feat: add common properties with different nullability to base mixin

packages/freezed/lib/src/freezed_generator.dart

@@ -128,27 +128,19 @@ class FreezedGenerator extends ParserGenerator<GlobalData, Data, Freezed> {
   List<Property> _commonProperties(
     List<ConstructorDetails> constructorsNeedsGeneration,
   ) {
-    final commonParameters =
-        _commonParametersBetweenAllConstructors(constructorsNeedsGeneration);
-
-    return [
-      for (final commonParameter in commonParameters)
-        Property(
-          decorators: commonParameter.decorators,
-          name: commonParameter.name,
-          isFinal: commonParameter.isFinal,
-          doc: commonParameter.doc,
-          type: commonParameter.type,
-          defaultValueSource: commonParameter.defaultValueSource,
-          isNullable: commonParameter.isNullable,
-          isDartList: commonParameter.isDartList,
-          isDartMap: commonParameter.isDartMap,
-          isDartSet: commonParameter.isDartSet,
-          isPossiblyDartCollection: commonParameter.isPossiblyDartCollection,
-          // TODO: support hasJsonKey
-          hasJsonKey: false,
-        ),
-    ];
+    return _commonParametersBetweenAllConstructors(
+      constructorsNeedsGeneration,
+      allowCommonSuperType: false,
+    ).map(Property.fromParameter).toList();
+  }
+
+  List<Property> _commonGetters(
+    List<ConstructorDetails> constructorsNeedsGeneration,
+  ) {
+    return _commonParametersBetweenAllConstructors(
+      constructorsNeedsGeneration,
+      allowCommonSuperType: true,
+    ).map(Property.fromParameter).toList();
   }
 
   void _assertValidClassUsage(ClassElement element) {
@@ -248,26 +240,48 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
   }
 
   List<Parameter> _commonParametersBetweenAllConstructors(
-    List<ConstructorDetails> constructorsNeedsGeneration,
-  ) {
+    List<ConstructorDetails> constructorsNeedsGeneration, {
+    required bool allowCommonSuperType,
+  }) {
     return constructorsNeedsGeneration.first.parameters.allParameters
         .map((parameter) {
-          var hasAnyFinalProperty = false;
-          for (final constructor in constructorsNeedsGeneration) {
-            final matchingParameter =
-                constructor.parameters.allParameters.firstWhereOrNull((p) {
-              return p.name == parameter.name && p.type == parameter.type;
-            });
+          var anyMatchingPropertyIsFinal = false;
+          var isCommonWithDifferentNullability = false;
+
+          DartType? commonType;
+
+          for (final constructor in constructorsNeedsGeneration.skip(1)) {
+            final matchingParameter = constructor.parameters.allParameters
+                .firstWhereOrNull((p) => p.name == parameter.name);
 
             if (matchingParameter == null) return null;
-            if (matchingParameter.isFinal) hasAnyFinalProperty = true;
-          }
 
-          if (hasAnyFinalProperty) {
-            return parameter.copyWith(isFinal: true);
+            final commonTypeWithMatch =
+                parameter.parameterElement!.library!.typeSystem.leastUpperBound(
+              parameter.parameterElement!.type,
+              matchingParameter.parameterElement!.type,
+            );
+
+            if (commonTypeWithMatch.isDartCoreObject) return null;
+
+            if (!allowCommonSuperType &&
+                commonTypeWithMatch.getDisplayString(withNullability: false) !=
+                    parameter.type?.replaceAll(r'?$', '')) return null;
+
+            if (commonType != null && commonType != commonTypeWithMatch)
+              return null;
+
+            commonType = commonTypeWithMatch;
+            if (matchingParameter.isFinal) anyMatchingPropertyIsFinal = true;
+            if (parameter.isNullable != matchingParameter.isNullable)
+              isCommonWithDifferentNullability = true;
           }
 
-          return parameter;
+          return parameter.copyWith(
+            isFinal: parameter.isFinal || anyMatchingPropertyIsFinal,
+            type: commonType?.getDisplayString(withNullability: true),
+            isCommonWithDifferentNullability: isCommonWithDifferentNullability,
+          );
         })
         .whereNotNull()
         .toList();
@@ -311,7 +325,7 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
           escapedName: _escapedName(element, constructor),
           impliedProperties: [
             for (final parameter in constructor.parameters)
-              await Property.fromParameter(
+              await Property.fromParameterElement(
                 parameter,
                 buildStep,
                 addImplicitFinal: options.addImplicitFinal,
@@ -595,6 +609,7 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
     }
 
     final commonProperties = _commonProperties(data.constructors);
+    final commonGetters = _commonGetters(data.constructors);
 
     final commonCopyWith = !data.generateCopyWith
         ? null
@@ -613,6 +628,7 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
     yield Abstract(
       data: data,
       copyWith: commonCopyWith,
+      commonGetters: commonGetters,
       commonProperties: commonProperties,
     );
 

packages/freezed/lib/src/templates/abstract_template.dart

@@ -9,15 +9,17 @@ class Abstract {
     required this.data,
     required this.copyWith,
     required this.commonProperties,
+    required this.commonGetters,
   });
 
   final Data data;
   final CopyWith? copyWith;
   final List<Property> commonProperties;
+  final List<Property> commonGetters;
 
