Merge branch 'sj/ref-consistency-checks-more'

"git fsck" becomes more careful when checking the refs.

* sj/ref-consistency-checks-more:
  builtin/fsck: add `git refs verify` child process
  packed-backend: check whether the "packed-refs" is sorted
  packed-backend: add "packed-refs" entry consistency check
  packed-backend: check whether the refname contains NUL characters
  packed-backend: add "packed-refs" header consistency check
  packed-backend: check if header starts with "# pack-refs with: "
  packed-backend: check whether the "packed-refs" is regular file
  builtin/refs: get worktrees without reading head information
  t0602: use subshell to ensure working directory unchanged

Documentation/fsck-msgids.adoc

@@ -16,6 +16,13 @@
 `badObjectSha1`::
 	(ERROR) An object has a bad sha1.
 
+`badPackedRefEntry`::
+	(ERROR) The "packed-refs" file contains an invalid entry.
+
+`badPackedRefHeader`::
+	(ERROR) The "packed-refs" file contains an invalid
+	header.
+
 `badParentSha1`::
 	(ERROR) A commit object has a bad parent sha1.
 
@@ -176,6 +183,13 @@
 `nullSha1`::
 	(WARN) Tree contains entries pointing to a null sha1.
 
+`packedRefEntryNotTerminated`::
+	(ERROR) The "packed-refs" file contains an entry that is
+	not terminated by a newline.
+
+`packedRefUnsorted`::
+	(ERROR) The "packed-refs" file is not sorted.
+
 `refMissingNewline`::
 	(INFO) A loose ref that does not end with newline(LF). As
 	valid implementations of Git never created such a loose ref

Documentation/git-fsck.adoc

@@ -12,7 +12,7 @@ SYNOPSIS
 'git fsck' [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]
 	 [--[no-]full] [--strict] [--verbose] [--lost-found]
 	 [--[no-]dangling] [--[no-]progress] [--connectivity-only]
-	 [--[no-]name-objects] [<object>...]
+	 [--[no-]name-objects] [--[no-]references] [<object>...]
 
 DESCRIPTION
 -----------
@@ -104,6 +104,11 @@ care about this output and want to speed it up further.
 	progress status even if the standard error stream is not
 	directed to a terminal.
 
+--[no-]references::
+	Control whether to check the references database consistency
+	via 'git refs verify'. See linkgit:git-refs[1] for details.
+	The default is to check the references database.
+
 CONFIGURATION
 -------------
 

builtin/fsck.c

@@ -50,6 +50,7 @@ static int verbose;
 static int show_progress = -1;
 static int show_dangling = 1;
 static int name_objects;
+static int check_references = 1;
 #define ERROR_OBJECT 01
 #define ERROR_REACHABLE 02
 #define ERROR_PACK 04
@@ -905,11 +906,37 @@ static int check_pack_rev_indexes(struct repository *r, int show_progress)
 	return res;
 }
 
+static void fsck_refs(struct repository *r)
+{
+	struct child_process refs_verify = CHILD_PROCESS_INIT;
+	struct progress *progress = NULL;
+
+	if (show_progress)
+		progress = start_progress(r, _("Checking ref database"), 1);
+
+	if (verbose)
+		fprintf_ln(stderr, _("Checking ref database"));
+
+	child_process_init(&refs_verify);
+	refs_verify.git_cmd = 1;
+	strvec_pushl(&refs_verify.args, "refs", "verify", NULL);
+	if (verbose)
+		strvec_push(&refs_verify.args, "--verbose");
+	if (check_strict)
+		strvec_push(&refs_verify.args, "--strict");
+
+	if (run_command(&refs_verify))
+		errors_found |= ERROR_REFS;
+
+	display_progress(progress, 1);
+	stop_progress(&progress);
+}
+
 static char const * const fsck_usage[] = {
 	N_("git fsck [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]\n"
 	   "         [--[no-]full] [--strict] [--verbose] [--lost-found]\n"
 	   "         [--[no-]dangling] [--[no-]progress] [--connectivity-only]\n"
-	   "         [--[no-]name-objects] [<object>...]"),
+	   "         [--[no-]name-objects] [--[no-]references] [<object>...]"),
 	NULL
 };
 
