stash: eliminate crude option parsing

Eliminate crude option parsing and rely on real parsing instead, because
1) Crude parsing is crude, for example it's not capable of
   handling things like `git stash -m Message`
2) Adding options in two places is inconvenient and prone to bugs

As a side result, the case of `git stash -m Message` gets fixed.
Also give a good error message instead of just throwing usage at user.

----

Some review of what's been happening to this code:

Before [1], `git-stash.sh` only verified that all args begin with `-` :

	# The default command is "push" if nothing but options are given
	seen_non_option=
	for opt
	do
		case "$opt" in
		--) break ;;
		-*) ;;
		*) seen_non_option=t; break ;;
		esac
	done

Later, [1] introduced the duplicate code I'm now removing, also making
the previous test more strict by white-listing options.

----

[1] Commit 40af1468 ("stash: convert `stash--helper.c` into `stash.c`" 2019-02-26)

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stash.c

@@ -1448,8 +1448,10 @@ done:
 	return ret;
 }
 
-static int push_stash(int argc, const char **argv, const char *prefix)
+static int push_stash(int argc, const char **argv, const char *prefix,
+		      int push_assumed)
 {
+	int force_assume = 0;
 	int keep_index = -1;
 	int patch_mode = 0;
 	int include_untracked = 0;
@@ -1471,10 +1473,22 @@ static int push_stash(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
-	if (argc)
+	if (argc) {
+		force_assume = !strcmp(argv[0], "-p");
 		argc = parse_options(argc, argv, prefix, options,
 				     git_stash_push_usage,
-				     0);
+				     PARSE_OPT_KEEP_DASHDASH);
+	}
+
+	if (argc) {
+		if (!strcmp(argv[0], "--")) {
+			argc--;
+			argv++;
+		} else if (push_assumed && !force_assume) {
+			die("subcommand wasn't specified; 'push' can't be assumed due to unexpected token '%s'",
+			    argv[0]);
+		}
+	}
 
 	parse_pathspec(&ps, 0, PATHSPEC_PREFER_FULL | PATHSPEC_PREFIX_ORIGIN,
 		       prefix, argv);
@@ -1547,7 +1561,6 @@ static int use_builtin_stash(void)
 
 int cmd_stash(int argc, const char **argv, const char *prefix)
 {
-	int i = -1;
 	pid_t pid = getpid();
 	const char *index_file;
 	struct argv_array args = ARGV_ARRAY_INIT;
@@ -1580,7 +1593,7 @@ int cmd_stash(int argc, const char **argv, const char *prefix)
 		    (uintmax_t)pid);
 
 	if (!argc)
-		return !!push_stash(0, NULL, prefix);
+		return !!push_stash(0, NULL, prefix, 0);
 	else if (!strcmp(argv[0], "apply"))
 		return !!apply_stash(argc, argv, prefix);
 	else if (!strcmp(argv[0], "clear"))
@@ -1600,45 +1613,15 @@ int cmd_stash(int argc, const char **argv, const char *prefix)
 	else if (!strcmp(argv[0], "create"))
 		return !!create_stash(argc, argv, prefix);
 	else if (!strcmp(argv[0], "push"))
-		return !!push_stash(argc, argv, prefix);
+		return !!push_stash(argc, argv, prefix, 0);
 	else if (!strcmp(argv[0], "save"))
 		return !!save_stash(argc, argv, prefix);
 	else if (*argv[0] != '-')
 		usage_msg_opt(xstrfmt(_("unknown subcommand: %s"), argv[0]),
 			      git_stash_usage, options);
 
-	if (strcmp(argv[0], "-p")) {
-		while (++i < argc && strcmp(argv[i], "--")) {
-			/*
-			 * `akpqu` is a string which contains all short options,
-			 * except `-m` which is verified separately.
-			 */
-			if ((strlen(argv[i]) == 2) && *argv[i] == '-' &&
-			    strchr("akpqu", argv[i][1]))
-				continue;
-
-			if (!strcmp(argv[i], "--all") ||
-			    !strcmp(argv[i], "--keep-index") ||
-			    !strcmp(argv[i], "--no-keep-index") ||
-			    !strcmp(argv[i], "--patch") ||
-			    !strcmp(argv[i], "--quiet") ||
-			    !strcmp(argv[i], "--include-untracked"))
-				continue;
-
-			/*
-			 * `-m` and `--message=` are verified separately because
-			 * they need to be immediately followed by a string
-			 * (i.e.`-m"foobar"` or `--message="foobar"`).
-			 */
-			if (starts_with(argv[i], "-m") ||
-			    starts_with(argv[i], "--message="))
-				continue;
-
-			usage_with_options(git_stash_usage, options);
-		}
-	}
-
+	/* Assume 'stash push' */
 	argv_array_push(&args, "push");
 	argv_array_pushv(&args, argv);
-	return !!push_stash(args.argc, args.argv, prefix);
+	return !!push_stash(args.argc, args.argv, prefix, 1);
 }

t/t3903-stash.sh

@@ -285,6 +285,11 @@ test_expect_success 'stash --no-keep-index' '
 	test bar,bar2 = $(cat file),$(cat file2)
 '
 
+test_expect_success 'dont assume push with non-option args' '
+	test_must_fail git stash -q drop 2>err &&
+	test_i18ngrep -e "subcommand wasn'\''t specified; '\''push'\'' can'\''t be assumed due to unexpected token '\''drop'\''" err
+'
+
 test_expect_success 'stash --invalid-option' '
 	echo bar5 >file &&
 	echo bar6 >file2 &&