5 files changed, 177 insertions, 3 deletions
diff --git a/ext/json/generator/generator.c b/ext/json/generator/generator.c
index 62c0c420cc..bc08c01008 100644
--- a/ext/json/generator/generator.c
+++ b/ext/json/generator/generator.c
@@ -12,6 +12,7 @@ typedef struct JSON_Generator_StateStruct {
     VALUE space_before;
     VALUE object_nl;
     VALUE array_nl;
+    VALUE as_json;
 
     long max_nesting;
     long depth;
@@ -30,8 +31,8 @@ typedef struct JSON_Generator_StateStruct {
 static VALUE mJSON, cState, cFragment, mString_Extend, eGeneratorError, eNestingError, Encoding_UTF_8;
 
 static ID i_to_s, i_to_json, i_new, i_pack, i_unpack, i_create_id, i_extend, i_encode;
-static ID sym_indent, sym_space, sym_space_before, sym_object_nl, sym_array_nl, sym_max_nesting, sym_allow_nan,
-          sym_ascii_only, sym_depth, sym_buffer_initial_length, sym_script_safe, sym_escape_slash, sym_strict;
+static VALUE sym_indent, sym_space, sym_space_before, sym_object_nl, sym_array_nl, sym_max_nesting, sym_allow_nan,
+             sym_ascii_only, sym_depth, sym_buffer_initial_length, sym_script_safe, sym_escape_slash, sym_strict, sym_as_json;
 
 
 #define GET_STATE_TO(self, state) \
@@ -648,6 +649,7 @@ static void State_mark(void *ptr)
     rb_gc_mark_movable(state->space_before);
     rb_gc_mark_movable(state->object_nl);
     rb_gc_mark_movable(state->array_nl);
+    rb_gc_mark_movable(state->as_json);
 }
 
 static void State_compact(void *ptr)
@@ -658,6 +660,7 @@ static void State_compact(void *ptr)
     state->space_before = rb_gc_location(state->space_before);
     state->object_nl = rb_gc_location(state->object_nl);
     state->array_nl = rb_gc_location(state->array_nl);
+    state->as_json = rb_gc_location(state->as_json);
 }
 
 static void State_free(void *ptr)
@@ -714,6 +717,7 @@ static void vstate_spill(struct generate_json_data *data)
     RB_OBJ_WRITTEN(vstate, Qundef, state->space_before);
     RB_OBJ_WRITTEN(vstate, Qundef, state->object_nl);
     RB_OBJ_WRITTEN(vstate, Qundef, state->array_nl);
+    RB_OBJ_WRITTEN(vstate, Qundef, state->as_json);
 }
 
 static inline VALUE vstate_get(struct generate_json_data *data)
@@ -982,6 +986,8 @@ static void generate_json_fragment(FBuffer *buffer, struct generate_json_data *d
 static void generate_json(FBuffer *buffer, struct generate_json_data *data, JSON_Generator_State *state, VALUE obj)
 {
     VALUE tmp;
+    bool as_json_called = false;
+start:
     if (obj == Qnil) {
         generate_json_null(buffer, data, state, obj);
     } else if (obj == Qfalse) {
@@ -1025,7 +1031,13 @@ static void generate_json(FBuffer *buffer, struct generate_json_data *data, JSON
             default:
             general:
                 if (state->strict) {
-                    raise_generator_error(obj, "%"PRIsVALUE" not allowed in JSON", CLASS_OF(obj));
+                    if (RTEST(state->as_json) && !as_json_called) {
+                        obj = rb_proc_call_with_block(state->as_json, 1, &obj, Qnil);
+                        as_json_called = true;
+                        goto start;
+                    } else {
+                        raise_generator_error(obj, "%"PRIsVALUE" not allowed in JSON", CLASS_OF(obj));
+                    }
                 } else if (rb_respond_to(obj, i_to_json)) {
                     tmp = rb_funcall(obj, i_to_json, 1, vstate_get(data));
                     Check_Type(tmp, T_STRING);
@@ -1126,6 +1138,7 @@ static VALUE cState_init_copy(VALUE obj, VALUE orig)
     objState->space_before = origState->space_before;
     objState->object_nl = origState->object_nl;
     objState->array_nl = origState->array_nl;
+    objState->as_json = origState->as_json;
     return obj;
 }
 
@@ -1277,6 +1290,28 @@ static VALUE cState_array_nl_set(VALUE self, VALUE array_nl)
     return Qnil;
 }
 
