(stderr, _("no attribute source given for --attr-source\n" ));
      +				usage(git_usage_string);
      +			}
     -+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
     ++			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
      +			if (envchanged)
      +				*envchanged = 1;
      +			(*argv)++;
      +			(*argc)--;
      +		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
      +			set_git_attr_source(cmd);
     -+			setenv(GIT_ATTR_SOURCE, (*argv)[1], 1);
     ++			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
      +			if (envchanged)
      +				*envchanged = 1;
       		} else {


 Documentation/git.txt     |  8 ++++++++
 archive.c                 |  2 +-
 attr.c                    | 37 +++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++++----
 builtin/check-attr.c      | 17 ++++++++---------
 builtin/pack-objects.c    |  2 +-
 convert.c                 |  2 +-
 environment.h             |  1 +
 git.c                     | 16 ++++++++++++++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 ++++++++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 ++++++++++-
 t/t4018-diff-funcname.sh  | 19 +++++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 140 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..02707cb01d1 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,11 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree. See
+	linkgit:gitattributes[5]. This is equivalent to setting the
+	`GIT_ATTR_SOURCE` environment variable.
+
 GIT COMMANDS
 ------------
 
@@ -686,6 +691,9 @@ for further details.
 	tells Git not to verify the SSL certificate when fetching or
 	pushing over HTTPS.
 
+`GIT_ATTR_SOURCE`::
+	Sets the treeish that gitattributes will be read from.
+
 `GIT_ASKPASS`::
 	If this environment variable is set, then Git commands which need to
 	acquire passwords or passphrases (e.g. for HTTP or IMAP authentication)
diff --git a/archive.c b/archive.c
index 8570cf37ff7..e809514fe70 100644
--- a/archive.c
+++ b/archive.c
@@ -128,7 +128,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 2d8aeb8b58c..11238d6083d 100644
--- a/attr.c
+++ b/attr.c
@@ -20,6 +20,7 @@
 #include "object-store.h"
 #include "setup.h"
 #include "thread-utils.h"
+#include "object-name.h"
 
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
@@ -1169,11 +1170,42 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	if (!default_attr_source_tree_object_name)
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE_ENVIRONMENT);
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source))
+		die(_("bad --attr-source or GIT_ATTR_SOURCE"));
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1186,10 +1218,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index 037bf1aaa2a..748f3578b2a 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -63,7 +63,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -71,9 +71,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -81,7 +81,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -95,7 +95,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -111,7 +111,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -187,14 +186,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index a5b466839ba..9cfc8801f9b 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1331,7 +1331,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/convert.c b/convert.c
index 5a2ea5308d6..e65938bb1a8 100644
--- a/convert.c
+++ b/convert.c
@@ -1314,7 +1314,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/environment.h b/environment.h
index a63f0c6a24f..30cb7e0fa34 100644
--- a/environment.h
+++ b/environment.h
@@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/git.c b/git.c
index 45899be8265..dc54541f6e3 100644
--- a/git.c
+++ b/git.c
@@ -9,6 +9,7 @@
 #include "alias.h"
 #include "replace-object.h"
 #include "setup.h"
+#include "attr.h"
 #include "shallow.h"
 #include "trace.h"
 #include "trace2.h"
@@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (!strcmp(cmd, "--attr-source")) {
+			if (*argc < 2) {
+				fprintf(stderr, _("no attribute source given for --attr-source\n" ));
+				usage(git_usage_string);
+			}
+			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 28bc94c45d6..6580970a670 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -393,7 +393,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -421,7 +421,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index 6972d515f0c..09103a137ef 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -734,7 +734,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index eaec6ebb5e9..664c7c14025 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -444,7 +444,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: f85cd430b12b0d3e4f1a30ef3239a1b73d5f6331
-- 
gitgitgadget

Re: [PATCH v5] attr: teach "--attr-source=<tree>" global option to "git"

[Christian Couder]

