Allow types with record fields to be serialized via typedef and custo…

…m serializer.

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+# 8.8.0 (unreleased)
+
+- Allow classes with record fields to be serialized if they use a typedef for
+  the record type and install a custom `Serializer` for it.
+
 # 8.7.0
 
 - Add `Int32` serializer.

built_value/lib/src/built_json_serializers.dart

@@ -77,7 +77,8 @@ class BuiltJsonSerializers implements Serializers {
     if (specifiedType.isUnspecified) {
       final serializer = serializerForType(object.runtimeType);
       if (serializer == null) {
-        throw StateError("No serializer for '${object.runtimeType}'.");
+        throw StateError(
+            _noSerializerMessageFor(object.runtimeType.toString()));
       }
       if (serializer is StructuredSerializer) {
         final result = <Object?>[serializer.wireName];
@@ -135,7 +136,7 @@ class BuiltJsonSerializers implements Serializers {
 
       final serializer = serializerForWireName(wireName);
       if (serializer == null) {
-        throw StateError("No serializer for '$wireName'.");
+        throw StateError(_noSerializerMessageFor(wireName));
       }
 
       if (serializer is StructuredSerializer) {
@@ -164,7 +165,8 @@ class BuiltJsonSerializers implements Serializers {
           // Might be an interface; try resolving using the type on the wire.
           return deserialize(objectBeforePlugins);
         } else {
-          throw StateError("No serializer for '${specifiedType.root}'.");
+          throw StateError(
+              _noSerializerMessageFor(specifiedType.root.toString()));
         }
       }
 
@@ -321,3 +323,11 @@ String _getRawName(Type? type) {
   var genericsStart = name.indexOf('<');
   return genericsStart == -1 ? name : name.substring(0, genericsStart);
 }
+
+String _noSerializerMessageFor(String typeName) {
+  final maybeRecordAdvice = typeName.contains('(')
+      ? ' Note that record types are not automatically serializable, '
+          'please write and install your own `Serializer`.'
+      : '';
+  return "No serializer for '$typeName'.$maybeRecordAdvice";
+}

built_value_generator/lib/src/serializer_source_field.dart

@@ -203,10 +203,16 @@ abstract class SerializerSourceField
       ];
     }
 
-    if (isSerializable && element.getter!.returnType is RecordType) {
+    if (isSerializable &&
+        element.getter!.returnType is RecordType &&
+        typeWithPrefix.contains('(')) {
       return [
-        'Record fields are not (yet) serializable. '
-            'Remove "$name" or mark it "@BuiltValueField(serialize: false)".'
+        'Fields declared with record types are not automatically serializable. '
+            'To allow the class to be serialized, modify "$name" by: '
+            'a) removing it,  or '
+            'b) marking it "@BuiltValueField(serialize: false)", or '
+            'c) creating a `typedef` to represent the record type then '
+            'writing and installing a custom `Serializer` for it.'
       ];
     }
 

built_value_generator/test/serializer_generator_test.dart

@@ -243,9 +243,9 @@ abstract class Value implements Built<Value, ValueBuilder> {
   factory Value([void Function(ValueBuilder) updates]) = _$Value;
 }
 '''),
-          contains(r'1. Record fields are not (yet) serializable. '
-              'Remove "record" or mark it '
-              '"@BuiltValueField(serialize: false)".'));
+          contains(r'1. Fields declared with record types are not '
+              'automatically serializable. '
+              'To allow the class to be serialized, modify "record" by'));
     });
   });
 }

end_to_end_test/lib/records.dart

@@ -55,6 +55,8 @@ abstract class ComplexRecordValue
   ComplexRecordValue._();
 }
 
+typedef RecordOfIntInt = (int, int);
+
 // Record serialization is not supported, so a class with records is only
 // serializable if record fields are not serialized.
 abstract class SerializableRecordValue
@@ -63,11 +65,31 @@ abstract class SerializableRecordValue
       _$serializableRecordValueSerializer;
 
   int get value;
-  @BuiltValueField(serialize: false)
-  (int, int)? get record;
+  RecordOfIntInt? get record;
 
   factory SerializableRecordValue(
           [void Function(SerializableRecordValueBuilder) updates]) =
       _$SerializableRecordValue;
   SerializableRecordValue._();
 }
+
+class RecordOfIntIntSerializer implements StructuredSerializer<RecordOfIntInt> {
+  @override
+  RecordOfIntInt deserialize(
+      Serializers serializers, Iterable<Object?> serialized,
+      {FullType specifiedType = FullType.unspecified}) {
+    return (serialized.elementAt(0)! as int, serialized.elementAt(1)! as int);
+  }
+
+  @override
+  Iterable<Object?> serialize(Serializers serializers, RecordOfIntInt object,
+      {FullType specifiedType = FullType.unspecified}) {
+    return [object.$1, object.$2];
+  }
+
+  @override
+  Iterable<Type> get types => [RecordOfIntInt];
+
+  @override
+  String get wireName => 'RecordOfIntInt';
+}

end_to_end_test/test/records_serializer_test.dart

@@ -4,12 +4,13 @@
 
 import 'dart:convert';
 
+import 'package:end_to_end_test/errors_matchers.dart';
 import 'package:end_to_end_test/records.dart';
 import 'package:end_to_end_test/serializers.dart';
 import 'package:test/test.dart';
 
 void main() {
-  group(SerializableRecordValue, () {
+  group('$SerializableRecordValue with no record value', () {
     var data = SerializableRecordValue((b) => b..value = 1);
     var serialized = json.decode(json.encode([
       'SerializableRecordValue',
@@ -25,4 +26,41 @@ void main() {
       expect(serializers.deserialize(serialized), data);
     });
   });
+
+  group('$SerializableRecordValue with a record value', () {
+    var data = SerializableRecordValue((b) => b
+      ..value = 1
+      ..record = (1, 2));
+    var serialized = json.decode(json.encode([
+      'SerializableRecordValue',
+      'value',
+      1,
+      'record',
+      [1, 2],
+    ])) as Object;
+    var serializersWithCustomSerializer =
+        (serializers.toBuilder()..add(RecordOfIntIntSerializer())).build();
+
+    test('gives advice about custom serializer on failure to serialize', () {
+      expect(
+          () => serializers.serialize(data),
+          throwsA(isErrorContaining(
+              'record types are not automatically serializable')));
+    });
+
+    test('gives advice about custom serializer on failure to deserialize', () {
+      expect(
+          () => serializers.deserialize(serialized),
+          throwsA(isErrorContaining(
+              'record types are not automatically serializable')));
+    });
+
+    test('can be serialized with custom serializer', () {
+      expect(serializersWithCustomSerializer.serialize(data), serialized);
+    });
+
+    test('can be deserialized with custom deserializer', () {
+      expect(serializersWithCustomSerializer.deserialize(serialized), data);
+    });
+  });
 }