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

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>

3 files changed, 55 insertions, 6 deletions

diff --git a/t/lib-diff-alternative.sh b/t/lib-diff-alternative.sh
index a8f5d3274a..c4dc2d46dc 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 89b306cb11..26e082f05b 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 42a2b9a13b..c8d555771d 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' '