Check that there are no keyword arguments with **nil implicitly

Actually **nil isn't supported yet so no exception is raised now.

Author: andrykonchin

spec/ruby/core/enumerator/product_spec.rb

@@ -48,6 +48,7 @@
       Enumerator.product(1..2) {}.should == nil
     end
 
+    # https://bugs.ruby-lang.org/issues/19829
     it "reject keyword arguments" do
       -> {
         Enumerator.product(1..3, foo: 1, bar: 2)

spec/ruby/language/method_spec.rb

@@ -1107,9 +1107,9 @@ def m(a, **nil); a end;
       m({a: 1}).should == {a: 1}
       m({"a" => 1}).should == {"a" => 1}
 
-      -> { m(a: 1) }.should raise_error(ArgumentError)
-      -> { m(**{a: 1}) }.should raise_error(ArgumentError)
-      -> { m("a" => 1) }.should raise_error(ArgumentError)
+      -> { m(a: 1) }.should raise_error(ArgumentError, 'no keywords accepted')
+      -> { m(**{a: 1}) }.should raise_error(ArgumentError, 'no keywords accepted')
+      -> { m("a" => 1) }.should raise_error(ArgumentError, 'no keywords accepted')
     end
 
     evaluate <<-ruby do

spec/tags/core/enumerator/product_tags.txt

@@ -0,0 +1 @@
+fails:Enumerator.product reject keyword arguments

spec/tags/language/method_tags.txt

@@ -6,3 +6,4 @@ fails:kwarg with omitted value in a method call accepts short notation 'kwarg' i
 fails:"kwarg with omitted value in a method call with methods and local variables for definition \n    def call(*args, **kwargs) = [args, kwargs]\n    def bar\n      "baz"\n    end\n    def foo(val)\n      call bar:, val:\n    end"
 fails:An endless method definition without arguments without parenthesis for definition 'def m = 42'
 fails:Inside 'endless' method definitions allows method calls without parenthesis
+fails:A method assigns local variables from method parameters for definition 'def m(a, **nil); a end;'

src/main/ruby/truffleruby/core/enumerator.rb

@@ -231,12 +231,9 @@ def self.produce(initial = nil)
     end
   end
 
-  def self.product(*enums, **kwargs, &block)
-    Truffle::KernelOperations.validate_no_kwargs(kwargs)
+  def self.product(*enums, **nil, &block)
     return Product.new(*enums) if Primitive.nil?(block)
-
     Truffle::EnumeratorOperations.product_iterator([], enums, &block)
-
     nil
   end
 

src/main/ruby/truffleruby/core/truffle/kernel_operations.rb

@@ -242,13 +242,6 @@ def self.value_frozen?(value)
       KERNEL_FROZEN.bind(value).call
     end
 
-    def self.validate_no_kwargs(kwargs)
-      return if (kwargs_size = kwargs.size) == 0
-
-      raise ArgumentError, "unknown keyword: #{kwargs.keys.first.inspect}" if kwargs_size == 1
-      raise ArgumentError, "unknown keywords: #{kwargs.keys.map(&:inspect).join(', ')}"
-    end
-
     # To get the class even if the value's class does not include `Kernel`, use `Primitive.class`.
   end
 end