ripper: dispatch new parser event 'kwrest_param' on f_kwresttopic/ripper-unnamed-kwrest

Ripper has an issue in handling bare kwrest:

  $ ruby -rpp -rripper -e'pp Ripper.sexp("def a(**) end")'
  [:program,
   [[:def,
     [:@ident, "a", [1, 4]],
     [:paren, [:params, nil, nil, nil, nil, nil, 183, nil]],
     [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]

The mysterious 183 is the problem: this is an ID generated by
internal_id(). This patch introduces a new 'kwrest_param' parser event
that works just like 'rest_param' event that corresponds to rest params
(def a(*rest) end). After applying this, the result will be:

  $ ruby -rpp -rripper -e'pp Ripper.sexp("def a(**name) end")'
  [:program,
   [[:def,
     [:@ident, "a", [1, 4]],
     [:paren,
      [:params,
       nil,
       nil,
       nil,
       nil,
       nil,
       [:kwrest_param, [:@ident, "name", [1, 8]]],
       nil]],
     [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]

  $ ruby -rpp -rripper -e'pp Ripper.sexp("def a(**) end")'
  [:program,
   [[:def,
     [:@ident, "a", [1, 4]],
     [:paren, [:params, nil, nil, nil, nil, nil, [:kwrest_param, nil], nil]],
     [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]

* parse.y (f_kwrest): dispatch kwrest_param event, just like rest_param.
* test/ripper/dummyparser.rb (on_kwrest_param): add kwrest_param parser
  event handler.
* test/ripper/test_parser_events.rb (test_params): adjust.
* test/ripper/test_parser_events.rb (test_kwrest_param): test that
  kwrest_param event handler is properly called.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/ripper/dummyparser.rb b/test/ripper/dummyparser.rb
index 3c196d9a23..9d9de7f641 100644
--- a/test/ripper/dummyparser.rb
+++ b/test/ripper/dummyparser.rb
@@ -148,6 +148,10 @@ class DummyParser < Ripper
     "*#{var}"
   end
 
+  def on_kwrest_param(var)
+    "**#{var}"
+  end
+
   def on_blockarg(var)
     "&#{var}"
   end