Ensure default_sort_keys_proc isn't reassigned.

It's assignable from Ruby simply for the gem's own initialization,
but it should never be re-assigned later.

Fix: #1079

Author: byroot

ext/json/ext/generator/generator.c

@@ -1733,6 +1733,9 @@ static VALUE cState_set_default_sort_keys_proc(VALUE self, VALUE proc)
     if (!rb_obj_is_proc(proc)) {
         rb_raise(rb_eTypeError, "sort_key_proc must be a Proc");
     }
+    if (default_sort_keys_proc) {
+        rb_raise(rb_eArgError, "sort_key_proc can only be set once");
+    }
     return default_sort_keys_proc = proc;
 }
 

lib/json/common.rb

@@ -80,14 +80,6 @@ def parser=(parser) # :nodoc:
     def generator=(generator) # :nodoc:
       old, $VERBOSE = $VERBOSE, nil
 
-      # The default proc used when the +sort_keys+ generation option is +true+.
-      # It returns a new hash with the entries sorted by their keys.
-      sort_keys_proc = ->(hash) { hash.sort.to_h }
-      if defined?(::Ractor) && Ractor.respond_to?(:shareable_lambda)
-        sort_keys_proc = Ractor.shareable_lambda(&sort_keys_proc)
-      end
-      generator::State.default_sort_keys_proc = sort_keys_proc
-
       @generator = generator
       if generator.const_defined?(:GeneratorMethods)
         generator_methods = generator::GeneratorMethods

lib/json/ext.rb

@@ -32,13 +32,22 @@ def parse
     Ext::Parser::Config = Ext::ParserConfig
     JSON.parser = Ext::Parser
 
-    if RUBY_ENGINE == 'truffleruby'
+    generator = if RUBY_ENGINE == 'truffleruby'
       require 'json/truffle_ruby/generator'
-      JSON.generator = JSON::TruffleRuby::Generator
+      JSON::TruffleRuby::Generator
     else
       require 'json/ext/generator'
-      JSON.generator = Generator
+      Generator
     end
+
+    # The default proc used when the +sort_keys+ generation option is +true+.
+    # It returns a new hash with the entries sorted by their keys.
+    sort_keys_proc = ->(hash) { hash.sort.to_h }
+    if defined?(::Ractor) && Ractor.respond_to?(:shareable_lambda)
+      sort_keys_proc = Ractor.shareable_lambda(&sort_keys_proc)
+    end
+    generator::State.default_sort_keys_proc = sort_keys_proc
+    JSON.generator = generator
   end
 
   if defined?(ResumableParser) # Not yet available on JRuby