On Wed, May 3, 2023 at 10:09 PM John Cai via GitGitGadget
<gitgitgadget@gmail.com> wrote:

> @@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
>                         } else {
>                                 exit(list_cmds(cmd));
>                         }
> +               } else if (!strcmp(cmd, "--attr-source")) {
> +                       if (*argc < 2) {
> +                               fprintf(stderr, _("no attribute source given for --attr-source\n" ));
> +                               usage(git_usage_string);
> +                       }
> +                       setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
> +                       if (envchanged)
> +                               *envchanged = 1;
> +                       (*argv)++;
> +                       (*argc)--;
> +               } else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
> +                       set_git_attr_source(cmd);
> +                       setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);

It seems to me that for other options "cmd" is used here instead of
"(*argv)[1]" as the second argument to setenv(), for example:

setenv(GIT_SUPER_PREFIX_ENVIRONMENT, cmd, 1);

> +                       if (envchanged)
> +                               *envchanged = 1;
>                 } else {
>                         fprintf(stderr, _("unknown option: %s\n"), cmd);
>                         usage(git_usage_string);

[PATCH v6] attr: teach "--attr-source=<tree>" global option to "git"

[John Cai via GitGitGadget]

From: John Cai <johncai86@gmail.com>

Earlier, 47cfc9bd (attr: add flag `--source` to work with tree-ish,
2023-01-14) taught "git check-attr" the "--source=<tree>" option to
allow it to read attribute files from a tree-ish, but did so only
for the command.  Just like "check-attr" users wanted a way to use
attributes from a tree-ish and not from the working tree files,
users of other commands (like "git diff") would benefit from the
same.

Undo most of the UI change the commit made, while keeping the
internal logic to read attributes from a given tree-ish. Expose the
internal logic via a new "--attr-source=<tree>" command line option
given to "git", so that it can be used with any git command that
runs as part of the main git process.

Additionally, add an environment variable GIT_ATTR_SOURCE that is set
when --attr-source is passed in, so that subprocesses use the same value
for the attributes source tree.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
    attr: teach "--attr-source=" global option to "git"
    
    [1] aimed to allow gitattributes to be read from bare repositories when
    running git-diff(1). Through discussion, a more general solution emerged
    (represented by this patch), which allows the attribute machinery to
    read attributes from a source passed in through a git flag.
    
    Changes since v5:
    
     * fixed setenv call in option parsing code
    
    Changes since v4:
    
     * adjusted env var variable name
     * added documentation for GIT_ATTR_SOURCE env var
     * fixed error message when handling git option
    
    Changes since v3:
    
     * fixed documentation link
     * simplified error message handling when --attr-source or
       GIT_ATTR_SOURCE is bad
    
    Changes since v2:
    
     * allow --attr-source= and --attr-source
     * fixes to commit message
     * fix error message to distinguish between --attr-source and
       GIT_ATTR_SOURCE
    
     1. https://lore.kernel.org/git/pull.1459.git.git.1678758818.gitgitgadget@gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1470%2Fjohn-cai%2Fjc%2Fattr-source-git-flag-v6
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1470/john-cai/jc/attr-source-git-flag-v6
Pull-Request: https://github.com/git/git/pull/1470

Range-diff vs v5:

 1:  b3b696bd135 ! 1:  8389cc1c909 attr: teach "--attr-source=<tree>" global option to "git"
     @@ git.c: static int handle_options(const char ***argv, int *argc, int *envchanged)
      +			(*argc)--;
      +		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
      +			set_git_attr_source(cmd);
     -+			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
     ++			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, cmd, 1);
      +			if (envchanged)
      +				*envchanged = 1;
       		} else {


