Merge branch 'ps/refstorage-extension'

Introduce a new extension "refstorage" so that we can mark a
repository that uses a non-default ref backend, like reftable.

* ps/refstorage-extension:
  t9500: write "extensions.refstorage" into config
  builtin/clone: introduce `--ref-format=` value flag
  builtin/init: introduce `--ref-format=` value flag
  builtin/rev-parse: introduce `--show-ref-format` flag
  t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
  setup: introduce GIT_DEFAULT_REF_FORMAT envvar
  setup: introduce "extensions.refStorage" extension
  setup: set repository's formats on init
  setup: start tracking ref storage format
  refs: refactor logic to look up storage backends
  worktree: skip reading HEAD when repairing worktrees
  t: introduce DEFAULT_REPO_FORMAT prereq

8 files changed, 132 insertions, 2 deletions

diff --git a/t/README b/t/README
index 36463d0742..621d3b8c09 100644
--- a/t/README
+++ b/t/README
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 2b78e3be47..b131d665db 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -532,6 +532,76 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 3f9e7f62e4..a669e592f1 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 6a316f081e..de7d3014e4 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 47eae641f0..fb1b9c686d 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&
diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index 0333065d4d..7679780fb8 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]
@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 1213b8398b..b5eaf7fdc1 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 876b99562a..fc93aa57e6 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 
@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL
@@ -1936,6 +1945,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1,REFFILES
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.