Support **nil syntax for specifying a method does not accept keyword arguments

This syntax means the method should be treated as a method that
uses keyword arguments, but no specific keyword arguments are
supported, and therefore calling the method with keyword arguments
will raise an ArgumentError.  It is still allowed to double splat
an empty hash when calling the method, as that does not pass
any keyword arguments.

2 files changed, 44 insertions, 0 deletions

diff --git a/test/ruby/test_keyword.rb b/test/ruby/test_keyword.rb
index 791d60b70a..1e707170fd 100644
--- a/test/ruby/test_keyword.rb
+++ b/test/ruby/test_keyword.rb
@@ -126,6 +126,34 @@ class TestKeywordArguments < Test::Unit::TestCase
     assert_equal(1, f10(b: 42))
   end
 
+  def f11(**nil)
+    local_variables
+  end
+
+  def test_f11
+    h = {}
+
+    assert_equal([], f11)
+    assert_equal([], f11(**{}))
+    assert_equal([], f11(**h))
+  end
+
+  def f12(**nil, &b)
+    [b, local_variables]
+  end
+
+  def test_f12
+    h = {}
+    b = proc{}
+
+    assert_equal([nil, [:b]], f12)
+    assert_equal([nil, [:b]], f12(**{}))
+    assert_equal([nil, [:b]], f12(**h))
+    assert_equal([b, [:b]], f12(&b))
+    assert_equal([b, [:b]], f12(**{}, &b))
+    assert_equal([b, [:b]], f12(**h, &b))
+  end
+
   def test_method_parameters
     assert_equal([[:key, :str], [:key, :num]], method(:f1).parameters);
     assert_equal([[:req, :x], [:key, :str], [:key, :num]], method(:f2).parameters);
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 02a95bc60b..72a3cc2fc7 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -249,6 +249,22 @@ class TestSyntax < Test::Unit::TestCase
     assert_syntax_error('def o.foo(@@foo: a) end', /class variable/)
   end
 
+  def test_keywords_specified_and_not_accepted
+    assert_syntax_error('def o.foo(a:, **nil) end', /unexpected/)
+    assert_syntax_error('def o.foo(a:, **nil, &b) end', /unexpected/)
+    assert_syntax_error('def o.foo(**a, **nil) end', /unexpected/)
+    assert_syntax_error('def o.foo(**a, **nil, &b) end', /unexpected/)
+    assert_syntax_error('def o.foo(**nil, **a) end', /unexpected/)
+    assert_syntax_error('def o.foo(**nil, **a, &b) end', /unexpected/)
+
+    assert_syntax_error('proc do |a:, **nil| end', /unexpected/)
+    assert_syntax_error('proc do |a:, **nil, &b| end', /unexpected/)
+    assert_syntax_error('proc do |**a, **nil| end', /unexpected/)
+    assert_syntax_error('proc do |**a, **nil, &b| end', /unexpected/)
+    assert_syntax_error('proc do |**nil, **a| end', /unexpected/)
+    assert_syntax_error('proc do |**nil, **a, &b| end', /unexpected/)
+  end
+
   def test_optional_self_reference
     bug9593 = '[ruby-core:61299] [Bug #9593]'
     o = Object.new