merge: Honor prepare-commit-msg return code

65969d4 (merge: honor prepare-commit-msg hook, 2011-02-14) tried to
make "git commit" and "git merge" consistent, because a merge that
required user assistance has to be concluded with "git commit", but
back then only "git commit" triggered prepare-commit-msg hook.

When it added a call to run the prepare-commit-msg hook, however, it
forgot to check the exit code from the hook like "git commit" does,
and ended up replacing one inconsistency with another.

When prepare-commit-msg hook that is run from "git merge" exits with
a non-zero status, abort the commit.

Signed-off-by: Antoine Pelisse <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: apelisse

builtin/merge.c

@@ -903,8 +903,9 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 	if (0 < option_edit)
 		strbuf_add_lines(&msg, "# ", comment, strlen(comment));
 	write_merge_msg(&msg);
-	run_hook(get_index_file(), "prepare-commit-msg",
-		 git_path("MERGE_MSG"), "merge", NULL, NULL);
+	if (run_hook(get_index_file(), "prepare-commit-msg",
+		     git_path("MERGE_MSG"), "merge", NULL, NULL))
+		abort_commit(remoteheads, NULL);
 	if (0 < option_edit) {
 		if (launch_editor(git_path("MERGE_MSG"), NULL, NULL))
 			abort_commit(remoteheads, NULL);

t/t7505-prepare-commit-msg-hook.sh

@@ -167,5 +167,19 @@ test_expect_success 'with failing hook (--no-verify)' '
 
 '
 
+test_expect_success 'with failing hook (merge)' '
+
+	git checkout -B other HEAD@{1} &&
+	echo "more" >> file &&
+	git add file &&
+	rm -f "$HOOK" &&
+	git commit -m other &&
+	write_script "$HOOK" <<-EOF
+	exit 1
+	EOF
+	git checkout - &&
+	test_must_fail git merge other
+
+'
 
 test_done