switch: stop accepting pathspec

This command is about switching branch (or creating a new one) and
should not accept pathspec. This helps simplify ambiguation
handling. The other two ("git checkout" and "git restore") of
course do accept pathspec as before.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -54,6 +54,7 @@ struct checkout_opts {
 	int overlay_mode;
 	int no_dwim_new_local_branch;
 	int discard_changes;
+	int accept_pathspec;
 
 	/*
 	 * If new checkout options are added, skip_merge_working_tree
@@ -1176,10 +1177,16 @@ static int parse_branchname_arg(int argc, const char **argv,
 	if (!argc)
 		return 0;
 
+	if (!opts->accept_pathspec) {
+		if (argc > 1)
+			die(_("only one reference expected"));
+		has_dash_dash = 1; /* helps disambiguate */
+	}
+
 	arg = argv[0];
 	dash_dash_pos = -1;
 	for (i = 0; i < argc; i++) {
-		if (!strcmp(argv[i], "--")) {
+		if (opts->accept_pathspec && !strcmp(argv[i], "--")) {
 			dash_dash_pos = i;
 			break;
 		}
@@ -1213,11 +1220,12 @@ static int parse_branchname_arg(int argc, const char **argv,
 			recover_with_dwim = 0;
 
 		/*
-		 * Accept "git checkout foo" and "git checkout foo --"
-		 * as candidates for dwim.
+		 * Accept "git checkout foo", "git checkout foo --"
+		 * and "git switch foo" as candidates for dwim.
 		 */
 		if (!(argc == 1 && !has_dash_dash) &&
-		    !(argc == 2 && has_dash_dash))
+		    !(argc == 2 && has_dash_dash) &&
+		    opts->accept_pathspec)
 			recover_with_dwim = 0;
 
 		if (recover_with_dwim) {
@@ -1262,7 +1270,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 		 */
 		if (argc)
 			verify_non_filename(opts->prefix, arg);
-	} else {
+	} else if (opts->accept_pathspec) {
 		argcount++;
 		argv++;
 		argc--;
@@ -1585,6 +1593,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	memset(&opts, 0, sizeof(opts));
 	opts.no_dwim_new_local_branch = 0;
+	opts.accept_pathspec = 1;
 
 	options = parse_options_dup(checkout_options);
 	options = add_common_options(&opts, options);
@@ -1614,6 +1623,7 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 
 	memset(&opts, 0, sizeof(opts));
 	opts.no_dwim_new_local_branch = 0;
+	opts.accept_pathspec = 0;
 
 	options = parse_options_dup(switch_options);
 	options = add_common_options(&opts, options);