Add option for implicitToJson

json_serializable/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 * `enum` deserialization now uses helpers provided by `json_annotation`.
 
+* Added `implicit_to_json` configuration option.
+
 * Small change to how nullable `Map` values are deserialized.
 
 * Small whitespace changes to `JsonLiteral` generation to align with `dartfmt`.

json_serializable/README.md

@@ -83,13 +83,14 @@ targets:
           # Options configure how source code is generated for every
           # `@JsonSerializable`-annotated class in the package.
           #
-          # The default value for each of them: `false`.
+          # The default value for each is shown.
           #
           # For usage information, reference the corresponding field in
           # `JsonSerializableGenerator`.
-          use_wrappers: true
-          any_map: true
-          checked: true
+          use_wrappers: false
+          any_map: false
+          checked: false
+          implicit_to_json: true
 ```
 
 [example]: https://github.com/dart-lang/json_serializable/blob/master/example

json_serializable/lib/builder.dart

@@ -26,10 +26,12 @@ Builder jsonSerializable(BuilderOptions options) {
   var optionsMap = new Map<String, dynamic>.from(options.config);
 
   var builder = jsonPartBuilder(
-      header: optionsMap.remove('header') as String,
-      useWrappers: optionsMap.remove('use_wrappers') as bool,
-      checked: optionsMap.remove('checked') as bool,
-      anyMap: optionsMap.remove('any_map') as bool);
+    header: optionsMap.remove('header') as String,
+    useWrappers: optionsMap.remove('use_wrappers') as bool,
+    checked: optionsMap.remove('checked') as bool,
+    anyMap: optionsMap.remove('any_map') as bool,
+    implicitToJson: optionsMap.remove('implicit_to_json') as bool,
+  );
 
   if (optionsMap.isNotEmpty) {
     if (log == null) {

json_serializable/lib/src/json_part_builder.dart

@@ -20,15 +20,21 @@ import 'json_serializable_generator.dart';
 ///
 /// For details on [useWrappers], [anyMap], and [checked] see
 /// [JsonSerializableGenerator].
-Builder jsonPartBuilder(
-    {String header,
-    String formatOutput(String code),
-    bool useWrappers: false,
-    bool anyMap: false,
-    bool checked: false}) {
+Builder jsonPartBuilder({
+  String header,
+  String formatOutput(String code),
+  bool useWrappers: false,
+  bool anyMap: false,
+  bool checked: false,
+  bool implicitToJson: true,
+}) {
   return new PartBuilder([
     new JsonSerializableGenerator(
-        useWrappers: useWrappers, anyMap: anyMap, checked: checked),
+      useWrappers: useWrappers,
+      anyMap: anyMap,
+      checked: checked,
+      implicitToJson: implicitToJson,
+    ),
     const JsonLiteralGenerator()
   ], header: header, formatOutput: formatOutput);
 }

json_serializable/lib/src/json_serializable_generator.dart

@@ -66,6 +66,26 @@ class JsonSerializableGenerator
   /// [CheckedFromJsonException] is thrown.
   final bool checked;
 
+  /// If `false`, generated `toJson` methods will explicitly call `toJson` on
+  /// nested objects.
+  ///
+  /// When using JSON encoding support in `dart:convert`, `toJson` is
+  /// automatically called on objects, so the default behavior
+  /// (`implicitToJson: true`) is to omit the `toJson` call.
+  ///
+  /// Example of `implicitToJson: true` (default)
+  ///
+  /// ```dart
+  /// Map<String, dynamic> toJson() => {'child': child};
+  /// ```
+  ///
+  /// Example of `implicitToJson: false`
+  ///
+  /// ```dart
+  /// Map<String, dynamic> toJson() => {'child': child?.toJson()};
+  /// ```
+  final bool implicitToJson;
+
   /// Creates an instance of [JsonSerializableGenerator].
   ///
   /// If [typeHelpers] is not provided, two built-in helpers are used:
@@ -75,9 +95,11 @@ class JsonSerializableGenerator
     bool useWrappers: false,
     bool anyMap: false,
     bool checked: false,
+    bool implicitToJson: true,
   })  : this.useWrappers = useWrappers ?? false,
         this.anyMap = anyMap ?? false,
         this.checked = checked ?? false,
+        this.implicitToJson = implicitToJson ?? true,
         this._typeHelpers = typeHelpers ?? _defaultHelpers;
 
   /// Creates an instance of [JsonSerializableGenerator].

json_serializable/lib/src/type_helper_context.dart

@@ -28,6 +28,8 @@ class TypeHelperContext implements SerializeContext, DeserializeContext {
   // Consider exposing it if there is interest
   bool get anyMap => _generator.anyMap;
 
+  bool get implicitToJson => _generator.implicitToJson;
+
   TypeHelperContext(this._generator, this.metadata, this.nullable,
       this.fromJsonData, this.toJsonData);
 

json_serializable/lib/src/type_helpers/json_helper.dart

@@ -16,17 +16,24 @@ import '../utils.dart';
 class JsonHelper extends TypeHelper {
