sequencer: tighten label lookups

The `label` command creates a ref refs/rewritten/<label> that the
`reset` and `merge` commands resolve by calling lookup_label(). That
uses lookup_commit_reference_by_name() to look up the label ref. As
lookup_commit_reference_by_name() uses the dwim rules when looking up
the label it will look for a branch named
refs/heads/refs/rewritten/<label> and return that instead of an error if
the branch exists and the label does not. Fix this by using read_ref()
followed by lookup_commit_object() when looking up labels.

Signed-off-by: Phillip Wood <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: phillipwood

sequencer.c

@@ -3694,15 +3694,17 @@ static const char *reflog_message(struct replay_opts *opts,
 	return buf.buf;
 }
 
-static struct commit *lookup_label(const char *label, int len,
-				   struct strbuf *buf)
+static struct commit *lookup_label(struct repository *r, const char *label,
+				   int len, struct strbuf *buf)
 {
 	struct commit *commit;
+	struct object_id oid;
 
 	strbuf_reset(buf);
 	strbuf_addf(buf, "refs/rewritten/%.*s", len, label);
-	commit = lookup_commit_reference_by_name(buf->buf);
-	if (!commit) {
+	if (!read_ref(buf->buf, &oid)) {
+		commit = lookup_commit_object(r, &oid);
+	} else {
 		/* fall back to non-rewritten ref or commit */
 		strbuf_splice(buf, 0, strlen("refs/rewritten/"), "", 0);
 		commit = lookup_commit_reference_by_name(buf->buf);
@@ -3753,7 +3755,7 @@ static int do_reset(struct repository *r,
 				break;
 		len = i;
 
-		commit = lookup_label(name, len, &ref_name);
+		commit = lookup_label(r, name, len, &ref_name);
 		if (!commit) {
 			ret = -1;
 			goto cleanup;
@@ -3852,7 +3854,7 @@ static int do_merge(struct repository *r,
 		k = strcspn(p, " \t\n");
 		if (!k)
 			continue;
-		merge_commit = lookup_label(p, k, &ref_name);
+		merge_commit = lookup_label(r, p, k, &ref_name);
 		if (!merge_commit) {
 			ret = error(_("unable to parse '%.*s'"), k, p);
 			goto leave_merge;

t/t3430-rebase-merges.sh

@@ -146,6 +146,15 @@ test_expect_success '`reset` rejects trees' '
 	test_must_be_empty out
 '
 
+test_expect_success '`reset` only looks for labels under refs/rewritten/' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git branch refs/rewritten/my-label A &&
+	test_must_fail env GIT_SEQUENCE_EDITOR="echo reset my-label >" \
+		git rebase -i B C >out 2>err &&
+	grep "could not resolve ${SQ}my-label${SQ}" err &&
+	test_must_be_empty out
+'
+
 test_expect_success 'failed `merge -C` writes patch (may be rescheduled, too)' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout -b conflicting-merge A &&