 Documentation/git.txt     |  8 ++++++++
 archive.c                 |  2 +-
 attr.c                    | 37 +++++++++++++++++++++++++++++++++++--
 attr.h                    | 13 +++++++++----
 builtin/check-attr.c      | 17 ++++++++---------
 builtin/pack-objects.c    |  2 +-
 convert.c                 |  2 +-
 environment.h             |  1 +
 git.c                     | 16 ++++++++++++++++
 ll-merge.c                |  4 ++--
 pathspec.c                |  2 +-
 t/lib-diff-alternative.sh | 31 ++++++++++++++++++++++++++-----
 t/t0003-attributes.sh     | 11 ++++++++++-
 t/t4018-diff-funcname.sh  | 19 +++++++++++++++++++
 userdiff.c                |  2 +-
 ws.c                      |  2 +-
 16 files changed, 140 insertions(+), 29 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 74973d3cc40..02707cb01d1 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -212,6 +212,11 @@ If you just want to run git as if it was started in `<path>` then use
 	nohelpers (exclude helper commands), alias and config
 	(retrieve command list from config variable completion.commands)
 
+--attr-source=<tree-ish>::
+	Read gitattributes from <tree-ish> instead of the worktree. See
+	linkgit:gitattributes[5]. This is equivalent to setting the
+	`GIT_ATTR_SOURCE` environment variable.
+
 GIT COMMANDS
 ------------
 
@@ -686,6 +691,9 @@ for further details.
 	tells Git not to verify the SSL certificate when fetching or
 	pushing over HTTPS.
 
+`GIT_ATTR_SOURCE`::
+	Sets the treeish that gitattributes will be read from.
+
 `GIT_ASKPASS`::
 	If this environment variable is set, then Git commands which need to
 	acquire passwords or passphrases (e.g. for HTTP or IMAP authentication)
diff --git a/archive.c b/archive.c
index 8570cf37ff7..e809514fe70 100644
--- a/archive.c
+++ b/archive.c
@@ -128,7 +128,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }
 
diff --git a/attr.c b/attr.c
index 2d8aeb8b58c..11238d6083d 100644
--- a/attr.c
+++ b/attr.c
@@ -20,6 +20,7 @@
 #include "object-store.h"
 #include "setup.h"
 #include "thread-utils.h"
+#include "object-name.h"
 
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
@@ -1169,11 +1170,42 @@ static void collect_some_attrs(struct index_state *istate,
 	fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
 }
 
+static const char *default_attr_source_tree_object_name;
+
+void set_git_attr_source(const char *tree_object_name)
+{
+	default_attr_source_tree_object_name = xstrdup(tree_object_name);
+}
+
+static void compute_default_attr_source(struct object_id *attr_source)
+{
+	if (!default_attr_source_tree_object_name)
+		default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE_ENVIRONMENT);
+
+	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
+		return;
+
+	if (repo_get_oid_treeish(the_repository, default_attr_source_tree_object_name, attr_source))
+		die(_("bad --attr-source or GIT_ATTR_SOURCE"));
+}
+
+static struct object_id *default_attr_source(void)
+{
+	static struct object_id attr_source;
+
+	if (is_null_oid(&attr_source))
+		compute_default_attr_source(&attr_source);
+	if (is_null_oid(&attr_source))
+		return NULL;
+	return &attr_source;
+}
+
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	collect_some_attrs(istate, tree_oid, path, check);
 
@@ -1186,10 +1218,11 @@ void git_check_attr(struct index_state *istate,
 	}
 }
 
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check)
 {
 	int i;
+	const struct object_id *tree_oid = default_attr_source();
 
 	attr_check_reset(check);
 	collect_some_attrs(istate, tree_oid, path, check);
diff --git a/attr.h b/attr.h
index 9884ea2bc60..676bd17ce27 100644
--- a/attr.h
+++ b/attr.h
@@ -45,7 +45,7 @@
  * const char *path;
  *
  * setup_check();
- * git_check_attr(&the_index, tree_oid, path, check);
+ * git_check_attr(&the_index, path, check);
  * ------------
  *
  * - Act on `.value` member of the result, left in `check->items[]`:
@@ -120,7 +120,6 @@
 #define ATTR_MAX_FILE_SIZE (100 * 1024 * 1024)
 
 struct index_state;
-struct object_id;
 
