[PATCH 1/2] Modify pseudo refs through ref backend storage

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com>]

From: Han-Wen Nienhuys <hanwen@google.com>

The previous behavior was introduced in commit 74ec19d4be
("pseudorefs: create and use pseudoref update and delete functions",
Jul 31, 2015), with the justification "alternate ref backends still
need to store pseudorefs in GIT_DIR".

Refs such as REBASE_HEAD are read through the ref backend. This can
only work consistently if they are written through the ref backend as
well. Tooling that works directly on files under .git should be
updated to use git commands to read refs instead.

This needs the following fixes

* Only write log for HEAD pseudo ref. Fixes t1400
  'core.logAllRefUpdates=always creates no reflog for ORIG_HEAD'

* t1400: change hard coded error messages to check for.

* don't deref non-HEAD pseudoref symrefs. This fixes t1405. Without
  this, a deleting a FOO symref pointing to refs/heads/master will remove
  master too.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
---
 refs.c                | 120 +++---------------------------------------
 refs/files-backend.c  |  11 ++--
 t/t1400-update-ref.sh |   6 +--
 3 files changed, 17 insertions(+), 120 deletions(-)

diff --git a/refs.c b/refs.c
index 224ff66c7b..a2fd42364f 100644
--- a/refs.c
+++ b/refs.c
@@ -739,102 +739,6 @@ long get_files_ref_lock_timeout_ms(void)
 	return timeout_ms;
 }
 
-static int write_pseudoref(const char *pseudoref, const struct object_id *oid,
-			   const struct object_id *old_oid, struct strbuf *err)
-{
-	const char *filename;
-	int fd;
-	struct lock_file lock = LOCK_INIT;
-	struct strbuf buf = STRBUF_INIT;
-	int ret = -1;
-
-	if (!oid)
-		return 0;
-
-	strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
-
-	filename = git_path("%s", pseudoref);
-	fd = hold_lock_file_for_update_timeout(&lock, filename, 0,
-					       get_files_ref_lock_timeout_ms());
-	if (fd < 0) {
-		strbuf_addf(err, _("could not open '%s' for writing: %s"),
-			    filename, strerror(errno));
-		goto done;
-	}
-
-	if (old_oid) {
-		struct object_id actual_old_oid;
-
-		if (read_ref(pseudoref, &actual_old_oid)) {
-			if (!is_null_oid(old_oid)) {
-				strbuf_addf(err, _("could not read ref '%s'"),
-					    pseudoref);
-				rollback_lock_file(&lock);
-				goto done;
-			}
-		} else if (is_null_oid(old_oid)) {
-			strbuf_addf(err, _("ref '%s' already exists"),
-				    pseudoref);
-			rollback_lock_file(&lock);
-			goto done;
-		} else if (!oideq(&actual_old_oid, old_oid)) {
-			strbuf_addf(err, _("unexpected object ID when writing '%s'"),
-				    pseudoref);
-			rollback_lock_file(&lock);
-			goto done;
-		}
-	}
-
-	if (write_in_full(fd, buf.buf, buf.len) < 0) {
-		strbuf_addf(err, _("could not write to '%s'"), filename);
-		rollback_lock_file(&lock);
-		goto done;
-	}
-
-	commit_lock_file(&lock);
-	ret = 0;
-done:
-	strbuf_release(&buf);
-	return ret;
-}
-
-static int delete_pseudoref(const char *pseudoref, const struct object_id *old_oid)
-{
-	const char *filename;
-
-	filename = git_path("%s", pseudoref);
-
-	if (old_oid && !is_null_oid(old_oid)) {
-		struct lock_file lock = LOCK_INIT;
-		int fd;
-		struct object_id actual_old_oid;
-
-		fd = hold_lock_file_for_update_timeout(
-				&lock, filename, 0,
-				get_files_ref_lock_timeout_ms());
-		if (fd < 0) {
-			error_errno(_("could not open '%s' for writing"),
-				    filename);
-			return -1;
-		}
-		if (read_ref(pseudoref, &actual_old_oid))
-			die(_("could not read ref '%s'"), pseudoref);
-		if (!oideq(&actual_old_oid, old_oid)) {
-			error(_("unexpected object ID when deleting '%s'"),
-			      pseudoref);
-			rollback_lock_file(&lock);
-			return -1;
-		}
-
-		unlink(filename);
-		rollback_lock_file(&lock);
-	} else {
-		unlink(filename);
-	}
-
-	return 0;
-}
-
 int refs_delete_ref(struct ref_store *refs, const char *msg,
 		    const char *refname,
 		    const struct object_id *old_oid,
@@ -843,11 +747,6 @@ int refs_delete_ref(struct ref_store *refs, const char *msg,
 	struct ref_transaction *transaction;
 	struct strbuf err = STRBUF_INIT;
 
