Fix duplicated key warning location

Followup: #818

Now the warning should point at the `JSON.parse` caller, and not
inside the json gem itself.

Author: byroot

ext/json/ext/parser/parser.c

@@ -422,7 +422,8 @@ static void emit_parse_warning(const char *message, JSON_ParserState *state)
     long line, column;
     cursor_position(state, &line, &column);
 
-    rb_warn("%s at line %ld column %ld", message, line, column);
+    VALUE warning = rb_sprintf("%s at line %ld column %ld", message, line, column);
+    rb_funcall(mJSON, rb_intern("deprecation_warning"), 1, warning);
 }
 
 #define PARSE_ERROR_FRAGMENT_LEN 32

lib/json/common.rb

@@ -48,7 +48,7 @@ def array_class_proc(array_class, on_load)
         end
       end
 
-      # TODO: exctract :create_additions support to another gem for version 3.0
+      # TODO: extract :create_additions support to another gem for version 3.0
       def create_additions_proc(opts)
         if opts[:symbolize_names]
           raise ArgumentError, "options :symbolize_names and :create_additions cannot be  used in conjunction"
@@ -87,31 +87,32 @@ def create_additions_proc(opts)
         opts
       end
 
-      GEM_ROOT = File.expand_path("../../../", __FILE__) + "/"
       def create_additions_warning
-        message = "JSON.load implicit support for `create_additions: true` is deprecated " \
+        JSON.deprecation_warning "JSON.load implicit support for `create_additions: true` is deprecated " \
           "and will be removed in 3.0, use JSON.unsafe_load or explicitly " \
           "pass `create_additions: true`"
+      end
+    end
+  end
 
-        uplevel = 4
-        caller_locations(uplevel, 10).each do |frame|
-          if frame.path.nil? || frame.path.start_with?(GEM_ROOT) || frame.path.end_with?("/truffle/cext_ruby.rb", ".c")
-            uplevel += 1
-          else
-            break
-          end
-        end
-
-        if RUBY_VERSION >= "3.0"
-          warn(message, uplevel: uplevel - 1, category: :deprecated)
+  class << self
+    def deprecation_warning(message, uplevel = 4) # :nodoc:
+      gem_root = File.expand_path("../../../", __FILE__) + "/"
+      caller_locations(uplevel, 10).each do |frame|
+        if frame.path.nil? || frame.path.start_with?(gem_root) || frame.path.end_with?("/truffle/cext_ruby.rb", ".c")
+          uplevel += 1
         else
-          warn(message, uplevel: uplevel - 1)
+          break
         end
       end
+
+      if RUBY_VERSION >= "3.0"
+        warn(message, uplevel: uplevel - 1, category: :deprecated)
+      else
+        warn(message, uplevel: uplevel - 1)
+      end
     end
-  end
 
-  class << self
     # :call-seq:
     #   JSON[object] -> new_array or new_string
     #

test/json/json_parser_test.rb

@@ -346,6 +346,12 @@ def test_parse_duplicate_key
       assert_equal expected_sym, parse('{"a": 1, "a": 2}', symbolize_names: true)
     end
 
+    if RUBY_ENGINE == 'RUBY_ENGINE'
+      assert_deprecated_warning(/#{File.basename(__FILE__)}\:#{__LINE__ + 1}/) do
+        assert_equal expected, parse('{"a": 1, "a": 2}')
+      end
+    end
+
     unless RUBY_ENGINE == 'jruby'
       assert_raise(ParserError) do
         fake_key = Object.new