   @override
   String toString() {
-    final abstractProperties = commonProperties
+    final abstractProperties = commonGetters
         .expand((e) => [
               e.unimplementedGetter,
               if (!e.isFinal) e.unimplementedSetter,

packages/freezed/lib/src/templates/concrete_template.dart

@@ -135,6 +135,8 @@ ${copyWith?.abstractCopyWithGetter ?? ''}
         doc: '',
         isPossiblyDartCollection: false,
         showDefaultValue: false,
+        isCommonWithDifferentNullability: false,
+        parameterElement: null,
       );
 
       parameters = ParametersTemplate(

packages/freezed/lib/src/templates/copy_with.dart

@@ -80,6 +80,9 @@ ${_abstractDeepCopyMethods().join()}
               type: e.type,
               doc: e.doc,
               isPossiblyDartCollection: e.isPossiblyDartCollection,
+              isCommonWithDifferentNullability:
+                  e.isCommonWithDifferentNullability,
+              parameterElement: null,
             );
           }).toList(),
         ),
@@ -133,7 +136,11 @@ ${_deepCopyMethods().join()}
     required List<Property> properties,
   }) {
     final parameters = properties.map((p) {
-      return '${p.decorators.join()} ${p.type} ${p.name}';
+      final type = p.isCommonWithDifferentNullability
+          ? p.type.replaceFirst(RegExp(r'\?$'), '')
+          : p.type;
+
+      return '${p.decorators.join()} covariant $type ${p.name}';
     }).join(',');
 
     return _maybeOverride('''
@@ -197,10 +204,18 @@ $s''';
           data.makeCollectionsImmutable) {
         propertyName = '_$propertyName';
       }
-      var ternary =
-          '${p.name} == freezed ? $accessor.$propertyName : ${p.name} ';
+      final type = p.isCommonWithDifferentNullability
+          ? p.type!.replaceFirst(RegExp(r'\?$'), '')
+          : p.type;
+      var ternary = '${p.name} == freezed ? $accessor.$propertyName ';
+
+      if (p.isCommonWithDifferentNullability) {
+        ternary += 'as $type ';
+      }
+
+      ternary += ': ${p.name} ';
       if (p.type != 'Object?' && p.type != null) {
-        ternary += _ignoreLints('as ${p.type}');
+        ternary += _ignoreLints('as $type');
       }
       return '$ternary,';
     }

packages/freezed/lib/src/templates/parameter_template.dart

@@ -82,6 +82,8 @@ class ParametersTemplate {
         doc: await documentationOfParameter(e, buildStep),
         isPossiblyDartCollection: e.type.isPossiblyDartCollection,
         showDefaultValue: true,
+        isCommonWithDifferentNullability: false,
+        parameterElement: e,
       );
 
       if (isAssignedToThis) return LocalParameter.fromParameter(value);
@@ -184,6 +186,8 @@ class Parameter {
     required this.isFinal,
     required this.isPossiblyDartCollection,
     required this.showDefaultValue,
+    required this.isCommonWithDifferentNullability,
+    required this.parameterElement,
   });
 
   Parameter.fromParameter(Parameter p)
@@ -201,6 +205,8 @@ class Parameter {
           showDefaultValue: p.showDefaultValue,
           doc: p.doc,
           isPossiblyDartCollection: p.isPossiblyDartCollection,
+          isCommonWithDifferentNullability: p.isCommonWithDifferentNullability,
+          parameterElement: p.parameterElement,
         );
 
   final String? type;
@@ -216,6 +222,8 @@ class Parameter {
   final bool isPossiblyDartCollection;
   final bool isFinal;
   final String doc;
+  final bool isCommonWithDifferentNullability;
+  final ParameterElement? parameterElement;
 
   Parameter copyWith({
     String? type,
@@ -232,6 +240,7 @@ class Parameter {
     bool? isDartMap,
     bool? isDartSet,
     bool? isFinal,
+    bool? isCommonWithDifferentNullability,
   }) =>
       Parameter(
         type: type ?? this.type,
@@ -248,6 +257,9 @@ class Parameter {
         isFinal: isFinal ?? this.isFinal,
         isPossiblyDartCollection:
             isPossiblyDartCollection ?? this.isPossiblyDartCollection,
+        isCommonWithDifferentNullability: isCommonWithDifferentNullability ??
+            this.isCommonWithDifferentNullability,
+        parameterElement: parameterElement,
       );
 
