Change to not use native parser backend anymore

Author: mbj

README.md

@@ -4,7 +4,9 @@ unparser
 ![CI](https://github.com/mbj/unparser/workflows/CI/badge.svg)
 [![Gem Version](https://img.shields.io/gem/v/unparser.svg)](https://rubygems.org/gems/unparser)
 
-Generate equivalent source for ASTs from [parser](https://github.com/whitequark/parser).
+Generate equivalent source for ASTs from [prism](https://github.com/ruby/prism) via its parser translation layer.
+
+**Parser Backend**: Unparser uses [Prism](https://github.com/ruby/prism) (Ruby's official parser) with its [parser translation layer](https://github.com/ruby/prism/blob/main/docs/parser_translation.md) to produce `Parser::AST::Node` compatible ASTs. This requires both the `prism` and `parser` gems as dependencies.
 
 The following constraints apply:
 
@@ -30,7 +32,6 @@ Usage
 -----
 
 ```ruby
-require 'parser/current'
 require 'unparser'
 
 ast = Unparser.parse('your(ruby(code))')
@@ -41,7 +42,6 @@ Unparser.unparse(ast) # => 'your(ruby(code))'
 To preserve the comments from the source:
 
 ```ruby
-require 'parser/current'
 require 'unparser'
 
 ast, comments = Unparser.parser.parse_with_comments(Unparser.buffer('your(ruby(code)) # with comments'))

bin/parser-round-trip-test

@@ -1,8 +1,5 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-if Gem::Version.new(RUBY_VERSION) <= '3.4'
-  load 'bin/parser-whitequark-round-trip-test'
-else
-  load 'bin/parser-prism-round-trip-test'
-end
+# Unparser now uses Prism translation layer for all Ruby 3.3+ versions
+load 'bin/parser-prism-round-trip-test'

lib/unparser.rb

@@ -18,52 +18,41 @@
 
 # Library namespace
 module Unparser # rubocop:disable Metrics/ModuleLength
-  # Unparser specific AST builder defaulting to modern AST format
-  if Gem::Version.new(RUBY_VERSION) <= '3.4'
-    require 'parser/current'
-    class Builder < Parser::Builders::Default
-      modernize
-
-      # mutant:disable
-      def initialize
-        super
+  require 'prism'
 
-        self.emit_file_line_as_literals = false
-      end
-    end
-  else
-    require 'prism'
-    class Builder < Prism::Translation::Parser::Builder
-      modernize
+  # Unparser specific AST builder defaulting to modern AST format
+  class Builder < Prism::Translation::Parser::Builder
+    modernize
 
-      # mutant:disable
-      def initialize
-        super
+    # mutant:disable
+    def initialize
+      super
 
-        self.emit_file_line_as_literals = false
-      end
+      self.emit_file_line_as_literals = false
     end
   end
 
+  # Select appropriate Prism translation parser based on Ruby version
   PARSER_CLASS =
-    if Gem::Version.new(RUBY_VERSION) <= '3.4'
-      Class.new(Parser::CurrentRuby) do
-        def declare_local_variable(local_variable)
-          static_env.declare(local_variable)
-        end
-      end
+    if RUBY_VERSION >= '3.5'
+      Prism::Translation::Parser35
+    elsif RUBY_VERSION >= '3.4'
+      Prism::Translation::Parser34
     else
-      Class.new(Prism::Translation::Parser34) do
-        def declare_local_variable(local_variable)
-          (@local_variables ||= Set.new) << local_variable
-        end
-
-        def prism_options
-          super.merge(scopes: [@local_variables.to_a])
-        end
-      end
+      Prism::Translation::Parser33
+    end
+
+  # Create parser instance with local variable declaration support
+  PARSER_INSTANCE_CLASS = Class.new(PARSER_CLASS) do
+    def declare_local_variable(local_variable)
+      (@local_variables ||= Set.new) << local_variable
     end
 
+    def prism_options
+      super.merge(scopes: [@local_variables.to_a])
+    end
+  end
+
   EMPTY_STRING = ''.freeze
   EMPTY_ARRAY  = [].freeze
 
@@ -238,7 +227,7 @@ def self.parse_ast(source, static_local_variables: Set.new)
   # @api private
   # mutant:disable
   def self.parser
-    PARSER_CLASS.new(Builder.new).tap do |parser|
+    PARSER_INSTANCE_CLASS.new(Builder.new).tap do |parser|
       parser.diagnostics.tap do |diagnostics|
         diagnostics.all_errors_are_fatal = true
       end

spec/spec_helper.rb

@@ -4,8 +4,6 @@
 require 'mutant'
 require 'yaml'
 
-require 'parser/current'
-
 RSpec.shared_examples_for 'a command method' do
   it 'returns self' do
     should equal(object)

spec/unit/unparser_spec.rb

@@ -459,13 +459,13 @@ def foo(bar)
     let(:version_excludes) do
       excludes = []
 
-      if RUBY_VERSION >= '3.4.'
-        excludes.concat(
-          %w[
-            test/corpus/literal/before/34.rb
-          ]
-        )
-      end
+      # "before/34.rb" contains syntax valid before Ruby 3.4 but invalid in 3.4+
+      # So we need to exclude it on ALL versions (3.3 can't parse it, 3.4+ rejects it)
+      excludes.concat(
+        %w[
+          test/corpus/literal/before/34.rb
+        ]
+      )
 
       excludes.flat_map { |file| ['--ignore', file] }
     end