 /**
  * An attribute is an opaque object that is identified by its name. Pass the
@@ -135,6 +134,12 @@ struct git_attr;
 struct all_attrs_item;
 struct attr_stack;
 
+/*
+ * The textual object name for the tree-ish used by git_check_attr()
+ * to read attributes from (instead of from the working tree).
+ */
+void set_git_attr_source(const char *);
+
 /*
  * Given a string, return the gitattribute object that
  * corresponds to it.
@@ -203,14 +208,14 @@ void attr_check_free(struct attr_check *check);
 const char *git_attr_name(const struct git_attr *);
 
 void git_check_attr(struct index_state *istate,
-		    const struct object_id *tree_oid, const char *path,
+		    const char *path,
 		    struct attr_check *check);
 
 /*
  * Retrieve all attributes that apply to the specified path.
  * check holds the attributes and their values.
  */
-void git_all_attrs(struct index_state *istate, const struct object_id *tree_oid,
+void git_all_attrs(struct index_state *istate,
 		   const char *path, struct attr_check *check);
 
 enum git_attr_direction {
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index 037bf1aaa2a..748f3578b2a 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -63,7 +63,7 @@ static void output_attr(struct attr_check *check, const char *file)
 }
 
 static void check_attr(const char *prefix, struct attr_check *check,
-		       const struct object_id *tree_oid, int collect_all,
+		       int collect_all,
 		       const char *file)
 
 {
@@ -71,9 +71,9 @@ static void check_attr(const char *prefix, struct attr_check *check,
 		prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
 
 	if (collect_all) {
-		git_all_attrs(&the_index, tree_oid, full_path, check);
+		git_all_attrs(&the_index, full_path, check);
 	} else {
-		git_check_attr(&the_index, tree_oid, full_path, check);
+		git_check_attr(&the_index, full_path, check);
 	}
 	output_attr(check, file);
 
@@ -81,7 +81,7 @@ static void check_attr(const char *prefix, struct attr_check *check,
 }
 
 static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
-				   const struct object_id *tree_oid, int collect_all)
+				   int collect_all)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf unquoted = STRBUF_INIT;
@@ -95,7 +95,7 @@ static void check_attr_stdin_paths(const char *prefix, struct attr_check *check,
 				die("line is badly quoted");
 			strbuf_swap(&buf, &unquoted);
 		}
-		check_attr(prefix, check, tree_oid, collect_all, buf.buf);
+		check_attr(prefix, check, collect_all, buf.buf);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 	strbuf_release(&buf);
@@ -111,7 +111,6 @@ static NORETURN void error_with_usage(const char *msg)
 int cmd_check_attr(int argc, const char **argv, const char *prefix)
 {
 	struct attr_check *check;
-	struct object_id *tree_oid = NULL;
 	struct object_id initialized_oid;
 	int cnt, i, doubledash, filei;
 
@@ -187,14 +186,14 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	if (source) {
 		if (repo_get_oid_tree(the_repository, source, &initialized_oid))
 			die("%s: not a valid tree-ish source", source);
-		tree_oid = &initialized_oid;
+		set_git_attr_source(source);
 	}
 
 	if (stdin_paths)
-		check_attr_stdin_paths(prefix, check, tree_oid, all_attrs);
+		check_attr_stdin_paths(prefix, check, all_attrs);
 	else {
 		for (i = filei; i < argc; i++)
-			check_attr(prefix, check, tree_oid, all_attrs, argv[i]);
+			check_attr(prefix, check, all_attrs, argv[i]);
 		maybe_flush_or_die(stdout, "attribute to stdout");
 	}
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index a5b466839ba..9cfc8801f9b 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1331,7 +1331,7 @@ static int no_try_delta(const char *path)
 
