Warn for keyword to last hash parameter when method has no optional/rest parameters

Previously, there was no warning in this case, even though we will
be changing the behavior in Ruby 3.

Fixes [Bug #14130]

spec/ruby/language/method_spec.rb

@@ -717,8 +717,10 @@ describe "A method" do
       ruby
 
       m(1, b: 2).should == [1, 2]
+      suppress_keyword_warning.call do
         -> { m("a" => 1, b: 2) }.should raise_error(ArgumentError)
       end
+    end
 
     evaluate <<-ruby do
         def m(a, b: 1) [a, b] end
@@ -726,8 +728,10 @@ describe "A method" do
 
       m(2).should == [2, 1]
       m(1, b: 2).should == [1, 2]
+      suppress_keyword_warning.call do
         m("a" => 1, b: 2).should == [{"a" => 1, b: 2}, 1]
       end
+    end
 
     evaluate <<-ruby do
         def m(a, **) a end
@@ -735,8 +739,10 @@ describe "A method" do
 
       m(1).should == 1
       m(1, a: 2, b: 3).should == 1
+      suppress_keyword_warning.call do
         m("a" => 1, b: 2).should == {"a" => 1, b: 2}
       end
+    end
 
     evaluate <<-ruby do
         def m(a, **k) [a, k] end
@@ -744,8 +750,10 @@ describe "A method" do
 
       m(1).should == [1, {}]
       m(1, a: 2, b: 3).should == [1, {a: 2, b: 3}]
+      suppress_keyword_warning.call do
         m("a" => 1, b: 2).should == [{"a" => 1, b: 2}, {}]
       end
+    end
 
     evaluate <<-ruby do
         def m(a, &b) [a, b] end

test/ruby/test_keyword.rb

@@ -22,8 +22,10 @@ class TestKeywordArguments < Test::Unit::TestCase
 
   def test_f2
     assert_equal([:xyz, "foo", 424242], f2(:xyz))
+    assert_warn(/The keyword argument for `f2' .* is passed as the last hash parameter/) do
       assert_equal([{"bar"=>42}, "foo", 424242], f2("bar"=>42))
     end
+  end
 
 
   def f3(str: "foo", num: 424242, **h)
@@ -322,6 +324,10 @@ class TestKeywordArguments < Test::Unit::TestCase
     end
   end
 
+  def req_plus_keyword(x, **h)
+    [x, h]
+  end
+
   def opt_plus_keyword(x=1, **h)
     [x, h]
   end
@@ -331,6 +337,19 @@ class TestKeywordArguments < Test::Unit::TestCase
   end
 
   def test_keyword_split
+    assert_warn(/The keyword argument for `req_plus_keyword' .* is passed as the last hash parameter/) do
+      assert_equal([{:a=>1}, {}], req_plus_keyword(:a=>1))
+    end
+    assert_warn(/The keyword argument for `req_plus_keyword' .* is passed as the last hash parameter/) do
+      assert_equal([{"a"=>1}, {}], req_plus_keyword("a"=>1))
+    end
+    assert_warn(/The keyword argument for `req_plus_keyword' .* is passed as the last hash parameter/) do
+      assert_equal([{"a"=>1, :a=>1}, {}], req_plus_keyword("a"=>1, :a=>1))
+    end
+    assert_equal([{:a=>1}, {}], req_plus_keyword({:a=>1}))
+    assert_equal([{"a"=>1}, {}], req_plus_keyword({"a"=>1}))
+    assert_equal([{"a"=>1, :a=>1}, {}], req_plus_keyword({"a"=>1, :a=>1}))
+
     assert_equal([1, {:a=>1}], opt_plus_keyword(:a=>1))
     assert_equal([1, {"a"=>1}], opt_plus_keyword("a"=>1))
     assert_equal([1, {"a"=>1, :a=>1}], opt_plus_keyword("a"=>1, :a=>1))
@@ -536,8 +555,10 @@ class TestKeywordArguments < Test::Unit::TestCase
         [a, b, c, d, e, f, g]
       end
     end
+    assert_warn(/The keyword argument for `foo' .* is passed as the last hash parameter/) do
       assert_equal([1, 2, 1, [], {:f=>5}, 2, {}], a.new.foo(1, 2, f:5), bug8993)
     end
+  end
 
   def test_splat_keyword_nondestructive
     bug9776 = '[ruby-core:62161] [Bug #9776]'

vm_args.c

@@ -756,10 +756,10 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
     if (kw_flag & VM_CALL_KW_SPLAT) {
 	kw_splat = !iseq->body->param.flags.has_rest;
     }
-    if (given_argc > min_argc &&
-	(iseq->body->param.flags.has_kw || iseq->body->param.flags.has_kwrest ||
+    if ((iseq->body->param.flags.has_kw || iseq->body->param.flags.has_kwrest ||
 	 (kw_splat && given_argc > max_argc)) &&
 	args->kw_argv == NULL) {
+        if (given_argc > min_argc) {
             if (((kw_flag & (VM_CALL_KWARG | VM_CALL_KW_SPLAT)) || !ec->cfp->iseq /* called from C */)) {
                 int check_only_symbol = (kw_flag & VM_CALL_KW_SPLAT) &&
                                         iseq->body->param.flags.has_kw &&
@@ -792,6 +792,10 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
                 rb_warn_split_last_hash_to_keyword(calling, ci);
             }
         }
+        else if (given_argc == min_argc && kw_flag) {
+            rb_warn_keyword_to_last_hash(calling, ci);
+        }
+    }
 
     if (given_argc > max_argc && max_argc != UNLIMITED_ARGUMENTS) {
 	if (arg_setup_type == arg_setup_block) {