Allow extra non-serializable fields to be passed into fromJson and ignored in toJson

Author: hacker1024

json_annotation/lib/src/json_key.dart

@@ -90,6 +90,8 @@ class JsonKey {
   /// Valid only on enum fields with a compatible enum value.
   final Object? unknownEnumValue;
 
+  final bool? extra;
+
   /// Creates a new [JsonKey] instance.
   ///
   /// Only required when the default behavior is not desired.
@@ -104,5 +106,6 @@ class JsonKey {
     this.required,
     this.toJson,
     this.unknownEnumValue,
+    this.extra,
   });
 }

json_serializable/lib/src/decode_helper.dart

@@ -24,6 +24,7 @@ abstract class DecodeHelper implements HelperCore {
   CreateFactoryResult createFactory(
     Map<String, FieldElement> accessibleFields,
     Map<String, String> unavailableReasons,
+    List<FieldElement> extras,
   ) {
     assert(config.createFactory);
     final buffer = StringBuffer();
@@ -46,16 +47,27 @@ abstract class DecodeHelper implements HelperCore {
       }
     }
 
+    if (extras.isNotEmpty) {
+      buffer.writeln(', {');
+      for (final extra in extras) {
+        if (!extra.type.isNullableType) buffer.write('required ');
+        buffer.writeln(
+            '${extra.type.getDisplayString(withNullability: true)} ${extra.name},');
+      }
+      buffer.write('}');
+    }
+
     buffer.write(') {\n');
 
     String deserializeFun(String paramOrFieldName,
             {ParameterElement ctorParam}) =>
         _deserializeForField(accessibleFields[paramOrFieldName],
             ctorParam: ctorParam);
 
+    final extraNames = [for (final extra in extras) extra.name];
     final data = _writeConstructorInvocation(
       element,
-      accessibleFields.keys,
+      [...accessibleFields.keys, ...extraNames],
       accessibleFields.values
           .where((fe) =>
               !fe.isFinal ||
@@ -66,6 +78,7 @@ abstract class DecodeHelper implements HelperCore {
           .map((fe) => fe.name)
           .toList(),
       unavailableReasons,
+      extraNames,
       deserializeFun,
     );
 
@@ -237,6 +250,7 @@ _ConstructorData _writeConstructorInvocation(
   Iterable<String> availableConstructorParameters,
   Iterable<String> writableFields,
   Map<String, String> unavailableReasons,
+  List<String> extras,
   String Function(String paramOrFieldName, {ParameterElement ctorParam})
       deserializeForField,
 ) {
@@ -278,7 +292,7 @@ _ConstructorData _writeConstructorInvocation(
     } else {
       constructorArguments.add(arg);
     }
-    usedCtorParamsAndFields.add(arg.name);
+    if (!extras.contains(arg.name)) usedCtorParamsAndFields.add(arg.name);
   }
 
   // fields that aren't already set by the constructor and that aren't final
@@ -291,17 +305,19 @@ _ConstructorData _writeConstructorInvocation(
     buffer
       ..writeln()
       ..writeAll(constructorArguments.map((paramElement) {
-        final content =
-            deserializeForField(paramElement.name, ctorParam: paramElement);
+        final content = extras.contains(paramElement.name)
+            ? paramElement.name
+            : deserializeForField(paramElement.name, ctorParam: paramElement);
         return '      $content,\n';
       }));
   }
   if (namedConstructorArguments.isNotEmpty) {
     buffer
       ..writeln()
       ..writeAll(namedConstructorArguments.map((paramElement) {
-        final value =
-            deserializeForField(paramElement.name, ctorParam: paramElement);
+        final value = extras.contains(paramElement.name)
+            ? paramElement.name
+            : deserializeForField(paramElement.name, ctorParam: paramElement);
         return '      ${paramElement.name}: $value,\n';
       }));
   }

json_serializable/lib/src/generator_helper.dart

@@ -58,6 +58,8 @@ class GeneratorHelper extends HelperCore with EncodeHelper, DecodeHelper {
     // these fields.
     final unavailableReasons = <String, String>{};
 
+    final extras = <FieldElement>[];
+
     final accessibleFields = sortedFields.fold<Map<String, FieldElement>>(
       <String, FieldElement>{},
       (map, field) {
@@ -68,21 +70,26 @@ class GeneratorHelper extends HelperCore with EncodeHelper, DecodeHelper {
           unavailableReasons[field.name] =
               'Setter-only properties are not supported.';
           log.warning('Setters are ignored: ${element.name}.${field.name}');
-        } else if (jsonKeyFor(field).ignore) {
-          unavailableReasons[field.name] =
-              'It is assigned to an ignored field.';
         } else {
-          assert(!map.containsKey(field.name));
-          map[field.name] = field;
+          final jsonKey = jsonKeyFor(field);
+          if (jsonKey.ignore) {
+            unavailableReasons[field.name] =
+                'It is assigned to an ignored field.';
+          } else if (jsonKey.extra) {
+            extras.add(field);
+          } else {
+            assert(!map.containsKey(field.name));
+            map[field.name] = field;
+          }
         }
-
         return map;
       },
     );
 
     var accessibleFieldSet = accessibleFields.values.toSet();
     if (config.createFactory) {
-      final createResult = createFactory(accessibleFields, unavailableReasons);
+      final createResult =
+          createFactory(accessibleFields, unavailableReasons, extras);
       yield createResult.output;
 
       accessibleFieldSet = accessibleFields.entries

json_serializable/lib/src/json_key_utils.dart

@@ -181,6 +181,7 @@ JsonKey _from(FieldElement element, JsonSerializable classAnnotation) {
     name: obj.read('name').literalValue as String,
     required: obj.read('required').literalValue as bool,
     unknownEnumValue: _annotationValue('unknownEnumValue', mustBeEnum: true),
+    extra: obj.read('extra').literalValue as bool,
   );
 }
 
@@ -194,6 +195,7 @@ JsonKey _populateJsonKey(
   String name,
   bool required,
   Object unknownEnumValue,
+  bool extra,
 }) {
   if (disallowNullValue == true) {
     if (includeIfNull == true) {
@@ -213,6 +215,7 @@ JsonKey _populateJsonKey(
     name: _encodedFieldName(classAnnotation, name, element),
     required: required ?? false,
     unknownEnumValue: unknownEnumValue,
+    extra: extra ?? false,
   );
 
   return jsonKey;