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, 10 insertions, 0 deletions

diff --git a/refs.h b/refs.h
index d9051bbb04..d91fcb2d2f 100644
--- a/refs.h
+++ b/refs.h
@@ -653,6 +653,16 @@ int refs_for_each_reflog(struct ref_store *refs, each_reflog_fn fn, void *cb_dat
  */
 int check_refname_format(const char *refname, int flags);
 
+struct fsck_ref_report;
+
+/*
+ * Perform generic checks for a specific symref target. This function is
+ * expected to be called by the ref backends for every symbolic ref.
+ */
+int refs_fsck_symref(struct ref_store *refs, struct fsck_options *o,
+		     struct fsck_ref_report *report,
+		     const char *refname, const char *target);
+
 /*
  * Check the reference database for consistency. Return 0 if refs and
  * reflogs are consistent, and non-zero otherwise. The errors will be