Support more non-String Map keys of obvious dart:core types (#493)

Partially addresses #396

json_serializable/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.1.0
+
+- Support `Map` keys of type `int`, `BigInt`, `DateTime`, and `Uri`.
+
 ## 3.0.0
 
 This release is entirely **BREAKING** changes. It removes underused features

json_serializable/lib/src/type_helpers/map_helper.dart

@@ -8,6 +8,7 @@ import '../constants.dart';
 import '../shared_checkers.dart';
 import '../type_helper.dart';
 import '../utils.dart';
+import 'to_from_string.dart';
 
 const _keyParam = 'k';
 
@@ -29,7 +30,9 @@ class MapHelper extends TypeHelper<TypeHelperContextWithConfig> {
     _checkSafeKeyType(expression, keyType);
 
     final subFieldValue = context.serialize(valueType, closureArg);
-    final subKeyValue = context.serialize(keyType, _keyParam);
+    final subKeyValue =
+        _forType(keyType)?.serialize(keyType, _keyParam, false) ??
+            context.serialize(keyType, _keyParam);
 
     if (closureArg == subFieldValue && _keyParam == subKeyValue) {
       return expression;
@@ -56,9 +59,9 @@ class MapHelper extends TypeHelper<TypeHelperContextWithConfig> {
     _checkSafeKeyType(expression, keyArg);
 
     final valueArgIsAny = _isObjectOrDynamic(valueArg);
-    final isEnumKey = isEnum(keyArg);
+    final isKeyStringable = _isKeyStringable(keyArg);
 
-    if (!isEnumKey) {
+    if (!isKeyStringable) {
       if (valueArgIsAny) {
         if (context.config.anyMap) {
           if (_isObjectOrDynamic(keyArg)) {
@@ -90,30 +93,65 @@ class MapHelper extends TypeHelper<TypeHelperContextWithConfig> {
         context.config.anyMap ? 'as Map' : 'as Map<String, dynamic>';
 
     String keyUsage;
-    if (isEnumKey) {
+    if (isEnum(keyArg)) {
       keyUsage = context.deserialize(keyArg, _keyParam).toString();
     } else if (context.config.anyMap && !_isObjectOrDynamic(keyArg)) {
       keyUsage = '$_keyParam as String';
     } else {
       keyUsage = _keyParam;
     }
 
+    final toFromString = _forType(keyArg);
+    if (toFromString != null) {
+      keyUsage = toFromString.deserialize(keyArg, keyUsage, false, true);
+    }
+
     return '($expression $mapCast)$optionalQuestion.map('
         '($_keyParam, $closureArg) => MapEntry($keyUsage, $itemSubVal),)';
   }
 }
 
+final _intString = ToFromStringHelper('int.parse', 'toString()', 'int');
+
+/// [ToFromStringHelper] instances representing non-String types that can
+/// be used as [Map] keys.
+final _instances = [
+  bigIntString,
+  dateTimeString,
+  _intString,
+  uriString,
+];
+
+ToFromStringHelper _forType(DartType type) =>
+    _instances.singleWhere((i) => i.matches(type), orElse: () => null);
+
 bool _isObjectOrDynamic(DartType type) => type.isObject || type.isDynamic;
 
+/// Returns `true` if [keyType] can be automatically converted to/from String –
+/// and is therefor usable as a key in a [Map].
+bool _isKeyStringable(DartType keyType) =>
+    isEnum(keyType) || _instances.any((inst) => inst.matches(keyType));
+
 void _checkSafeKeyType(String expression, DartType keyArg) {
   // We're not going to handle converting key types at the moment
   // So the only safe types for key are dynamic/Object/String/enum
   final safeKey = _isObjectOrDynamic(keyArg) ||
       coreStringTypeChecker.isExactlyType(keyArg) ||
-      isEnum(keyArg);
+      _isKeyStringable(keyArg);
 
   if (!safeKey) {
     throw UnsupportedTypeError(keyArg, expression,
-        'Map keys must be of type `String`, enum, `Object` or `dynamic`.');
+        'Map keys must be one of: ${_allowedTypeNames.join(', ')}.');
   }
 }
+
+/// The names of types that can be used as [Map] keys.
+///
+/// Used in [_checkSafeKeyType] to provide a helpful error with unsupported
+/// types.
+Iterable<String> get _allowedTypeNames => const [
+      'Object',
+      'dynamic',
+      'enum',
+      'String',
+    ].followedBy(_instances.map((i) => i.coreTypeName));

json_serializable/lib/src/type_helpers/to_from_string.dart

@@ -7,22 +7,22 @@ import 'package:source_gen/source_gen.dart';
 
 import '../type_helper.dart';
 