@@ -928,6 +955,7 @@ static struct option fsck_opts[] = {
 				N_("write dangling objects in .git/lost-found")),
 	OPT_BOOL(0, "progress", &show_progress, N_("show progress")),
 	OPT_BOOL(0, "name-objects", &name_objects, N_("show verbose names for reachable objects")),
+	OPT_BOOL(0, "references", &check_references, N_("check reference database consistency")),
 	OPT_END(),
 };
 
@@ -970,6 +998,9 @@ int cmd_fsck(int argc,
 	git_config(git_fsck_config, &fsck_obj_options);
 	prepare_repo_settings(the_repository);
 
+	if (check_references)
+		fsck_refs(the_repository);
+
 	if (connectivity_only) {
 		for_each_loose_object(mark_loose_for_connectivity, NULL, 0);
 		for_each_packed_object(the_repository,

builtin/refs.c

@@ -91,7 +91,7 @@ static int cmd_refs_verify(int argc, const char **argv, const char *prefix,
 	git_config(git_fsck_config, &fsck_refs_options);
 	prepare_repo_settings(the_repository);
 
-	worktrees = get_worktrees();
+	worktrees = get_worktrees_without_reading_head();
 	for (size_t i = 0; worktrees[i]; i++)
 		ret |= refs_fsck(get_worktree_ref_store(worktrees[i]),
 				 &fsck_refs_options, worktrees[i]);

fsck.h

@@ -30,6 +30,8 @@ enum fsck_msg_type {
 	FUNC(BAD_EMAIL, ERROR) \
 	FUNC(BAD_NAME, ERROR) \
 	FUNC(BAD_OBJECT_SHA1, ERROR) \
+	FUNC(BAD_PACKED_REF_ENTRY, ERROR) \
+	FUNC(BAD_PACKED_REF_HEADER, ERROR) \
 	FUNC(BAD_PARENT_SHA1, ERROR) \
 	FUNC(BAD_REF_CONTENT, ERROR) \
 	FUNC(BAD_REF_FILETYPE, ERROR) \
@@ -53,6 +55,8 @@ enum fsck_msg_type {
 	FUNC(MISSING_TYPE, ERROR) \
 	FUNC(MISSING_TYPE_ENTRY, ERROR) \
 	FUNC(MULTIPLE_AUTHORS, ERROR) \
+	FUNC(PACKED_REF_ENTRY_NOT_TERMINATED, ERROR) \
+	FUNC(PACKED_REF_UNSORTED, ERROR) \
 	FUNC(TREE_NOT_SORTED, ERROR) \
 	FUNC(UNKNOWN_TYPE, ERROR) \
 	FUNC(ZERO_PADDED_DATE, ERROR) \

refs/packed-backend.c

@@ -4,6 +4,7 @@
 #include "../git-compat-util.h"
 #include "../config.h"
 #include "../dir.h"
+#include "../fsck.h"
 #include "../gettext.h"
 #include "../hash.h"
 #include "../hex.h"
@@ -299,14 +300,9 @@ struct snapshot_record {
 	size_t len;
 };
 
-static int cmp_packed_ref_records(const void *v1, const void *v2,
-				  void *cb_data)
-{
-	const struct snapshot *snapshot = cb_data;
-	const struct snapshot_record *e1 = v1, *e2 = v2;
-	const char *r1 = e1->start + snapshot_hexsz(snapshot) + 1;
-	const char *r2 = e2->start + snapshot_hexsz(snapshot) + 1;
 
+static int cmp_packed_refname(const char *r1, const char *r2)
+{
 	while (1) {
 		if (*r1 == '\n')
 			return *r2 == '\n' ? 0 : -1;
@@ -321,6 +317,17 @@ static int cmp_packed_ref_records(const void *v1, const void *v2,
 	}
 }
 
+static int cmp_packed_ref_records(const void *v1, const void *v2,
+				  void *cb_data)
+{
+	const struct snapshot *snapshot = cb_data;
+	const struct snapshot_record *e1 = v1, *e2 = v2;
+	const char *r1 = e1->start + snapshot_hexsz(snapshot) + 1;
+	const char *r2 = e2->start + snapshot_hexsz(snapshot) + 1;
+
+	return cmp_packed_refname(r1, r2);
+}
+
 /*
  * Compare a snapshot record at `rec` to the specified NUL-terminated
  * refname.
@@ -493,6 +500,21 @@ static void verify_buffer_safe(struct snapshot *snapshot)
 				 last_line, eof - last_line);
 }
 
