[Fixes rubocop#44] Use parser's new emit_forward_arg by default

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 * [#50](https://github.com/rubocop-hq/rubocop-ast/pull/50): Support find pattern matching for Ruby 2.8 (3.0) parser. ([@koic][])
 
+### Changes
+
+* [#44](https://github.com/rubocop-hq/rubocop-ast/issue/44): **(Breaking)** Use `parser` flag `self.emit_forward_arg = true` by default. ([@marcandre][])
+
 ## 0.1.0 (2020-06-26)
 
 ### New features

README.md

@@ -35,8 +35,9 @@ See the [docs site](https://docs.rubocop.org/rubocop-ast) for more details.
 
 ### Parser compatibility switches
 
-The main `RuboCop` gem uses [legacy AST output from parser](https://github.com/whitequark/parser/#usage).
-This gem is meant to be compatible with all settings. For example, to have `-> { ... }` emitted
+This gem, by default, uses most [legacy AST output from parser](https://github.com/whitequark/parser/#usage), except for `emit_forward_arg` which is set to `true`.
+
+The main `RuboCop` gem uses these defaults (and is currently only compatible with these), but this gem can be used separately from `RuboCop` and is meant to be compatible with all settings. For example, to have `-> { ... }` emitted
 as `LambdaNode` instead of `SendNode`:
 
 ```ruby

lib/rubocop/ast/builder.rb

@@ -14,6 +14,8 @@ module AST
     #   parser = Parser::Ruby25.new(builder)
     #   root_node = parser.parse(buffer)
     class Builder < Parser::Builders::Default
+      self.emit_forward_arg = true
+
       NODE_MAP = {
         and:          AndNode,
         alias:        AliasNode,

rubocop-ast.gemspec

@@ -29,7 +29,7 @@ Gem::Specification.new do |s|
     'bug_tracker_uri' => 'https://github.com/rubocop-hq/rubocop-ast/issues'
   }
 
-  s.add_runtime_dependency('parser', '>= 2.7.0.1')
+  s.add_runtime_dependency('parser', '>= 2.7.1.4')
 
   s.add_development_dependency('bundler', '>= 1.15.0', '< 3.0')
 

spec/spec_helper.rb

@@ -8,7 +8,10 @@
 end
 
 require 'rubocop-ast'
-RuboCop::AST::Builder.modernize if ENV['MODERNIZE']
+if ENV['MODERNIZE']
+  RuboCop::AST::Builder.modernize
+  RuboCop::AST::Builder.emit_forward_arg = false # inverse of default
+end
 
 RSpec.shared_context 'ruby 2.3', :ruby23 do
   let(:ruby_version) { 2.3 }