+/*
+ * call-seq: as_json()
+ *
+ * This string is put at the end of a line that holds a JSON array.
+ */
+static VALUE cState_as_json(VALUE self)
+{
+    GET_STATE(self);
+    return state->as_json;
+}
+
+/*
+ * call-seq: as_json=(as_json)
+ *
+ * This string is put at the end of a line that holds a JSON array.
+ */
+static VALUE cState_as_json_set(VALUE self, VALUE as_json)
+{
+    GET_STATE(self);
+    RB_OBJ_WRITE(self, &state->as_json, rb_convert_type(as_json, T_DATA, "Proc", "to_proc"));
+    return Qnil;
+}
 
 /*
 * call-seq: check_circular?
@@ -1498,6 +1533,7 @@ static int configure_state_i(VALUE key, VALUE val, VALUE _arg)
     else if (key == sym_script_safe)           { state->script_safe = RTEST(val); }
     else if (key == sym_escape_slash)          { state->script_safe = RTEST(val); }
     else if (key == sym_strict)                { state->strict = RTEST(val); }
+    else if (key == sym_as_json)               { state->as_json = rb_convert_type(val, T_DATA, "Proc", "to_proc"); }
     return ST_CONTINUE;
 }
 
@@ -1589,6 +1625,8 @@ void Init_generator(void)
     rb_define_method(cState, "object_nl=", cState_object_nl_set, 1);
     rb_define_method(cState, "array_nl", cState_array_nl, 0);
     rb_define_method(cState, "array_nl=", cState_array_nl_set, 1);
+    rb_define_method(cState, "as_json", cState_as_json, 0);
+    rb_define_method(cState, "as_json=", cState_as_json_set, 1);
     rb_define_method(cState, "max_nesting", cState_max_nesting, 0);
     rb_define_method(cState, "max_nesting=", cState_max_nesting_set, 1);
     rb_define_method(cState, "script_safe", cState_script_safe, 0);
@@ -1610,6 +1648,7 @@ void Init_generator(void)
     rb_define_method(cState, "buffer_initial_length", cState_buffer_initial_length, 0);
     rb_define_method(cState, "buffer_initial_length=", cState_buffer_initial_length_set, 1);
     rb_define_method(cState, "generate", cState_generate, -1);
+    rb_define_alias(cState, "generate_new", "generate"); // :nodoc:
 
     rb_define_singleton_method(cState, "generate", cState_m_generate, 3);
 
@@ -1680,6 +1719,7 @@ void Init_generator(void)
     sym_script_safe = ID2SYM(rb_intern("script_safe"));
     sym_escape_slash = ID2SYM(rb_intern("escape_slash"));
     sym_strict = ID2SYM(rb_intern("strict"));
+    sym_as_json = ID2SYM(rb_intern("as_json"));
 
     usascii_encindex = rb_usascii_encindex();
     utf8_encindex = rb_utf8_encindex();
diff --git a/ext/json/lib/json/common.rb b/ext/json/lib/json/common.rb
index ea15b70686..dfb9f580bd 100644
--- a/ext/json/lib/json/common.rb
+++ b/ext/json/lib/json/common.rb
@@ -174,7 +174,18 @@ module JSON
   # This allows to easily assemble multiple JSON fragments that have
   # been peristed somewhere without having to parse them nor resorting
   # to string interpolation.
+  #
+  # Note: no validation is performed on the provided string. it is the
+  # responsability of the caller to ensure the string contains valid JSON.
   Fragment = Struct.new(:json) do
+    def initialize(json)
+      unless string = String.try_convert(json)
+        raise TypeError, " no implicit conversion of #{json.class} into String"
+      end
+
+      super(string)
+    end
+
     def to_json(state = nil, *)
       json
     end
@@ -851,6 +862,82 @@ module JSON
   class << self
     private :merge_dump_options
   end
+
+  # JSON::Coder holds a parser and generator configuration.
+  #
+  #   module MyApp
+  #     JSONC_CODER = JSON::Coder.new(
+  #       allow_trailing_comma: true
+  #     )
+  #   end
+  #
+  #   MyApp::JSONC_CODER.load(document)
+  #
+  class Coder
+    # :call-seq:
+    #   JSON.new(options = nil, &block)
+    #
+    # Argument +options+, if given, contains a \Hash of options for both parsing and generating.
+    # See {Parsing Options}[#module-JSON-label-Parsing+Options], and {Generating Options}[#module-JSON-label-Generating+Options].
+    #
+    # For generation, the <tt>strict: true</tt> option is always set. When a Ruby object with no native \JSON counterpart is
+    # encoutered, the block provided to the initialize method is invoked, and must return a Ruby object that has a native
+    # \JSON counterpart:
+    #
+    #  module MyApp
+    #    API_JSON_CODER = JSON::Coder.new do |object|
+    #      case object
+    #      when Time
+    #        object.iso8601(3)
+    #      else
+    #        object # Unknown type, will raise
+    #      end
+    #    end
+    #  end
+    #
+    #  puts MyApp::API_JSON_CODER.dump(Time.now.utc) # => "2025-01-21T08:41:44.286Z"
+    #
+    def initialize(options = nil, &as_json)
+      if options.nil?
+        options = { strict: true }
+      else
+        options = options.dup
+        options[:strict] = true
+      end
+      options[:as_json] = as_json if as_json
+      options[:create_additions] = false unless options.key?(:create_additions)
+
+      @state = State.new(options).freeze
+      @parser_config = Ext::Parser::Config.new(options)
+    end
+
+    # call-seq:
+    #   dump(object) -> String
+    #   dump(object, io) -> io
+    #
+    # Serialize the given object into a \JSON document.
+    def dump(object, io = nil)
+      @state.generate_new(object, io)
+    end
+    alias_method :generate, :dump
+
+    # call-seq:
+    #   load(string) -> Object
+    #
+    # Parse the given \JSON document and return an equivalent Ruby object.
+    def load(source)
+      @parser_config.parse(source)
+    end
+    alias_method :parse, :load
+
+    # call-seq:
+    #   load(path) -> Object
+    #
+    # Parse the given \JSON document and return an equivalent Ruby object.
+    def load_file(path)
+      load(File.read(path, encoding: Encoding::UTF_8))
+    end
+  end
 end
 
