vm_args.c: improve keyword argument errors

* vm_args.c (argument_arity_error): improve required keyword
  argument errors when non-keyword arguments given.
  [ruby-core:79439] [Bug #13196]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59259 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_keyword.rb

@@ -641,4 +641,17 @@ class TestKeywordArguments < Test::Unit::TestCase
     assert_equal(x, result)
     assert_kind_of(klass, result, bug12884)
   end
+
+  def test_arity_error_message
+    obj = Object.new
+    def obj.t(x:) end
+    assert_raise_with_message(ArgumentError, /required keyword: x\)/) do
+      obj.t(42)
+    end
+    obj = Object.new
+    def obj.t(x:, y:, z: nil) end
+    assert_raise_with_message(ArgumentError, /required keywords: x, y\)/) do
+      obj.t(42)
+    end
+  end
 end

vm_args.c

@@ -719,7 +719,26 @@ raise_argument_error(rb_thread_t *th, const rb_iseq_t *iseq, const VALUE exc)
 static void
 argument_arity_error(rb_thread_t *th, const rb_iseq_t *iseq, const int miss_argc, const int min_argc, const int max_argc)
 {
-    raise_argument_error(th, iseq, rb_arity_error_new(miss_argc, min_argc, max_argc));
+    VALUE exc = rb_arity_error_new(miss_argc, min_argc, max_argc);
+    if (iseq->body->param.flags.has_kw) {
+	const struct rb_iseq_param_keyword *const kw = iseq->body->param.keyword;
+	const ID *keywords = kw->table;
+	int req_key_num = kw->required_num;
+	if (req_key_num > 0) {
+	    static const char required[] = "; required keywords";
+	    VALUE mesg = rb_attr_get(exc, idMesg);
+	    rb_str_resize(mesg, RSTRING_LEN(mesg)-1);
+	    rb_str_cat(mesg, required, sizeof(required) - 1 - (req_key_num == 1));
+	    rb_str_cat_cstr(mesg, ":");
+	    do {
+		rb_str_cat_cstr(mesg, " ");
+		rb_str_append(mesg, rb_id2str(*keywords++));
+		rb_str_cat_cstr(mesg, ",");
+	    } while (--req_key_num);
+	    RSTRING_PTR(mesg)[RSTRING_LEN(mesg)-1] = ')';
+	}
+    }
+    raise_argument_error(th, iseq, exc);
 }
 
 static void