feat: add common properties with different nullability to base mixin

packages/freezed/lib/src/freezed_generator.dart

@@ -128,27 +128,9 @@ 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 _commonPropertiesBetweenAllConstructors(constructorsNeedsGeneration)
+        .map(Property.fromParameter)
+        .toList();
   }
 
   void _assertValidClassUsage(ClassElement element) {
@@ -247,27 +229,89 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
     return false;
   }
 
-  List<Parameter> _commonParametersBetweenAllConstructors(
+  List<Parameter> _commonPropertiesBetweenAllConstructors(
     List<ConstructorDetails> constructorsNeedsGeneration,
   ) {
     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;
-            });
+          final library = parameter.parameterElement!.library!;
+
+          String typeString(DartType type, {bool withNullability = true}) {
+            return resolveFullTypeStringFrom(
+              library,
+              type,
+              withNullability: withNullability,
+            );
+          }
+
+          var anyMatchingPropertyIsFinal = false;
+
+          var commonSupertypeDartType = parameter.parameterElement!.type;
+          var commonSubTypeDartType = parameter.parameterElement?.type;
+
+          String? commonSupertypeString;
+          String? commonSubtypeString;
+
+          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 matchingParameterType =
+                matchingParameter.parameterElement!.type;
+            if (matchingParameter.isFinal) anyMatchingPropertyIsFinal = true;
+
+            if (commonSupertypeDartType is FunctionType ||
+                commonSupertypeDartType.isDynamic) {
+              // If the type is a typedef, by finding the upper bound we would lose
+              // the initial definition. Therefore FunctionTypes are currently not
+              // supported for finding in finding common super types.
+              // => Resort back to type string matching.
+              commonSupertypeString ??= parameter.type!;
+              if (commonSupertypeString.contains('dynamic')) return null;
+
+              if (!typeStringsEqualIgnoringNullability(
+                  commonSupertypeString, matchingParameter.type!)) {
+                return null;
+              }
+
+              if (commonSupertypeDartType.isNullable !=
+                  matchingParameterType.isNullable) {
+                commonSupertypeString =
+                    typeStringWithNullability(commonSupertypeString);
+                commonSubtypeString =
+                    typeStringWithoutNullability(commonSupertypeString);
+              }
+            } else {
+              commonSupertypeDartType = library.typeSystem.leastUpperBound(
+                commonSupertypeDartType,
+                matchingParameterType,
+              );
+
+              if (commonSupertypeDartType
+                  .getDisplayString(withNullability: true)
+                  .contains('dynamic')) return null;
+
+              if (commonSubTypeDartType != null) {
+                if (library.typeSystem.isSubtypeOf(
+                    matchingParameterType, commonSubTypeDartType)) {
+                  commonSubTypeDartType = matchingParameterType;
+                } else if (!library.typeSystem.isSubtypeOf(
+                    commonSubTypeDartType, matchingParameterType)) {
+                  commonSubTypeDartType = null;
+                }
+              }
+            }
           }
 
-          return parameter;
+          return parameter.copyWith(
+            isFinal: parameter.isFinal || anyMatchingPropertyIsFinal,
+            commonSupertype:
+                commonSupertypeString ?? typeString(commonSupertypeDartType),
+            commonSubtype:
+                commonSubtypeString ?? commonSubTypeDartType?.let(typeString),
+          );
         })
         .whereNotNull()
         .toList();
@@ -311,7 +355,7 @@ 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,
@@ -595,18 +639,20 @@ Read here: https://github.com/rrousselGit/freezed/blob/master/packages/freezed/C
     }
 
     final commonProperties = _commonProperties(data.constructors);
+    final commonCopyableProperties =
+        commonProperties.where((p) => p.isCopyable).toList();
 
     final commonCopyWith = !data.generateCopyWith
         ? null
         : CopyWith(
             clonedClassName: data.name,
             cloneableProperties: _commonCloneableProperties(
               data.constructors,
-              commonProperties,
+              commonCopyableProperties,
             ).toList(),
             genericsDefinition: data.genericsDefinitionTemplate,
             genericsParameter: data.genericsParameterTemplate,
-            allProperties: commonProperties,
+            allProperties: commonCopyableProperties,
             data: data,
           );
 