+/*
+ * When parsing the "packed-refs" file, we will parse it line by line.
+ * Because we know the start pointer of the refname and the next
+ * newline pointer, we could calculate the length of the refname by
+ * subtracting the two pointers. However, there is a corner case where
+ * the refname contains corrupted embedded NUL characters. And
+ * `check_refname_format()` will not catch this when the truncated
+ * refname is still a valid refname. To prevent this, we need to check
+ * whether the refname contains the NUL characters.
+ */
+static int refname_contains_nul(struct strbuf *refname)
+{
+	return !!memchr(refname->buf, '\0', refname->len);
+}
+
 #define SMALL_FILE_SIZE (32*1024)
 
 /*
@@ -693,7 +715,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
 
 		tmp = xmemdupz(snapshot->buf, eol - snapshot->buf);
 
-		if (!skip_prefix(tmp, "# pack-refs with:", (const char **)&p))
+		if (!skip_prefix(tmp, "# pack-refs with: ", (const char **)&p))
 			die_invalid_line(refs->path,
 					 snapshot->buf,
 					 snapshot->eof - snapshot->buf);
@@ -894,6 +916,9 @@ static int next_record(struct packed_ref_iterator *iter)
 	strbuf_add(&iter->refname_buf, p, eol - p);
 	iter->base.refname = iter->refname_buf.buf;
 
+	if (refname_contains_nul(&iter->refname_buf))
+		die("packed refname contains embedded NULL: %s", iter->base.refname);
+
 	if (check_refname_format(iter->base.refname, REFNAME_ALLOW_ONELEVEL)) {
 		if (!refname_is_safe(iter->base.refname))
 			die("packed refname is dangerous: %s",
@@ -1748,15 +1773,329 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 	return empty_ref_iterator_begin();
 }
 