 module ::Kernel
diff --git a/ext/json/lib/json/ext/generator/state.rb b/ext/json/lib/json/ext/generator/state.rb
index 6cd9496e67..d40c3b5ec3 100644
--- a/ext/json/lib/json/ext/generator/state.rb
+++ b/ext/json/lib/json/ext/generator/state.rb
@@ -58,6 +58,7 @@ module JSON
             space_before: space_before,
             object_nl: object_nl,
             array_nl: array_nl,
+            as_json: as_json,
             allow_nan: allow_nan?,
             ascii_only: ascii_only?,
             max_nesting: max_nesting,
diff --git a/test/json/json_coder_test.rb b/test/json/json_coder_test.rb
new file mode 100755
index 0000000000..37331c4eb8
--- /dev/null
+++ b/test/json/json_coder_test.rb
@@ -0,0 +1,38 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require_relative 'test_helper'
+
+class JSONCoderTest < Test::Unit::TestCase
+  def test_json_coder_with_proc
+    coder = JSON::Coder.new do |object|
+      "[Object object]"
+    end
+    assert_equal %(["[Object object]"]), coder.dump([Object.new])
+  end
+
+  def test_json_coder_with_proc_with_unsupported_value
+    coder = JSON::Coder.new do |object|
+      Object.new
+    end
+    assert_raise(JSON::GeneratorError) { coder.dump([Object.new]) }
+  end
+
+  def test_json_coder_options
+    coder = JSON::Coder.new(array_nl: "\n") do |object|
+      42
+    end
+
+    assert_equal "[\n42\n]", coder.dump([Object.new])
+  end
+
+  def test_json_coder_load
+    coder = JSON::Coder.new
+    assert_equal [1,2,3], coder.load("[1,2,3]")
+  end
+
+  def test_json_coder_load_options
+    coder = JSON::Coder.new(symbolize_names: true)
+    assert_equal({a: 1}, coder.load('{"a":1}'))
+  end
+end
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index 824de2c1a6..92115637e1 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -200,6 +200,7 @@ class JSONGeneratorTest < Test::Unit::TestCase
     assert_equal({
       :allow_nan             => false,
       :array_nl              => "\n",
+      :as_json               => false,
       :ascii_only            => false,
       :buffer_initial_length => 1024,
       :depth                 => 0,
@@ -218,6 +219,7 @@ class JSONGeneratorTest < Test::Unit::TestCase
     assert_equal({
       :allow_nan             => false,
       :array_nl              => "",
+      :as_json               => false,
       :ascii_only            => false,
       :buffer_initial_length => 1024,
       :depth                 => 0,
@@ -236,6 +238,7 @@ class JSONGeneratorTest < Test::Unit::TestCase
     assert_equal({
       :allow_nan             => false,
       :array_nl              => "",
+      :as_json               => false,
       :ascii_only            => false,
       :buffer_initial_length => 1024,
       :depth                 => 0,
@@ -666,4 +669,9 @@ class JSONGeneratorTest < Test::Unit::TestCase
     fragment = JSON::Fragment.new(" 42")
     assert_equal '{"number": 42}', JSON.generate({ number: fragment })
   end
+
+  def test_json_generate_as_json_convert_to_proc
+    object = Object.new
+    assert_equal object.object_id.to_json, JSON.generate(object, strict: true, as_json: :object_id)
+  end
 end