Private unions (#1159)

Author: rrousselGit

packages/freezed/CHANGELOG.md

@@ -161,6 +161,19 @@ This feature offers fine-grained control over every parts of your models.
 Unfortunately, it is kind of required to "extend" the parent class (so here `extends Result<T>`). This is because Dart doesn't support `sealed mixin class`, so you can't do
 `with Result<T>` instead.
 
+### New: private unions
+
+It is now possible to have a private constructor for unions:
+
+```dart
+@freezed
+sealed class Result<T> with _$Result {
+  // It wasn't possible to write _data before, but now is.
+  factory Result._data(T data) = ResultData;
+  factory Result.error(Object error) = ResultError;
+}
+```
+
 ## 2.5.8 - 2025-01-06
 
 Support analyzer 7.0.0

packages/freezed/lib/src/models.dart

@@ -195,15 +195,15 @@ class ConstructorDetails {
     );
 
     if (constructor.factoryKeyword == null &&
-        constructor.name?.lexeme != '_' &&
+        !constructor.isManualCtor &&
         freezedCtors.isNotEmpty) {
       throw InvalidGenerationSourceError(
         'Classes decorated with @freezed can only have a single non-factory constructor.',
         element: constructor.declaredElement,
       );
     }
 
-    if (constructor.name?.lexeme == '_') {
+    if (constructor.isManualCtor) {
       for (final param in constructor.parameters.parameters) {
         if (param.isPositional) {
           for (final ctor in freezedCtors) {
@@ -259,9 +259,7 @@ When specifying fields in non-factory constructor then specifying factory constr
   }) {
     final result = <ConstructorDetails>[];
 
-    final manualConstructor = declaration.constructors
-        .where((e) => e.name?.lexeme == '_')
-        .firstOrNull;
+    final manualConstructor = declaration.manualConstructor;
 
     for (final constructor in declaration.constructors) {
       if (constructor.factoryKeyword == null ||
@@ -352,13 +350,6 @@ When specifying fields in non-factory constructor then specifying factory constr
       );
     }
 
-    if (result.length > 1 && result.any((c) => c.name.startsWith('_'))) {
-      throw InvalidGenerationSourceError(
-        'A freezed union cannot have private constructors',
-        element: declaration.declaredElement,
-      );
-    }
-
     if (configs.annotation.fallbackUnion != null &&
         result.none((c) => c.isFallback)) {
       throw InvalidGenerationSourceError(
@@ -524,9 +515,7 @@ class Class {
     required Freezed globalConfigs,
     required List<CompilationUnit> unitsExcludingGeneratedFiles,
   }) {
-    final privateCtor = declaration.constructors.where((ctor) {
-      return ctor.name?.lexeme == '_' && ctor.factoryKeyword == null;
-    }).firstOrNull;
+    final privateCtor = declaration.manualConstructor;
 
     for (final field in declaration.declaredElement!.fields) {
       _assertValidFieldUsage(field, shouldUseExtends: privateCtor != null);
@@ -1147,6 +1136,10 @@ class ClassConfig {
   final Freezed annotation;
 }
 
+extension on ConstructorDeclaration {
+  bool get isManualCtor => name?.lexeme == '_' && factoryKeyword == null;
+}
+
 extension ClassDeclarationX on ClassDeclaration {
   /// Pick either Class(), Class._() or the first constructor found, in that order.
   ConstructorDeclaration? get copyWithTarget {
@@ -1158,6 +1151,10 @@ extension ClassDeclarationX on ClassDeclaration {
         constructors.firstOrNull;
   }
 
+  ConstructorDeclaration? get manualConstructor {
+    return constructors.where((e) => e.isManualCtor).firstOrNull;
+  }
+
   Iterable<ConstructorDeclaration> get constructors {
     return members.whereType<ConstructorDeclaration>();
   }

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

@@ -117,12 +117,14 @@ ${copyWith?.concreteImpl(constructor.parameters) ?? ''}
         );
       }
 
-      final superCall = data.superCall!;
+      final superCall = data.superCall;
 
       // Attempt to use super.field when possible.
       // For now, we only do so for named parameters as positional parameters
       // are trickier.
-      if (isNamed && superCall.positional.contains(p.name)) {
+      if (superCall != null &&
+          isNamed &&
+          superCall.positional.contains(p.name)) {
         superParameters.add(p.name);
         return (
           SuperParameter.fromParameter(p),

packages/freezed/test/integration/multiple_constructors.dart

@@ -2,6 +2,14 @@ import 'package:freezed_annotation/freezed_annotation.dart';
 
 part 'multiple_constructors.freezed.dart';
 
+@freezed
+sealed class PrivateUnion with _$PrivateUnion {
+  // ignore: unused_element
+  const factory PrivateUnion._(int value) = _PrivateUnion;
+  // ignore: unused_element
+  const factory PrivateUnion._b(int value) = _PrivateUnionB;
+}
+
 @freezed
 sealed class Response<T> with _$Response<T> {
   Response._({DateTime? time}) : time = time ?? DateTime(0, 0, 0);

packages/freezed/test/source_gen_src.dart

@@ -96,13 +96,6 @@ class _DefaultOnRequiredPositional implements DefaultOnRequiredPositional {
   _DefaultOnRequiredPositional(int a);
 }
 
-@ShouldThrow('A freezed union cannot have private constructors')
-@freezed
-abstract class Mixed {
-  factory Mixed._internal(String a) = Mixed0;
-  factory Mixed.named(String b) = Mixed1;
-}
-
 @ShouldThrow('Fallback union was specified but no fallback constructor exists.')
 @Freezed(fallbackUnion: 'fallback')
 class FallbackUnionMissing {
@@ -135,24 +128,16 @@ class _MutableProperty implements MutableProperty {
   int? a;
 }
 
-class Mixed1 implements Mixed {
-  Mixed1(String b);
-}
-
-class Mixed0 implements Mixed {
-  Mixed0(String a);
-}
-
 @ShouldGenerate(
   '',
   contains: true,
   expectedLogItems: [],
 )
 @freezed
-abstract class AstractClass {
-  const factory AstractClass() = _AstractClass;
+abstract class AbstractClass {
+  const factory AbstractClass() = _AbstractClass;
 }
 
-class _AstractClass implements AstractClass {
-  const _AstractClass();
+class _AbstractClass implements AbstractClass {
+  const _AbstractClass();
 }