 	if (!check)
 		check = attr_check_initl("delta", NULL);
-	git_check_attr(the_repository->index, NULL, path, check);
+	git_check_attr(the_repository->index, path, check);
 	if (ATTR_FALSE(check->items[0].value))
 		return 1;
 	return 0;
diff --git a/convert.c b/convert.c
index 5a2ea5308d6..e65938bb1a8 100644
--- a/convert.c
+++ b/convert.c
@@ -1314,7 +1314,7 @@ void convert_attrs(struct index_state *istate,
 		git_config(read_convert_config, NULL);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ccheck = check->items;
 	ca->crlf_action = git_path_check_crlf(ccheck + 4);
 	if (ca->crlf_action == CRLF_UNDEFINED)
diff --git a/environment.h b/environment.h
index a63f0c6a24f..30cb7e0fa34 100644
--- a/environment.h
+++ b/environment.h
@@ -55,6 +55,7 @@ const char *getenv_safe(struct strvec *argv, const char *name);
 #define GIT_QUARANTINE_ENVIRONMENT "GIT_QUARANTINE_PATH"
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
+#define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
 
 /*
  * Environment variable used in handshaking the wire protocol.
diff --git a/git.c b/git.c
index 45899be8265..2f42da20f4e 100644
--- a/git.c
+++ b/git.c
@@ -9,6 +9,7 @@
 #include "alias.h"
 #include "replace-object.h"
 #include "setup.h"
+#include "attr.h"
 #include "shallow.h"
 #include "trace.h"
 #include "trace2.h"
@@ -314,6 +315,21 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			} else {
 				exit(list_cmds(cmd));
 			}
+		} else if (!strcmp(cmd, "--attr-source")) {
+			if (*argc < 2) {
+				fprintf(stderr, _("no attribute source given for --attr-source\n" ));
+				usage(git_usage_string);
+			}
+			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, (*argv)[1], 1);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (skip_prefix(cmd, "--attr-source=", &cmd)) {
+			set_git_attr_source(cmd);
+			setenv(GIT_ATTR_SOURCE_ENVIRONMENT, cmd, 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);
diff --git a/ll-merge.c b/ll-merge.c
index 28bc94c45d6..6580970a670 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -393,7 +393,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 		normalize_file(theirs, path, istate);
 	}
 
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	ll_driver_name = check->items[0].value;
 	if (check->items[1].value) {
 		marker_size = atoi(check->items[1].value);
@@ -421,7 +421,7 @@ int ll_merge_marker_size(struct index_state *istate, const char *path)
 
 	if (!check)
 		check = attr_check_initl("conflict-marker-size", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	if (check->items[0].value) {
 		marker_size = atoi(check->items[0].value);
 		if (marker_size <= 0)
diff --git a/pathspec.c b/pathspec.c
index 6972d515f0c..09103a137ef 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -734,7 +734,7 @@ int match_pathspec_attrs(struct index_state *istate,
 	if (name[namelen])
 		name = to_free = xmemdupz(name, namelen);
 
-	git_check_attr(istate, NULL, name, item->attr_check);
+	git_check_attr(istate, name, item->attr_check);
 
 	free(to_free);
 
diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a5..c4dc2d46dc1 100644
--- a/t/lib-diff-alternative.sh
+++ b/t/lib-diff-alternative.sh
@@ -112,15 +112,36 @@ EOF
 
 	STRATEGY=$1
 
-	test_expect_success "$STRATEGY diff from attributes" '
+	test_expect_success "setup attributes files for tests with $STRATEGY" '
+		git checkout -b master &&
 		echo "file* diff=driver" >.gitattributes &&
-		git config diff.driver.algorithm "$STRATEGY" &&
-		test_must_fail git diff --no-index file1 file2 > output &&
-		cat expect &&
-		cat output &&
+		git add file1 file2 .gitattributes &&
+		git commit -m "adding files" &&
+		git checkout -b branchA &&
+		echo "file* diff=driverA" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -m "adding driverA as diff driver" &&
+		git checkout master &&
+		git clone --bare --no-local . bare.git
+	'
+
+	test_expect_success "$STRATEGY diff from attributes" '
+		test_must_fail git -c diff.driver.algorithm=$STRATEGY diff --no-index file1 file2 > output &&
 		test_cmp expect output
 	'
 