-static int packed_fsck(struct ref_store *ref_store UNUSED,
+static int packed_fsck_ref_next_line(struct fsck_options *o,
-		       struct fsck_options *o UNUSED,
+				     unsigned long line_number, const char *start,
+				     const char *eof, const char **eol)
+{
+	int ret = 0;
+
+	*eol = memchr(start, '\n', eof - start);
+	if (!*eol) {
+		struct strbuf packed_entry = STRBUF_INIT;
+		struct fsck_ref_report report = { 0 };
+
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_PACKED_REF_ENTRY_NOT_TERMINATED,
+				      "'%.*s' is not terminated with a newline",
+				      (int)(eof - start), start);
+
+		/*
+		 * There is no newline but we still want to parse it to the end of
+		 * the buffer.
+		 */
+		*eol = eof;
+		strbuf_release(&packed_entry);
+	}
+
+	return ret;
+}
+
+static int packed_fsck_ref_header(struct fsck_options *o,
+				  const char *start, const char *eol,
+				  unsigned int *sorted)
+{
+	struct string_list traits = STRING_LIST_INIT_NODUP;
+	char *tmp_line;
+	int ret = 0;
+	char *p;
+
+	tmp_line = xmemdupz(start, eol - start);
+	if (!skip_prefix(tmp_line, "# pack-refs with: ", (const char **)&p)) {
+		struct fsck_ref_report report = { 0 };
+		report.path = "packed-refs.header";
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_HEADER,
+				      "'%.*s' does not start with '# pack-refs with: '",
+				      (int)(eol - start), start);
+		goto cleanup;
+	}
+
+	string_list_split_in_place(&traits, p, " ", -1);
+	*sorted = unsorted_string_list_has_string(&traits, "sorted");
+
+cleanup:
+	free(tmp_line);
+	string_list_clear(&traits, 0);
+	return ret;
+}
+
+static int packed_fsck_ref_peeled_line(struct fsck_options *o,
+				       struct ref_store *ref_store,
+				       unsigned long line_number,
+				       const char *start, const char *eol)
+{
+	struct strbuf packed_entry = STRBUF_INIT;
+	struct fsck_ref_report report = { 0 };
+	struct object_id peeled;
+	const char *p;
+	int ret = 0;
+
+	/*
+	 * Skip the '^' and parse the peeled oid.
+	 */
+	start++;
+	if (parse_oid_hex_algop(start, &peeled, &p, ref_store->repo->hash_algo)) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_ENTRY,
+				      "'%.*s' has invalid peeled oid",
+				      (int)(eol - start), start);
+		goto cleanup;
+	}
+
+	if (p != eol) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_ENTRY,
+				      "has trailing garbage after peeled oid '%.*s'",
+				      (int)(eol - p), p);
+		goto cleanup;
+	}
+
+cleanup:
+	strbuf_release(&packed_entry);
+	return ret;
+}
+
+static int packed_fsck_ref_main_line(struct fsck_options *o,
+				     struct ref_store *ref_store,
+				     unsigned long line_number,
+				     struct strbuf *refname,
+				     const char *start, const char *eol)
+{
+	struct strbuf packed_entry = STRBUF_INIT;
+	struct fsck_ref_report report = { 0 };
+	struct object_id oid;
+	const char *p;
+	int ret = 0;
+
+	if (parse_oid_hex_algop(start, &oid, &p, ref_store->repo->hash_algo)) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_ENTRY,
+				      "'%.*s' has invalid oid",
+				      (int)(eol - start), start);
+		goto cleanup;
+	}
+
+	if (p == eol || !isspace(*p)) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_ENTRY,
+				      "has no space after oid '%s' but with '%.*s'",
+				      oid_to_hex(&oid), (int)(eol - p), p);
+		goto cleanup;
+	}
+
+	p++;
+	strbuf_reset(refname);
+	strbuf_add(refname, p, eol - p);
+	if (refname_contains_nul(refname)) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_PACKED_REF_ENTRY,
+				      "refname '%s' contains NULL binaries",
+				      refname->buf);
+	}
+
+	if (check_refname_format(refname->buf, 0)) {
+		strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+		report.path = packed_entry.buf;
+
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_REF_NAME,
+				      "has bad refname '%s'", refname->buf);
+	}
+
+cleanup:
+	strbuf_release(&packed_entry);
+	return ret;
+}
+
+static int packed_fsck_ref_sorted(struct fsck_options *o,
+				  struct ref_store *ref_store,
+				  const char *start, const char *eof)
+{
+	size_t hexsz = ref_store->repo->hash_algo->hexsz;
+	struct strbuf packed_entry = STRBUF_INIT;
+	struct fsck_ref_report report = { 0 };
+	struct strbuf refname1 = STRBUF_INIT;
+	struct strbuf refname2 = STRBUF_INIT;
+	unsigned long line_number = 1;
+	const char *former = NULL;
+	const char *current;
+	const char *eol;
+	int ret = 0;
+
+	if (*start == '#') {
+		eol = memchr(start, '\n', eof - start);
+		start = eol + 1;
+		line_number++;
+	}
+
+	for (; start < eof; line_number++, start = eol + 1) {
+		eol = memchr(start, '\n', eof - start);
+
+		if (*start == '^')
+			continue;
+
+		if (!former) {
+			former = start + hexsz + 1;
+			continue;
+		}
+
+		current = start + hexsz + 1;
+		if (cmp_packed_refname(former, current) >= 0) {
+			const char *err_fmt =
+				"refname '%s' is less than previous refname '%s'";
+
+			eol = memchr(former, '\n', eof - former);
+			strbuf_add(&refname1, former, eol - former);
+			eol = memchr(current, '\n', eof - current);
+			strbuf_add(&refname2, current, eol - current);
+
+			strbuf_addf(&packed_entry, "packed-refs line %lu", line_number);
+			report.path = packed_entry.buf;
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_PACKED_REF_UNSORTED,
+					      err_fmt, refname2.buf, refname1.buf);
+			goto cleanup;
+		}
+		former = current;
+	}
+
+cleanup:
+	strbuf_release(&packed_entry);
+	strbuf_release(&refname1);
+	strbuf_release(&refname2);
+	return ret;
+}
+
+static int packed_fsck_ref_content(struct fsck_options *o,
+				   struct ref_store *ref_store,
+				   unsigned int *sorted,
+				   const char *start, const char *eof)
+{
+	struct strbuf refname = STRBUF_INIT;
+	unsigned long line_number = 1;
+	const char *eol;
+	int ret = 0;
+
+	ret |= packed_fsck_ref_next_line(o, line_number, start, eof, &eol);
+	if (*start == '#') {
+		ret |= packed_fsck_ref_header(o, start, eol, sorted);
+
+		start = eol + 1;
+		line_number++;
+	}
+
+	while (start < eof) {
+		ret |= packed_fsck_ref_next_line(o, line_number, start, eof, &eol);
+		ret |= packed_fsck_ref_main_line(o, ref_store, line_number, &refname, start, eol);
+		start = eol + 1;
+		line_number++;
+		if (start < eof && *start == '^') {
+			ret |= packed_fsck_ref_next_line(o, line_number, start, eof, &eol);
+			ret |= packed_fsck_ref_peeled_line(o, ref_store, line_number,
+							   start, eol);
+			start = eol + 1;
+			line_number++;
+		}
+	}
+
+	strbuf_release(&refname);
+	return ret;
+}
+
+static int packed_fsck(struct ref_store *ref_store,
+		       struct fsck_options *o,
 		       struct worktree *wt)
 {
+	struct packed_ref_store *refs = packed_downcast(ref_store,
+							REF_STORE_READ, "fsck");
+	struct strbuf packed_ref_content = STRBUF_INIT;
+	unsigned int sorted = 0;
+	struct stat st;
+	int ret = 0;
+	int fd = -1;
 
