Use $enumEncode for non-nullable enum toJson lookups

_test_yaml/pubspec.yaml

@@ -12,7 +12,7 @@ dev_dependencies:
   build_runner: ^2.10.5
   build_verify: ^3.0.0
   checked_yaml: ^2.0.4
-  json_annotation: ^4.9.0
+  json_annotation: '>=4.13.0-0 <4.14.0'
   json_serializable: ^6.8.0
   path: ^1.9.0
   test: ^1.29.0

json_annotation/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 4.13.0-wip
+
+- Add `$enumEncode` helper for generated enum `toJson` code.
+
 ## 4.12.0
 
 - Add `JsonKey.explicitJsonNullWhenNonNullField` for PATCH-style tri-state JSON

json_annotation/lib/src/enum_helpers.dart

@@ -88,3 +88,15 @@ K $enumDecode<K extends Enum, V>(
 
   return unknownValue;
 }
+
+/// Returns the encoded JSON value associated with [value] in [enumValues].
+///
+/// [enumValues] is assumed to contain an entry for every possible value of
+/// type [K], so the returned value is never `null`.
+///
+/// Exposed only for code generated by `package:json_serializable`.
+/// Not meant to be used directly by user code.
+V $enumEncode<K extends Enum, V extends Object>(
+  Map<K, V> enumValues,
+  K value,
+) => enumValues[value]!;

json_annotation/pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_annotation
-version: 4.12.0
+version: 4.13.0-wip
 description: >-
   Classes and helper functions that support JSON code generation via the
   `json_serializable` package.

json_serializable/CHANGELOG.md

@@ -1,5 +1,10 @@
 ## 6.15.0-wip
 
+- Use `$enumEncode` for non-nullable enum `toJson` map lookups so generated
+  code no longer triggers `unnecessary_null_checks` on `_$EnumMap[value]!`.
+  ([#1515](https://github.com/google/json_serializable.dart/issues/1515))
+- Require `json_annotation: '>=4.13.0-0 <4.14.0'`
+
 - Fix `createJsonSchema` to emit an `enum` constraint (and `default`) for
   enum-typed fields, respecting `@JsonValue` and `JsonEnum.valueField`.
   ([#1577](https://github.com/google/json_serializable.dart/issues/1577))

json_serializable/README.md

@@ -351,15 +351,15 @@ targets:
 [`Enum`]: https://api.dart.dev/dart-core/Enum-class.html
 [`int`]: https://api.dart.dev/dart-core/int-class.html
 [`Iterable`]: https://api.dart.dev/dart-core/Iterable-class.html
-[`JsonConverter`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonConverter-class.html
-[`JsonEnum.valueField`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonEnum/valueField.html
-[`JsonEnum`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonEnum-class.html
-[`JsonKey.fromJson`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonKey/fromJson.html
-[`JsonKey.toJson`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonKey/toJson.html
-[`JsonKey`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonKey-class.html
-[`JsonLiteral`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonLiteral-class.html
-[`JsonSerializable`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonSerializable-class.html
-[`JsonValue`]: https://pub.dev/documentation/json_annotation/4.12.0/json_annotation/JsonValue-class.html
+[`JsonConverter`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonConverter-class.html
+[`JsonEnum.valueField`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonEnum/valueField.html
+[`JsonEnum`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonEnum-class.html
+[`JsonKey.fromJson`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonKey/fromJson.html
+[`JsonKey.toJson`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonKey/toJson.html
+[`JsonKey`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonKey-class.html
+[`JsonLiteral`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonLiteral-class.html
+[`JsonSerializable`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonSerializable-class.html
+[`JsonValue`]: https://pub.dev/documentation/json_annotation/latest/json_annotation/JsonValue-class.html
 [`List`]: https://api.dart.dev/dart-core/List-class.html
 [`Map`]: https://api.dart.dev/dart-core/Map-class.html
 [`num`]: https://api.dart.dev/dart-core/num-class.html

json_serializable/lib/src/check_dependencies.dart

@@ -15,7 +15,7 @@ const _annotationPkgName = 'json_annotation';
 final _supportLanguageRange = VersionConstraint.parse(
   supportedLanguageConstraint,
 );
-final requiredJsonAnnotationMinVersion = Version.parse('4.12.0');
+final requiredJsonAnnotationMinVersion = Version.parse('4.13.0-0');
 
 Future<void> pubspecHasRightVersion(BuildStep buildStep) async {
   final segments = buildStep.inputId.pathSegments;

json_serializable/lib/src/type_helpers/enum_helper.dart

@@ -33,7 +33,10 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
         enumFieldWithNullInEncodeMap(targetType) == true) {
       return '${constMapName(targetType)}[$expression]';
     } else {
-      return '${constMapName(targetType)}[$expression]!';
+      // Avoid `_$EnumMap[value]!` which triggers `unnecessary_null_checks` when
+      // the result is stored in a `Map<String, dynamic>` (#1515), while still
+      // producing a non-nullable value for Map keys (#1145).
+      return '\$enumEncode(${constMapName(targetType)}, $expression)';
     }
   }
 

json_serializable/pubspec.yaml

@@ -23,7 +23,7 @@ dependencies:
 
   # Use a tight version constraint to ensure that a constraint on
   # `json_annotation` properly constrains all features it provides.
-  json_annotation: '>=4.12.0 <4.13.0'
+  json_annotation: '>=4.13.0-0 <4.14.0'
   meta: ^1.16.0
   path: ^1.9.0
   pub_semver: ^2.1.4

json_serializable/test/integration/integration_test.dart

@@ -333,6 +333,14 @@ void main() {
     expect(dayTypeEnumValues, ['no-good', 'rotten', 'very-bad']);
   });
 
+  test('non-nullable enum toJson uses enumEncode without a bang', () {
+    final json = Issue1515Regression(
+      state: Issue1145RegressionEnum.alpha,
+    ).toJson();
+    expect(json, {'state': 'alpha'});
+    expect(json['state'], const TypeMatcher<String>());
+  });
+
   test('serializing a non-nullable enum as a key in a map should produce a '
       'non-nullable string key', () {
     final cls = Issue1145RegressionA(

json_serializable/test/integration/json_enum_example.dart

@@ -99,3 +99,12 @@ class Issue1226Regression {
 
   Map<String, dynamic> toJson() => _$Issue1226RegressionToJson(this);
 }
+
+@JsonSerializable(createFactory: false)
+class Issue1515Regression {
+  Issue1515Regression({required this.state});
+
+  Map<String, dynamic> toJson() => _$Issue1515RegressionToJson(this);
+
+  final Issue1145RegressionEnum state;
+}