refs/files: extract generic symref target checks

The consistency checks for the "files" backend contain a couple of
verifications for symrefs that verify generic properties of the target
reference. These properties need to hold for every backend, no matter
whether it's using the "files" or "reftable" backend.

Reimplementing these checks for every single backend doesn't really make
sense. Extract it into a generic `refs_fsck_symref()` function that can
be used by other backends, as well. The "reftable" backend will be wired
up in a subsequent commit.

While at it, improve the consistency checks so that we don't complain
about refs pointing to a non-ref target in case the target refname
format does not verify. Otherwise it's very likely that we'll generate
both error messages, which feels somewhat redundant in this case.

Note that the function has a couple of `UNUSED` parameters. These will
become referenced in a subsequent commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/refs.c b/refs.c
index e06e0cb072..739bf9fefc 100644
--- a/refs.c
+++ b/refs.c
@@ -320,6 +320,27 @@ int check_refname_format(const char *refname, int flags)
 	return check_or_sanitize_refname(refname, flags, NULL);
 }
 
+int refs_fsck_symref(struct ref_store *refs UNUSED, struct fsck_options *o,
+		     struct fsck_ref_report *report,
+		     const char *refname UNUSED, const char *target)
+{
+	if (is_root_ref(target))
+		return 0;
+
+	if (check_refname_format(target, 0) &&
+	    fsck_report_ref(o, report, FSCK_MSG_BAD_REFERENT_NAME,
+			    "points to invalid refname '%s'", target))
+		return -1;
+
+	if (!starts_with(target, "refs/") &&
+	    !starts_with(target, "worktrees/") &&
+	    fsck_report_ref(o, report, FSCK_MSG_SYMREF_TARGET_IS_NOT_A_REF,
+			    "points to non-ref target '%s'", target))
+		return -1;
+
+	return 0;
+}
+
 int refs_fsck(struct ref_store *refs, struct fsck_options *o,
 	      struct worktree *wt)
 {