-const bigIntString = ToFromStringHelper(
+final bigIntString = ToFromStringHelper(
   'BigInt.parse',
   'toString()',
-  TypeChecker.fromUrl('dart:core#BigInt'),
+  'BigInt',
 );
 
-const dateTimeString = ToFromStringHelper(
+final dateTimeString = ToFromStringHelper(
   'DateTime.parse',
   'toIso8601String()',
-  TypeChecker.fromUrl('dart:core#DateTime'),
+  'DateTime',
 );
 
-const uriString = ToFromStringHelper(
+final uriString = ToFromStringHelper(
   'Uri.parse',
   'toString()',
-  TypeChecker.fromUrl('dart:core#Uri'),
+  'Uri',
 );
 
 /// Package-internal helper that unifies implementations of [Type]s that convert
@@ -40,9 +40,11 @@ class ToFromStringHelper {
   ///
   /// Examples: `toString()` for a function or `stringValue` for a property.
   final String _toString;
+  final String coreTypeName;
   final TypeChecker _checker;
 
-  const ToFromStringHelper(this._parse, this._toString, this._checker);
+  ToFromStringHelper(this._parse, this._toString, this.coreTypeName)
+      : _checker = TypeChecker.fromUrl('dart:core#$coreTypeName');
 
   bool matches(DartType type) => _checker.isExactlyType(type);
 

json_serializable/pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_serializable
-version: 3.0.0
+version: 3.1.0-dev
 author: Dart Team <misc@dartlang.org>
 description: >-
   Automatically generate code for converting to and from JSON by annotating

json_serializable/test/integration/integration_test.dart

@@ -232,4 +232,17 @@ void main() {
       expect(() => Numbers.fromJson(value), throwsCastError);
     });
   });
+
+  test('MapKeyVariety', () {
+    final instance = MapKeyVariety()
+      ..bigIntMap = {BigInt.from(1): 1}
+      ..dateTimeIntMap = {DateTime.parse('2018-01-01'): 2}
+      ..intIntMap = {3: 3}
+      ..uriIntMap = {Uri.parse('https://example.com'): 4};
+
+    final roundTrip =
+        roundTripObject(instance, (j) => MapKeyVariety.fromJson(j));
+
+    expect(roundTrip, instance);
+  });
 }

json_serializable/test/integration/json_test_example.dart

@@ -6,6 +6,7 @@
 import 'dart:collection';
 
 import 'package:json_annotation/json_annotation.dart';
+
 import 'json_test_common.dart';
 
 part 'json_test_example.g.dart';
@@ -146,3 +147,26 @@ class Numbers {
       deepEquals(duration, other.duration) &&
       deepEquals(date, other.date);
 }
+
+@JsonSerializable()
+class MapKeyVariety {
+  Map<int, int> intIntMap;
+  Map<Uri, int> uriIntMap;
+  Map<DateTime, int> dateTimeIntMap;
+  Map<BigInt, int> bigIntMap;
+
+  MapKeyVariety();
+
+  factory MapKeyVariety.fromJson(Map<String, dynamic> json) =>
+      _$MapKeyVarietyFromJson(json);
+
+  Map<String, dynamic> toJson() => _$MapKeyVarietyToJson(this);
+
+  @override
+  bool operator ==(Object other) =>
+      other is MapKeyVariety &&
+      deepEquals(other.intIntMap, intIntMap) &&
+      deepEquals(other.uriIntMap, uriIntMap) &&
+      deepEquals(other.dateTimeIntMap, dateTimeIntMap) &&
+      deepEquals(other.bigIntMap, bigIntMap);
+}