@@ -829,3 +875,12 @@ String? parseLateGetterSource(String source) {
   }
   return null;
 }
+
+extension Let<T> on T {
+  @pragma('vm:prefer-inline')
+  R let<R>(R Function(T) f) => f(this);
+}
+
+extension on DartType {
+  bool get isNullable => nullabilitySuffix == NullabilitySuffix.question;
+}

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

@@ -18,10 +18,19 @@ class Abstract {
   @override
   String toString() {
     final abstractProperties = commonProperties
-        .expand((e) => [
-              e.unimplementedGetter,
-              if (!e.isFinal) e.unimplementedSetter,
-            ])
+        .expand((e) {
+          return <ClassMember?>[
+            e.unimplementedGetter,
+            if (!e.isFinal &&
+                // Don't add a setter for a field where the setters type is not
+                // a subtype of the getters type.
+                !(e.commonSupertype != null &&
+                    e.commonSubtype != e.commonSupertype))
+              e.unimplementedSetter,
+          ];
+        })
+        .whereType<ClassMember>()
+        .map((e) => e.toString())
         .join();
 
     return '''
@@ -41,7 +50,7 @@ ${copyWith?.abstractCopyWithGetter ?? ''}
 
 ${copyWith?.interface ?? ''}
 
-${copyWith?.commonContreteImpl(commonProperties) ?? ''}
+${copyWith?.commonContreteImpl ?? ''}
 ''';
   }
 

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

@@ -135,6 +135,9 @@ ${copyWith?.abstractCopyWithGetter ?? ''}
         doc: '',
         isPossiblyDartCollection: false,
         showDefaultValue: false,
+        commonSupertype: null,
+        commonSubtype: null,
+        parameterElement: null,
       );
 
       parameters = ParametersTemplate(

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

@@ -51,9 +51,7 @@ ${_abstractDeepCopyMethods().join()}
     return parent != null && parent!.allProperties.isNotEmpty;
   }
 
-  String commonContreteImpl(
-    List<Property> commonProperties,
-  ) {
+  String get commonContreteImpl {
     var copyWith = '';
 
     if (allProperties.isNotEmpty) {
@@ -65,7 +63,7 @@ ${_abstractDeepCopyMethods().join()}
       final body = _copyWithMethodBody(
         parametersTemplate: ParametersTemplate(
           const [],
-          namedParameters: commonProperties.map((e) {
+          namedParameters: allProperties.map((e) {
             return Parameter(
               decorators: e.decorators,
               name: e.name,
@@ -77,9 +75,12 @@ ${_abstractDeepCopyMethods().join()}
               showDefaultValue: false,
               isRequired: false,
               defaultValueSource: '',
-              type: e.type,
+              type: e.commonSupertype ?? e.type,
               doc: e.doc,
               isPossiblyDartCollection: e.isPossiblyDartCollection,
+              commonSupertype: e.commonSupertype,
+              commonSubtype: e.commonSubtype,
+              parameterElement: null,
             );
           }).toList(),
         ),
@@ -133,7 +134,9 @@ ${_deepCopyMethods().join()}
     required List<Property> properties,
   }) {
     final parameters = properties.map((p) {
-      return '${p.decorators.join()} ${p.type} ${p.name}';
+      final type = p.commonSubtype ?? p.type;
+
+      return '${p.decorators.join()} covariant $type ${p.name}';
     }).join(',');
 
