Fixed a bug in argument number check with kwargs; fix #4159

src/vm.c

@@ -1780,11 +1780,9 @@ RETRY_TRY_BLOCK:
 
       /* strict argument check */
       if (mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc)) {
-        if (argc >= 0 && !(argc <= 1 && kd)) {
-          if (argc < m1 + m2 + kd || (r == 0 && argc > len + kd)) {
-            argnum_error(mrb, m1+m2);
-            goto L_RAISE;
-          }
+        if (argc < m1 + m2 || (r == 0 && argc > len + kd)) {
+          argnum_error(mrb, m1+m2);
+          goto L_RAISE;
         }
       }
       /* extract first argument array to arguments */
@@ -1810,8 +1808,7 @@ RETRY_TRY_BLOCK:
             kargs = 0;
           }
           else {
-            mrb_value str = mrb_str_new_lit(mrb, "Excepcted `Hash` as last argument for keyword arguments");
-            mrb_exc_set(mrb, mrb_exc_new_str(mrb, E_ARGUMENT_ERROR, str));
+            argnum_error(mrb, m1+m2);
             goto L_RAISE;
           }
           if (MRB_ASPEC_KEY(a) > 0) {

test/t/syntax.rb

@@ -471,6 +471,10 @@ this is a comment that has extra after =begin and =end with tabs after it
 end
 
 assert 'keyword arguments' do
+  def m(a, b:1) [a, b] end
+  assert_equal [1, 1], m(1)
+  assert_equal [1, 2], m(1, b: 2)
+
   def m(a, b:) [a, b] end
   assert_equal [1, 2], m(1, b: 2)
   assert_raise(ArgumentError) { m b: 1 }