 	if (!is_main_worktree(wt))
-		return 0;
+		goto cleanup;
 
-	return 0;
+	if (o->verbose)
+		fprintf_ln(stderr, "Checking packed-refs file %s", refs->path);
+
+	fd = open_nofollow(refs->path, O_RDONLY);
+	if (fd < 0) {
+		/*
+		 * If the packed-refs file doesn't exist, there's nothing
+		 * to check.
+		 */
+		if (errno == ENOENT)
+			goto cleanup;
+
+		if (errno == ELOOP) {
+			struct fsck_ref_report report = { 0 };
+			report.path = "packed-refs";
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_BAD_REF_FILETYPE,
+					      "not a regular file but a symlink");
+			goto cleanup;
+		}
+
+		ret = error_errno(_("unable to open '%s'"), refs->path);
+		goto cleanup;
+	} else if (fstat(fd, &st) < 0) {
+		ret = error_errno(_("unable to stat '%s'"), refs->path);
+		goto cleanup;
+	} else if (!S_ISREG(st.st_mode)) {
+		struct fsck_ref_report report = { 0 };
+		report.path = "packed-refs";
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_REF_FILETYPE,
+				      "not a regular file");
+		goto cleanup;
+	}
+
+	if (strbuf_read(&packed_ref_content, fd, 0) < 0) {
+		ret = error_errno(_("unable to read '%s'"), refs->path);
+		goto cleanup;
+	}
+
+	ret = packed_fsck_ref_content(o, ref_store, &sorted, packed_ref_content.buf,
+				      packed_ref_content.buf + packed_ref_content.len);
+	if (!ret && sorted)
+		ret = packed_fsck_ref_sorted(o, ref_store, packed_ref_content.buf,
+					     packed_ref_content.buf + packed_ref_content.len);
+
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	strbuf_release(&packed_ref_content);
+	return ret;
 }
 
 struct ref_storage_be refs_be_packed = {

t/t0602-reffiles-fsck.sh

@@ -14,6 +14,7 @@ test_expect_success 'ref name should be checked' '
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
 	tag_dir_prefix=.git/refs/tags &&
+	(
 		cd repo &&
 
 		git commit --allow-empty -m initial &&
@@ -83,12 +84,14 @@ test_expect_success 'ref name should be checked' '
 			rm -r "$branch_dir_prefix/$refname" &&
 			test_cmp expect err || return 1
 		done
+	)
 '
 
