refs/reftable: perform explicit D/F check when writing symrefs

We already perform explicit D/F checks in all reftable callbacks which
write refs, except when writing symrefs. For one this leads to an error
message which isn't perfectly actionable because we only tell the user
that there was a D/F conflict, but not which refs conflicted with each
other. But second, once all ref updating callbacks explicitly check for
D/F conflicts, we can disable the D/F checks in the reftable library
itself and thus avoid some duplicated efforts.

Refactor the code that writes symref tables to explicitly call into
`refs_verify_refname_available()` when writing symrefs.

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

1 files changed, 17 insertions, 3 deletions

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 0358da14db..8a54b0d8b2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1217,6 +1217,7 @@ out:
 struct write_create_symref_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
+	struct strbuf *err;
 	const char *refname;
 	const char *target;
 	const char *logmsg;
@@ -1239,6 +1240,11 @@ static int write_create_symref_table(struct reftable_writer *writer, void *cb_da
 
 	reftable_writer_set_limits(writer, ts, ts);
 
+	ret = refs_verify_refname_available(&create->refs->base, create->refname,
+					    NULL, NULL, create->err);
+	if (ret < 0)
+		return ret;
+
 	ret = reftable_writer_add_ref(writer, &ref);
 	if (ret)
 		return ret;
@@ -1280,12 +1286,14 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 	struct reftable_ref_store *refs =
 		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
 	struct reftable_stack *stack = stack_for(refs, refname, &refname);
+	struct strbuf err = STRBUF_INIT;
 	struct write_create_symref_arg arg = {
 		.refs = refs,
 		.stack = stack,
 		.refname = refname,
 		.target = target,
 		.logmsg = logmsg,
+		.err = &err,
 	};
 	int ret;
 
@@ -1301,9 +1309,15 @@ static int reftable_be_create_symref(struct ref_store *ref_store,
 
 done:
 	assert(ret != REFTABLE_API_ERROR);
-	if (ret)
-		error("unable to write symref for %s: %s", refname,
-		      reftable_error_str(ret));
+	if (ret) {
+		if (err.len)
+			error("%s", err.buf);
+		else
+			error("unable to write symref for %s: %s", refname,
+			      reftable_error_str(ret));
+	}
+
+	strbuf_release(&err);
 	return ret;
 }