[WIP] Attempt regexp_parser 2.x upgrade

- 2.x fails because of this change: ammar/regexp_parser@f14a36b#diff-5bfe3942df5a59a97d7e5c7d3e918a1c704f964685e719c178af22401da46c23R25. Calling `#to_s` is no longer possible on a frozen instance of `Regexp::Expression::Group::Passive`.
- I have left a monkeypatch in as a demo of one way this problem could get resolved.

Gemfile.lock

@@ -14,7 +14,7 @@ PATH
       mprelude (~> 0.1.0)
       parser (~> 2.7.1)
       procto (~> 0.0.2)
-      regexp_parser (~> 1.8)
+      regexp_parser (~> 2.0, >= 2.0.1)
       unparser (~> 0.5.4)
       variable (~> 0.0.1)
 
@@ -52,7 +52,7 @@ GEM
       ast (~> 2.4.1)
     procto (0.0.3)
     rainbow (3.0.0)
-    regexp_parser (1.8.2)
+    regexp_parser (2.0.1)
     rexml (3.2.4)
     rspec (3.10.0)
       rspec-core (~> 3.10.0)

lib/mutant/ast/regexp.rb

@@ -1,5 +1,16 @@
 # frozen_string_literal: true
 
+class Regexp::Expression::Group::Passive
+  def initialize(*)
+    @implicit = false
+    super
+  end
+
+  def implicit?
+    @implicit
+  end
+end
+
 module Mutant
   module AST
     # Regexp source mapper
@@ -9,17 +20,9 @@ module Regexp
       # @param regexp [String]
       #
       # @return [Regexp::Expression, nil]
-      #
-      # rubocop:disable Lint/SuppressedException
       def self.parse(regexp)
         ::Regexp::Parser.parse(regexp)
-      # `regexp_parser` is more strict than MRI
-      # See: https://github.com/ammar/regexp_parser/issues/75
-      # Also: https://github.com/ammar/regexp_parser/issues/76
-      rescue ::Regexp::Scanner::PrematureEndError,
-             ::Regexp::Scanner::InvalidGroupOption
       end
-      # rubocop:enable Lint/SuppressedException
 
       # Convert expression into ast node
       #

lib/mutant/mutator/node/literal/regex.rb

@@ -32,7 +32,7 @@ def dispatch
           # body is composed of only strings. Regular expressions
           # with interpolation are skipped
           def mutate_body
-            return unless body.all?(&method(:n_str?)) && body_ast
+            return unless body.all?(&method(:n_str?))
 
             Mutator.mutate(body_ast).each do |mutation|
               source = AST::Regexp.to_expression(mutation).to_s
@@ -41,7 +41,7 @@ def mutate_body
           end
 
           def body_ast
-            body_expression and AST::Regexp.to_ast(body_expression)
+            AST::Regexp.to_ast(body_expression)
           end
 
           def body_expression

mutant.gemspec

@@ -34,7 +34,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency('mprelude',      '~> 0.1.0')
   gem.add_runtime_dependency('parser',        '~> 2.7.1')
   gem.add_runtime_dependency('procto',        '~> 0.0.2')
-  gem.add_runtime_dependency('regexp_parser', '~> 1.8')
+  gem.add_runtime_dependency('regexp_parser', '~> 2.0', '>= 2.0.1')
   gem.add_runtime_dependency('unparser',      '~> 0.5.4')
   gem.add_runtime_dependency('variable',      '~> 0.0.1')
 

spec/unit/mutant/ast/regexp/parse_spec.rb

@@ -10,16 +10,4 @@ def apply(input)
       expect(apply(/foo/).to_re).to eql(/foo/)
     end
   end
-
-  context 'when given a hex escape `regexp_parser` does not support' do
-    it 'returns nil' do
-      expect(apply(/\xA/)).to be(nil)
-    end
-  end
-
-  context 'when given a capture group `regexp_parser` does not support' do
-    it 'returns nil' do
-      expect(apply(/(?<æ>.)/)).to be(nil)
-    end
-  end
 end

test_app/Gemfile.minitest.lock

@@ -14,7 +14,7 @@ PATH
       mprelude (~> 0.1.0)
       parser (~> 2.7.1)
       procto (~> 0.0.2)
-      regexp_parser (~> 1.8)
+      regexp_parser (~> 2.0, >= 2.0.1)
       unparser (~> 0.5.4)
       variable (~> 0.0.1)
     mutant-minitest (0.10.21)
@@ -54,7 +54,7 @@ GEM
     parser (2.7.2.0)
       ast (~> 2.4.1)
     procto (0.0.3)
-    regexp_parser (1.8.2)
+    regexp_parser (2.0.1)
     thread_safe (0.3.6)
     unparser (0.5.4)
       abstract_type (~> 0.0.7)

test_app/Gemfile.rspec3.8.lock

@@ -14,7 +14,7 @@ PATH
       mprelude (~> 0.1.0)
       parser (~> 2.7.1)
       procto (~> 0.0.2)
-      regexp_parser (~> 1.8)
+      regexp_parser (~> 2.0, >= 2.0.1)
       unparser (~> 0.5.4)
       variable (~> 0.0.1)
     mutant-rspec (0.10.21)
@@ -53,7 +53,7 @@ GEM
     parser (2.7.2.0)
       ast (~> 2.4.1)
     procto (0.0.3)
-    regexp_parser (1.8.2)
+    regexp_parser (2.0.1)
     rspec (3.8.0)
       rspec-core (~> 3.8.0)
       rspec-expectations (~> 3.8.0)