[ruby/json] Refactor JSON::Ext::Parser to split configuration and par…

…sing state

Ref: ruby/json#718

The existing `Parser` interface is pretty bad, as it forces to
instantiate a new instance for each document.

Instead it's preferable to only take the config and do all the
initialization needed, and then keep the parsing state on the
stack on in ephemeral memory.

This refactor makes the `JSON::Coder` pull request much easier to
implement in a performant way.

ruby/json@c8d5236a92

Co-Authored-By: Étienne Barrié <[email protected]>

ext/json/lib/json/common.rb

@@ -232,12 +232,13 @@ def parse(source, opts = nil)
   # - Option +max_nesting+, if not provided, defaults to +false+,
   #   which disables checking for nesting depth.
   # - Option +allow_nan+, if not provided, defaults to +true+.
-  def parse!(source, opts = {})
-    opts = {
+  def parse!(source, opts = nil)
+    options = {
       :max_nesting  => false,
       :allow_nan    => true
-    }.merge(opts)
-    Parser.new(source, **(opts||{})).parse
+    }
+    options.merge!(opts) if opts
+    Parser.new(source, options).parse
   end
 
   # :call-seq:
@@ -258,7 +259,7 @@ def load_file(filespec, opts = nil)
   #   JSON.parse!(File.read(path, opts))
   #
   # See method #parse!
-  def load_file!(filespec, opts = {})
+  def load_file!(filespec, opts = nil)
     parse!(File.read(filespec, encoding: Encoding::UTF_8), opts)
   end
 

ext/json/lib/json/ext.rb

@@ -6,15 +6,36 @@ module JSON
   # This module holds all the modules/classes that implement JSON's
   # functionality as C extensions.
   module Ext
+    class Parser
+      class << self
+        def parse(...)
+          new(...).parse
+        end
+      end
+
+      def initialize(source, opts = nil)
+        @source = source
+        @config = Config.new(opts)
+      end
+
+      def source
+        @source.dup
+      end
+
+      def parse
+        @config.parse(@source)
+      end
+    end
+
+    require 'json/ext/parser'
+    Ext::Parser::Config = Ext::ParserConfig
+    JSON.parser = Ext::Parser
+
     if RUBY_ENGINE == 'truffleruby'
-      require 'json/ext/parser'
       require 'json/truffle_ruby/generator'
-      JSON.parser = Parser
       JSON.generator = ::JSON::TruffleRuby::Generator
     else
-      require 'json/ext/parser'
       require 'json/ext/generator'
-      JSON.parser = Parser
       JSON.generator = Generator
     end
   end