refs/reftable: print errors on compaction failure

When git-pack-refs(1) fails in the reftable backend we end up printing
no error message at all, leaving the caller puzzled as to why compaction
has failed. Fix this.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

refs/reftable-backend.c

@@ -1221,8 +1221,12 @@ static int reftable_be_pack_refs(struct ref_store *ref_store,
 		stack = refs->main_stack;
 
 	ret = reftable_stack_compact_all(stack, NULL);
-	if (ret)
+	if (ret < 0) {
+		ret = error(_("unable to compact stack: %s"),
+			    reftable_error_str(ret));
 		goto out;
+	}
+
 	ret = reftable_stack_clean(stack);
 	if (ret)
 		goto out;

t/t0610-reftable-basics.sh

@@ -375,6 +375,18 @@ test_expect_success 'pack-refs: compacts tables' '
 	test_line_count = 1 repo/.git/reftable/tables.list
 '
 
+test_expect_success 'pack-refs: compaction raises locking errors' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	test_commit -C repo A &&
+	touch repo/.git/reftable/tables.list.lock &&
+	cat >expect <<-EOF &&
+	error: unable to compact stack: data is locked
+	EOF
+	test_must_fail git -C repo pack-refs 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success 'pack-refs: prunes stale tables' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&