Add documentation and tests for keyword argument value omission

[Feature #14579]

NEWS.md

@@ -69,10 +69,10 @@ Note that each entry is kept to a minimum, see links for details.
 
     [[Bug #4443]]
 
-* Values in Hash literals can be omitted.  [[Feature #14579]]
+* Values in Hash literals and keyword arguments can be omitted.  [[Feature #14579]]
 
     `{x:, y:}` is a syntax sugar of `{x: x, y: y}`.
-
+    `foo(x:, y:)` is a syntax sugar of `foo(x: x, y: y)`.
 
 ## Command line options
 

test/ruby/test_hash.rb

@@ -2178,22 +2178,4 @@ class TestHash < Test::Unit::TestCase
       end;
     end
   end
-
-  def test_value_omission
-    x = 1
-    y = 2
-    assert_equal({x: 1, y: 2}, {x:, y:})
-    assert_equal({one: 1, two: 2}, {one:, two:})
-    assert_syntax_error('{"#{x}":}', /'\}'/)
-  end
-
-  private
-
-  def one
-    1
-  end
-
-  def two
-    2
-  end
 end

test/ruby/test_keyword.rb

@@ -4351,4 +4351,20 @@ class TestKeywordArgumentsSymProcRefinements < Test::Unit::TestCase
     assert_raise(TypeError, bug16603) { p(**42) }
     assert_raise(TypeError, bug16603) { p(k:1, **42) }
   end
+
+  def test_value_omission
+    f = ->(**kwargs) { kwargs }
+    x = 1
+    y = 2
+    assert_equal({x: 1, y: 2}, f.call(x:, y:))
+    assert_equal({one: 1, two: 2}, f.call(one:, two:))
+  end
+
+  private def one
+    1
+  end
+
+  private def two
+    2
+  end
 end

test/ruby/test_literal.rb

@@ -506,6 +506,22 @@ class TestRubyLiteral < Test::Unit::TestCase
     assert_equal(100, h['a'])
   end
 
+  def test_hash_value_omission
+    x = 1
+    y = 2
+    assert_equal({x: 1, y: 2}, {x:, y:})
+    assert_equal({one: 1, two: 2}, {one:, two:})
+    assert_syntax_error('{"#{x}":}', /'\}'/)
+  end
+
+  private def one
+    1
+  end
+
+  private def two
+    2
+  end
+
   def test_range
     assert_instance_of Range, (1..2)
     assert_equal(1..2, 1..2)