cgen: fix multi return auto str methods. closes #7726

vlib/v/gen/auto_str_methods.v

@@ -368,13 +368,13 @@ fn (mut g Gen) gen_str_for_multi_return(info table.MultiReturn, styp string, str
 			arg_str_fn_name = styp_to_str_fn_name(field_styp)
 		}
 		if sym.kind == .struct_ && !sym_has_str_method {
-			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, ${str_fn_name}(a.arg$i));')
+			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, ${arg_str_fn_name}(a.arg$i));')
 		} else if sym.kind in [.f32, .f64] {
 			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, _STR("%g", 1, a.arg$i));')
 		} else if sym.kind == .string {
 			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, _STR("\'%.*s\\000\'", 2, a.arg$i));')
 		} else if sym.kind == .function {
-			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, ${str_fn_name}());')
+			g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, ${arg_str_fn_name}());')
 		} else {
 			if (str_method_expects_ptr && is_arg_ptr) || (!str_method_expects_ptr && !is_arg_ptr) {
 				g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, ${arg_str_fn_name}(a.arg$i));')

vlib/v/tests/str_gen_test.v

@@ -357,4 +357,38 @@ fn test_struct_with_option() {
 	w := OptionWrapperInt{}
 	assert '$w' == 'OptionWrapperInt{\n    x: Option(error: \'\')\n}'
 }
-*/
+*/
+
+struct One {
+	value string = "one"
+}
+
+struct Two {
+	value string = "two"
+}
+
+fn mr_int_int() (int, int) {
+	return 111, 222
+}
+
+fn mr_one_two() (One, Two) {
+	one := One{}
+	two := Two{}
+	return one, two
+}
+
+fn mr_fn_fn() (fn(int), fn(int)) {
+	a := fn(a int) {}
+	b := fn(a int) {}
+	return a,b
+}
+
+fn test_multi_return() {
+	assert '$mr_int_int()' == '(111, 222)'
+	assert '$mr_fn_fn()' == '(fn (int), fn (int))'
+	assert '$mr_one_two()' == "(One{
+    value: 'one'
+}, Two{
+    value: 'two'
+})"
+}