builtin/apply: make check_apply_state() return -1 instead of die()ing

To libify `git apply` functionality we have to signal errors to the
caller instead of die()ing.

To do that in a compatible manner with the rest of the error handling
in "builtin/apply.c", check_apply_state() should return -1 instead of
calling die().

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -4551,17 +4551,17 @@ static int option_parse_directory(const struct option *opt,
 	return 0;
 }
 
-static void check_apply_state(struct apply_state *state, int force_apply)
+static int check_apply_state(struct apply_state *state, int force_apply)
 {
 	int is_not_gitdir = !startup_info->have_repository;
 
 	if (state->apply_with_reject && state->threeway)
-		die("--reject and --3way cannot be used together.");
+		return error("--reject and --3way cannot be used together.");
 	if (state->cached && state->threeway)
-		die("--cached and --3way cannot be used together.");
+		return error("--cached and --3way cannot be used together.");
 	if (state->threeway) {
 		if (is_not_gitdir)
-			die(_("--3way outside a repository"));
+			return error(_("--3way outside a repository"));
 		state->check_index = 1;
 	}
 	if (state->apply_with_reject)
@@ -4569,16 +4569,18 @@ static void check_apply_state(struct apply_state *state, int force_apply)
 	if (!force_apply && (state->diffstat || state->numstat || state->summary || state->check || state->fake_ancestor))
 		state->apply = 0;
 	if (state->check_index && is_not_gitdir)
-		die(_("--index outside a repository"));
+		return error(_("--index outside a repository"));
 	if (state->cached) {
 		if (is_not_gitdir)
-			die(_("--cached outside a repository"));
+			return error(_("--cached outside a repository"));
 		state->check_index = 1;
 	}
 	if (state->check_index)
 		state->unsafe_paths = 0;
 	if (!state->lock_file)
-		die("BUG: state->lock_file should not be NULL");
+		return error("BUG: state->lock_file should not be NULL");
+
+	return 0;
 }
 
 static int apply_all_patches(struct apply_state *state,
@@ -4747,7 +4749,8 @@ int cmd_apply(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, state.prefix, builtin_apply_options,
 			apply_usage, 0);
 
-	check_apply_state(&state, force_apply);
+	if (check_apply_state(&state, force_apply))
+		exit(128);
 
 	ret = apply_all_patches(&state, argc, argv, options);