     return _maybeOverride('''
@@ -197,10 +200,17 @@ $s''';
           data.makeCollectionsImmutable) {
         propertyName = '_$propertyName';
       }
-      var ternary =
-          '${p.name} == freezed ? $accessor.$propertyName : ${p.name} ';
+
+      var ternary = '${p.name} == freezed ? $accessor.$propertyName ';
+
+      final type = p.commonSubtype ?? p.type;
+      if (p.commonSubtype != null && p.type != p.commonSubtype) {
+        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 +82,9 @@ class ParametersTemplate {
         doc: await documentationOfParameter(e, buildStep),
         isPossiblyDartCollection: e.type.isPossiblyDartCollection,
         showDefaultValue: true,
+        commonSupertype: null,
+        commonSubtype: null,
+        parameterElement: e,
       );
 
       if (isAssignedToThis) return LocalParameter.fromParameter(value);
@@ -184,6 +187,9 @@ class Parameter {
     required this.isFinal,
     required this.isPossiblyDartCollection,
     required this.showDefaultValue,
+    required this.commonSupertype,
+    required this.commonSubtype,
+    required this.parameterElement,
   });
 
   Parameter.fromParameter(Parameter p)
@@ -201,6 +207,9 @@ class Parameter {
           showDefaultValue: p.showDefaultValue,
           doc: p.doc,
           isPossiblyDartCollection: p.isPossiblyDartCollection,
+          commonSubtype: p.commonSubtype,
+          commonSupertype: p.commonSupertype,
+          parameterElement: p.parameterElement,
         );
 
   final String? type;
@@ -216,6 +225,9 @@ class Parameter {
   final bool isPossiblyDartCollection;
   final bool isFinal;
   final String doc;
+  final String? commonSupertype;
+  final String? commonSubtype;
+  final ParameterElement? parameterElement;
 
   Parameter copyWith({
     String? type,
@@ -232,6 +244,8 @@ class Parameter {
     bool? isDartMap,
     bool? isDartSet,
     bool? isFinal,
+    String? commonSupertype,
+    String? commonSubtype,
   }) =>
       Parameter(
         type: type ?? this.type,
@@ -248,6 +262,9 @@ class Parameter {
         isFinal: isFinal ?? this.isFinal,
         isPossiblyDartCollection:
             isPossiblyDartCollection ?? this.isPossiblyDartCollection,
+        commonSupertype: commonSupertype ?? this.commonSupertype,
+        commonSubtype: commonSubtype ?? this.commonSubtype,
+        parameterElement: parameterElement,
       );
 
   @override
@@ -283,6 +300,9 @@ class LocalParameter extends Parameter {
     required List<String> decorators,
     required String doc,
     required bool isPossiblyDartCollection,
+    required String? commonSupertype,
+    required String? commonSubtype,
+    required ParameterElement? parameterElement,
   }) : super(
           name: name,
           type: type,
@@ -297,6 +317,9 @@ class LocalParameter extends Parameter {
           defaultValueSource: defaultValueSource,
           doc: doc,
           isPossiblyDartCollection: isPossiblyDartCollection,
+          commonSupertype: commonSupertype,
+          commonSubtype: commonSubtype,
+          parameterElement: parameterElement,
         );
 
   LocalParameter.fromParameter(Parameter p)
@@ -313,6 +336,9 @@ class LocalParameter extends Parameter {
           decorators: p.decorators,
           doc: p.doc,
           isPossiblyDartCollection: p.isPossiblyDartCollection,
+          commonSupertype: p.commonSupertype,
+          commonSubtype: p.commonSubtype,
+          parameterElement: p.parameterElement,
         );
 
   @override
@@ -346,6 +372,9 @@ class CallbackParameter extends Parameter {
     required this.parameters,
     required String doc,
     required bool isPossiblyDartCollection,
+    required String? commonSupertype,
+    required String? commonSubtype,
+    required ParameterElement? parameterElement,
   }) : super(
           name: name,
           type: type,
@@ -360,6 +389,9 @@ class CallbackParameter extends Parameter {
           defaultValueSource: defaultValueSource,
           doc: doc,
           isPossiblyDartCollection: isPossiblyDartCollection,
+          commonSupertype: commonSupertype,
+          commonSubtype: commonSubtype,
+          parameterElement: parameterElement,
         );
 
   final ParametersTemplate parameters;