Show unexpected keywords when no keywords accepcted

class.c

@@ -2347,7 +2347,17 @@ VALUE
 rb_keyword_error_new(const char *error, VALUE keys)
 {
     long i = 0, len = RARRAY_LEN(keys);
-    VALUE error_message = rb_sprintf("%s keyword%.*s", error, len > 1, "s");
+    VALUE error_message;
+
+    if (error) {
+        static const char keywords[] = " keywords";
+        int mlen = (int)sizeof(keywords) - 1;
+        error_message = rb_str_new_cstr(error);
+        rb_str_cat(error_message, keywords, mlen - (len == 1));
+    }
+    else {
+        error_message = rb_str_new_cstr("no keywords accepted");
+    }
 
     if (len > 0) {
         rb_str_cat_cstr(error_message, ": ");

enumerator.c

@@ -3736,7 +3736,7 @@ enumerator_s_product(int argc, VALUE *argv, VALUE klass)
     rb_scan_args(argc, argv, "*:&", &enums, &options, &block);
 
     if (!NIL_P(options) && !RHASH_EMPTY_P(options)) {
-        rb_exc_raise(rb_keyword_error_new("unknown", rb_hash_keys(options)));
+        rb_exc_raise(rb_keyword_error_new(NULL, rb_hash_keys(options)));
     }
 
     VALUE obj = enum_product_initialize(argc, argv, enum_product_allocate(rb_cEnumProduct));

test/ruby/test_keyword.rb

@@ -1,7 +1,9 @@
 # frozen_string_literal: false
 require 'test/unit'
-require '-test-/rb_call_super_kw'
-require '-test-/iter'
+%w[-test-/rb_call_super_kw -test-/iter].each do |r|
+  require r
+rescue LoadError
+end
 
 class TestKeywordArguments < Test::Unit::TestCase
   def f1(str: "foo", num: 424242)
@@ -138,6 +140,9 @@ def test_f11
     assert_equal([], f11)
     assert_equal([], f11(**{}))
     assert_equal([], f11(**h))
+    assert_raise_with_message(ArgumentError, "no keywords accepted: :a") {
+      f11(a: 1)
+    }
   end
 
   def f12(**nil, &b)
@@ -2068,7 +2073,7 @@ def c.method_missing(_, arg=1, **args)
     assert_equal([1, h2], c.m(**h2))
     assert_equal([1, h3], c.m(**h3))
     assert_equal([1, h3], c.m(a: 1, **h2))
-  end
+  end if defined?(Bug::RbCallSuperKw)
 
   def test_define_method_kwsplat
     kw = {}
@@ -3454,7 +3459,7 @@ def c.c(arg=1, **args)
     assert_equal([h, kw], c.m(:c, h))
     assert_equal([h2, kw], c.m(:c, h2))
     assert_equal([h3, kw], c.m(:c, h3))
-  end
+  end if defined?(Bug::Iter::Yield)
 
   def p1
     Proc.new do |str: "foo", num: 424242|

vm_args.c

@@ -620,6 +620,9 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
                     given_argc--;
                     keyword_hash = last_arg;
                 }
+                else if (ISEQ_BODY(iseq)->param.flags.accepts_no_kwarg) {
+                    keyword_hash = last_arg;
+                }
             }
         }
     }
@@ -629,7 +632,7 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
     }
 
     if (kw_flag && ISEQ_BODY(iseq)->param.flags.accepts_no_kwarg) {
-        rb_raise(rb_eArgError, "no keywords accepted");
+        argument_kw_error(ec, iseq, NULL, rb_hash_keys(keyword_hash));
     }
 
     switch (arg_setup_type) {