-	if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
-		assert(refs == get_main_ref_store(the_repository));
-		return delete_pseudoref(refname, old_oid);
-	}
-
 	transaction = ref_store_transaction_begin(refs, &err);
 	if (!transaction ||
 	    ref_transaction_delete(transaction, refname, old_oid,
@@ -1170,18 +1069,13 @@ int refs_update_ref(struct ref_store *refs, const char *msg,
 	struct strbuf err = STRBUF_INIT;
 	int ret = 0;
 
-	if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
-		assert(refs == get_main_ref_store(the_repository));
-		ret = write_pseudoref(refname, new_oid, old_oid, &err);
-	} else {
-		t = ref_store_transaction_begin(refs, &err);
-		if (!t ||
-		    ref_transaction_update(t, refname, new_oid, old_oid,
-					   flags, msg, &err) ||
-		    ref_transaction_commit(t, &err)) {
-			ret = 1;
-			ref_transaction_free(t);
-		}
+	t = ref_store_transaction_begin(refs, &err);
+	if (!t ||
+	    ref_transaction_update(t, refname, new_oid, old_oid, flags, msg,
+				   &err) ||
+	    ref_transaction_commit(t, &err)) {
+		ret = 1;
+		ref_transaction_free(t);
 	}
 	if (ret) {
 		const char *str = _("update_ref failed for ref '%s': %s");
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 6516c7bc8c..9951c2e403 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1228,7 +1228,6 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg,
 
 	for (i = 0; i < refnames->nr; i++) {
 		const char *refname = refnames->items[i].string;
-
 		if (refs_delete_ref(&refs->base, msg, refname, NULL, flags))
 			result |= error(_("could not remove reference %s"), refname);
 	}
@@ -2436,7 +2435,9 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 	update->backend_data = lock;
 
 	if (update->type & REF_ISSYMREF) {
-		if (update->flags & REF_NO_DEREF) {
+		if (update->flags & REF_NO_DEREF ||
+		    (ref_type(update->refname) == REF_TYPE_PSEUDOREF &&
+		     strcmp(update->refname, "HEAD"))) {
 			/*
 			 * We won't be reading the referent as part of
 			 * the transaction, so we have to read it here
@@ -2782,8 +2783,10 @@ static int files_transaction_finish(struct ref_store *ref_store,
 		struct ref_update *update = transaction->updates[i];
 		struct ref_lock *lock = update->backend_data;
 
-		if (update->flags & REF_NEEDS_COMMIT ||
-		    update->flags & REF_LOG_ONLY) {
+		if ((ref_type(lock->ref_name) != REF_TYPE_PSEUDOREF ||
+		     !strcmp(lock->ref_name, "HEAD")) &&
+		    (update->flags & REF_NEEDS_COMMIT ||
+		     update->flags & REF_LOG_ONLY)) {
 			if (files_log_ref_write(refs,
 						lock->ref_name,
 						&lock->old_oid,
diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index 27171f8261..6b8030e8fe 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -476,7 +476,7 @@ test_expect_success 'git cat-file blob master@{2005-05-26 23:42}:F (expect OTHER
 test_expect_success 'given old value for missing pseudoref, do not create' '
 	test_must_fail git update-ref PSEUDOREF $A $B 2>err &&
 	test_path_is_missing .git/PSEUDOREF &&
-	test_i18ngrep "could not read ref" err
+	test_i18ngrep "unable to resolve reference" err
 '
 
 test_expect_success 'create pseudoref' '
@@ -497,7 +497,7 @@ test_expect_success 'overwrite pseudoref with correct old value' '
 test_expect_success 'do not overwrite pseudoref with wrong old value' '
 	test_must_fail git update-ref PSEUDOREF $D $E 2>err &&
 	test $C = $(cat .git/PSEUDOREF) &&
-	test_i18ngrep "unexpected object ID" err
+	test_i18ngrep "cannot lock ref.*expected" err
 '
 
 test_expect_success 'delete pseudoref' '
@@ -509,7 +509,7 @@ test_expect_success 'do not delete pseudoref with wrong old value' '
 	git update-ref PSEUDOREF $A &&
 	test_must_fail git update-ref -d PSEUDOREF $B 2>err &&
 	test $A = $(cat .git/PSEUDOREF) &&
-	test_i18ngrep "unexpected object ID" err
+	test_i18ngrep "cannot lock ref.*expected" err
 '
 
 test_expect_success 'delete pseudoref with correct old value' '
-- 
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