   const JsonHelper();
 
-  /// Simply returns the [expression] provided.
+  /// If the builder is configured with `implicit_to_json: true`, simply returns
+  /// the [expression] provided.
   ///
-  /// By default, JSON encoding in from `dart:convert` calls `toJson()` on
-  /// provided objects.
+  /// Otherwise, returns [expression]`.toJson()` with proper `null` handling.
   @override
-  String serialize(DartType targetType, String expression, _) {
+  String serialize(
+      DartType targetType, String expression, SerializeContext context) {
     if (!_canSerialize(targetType)) {
       return null;
     }
 
-    return expression;
+    var ctx = context as TypeHelperContext;
+
+    if (ctx.implicitToJson) {
+      return expression;
+    }
+
+    return '$expression${context.nullable ? '?' : ''}.toJson()';
   }
 
   @override

json_serializable/test/config_test.dart

@@ -100,12 +100,14 @@ const _validConfig = const {
   'header': 'header',
   'use_wrappers': true,
   'any_map': true,
-  'checked': true
+  'checked': true,
+  'implicit_to_json': false
 };
 
 const _invalidConfig = const {
   'header': true,
   'use_wrappers': 42,
   'any_map': 42,
-  'checked': 42
+  'checked': 42,
+  'implicit_to_json': 42
 };

json_serializable/test/json_serializable_test.dart

@@ -66,6 +66,99 @@ void _registerTests(JsonSerializableGenerator generator) {
         _throwsInvalidGenerationSourceError(messageMatcher, todoMatcher));
   }
 
+  group('implicitToJson: false', () {
+    test('nullable', () async {
+      var output = await _runForElementNamed(
+          new JsonSerializableGenerator(
+              implicitToJson: false, useWrappers: generator.useWrappers),
+          'TrivialNestedNullable');
+
+      var expected = generator.useWrappers
+          ? r'''abstract class _$TrivialNestedNullableSerializerMixin {
+  TrivialNestedNullable get child;
+  int get otherField;
+  Map<String, dynamic> toJson() =>
+      new _$TrivialNestedNullableJsonMapWrapper(this);
+}
+
+class _$TrivialNestedNullableJsonMapWrapper extends $JsonMapWrapper {
+  final _$TrivialNestedNullableSerializerMixin _v;
+  _$TrivialNestedNullableJsonMapWrapper(this._v);
+
+  @override
+  Iterable<String> get keys => const ['child', 'otherField'];
+
+  @override
+  dynamic operator [](Object key) {
+    if (key is String) {
+      switch (key) {
+        case 'child':
+          return _v.child?.toJson();
+        case 'otherField':
+          return _v.otherField;
+      }
+    }
+    return null;
+  }
+}
+'''
+          : r'''abstract class _$TrivialNestedNullableSerializerMixin {
+  TrivialNestedNullable get child;
+  int get otherField;
+  Map<String, dynamic> toJson() =>
+      <String, dynamic>{'child': child?.toJson(), 'otherField': otherField};
+}
+''';
+
+      expect(output, expected);
+    });
+    test('non-nullable', () async {
+      var output = await _runForElementNamed(
+          new JsonSerializableGenerator(
+              implicitToJson: false, useWrappers: generator.useWrappers),
+          'TrivialNestedNonNullable');
+
+      var expected = generator.useWrappers
+          ? r'''abstract class _$TrivialNestedNonNullableSerializerMixin {
+  TrivialNestedNonNullable get child;
+  int get otherField;
+  Map<String, dynamic> toJson() =>
+      new _$TrivialNestedNonNullableJsonMapWrapper(this);
+}
+
+class _$TrivialNestedNonNullableJsonMapWrapper extends $JsonMapWrapper {
+  final _$TrivialNestedNonNullableSerializerMixin _v;
+  _$TrivialNestedNonNullableJsonMapWrapper(this._v);
+
+  @override
+  Iterable<String> get keys => const ['child', 'otherField'];
+
+  @override
+  dynamic operator [](Object key) {
+    if (key is String) {
+      switch (key) {
+        case 'child':
+          return _v.child.toJson();
+        case 'otherField':
+          return _v.otherField;
+      }
+    }
+    return null;
+  }
+}
+'''
+          : r'''abstract class _$TrivialNestedNonNullableSerializerMixin {
+  TrivialNestedNonNullable get child;
+  int get otherField;
+  Map<String, dynamic> toJson() =>
+      <String, dynamic>{'child': child.toJson(), 'otherField': otherField};
+}
+''';
+
+      expect(output, expected);
+    });
+  });
+
   group('non-classes', () {
     test('const field', () {
       expectThrows('theAnswer', 'Generator cannot target `theAnswer`.',

json_serializable/test/src/json_serializable_test_input.dart

@@ -214,3 +214,15 @@ class SuperType {
   int priceFraction(int other) =>
       superTypeViaCtor == null ? null : superTypeViaCtor ~/ other;
 }
+
+@JsonSerializable(createFactory: false)
+class TrivialNestedNullable {
+  TrivialNestedNullable child;
+  int otherField;
+}
+
+@JsonSerializable(createFactory: false, nullable: false)
+class TrivialNestedNonNullable {
+  TrivialNestedNonNullable child;
+  int otherField;
+}