   @override
@@ -283,6 +295,8 @@ class LocalParameter extends Parameter {
     required List<String> decorators,
     required String doc,
     required bool isPossiblyDartCollection,
+    required bool isCommonWithDifferentNullability,
+    required ParameterElement? parameterElement,
   }) : super(
           name: name,
           type: type,
@@ -297,6 +311,8 @@ class LocalParameter extends Parameter {
           defaultValueSource: defaultValueSource,
           doc: doc,
           isPossiblyDartCollection: isPossiblyDartCollection,
+          isCommonWithDifferentNullability: isCommonWithDifferentNullability,
+          parameterElement: parameterElement,
         );
 
   LocalParameter.fromParameter(Parameter p)
@@ -313,6 +329,8 @@ class LocalParameter extends Parameter {
           decorators: p.decorators,
           doc: p.doc,
           isPossiblyDartCollection: p.isPossiblyDartCollection,
+          isCommonWithDifferentNullability: p.isCommonWithDifferentNullability,
+          parameterElement: p.parameterElement,
         );
 
   @override
@@ -346,6 +364,8 @@ class CallbackParameter extends Parameter {
     required this.parameters,
     required String doc,
     required bool isPossiblyDartCollection,
+    required bool isCommonWithDifferentNullability,
+    required ParameterElement? parameterElement,
   }) : super(
           name: name,
           type: type,
@@ -360,6 +380,8 @@ class CallbackParameter extends Parameter {
           defaultValueSource: defaultValueSource,
           doc: doc,
           isPossiblyDartCollection: isPossiblyDartCollection,
+          isCommonWithDifferentNullability: isCommonWithDifferentNullability,
+          parameterElement: parameterElement,
         );
 
   final ParametersTemplate parameters;

packages/freezed/lib/src/templates/properties.dart

@@ -2,6 +2,7 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:build/build.dart';
+import 'package:freezed/src/templates/parameter_template.dart';
 import 'package:source_gen/source_gen.dart';
 
 import '../utils.dart';
@@ -31,9 +32,30 @@ class Property {
     required this.isDartMap,
     required this.isDartSet,
     required this.isPossiblyDartCollection,
+    required this.isCommonWithDifferentNullability,
+    required this.parameterElement,
   }) : type = type ?? 'dynamic';
 
-  static Future<Property> fromParameter(
+  Property.fromParameter(Parameter p)
+      : this(
+          decorators: p.decorators,
+          name: p.name,
+          isFinal: p.isFinal,
+          doc: p.doc,
+          type: p.type,
+          defaultValueSource: p.defaultValueSource,
+          isNullable: p.isNullable,
+          isDartList: p.isDartList,
+          isDartMap: p.isDartMap,
+          isDartSet: p.isDartSet,
+          isPossiblyDartCollection: p.isPossiblyDartCollection,
+          // TODO: support hasJsonKey
+          hasJsonKey: false,
+          isCommonWithDifferentNullability: p.isCommonWithDifferentNullability,
+          parameterElement: p.parameterElement,
+        );
+
+  static Future<Property> fromParameterElement(
     ParameterElement element,
     BuildStep buildStep, {
     required bool addImplicitFinal,
@@ -60,6 +82,8 @@ class Property {
       defaultValueSource: defaultValue,
       hasJsonKey: element.hasJsonKey,
       isPossiblyDartCollection: element.type.isPossiblyDartCollection,
+      isCommonWithDifferentNullability: false,
+      parameterElement: element,
     );
   }
 
@@ -75,6 +99,8 @@ class Property {
   final bool hasJsonKey;
   final String doc;
   final bool isPossiblyDartCollection;
+  final bool isCommonWithDifferentNullability;
+  final ParameterElement? parameterElement;
 
   @override
   String toString() {
@@ -135,6 +161,8 @@ class Property {
     bool? hasJsonKey,
     String? doc,
     bool? isPossiblyDartCollection,
+    bool? isCommonWithDifferentNullability,
+    ParameterElement? parameterElement,
   }) {
     return Property(
       type: type ?? this.type,
@@ -150,6 +178,9 @@ class Property {
       isDartSet: isDartSet ?? this.isDartSet,
       isPossiblyDartCollection:
           isPossiblyDartCollection ?? this.isPossiblyDartCollection,
+      isCommonWithDifferentNullability: isCommonWithDifferentNullability ??
+          this.isCommonWithDifferentNullability,
+      parameterElement: parameterElement ?? this.parameterElement,
     );
   }
 }

packages/freezed/lib/src/templates/prototypes.dart

@@ -127,6 +127,8 @@ String _mapPrototype(
           // TODO: do we want to support freezed classes that implements MapView/ListView?
           isPossiblyDartCollection: false,
           showDefaultValue: false,
+          isCommonWithDifferentNullability: false,
+          parameterElement: null,
         ),
       ]);
     },
@@ -191,6 +193,8 @@ String _unionPrototype(
       defaultValueSource: '',
       doc: '',
       isPossiblyDartCollection: false,
+      isCommonWithDifferentNullability: false,
+      parameterElement: null,
     );
 
     if (constructor.isDefault) {