Avoid to generate RBS with Syntax Error by prototype runtime

[pocke]

This pull request fixes a syntax error that is generated by rbs prototype runtime command on def f(...) end syntax.

Problem

rbs prototype runtime command generates RBS with a syntax error if a method is defined with argument forwarding syntax that is introduced since Ruby 2.7.

For example:

# test.rb

class C
  def f(...) end
end

$ rbs prototype runtime -R ./test.rb C
class C
  public

  def f: (*untyped *) { (*untyped) -> untyped } -> untyped
end

It displays *untyped * as the method arguments, but the trailing * is meaningless.

Cause

RubyVM::AST::Node includes :* as an argument name if the method is defined with argument forwarding syntax.
For example:

irb> pp RubyVM::AbstractSyntaxTree.parse('def f(...) end')
(SCOPE@1:0-1:14
 tbl: []
 args: nil
 body:
   (DEFN@1:0-1:14
    mid: :f
    body:
      (SCOPE@1:0-1:14
       tbl: [:*, :&]
       args:
         (ARGS@1:5-1:10
          pre_num: 0
          pre_init: nil
          opt: nil
          first_post: nil
          post_num: 0
          post_init: nil
          rest: :*        # <- HERE!
          kw: nil
          kwrest: nil
          block: :&)
       body: nil)))

Solution

Treat :* as an unnamed argument.

[soutaro]

👏