bisect: peel annotated tags to commits

This patch fixes a bug where git-bisect doesn't handle receiving
annotated tags as "git bisect good <tag>", etc. It's a regression in
27257bc466 (bisect--helper: reimplement `bisect_state` & `bisect_head`
shell functions in C, 2020-10-15).

The original shell code called:

  sha=$(git rev-parse --verify "$rev^{commit}") ||
          die "$(eval_gettext "Bad rev input: \$rev")"

which will peel the input to a commit (or complain if that's not
possible). But the C code just calls get_oid(), which will yield the oid
of the tag.

The fix is to peel to a commit. The error message here is a little
non-idiomatic for Git (since it starts with a capital). I've mostly left
it, as it matches the other converted messages (like the "Bad rev input"
we print when get_oid() fails), though I did add an indication that it
was the peeling that was the problem. It might be worth taking a pass
through this converted code to modernize some of the error messages.

Note also that the test does a bare "grep" (not i18ngrep) on the
expected "X is the first bad commit" output message. This matches the
rest of the test script.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/bisect--helper.c

@@ -875,12 +875,19 @@ static enum bisect_error bisect_state(struct bisect_terms *terms, const char **a
 	 */
 
 	for (; argc; argc--, argv++) {
+		struct commit *commit;
+
 		if (get_oid(*argv, &oid)){
 			error(_("Bad rev input: %s"), *argv);
 			oid_array_clear(&revs);
 			return BISECT_FAILED;
 		}
-		oid_array_append(&revs, &oid);
+
+		commit = lookup_commit_reference(the_repository, &oid);
+		if (!commit)
+			die(_("Bad rev input (not a commit): %s"), *argv);
+
+		oid_array_append(&revs, &commit->object.oid);
 	}
 
 	if (strbuf_read_file(&buf, git_path_bisect_expected_rev(), 0) < the_hash_algo->hexsz ||

t/t6030-bisect-porcelain.sh

@@ -936,4 +936,16 @@ test_expect_success 'git bisect reset cleans bisection state properly' '
 	test_path_is_missing ".git/BISECT_START"
 '
 
+test_expect_success 'bisect handles annotated tags' '
+	test_commit commit-one &&
+	git tag -m foo tag-one &&
+	test_commit commit-two &&
+	git tag -m foo tag-two &&
+	git bisect start &&
+	git bisect good tag-one &&
+	git bisect bad tag-two >output &&
+	bad=$(git rev-parse --verify tag-two^{commit}) &&
+	grep "$bad is the first bad commit" output
+'
+
 test_done