[PATCH v2 1/2] 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>

44451a2e5e (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 +++++++
 t/t0003-attributes.sh         | 4 ++++
 4 files changed, 18 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..e4f2122b7ab
--- /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]. This is equivalent to setting the
+	`GIT_ATTR_SOURCE` environment variable, or passing in --attr-source to
+	the Git command.
diff --git a/attr.c b/attr.c
index 71c84fbcf86..bb0d54eb967 100644
--- a/attr.c
+++ b/attr.c
@@ -1205,6 +1205,13 @@ 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) {
+		char *attr_tree;
+
+		if (!git_config_get_string("attr.tree", &attr_tree))
+			default_attr_source_tree_object_name = attr_tree;
+	}
+
 	if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
 		return;
 
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index 26e082f05b4..6342187c751 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
-- 
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