+	test_expect_success "diff from attributes with bare repo with source" '
+		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+			-c diff.driverA.algorithm=$STRATEGY \
+			diff HEAD:file1 HEAD:file2 >output &&
+		test_cmp expect output
+	'
+
+	test_expect_success "diff from attributes with bare repo with invalid source" '
+		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+			HEAD:file1 HEAD:file2
+	'
+
 	test_expect_success "$STRATEGY diff from attributes has valid diffstat" '
 		echo "file* diff=driver" >.gitattributes &&
 		git config diff.driver.algorithm "$STRATEGY" &&
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 89b306cb114..26e082f05b4 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -30,8 +30,17 @@ attr_check_quote () {
 attr_check_source () {
 	path="$1" expect="$2" source="$3" git_opts="$4" &&
 
-	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
 	echo "$path: test: $expect" >expect &&
+
+	git $git_opts check-attr --source $source test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err &&
+
+	git $git_opts --attr-source="$source" check-attr test -- "$path" >actual 2>err &&
+	test_cmp expect actual &&
+	test_must_be_empty err
+
+	GIT_ATTR_SOURCE="$source" git $git_opts check-attr test -- "$path" >actual 2>err &&
 	test_cmp expect actual &&
 	test_must_be_empty err
 }
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 42a2b9a13b7..c8d555771d5 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -63,6 +63,25 @@ do
 		test_i18ngrep ! fatal msg &&
 		test_i18ngrep ! error msg
 	'
+
+	test_expect_success "builtin $p pattern compiles on bare repo with --attr-source" '
+		test_when_finished "rm -rf bare.git" &&
+		git checkout -B master &&
+		git add . &&
+		echo "*.java diff=notexist" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git checkout -B branchA &&
+		echo "*.java diff=$p" >.gitattributes &&
+		git add .gitattributes &&
+		git commit -am "changing gitattributes" &&
+		git clone --bare --no-local . bare.git &&
+		git -C bare.git symbolic-ref HEAD refs/heads/master &&
+		test_expect_code 1 git -C bare.git --attr-source=branchA \
+			diff --exit-code HEAD:A.java HEAD:B.java 2>msg &&
+		test_i18ngrep ! fatal msg &&
+		test_i18ngrep ! error msg
+	'
 done
 
 test_expect_success 'last regexp must not be negated' '
diff --git a/userdiff.c b/userdiff.c
index eaec6ebb5e9..664c7c14025 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -444,7 +444,7 @@ struct userdiff_driver *userdiff_find_by_path(struct index_state *istate,
 		check = attr_check_initl("diff", NULL);
 	if (!path)
 		return NULL;
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 
 	if (ATTR_TRUE(check->items[0].value))
 		return &driver_true;
diff --git a/ws.c b/ws.c
index da3d0e28cbb..903bfcd53e4 100644
--- a/ws.c
+++ b/ws.c
@@ -79,7 +79,7 @@ unsigned whitespace_rule(struct index_state *istate, const char *pathname)
 	if (!attr_whitespace_rule)
 		attr_whitespace_rule = attr_check_initl("whitespace", NULL);
 
-	git_check_attr(istate, NULL, pathname, attr_whitespace_rule);
+	git_check_attr(istate, pathname, attr_whitespace_rule);
 	value = attr_whitespace_rule->items[0].value;
 	if (ATTR_TRUE(value)) {
 		/* true (whitespace) */

base-commit: f85cd430b12b0d3e4f1a30ef3239a1b73d5f6331
-- 
gitgitgadget