 test_expect_success 'ref name check should be adapted into fsck messages' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
+	(
 		cd repo &&
 		git commit --allow-empty -m initial &&
 		git checkout -b branch-1 &&
@@ -104,12 +107,13 @@ test_expect_success 'ref name check should be adapted into fsck messages' '
 		cp $branch_dir_prefix/branch-1 $branch_dir_prefix/.branch-1 &&
 		git -c fsck.badRefName=ignore refs verify 2>err &&
 		test_must_be_empty err
+	)
 '
 
 test_expect_success 'ref name check should work for multiple worktrees' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
-
+	(
 		cd repo &&
 		test_commit initial &&
 		git checkout -b branch-1 &&
@@ -155,12 +159,14 @@ test_expect_success 'ref name check should work for multiple worktrees' '
 				test_cmp expect sorted_err || return 1
 			)
 		done
+	)
 '
 
 test_expect_success 'regular ref content should be checked (individual)' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -230,6 +236,7 @@ test_expect_success 'regular ref content should be checked (individual)' '
 		EOF
 		rm $branch_dir_prefix/branch-garbage-special &&
 		test_cmp expect err
+	)
 '
 
 test_expect_success 'regular ref content should be checked (aggregate)' '
@@ -237,6 +244,7 @@ test_expect_success 'regular ref content should be checked (aggregate)' '
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
 	tag_dir_prefix=.git/refs/tags &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -260,12 +268,14 @@ test_expect_success 'regular ref content should be checked (aggregate)' '
 		EOF
 		sort err >sorted_err &&
 		test_cmp expect sorted_err
+	)
 '
 
 test_expect_success 'textual symref content should be checked (individual)' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -330,6 +340,7 @@ test_expect_success 'textual symref content should be checked (individual)' '
 		EOF
 		rm $branch_dir_prefix/a/b/branch-complicated &&
 		test_cmp expect err
+	)
 '
 
 test_expect_success 'textual symref content should be checked (aggregate)' '
@@ -337,6 +348,7 @@ test_expect_success 'textual symref content should be checked (aggregate)' '
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
 	tag_dir_prefix=.git/refs/tags &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -363,6 +375,7 @@ test_expect_success 'textual symref content should be checked (aggregate)' '
 		EOF
 		sort err >sorted_err &&
 		test_cmp expect sorted_err
+	)
 '
 
 test_expect_success 'the target of the textual symref should be checked' '
@@ -370,6 +383,7 @@ test_expect_success 'the target of the textual symref should be checked' '
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
 	tag_dir_prefix=.git/refs/tags &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -392,6 +406,7 @@ test_expect_success 'the target of the textual symref should be checked' '
 			rm $branch_dir_prefix/branch-bad-1 &&
 			test_cmp expect err || return 1
 		done
+	)
 '
 
 test_expect_success SYMLINKS 'symlink symref content should be checked' '
@@ -399,6 +414,7 @@ test_expect_success SYMLINKS 'symlink symref content should be checked' '
 	git init repo &&
 	branch_dir_prefix=.git/refs/heads &&
 	tag_dir_prefix=.git/refs/tags &&
+	(
 		cd repo &&
 		test_commit default &&
 		mkdir -p "$branch_dir_prefix/a/b" &&
@@ -437,11 +453,13 @@ test_expect_success SYMLINKS 'symlink symref content should be checked' '
 		EOF
 		rm $tag_dir_prefix/tag-symbolic-1 &&
 		test_cmp expect err
+	)
 '
 
 test_expect_success SYMLINKS 'symlink symref content should be checked (worktree)' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
+	(
 		cd repo &&
 		test_commit default &&
 		git branch branch-1 &&
@@ -533,11 +551,13 @@ test_expect_success SYMLINKS 'symlink symref content should be checked (worktree
 			rm $worktree2_refdir_prefix/bad-symbolic &&
 			test_cmp expect err || return 1
 		done
+	)
 '
 
