[PATCH v3 2/2] attr: add attr.tree for setting the treeish to read attributes from

["John Cai via GitGitGadget" <gitgitgadget@gmail.com>]

From: John Cai <johncai86@gmail.com>

44451a2 (attr: teach "--attr-source=<tree>" global option to "git",
2023-05-06) provided the ability to pass in a treeish as the attr
source. In the context of serving Git repositories as bare repos like we
do at GitLab however, it would be easier to point --attr-source to HEAD
for all commands by setting it once.

Add a new config attr.tree that allows this.

Signed-off-by: John Cai <johncai86@gmail.com>
---
 Documentation/config.txt      |  2 ++
 Documentation/config/attr.txt |  5 +++
 attr.c                        |  7 ++++
 attr.h                        |  2 ++
 config.c                      | 14 ++++++++
 t/t0003-attributes.sh         | 62 +++++++++++++++++++++++++++++++++++
 6 files changed, 92 insertions(+)
 create mode 100644 Documentation/config/attr.txt

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 229b63a454c..b1891c2b5af 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -371,6 +371,8 @@ other popular tools, and describe them in your documentation.
 
 include::config/advice.txt[]
 
+include::config/attr.txt[]
+
 include::config/core.txt[]
 
 include::config/add.txt[]
diff --git a/Documentation/config/attr.txt b/Documentation/config/attr.txt
new file mode 100644
index 00000000000..be882523f8b
--- /dev/null
+++ b/Documentation/config/attr.txt
@@ -0,0 +1,5 @@
+attr.tree:
+	A <tree-ish> to read gitattributes from instead of the worktree. See
+	linkgit:gitattributes[5]. If `attr.tree` does not resolve to a valid tree,
+	treat it as an empty tree. --attr-source and GIT_ATTR_SOURCE take
+	precedence over attr.tree.
diff --git a/attr.c b/attr.c
index bf2ea1626a6..0ae6852d12b 100644
--- a/attr.c
+++ b/attr.c
@@ -24,6 +24,8 @@
 #include "tree-walk.h"
 #include "object-name.h"
 
+const char *git_attr_tree;
+
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
 static const char git_attr__unknown[] = "(builtin)unknown";
@@ -1206,6 +1208,11 @@ 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) {
+		default_attr_source_tree_object_name = git_attr_tree;
+		ignore_bad_attr_tree = 1;
+	}
+
 	if (!default_attr_source_tree_object_name &&
 	    startup_info->have_repository &&
 	    is_bare_repository()) {
diff --git a/attr.h b/attr.h
index 2b745df4054..127998ae013 100644
--- a/attr.h
+++ b/attr.h
@@ -236,4 +236,6 @@ const char *git_attr_global_file(void);
 /* Return whether the system gitattributes file is enabled and should be used. */
 int git_attr_system_is_enabled(void);
 
+extern const char *git_attr_tree;
+
 #endif /* ATTR_H */
diff --git a/config.c b/config.c
index 3846a37be97..21a1590b505 100644
--- a/config.c
+++ b/config.c
@@ -18,6 +18,7 @@
 #include "repository.h"
 #include "lockfile.h"
 #include "mailmap.h"
+#include "attr.h"
 #include "exec-cmd.h"
 #include "strbuf.h"
 #include "quote.h"
@@ -1904,6 +1905,16 @@ static int git_default_mailmap_config(const char *var, const char *value)
 	return 0;
 }
 
+static int git_default_attr_config(const char *var, const char *value)
+{
+	if (!strcmp(var, "attr.tree"))
+		return git_config_string(&git_attr_tree, var, value);
+
+	/* Add other attribute related config variables here and to
+	   Documentation/config/attr.txt. */
+	return 0;
+}
+
 int git_default_config(const char *var, const char *value,
 		       const struct config_context *ctx, void *cb)
 {
@@ -1927,6 +1938,9 @@ int git_default_config(const char *var, const char *value,
 	if (starts_with(var, "mailmap."))
 		return git_default_mailmap_config(var, value);
 
+	if (starts_with(var, "attr."))
+		return git_default_attr_config(var, value);
+
 	if (starts_with(var, "advice.") || starts_with(var, "color.advice"))
 		return git_default_advice_config(var, value);
 
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index e6b1a117228..b0949125f26 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -40,6 +40,10 @@ attr_check_source () {
 	test_cmp expect actual &&
 	test_must_be_empty err
 
+	git $git_opts -c "attr.tree=$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
@@ -342,6 +346,46 @@ test_expect_success 'bare repository: check that .gitattribute is ignored' '
 	)
 '
 
+bad_attr_source_err="fatal: bad --attr-source or GIT_ATTR_SOURCE"
+
+test_expect_success 'attr.tree when HEAD is unborn' '
+	test_when_finished rm -rf empty &&
+	git init empty &&
+	(
+		cd empty &&
+		echo $bad_attr_source_err >expect_err &&
+		echo "f/path: test: unspecified" >expect &&
+		git -c attr.tree=HEAD check-attr test -- f/path >actual 2>err &&
+		test_must_be_empty err &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'attr.tree points to non-existing ref' '
+	test_when_finished rm -rf empty &&
+	git init empty &&
+	(
+		cd empty &&
+		echo $bad_attr_source_err >expect_err &&
+		echo "f/path: test: unspecified" >expect &&
+		git -c attr.tree=refs/does/not/exist check-attr test -- f/path >actual 2>err &&
+		test_must_be_empty err &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'bad attr source defaults to reading .gitattributes file' '
+	test_when_finished rm -rf empty &&
+	git init empty &&
+	(
+		cd empty &&
+		echo "f/path test=val" >.gitattributes &&
+		echo "f/path: test: val" >expect &&
+		git -c attr.tree=HEAD check-attr test -- f/path >actual 2>err &&
+		test_must_be_empty err &&
+		test_cmp expect actual
+	)
+'
 
 test_expect_success 'bare repo defaults to reading .gitattributes from HEAD' '
 	test_when_finished rm -rf test bare_with_gitattribute &&
@@ -356,6 +400,24 @@ test_expect_success 'bare repo defaults to reading .gitattributes from HEAD' '
 	test_cmp expect actual
 '
 
+test_expect_success '--attr-source and GIT_ATTR_SOURCE take precedence over attr.tree' '
+	test_when_finished rm -rf empty &&
+	git init empty &&
+	(
+		cd empty &&
+		git checkout -b attr-source &&
+		test_commit "val1" .gitattributes "f/path test=val1" &&
+		git checkout -b attr-tree &&
+		test_commit "val2" .gitattributes "f/path test=val2" &&
+		git checkout attr-source &&
+		echo "f/path: test: val1" >expect &&
+		git -c attr.tree=attr-tree --attr-source=attr-source check-attr test -- f/path >actual &&
+		test_cmp expect actual &&
+		GIT_ATTR_SOURCE=attr-source git -c attr.tree=attr-tree check-attr test -- f/path >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'bare repository: with --source' '
 	(
 		cd bare.git &&
-- 
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