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, 8 insertions, 0 deletions

diff --git a/parse.y b/parse.y
index 005e926ef0..d458e6adca 100644
--- a/parse.y
+++ b/parse.y
@@ -4853,12 +4853,20 @@ kwrest_mark	: tPOW
 f_kwrest	: kwrest_mark tIDENTIFIER
 		    {
 			shadowing_lvar(get_id($2));
+		    /*%%%*/
 			$$ = $2;
+		    /*%
+			$$ = dispatch1(kwrest_param, $2);
+		    %*/
 		    }
 		| kwrest_mark
 		    {
+		    /*%%%*/
 			$$ = internal_id();
 			arg_var($$);
+		    /*%
+			$$ = dispatch1(kwrest_param, Qnil);
+		    %*/
 		    }
 		;