 test_expect_success 'ref content checks should work with worktrees' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
+	(
 		cd repo &&
 		test_commit default &&
 		git branch branch-1 &&
@@ -594,6 +614,259 @@ test_expect_success 'ref content checks should work with worktrees' '
 		EOF
 		rm $worktree1_refdir_prefix/branch-garbage &&
 		test_cmp expect err
+	)
+'
+
+test_expect_success SYMLINKS 'the filetype of packed-refs should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git branch branch-3 &&
+		git pack-refs --all &&
+
+		mv .git/packed-refs .git/packed-refs-back &&
+		ln -sf packed-refs-back .git/packed-refs &&
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs: badRefFiletype: not a regular file but a symlink
+		EOF
+		rm .git/packed-refs &&
+		test_cmp expect err &&
+
+		mkdir .git/packed-refs &&
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs: badRefFiletype: not a regular file
+		EOF
+		rm -r .git/packed-refs &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'packed-refs header should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+
+		git refs verify 2>err &&
+		test_must_be_empty err &&
+
+		for bad_header in "# pack-refs wit: peeled fully-peeled sorted " \
+				  "# pack-refs with traits: peeled fully-peeled sorted " \
+				  "# pack-refs with a: peeled fully-peeled" \
+				  "# pack-refs with:peeled fully-peeled sorted"
+		do
+			printf "%s\n" "$bad_header" >.git/packed-refs &&
+			test_must_fail git refs verify 2>err &&
+			cat >expect <<-EOF &&
+			error: packed-refs.header: badPackedRefHeader: '\''$bad_header'\'' does not start with '\''# pack-refs with: '\''
+			EOF
+			rm .git/packed-refs &&
+			test_cmp expect err || return 1
+		done
+	)
+'
+
+test_expect_success 'packed-refs missing header should not be reported' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+
+		printf "$(git rev-parse HEAD) refs/heads/main\n" >.git/packed-refs &&
+		git refs verify 2>err &&
+		test_must_be_empty err
+	)
+'
+
+test_expect_success 'packed-refs unknown traits should not be reported' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+
+		printf "# pack-refs with: peeled fully-peeled sorted foo\n" >.git/packed-refs &&
+		git refs verify 2>err &&
+		test_must_be_empty err
+	)
+'
+
+test_expect_success 'packed-refs content should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git tag -a annotated-tag-1 -m tag-1 &&
+		git tag -a annotated-tag-2 -m tag-2 &&
+
+		branch_1_oid=$(git rev-parse branch-1) &&
+		branch_2_oid=$(git rev-parse branch-2) &&
+		tag_1_oid=$(git rev-parse annotated-tag-1) &&
+		tag_2_oid=$(git rev-parse annotated-tag-2) &&
+		tag_1_peeled_oid=$(git rev-parse annotated-tag-1^{}) &&
+		tag_2_peeled_oid=$(git rev-parse annotated-tag-2^{}) &&
+		short_oid=$(printf "%s" $tag_1_peeled_oid | cut -c 1-4) &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled sorted
+		$short_oid refs/heads/branch-1
+		${branch_1_oid}x
+		$branch_2_oid   refs/heads/bad-branch
+		$branch_2_oid refs/heads/branch.
+		$tag_1_oid refs/tags/annotated-tag-3
+		^$short_oid
+		$tag_2_oid refs/tags/annotated-tag-4.
+		^$tag_2_peeled_oid garbage
+		EOF
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs line 2: badPackedRefEntry: '\''$short_oid refs/heads/branch-1'\'' has invalid oid
+		error: packed-refs line 3: badPackedRefEntry: has no space after oid '\''$branch_1_oid'\'' but with '\''x'\''
+		error: packed-refs line 4: badRefName: has bad refname '\''  refs/heads/bad-branch'\''
+		error: packed-refs line 5: badRefName: has bad refname '\''refs/heads/branch.'\''
+		error: packed-refs line 7: badPackedRefEntry: '\''$short_oid'\'' has invalid peeled oid
+		error: packed-refs line 8: badRefName: has bad refname '\''refs/tags/annotated-tag-4.'\''
+		error: packed-refs line 9: badPackedRefEntry: has trailing garbage after peeled oid '\'' garbage'\''
+		EOF
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'packed-ref with sorted trait should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git tag -a annotated-tag-1 -m tag-1 &&
+		branch_1_oid=$(git rev-parse branch-1) &&
+		branch_2_oid=$(git rev-parse branch-2) &&
+		tag_1_oid=$(git rev-parse annotated-tag-1) &&
+		tag_1_peeled_oid=$(git rev-parse annotated-tag-1^{}) &&
+		refname1="refs/heads/main" &&
+		refname2="refs/heads/foo" &&
+		refname3="refs/tags/foo" &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled sorted
+		EOF
+		git refs verify 2>err &&
+		rm .git/packed-refs &&
+		test_must_be_empty err &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled sorted
+		$branch_2_oid $refname1
+		EOF
+		git refs verify 2>err &&
+		rm .git/packed-refs &&
+		test_must_be_empty err &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled sorted
+		$branch_2_oid $refname1
+		$branch_1_oid $refname2
+		$tag_1_oid $refname3
+		EOF
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs line 3: packedRefUnsorted: refname '\''$refname2'\'' is less than previous refname '\''$refname1'\''
+		EOF
+		rm .git/packed-refs &&
+		test_cmp expect err &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled sorted
+		$tag_1_oid $refname3
+		^$tag_1_peeled_oid
+		$branch_2_oid $refname2
+		EOF
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs line 4: packedRefUnsorted: refname '\''$refname2'\'' is less than previous refname '\''$refname3'\''
+		EOF
+		rm .git/packed-refs &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'packed-ref without sorted trait should not be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git tag -a annotated-tag-1 -m tag-1 &&
+		branch_1_oid=$(git rev-parse branch-1) &&
+		branch_2_oid=$(git rev-parse branch-2) &&
+		tag_1_oid=$(git rev-parse annotated-tag-1) &&
+		tag_1_peeled_oid=$(git rev-parse annotated-tag-1^{}) &&
+		refname1="refs/heads/main" &&
+		refname2="refs/heads/foo" &&
+		refname3="refs/tags/foo" &&
+
+		cat >.git/packed-refs <<-EOF &&
+		# pack-refs with: peeled fully-peeled
+		$branch_2_oid $refname1
+		$branch_1_oid $refname2
+		EOF
+		git refs verify 2>err &&
+		test_must_be_empty err
+	)
+'
+
+test_expect_success '--[no-]references option should apply to fsck' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	branch_dir_prefix=.git/refs/heads &&
+	(
+		cd repo &&
+		test_commit default &&
+		for trailing_content in " garbage" "    more garbage"
+		do
+			printf "%s" "$(git rev-parse HEAD)$trailing_content" >$branch_dir_prefix/branch-garbage &&
+			git fsck 2>err &&
+			cat >expect <<-EOF &&
+			warning: refs/heads/branch-garbage: trailingRefContent: has trailing garbage: '\''$trailing_content'\''
+			EOF
+			rm $branch_dir_prefix/branch-garbage &&
+			test_cmp expect err || return 1
+		done &&
+
+		for trailing_content in " garbage" "    more garbage"
+		do
+			printf "%s" "$(git rev-parse HEAD)$trailing_content" >$branch_dir_prefix/branch-garbage &&
+			git fsck --references 2>err &&
+			cat >expect <<-EOF &&
+			warning: refs/heads/branch-garbage: trailingRefContent: has trailing garbage: '\''$trailing_content'\''
+			EOF
+			rm $branch_dir_prefix/branch-garbage &&
+			test_cmp expect err || return 1
+		done &&
+
+		for trailing_content in " garbage" "    more garbage"
+		do
+			printf "%s" "$(git rev-parse HEAD)$trailing_content" >$branch_dir_prefix/branch-garbage &&
+			git fsck --no-references 2>err &&
+			rm $branch_dir_prefix/branch-garbage &&
+			test_must_be_empty err || return 1
+		done
+	)
 '
 
 test_done

worktree.c

@@ -199,6 +199,11 @@ struct worktree **get_worktrees(void)
 	return get_worktrees_internal(0);
 }
 
+struct worktree **get_worktrees_without_reading_head(void)
+{
+	return get_worktrees_internal(1);
+}
+
 char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)

worktree.h

@@ -30,6 +30,14 @@ struct worktree {
  */
 struct worktree **get_worktrees(void);
 
+/*
+ * Like `get_worktrees`, but does not read HEAD. Skip reading HEAD allows to
+ * get the worktree without worrying about failures pertaining to parsing
+ * the HEAD ref. This is useful in contexts where it is assumed that the
+ * refdb may not be in a consistent state.
+ */
+struct worktree **get_worktrees_without_reading_head(void);
+
 /*
  * Returns 1 if linked worktrees exist, 0 otherwise.
  */