[PrimaryConstructors] Update tests for var in enum declaring parameter

language/primary_constructors/header/enum_declaring_parameter_error_test is added exercise this.

language/primary_constructors/syntax/header_syntax_test and language/primary_constructors/syntax/final_formal_parameter_error_test are updated to not use 'var' modifier for enum declaring parameters.

A message is added to the CFE to avoid referring to the implicit const enum primary constructor as "marked as 'const'".

Part of #61524 #61700

Change-Id: Ic2c3c43d08c42d44dade04c116a73e3be1d22bd5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/478420
Reviewed-by: Erik Ernst <eernst@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/codes/diagnostic.g.dart

@@ -3604,6 +3604,13 @@ const MessageCode enumAbstractMember = const MessageCode(
   problemMessage: """Enums can't declare abstract members.""",
 );
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode enumConstructorNonFinalField = const MessageCode(
+  "EnumConstructorNonFinalField",
+  problemMessage:
+      """Enum constructors are constant so all fields must be final.""",
+);
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const MessageCode enumConstructorSuperInitializer = const MessageCode(
   "EnumConstructorSuperInitializer",

pkg/front_end/lib/src/kernel/kernel_target.dart

@@ -1558,7 +1558,9 @@ class KernelTarget {
       if (constructor.isEffectivelyRedirecting) continue;
       if (constructor.isConst && nonFinalFields.isNotEmpty) {
         classDeclaration.libraryBuilder.addProblem(
-          diag.constConstructorNonFinalField,
+          classDeclaration.isEnum
+              ? diag.enumConstructorNonFinalField
+              : diag.constConstructorNonFinalField,
           constructor.fileOffset,
           noLength,
           constructor.fileUri,

pkg/front_end/messages.yaml

@@ -3704,6 +3704,16 @@ constConstructorNonFinalField:
       const Foo(this.i);
     }
 
+enumConstructorNonFinalField:
+  parameters: none
+  problemMessage: "Enum constructors are constant so all fields must be final."
+  experiments: primary-constructors
+  script:
+    - |
+      enum E(var int x) { a(0) }
+    - |
+      enum E() { a; int x = 0; }
+
 constConstructorNonFinalFieldCause:
   parameters: none
   problemMessage: "Field isn't final, but constructor is 'const'."

pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart.strong.expect

@@ -7,7 +7,7 @@ library;
 //   final int? b; // Error
 //              ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E4() { // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:20:8: Context: Field isn't final, but constructor is 'const'.

pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart.strong.modular.expect

@@ -7,7 +7,7 @@ library;
 //   final int? b; // Error
 //              ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E4() { // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:20:8: Context: Field isn't final, but constructor is 'const'.

pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart.strong.transformed.expect

@@ -7,7 +7,7 @@ library;
 //   final int? b; // Error
 //              ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:18:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E4() { // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_constructor.dart:20:8: Context: Field isn't final, but constructor is 'const'.

pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart.strong.expect

@@ -10,7 +10,7 @@ library;
 // enum const E7({int? a, required int b, int c = 42]) {
 //                                                  ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E2(var int i) { x(0) } // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:23: Context: Field isn't final, but constructor is 'const'.

pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart.strong.modular.expect

@@ -10,7 +10,7 @@ library;
 // enum const E7({int? a, required int b, int c = 42]) {
 //                                                  ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E2(var int i) { x(0) } // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:23: Context: Field isn't final, but constructor is 'const'.

pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart.strong.transformed.expect

@@ -10,7 +10,7 @@ library;
 // enum const E7({int? a, required int b, int c = 42]) {
 //                                                  ^
 //
-// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Constructor is marked 'const' so all fields must be final.
+// pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:14: Error: Enum constructors are constant so all fields must be final.
 // enum const E2(var int i) { x(0) } // Error
 //              ^
 // pkg/front_end/testcases/primary_constructors/enum_primary_declaring_parameters.dart:7:23: Context: Field isn't final, but constructor is 'const'.

tests/language/primary_constructors/header/enum_declaring_parameter_error_test.dart

@@ -0,0 +1,24 @@
+// Copyright (c) 2026, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// An enum cannot declare mutable fields through declaring parameters.
+
+// SharedOptions=--enable-experiment=primary-constructors
+
+enum E1(var int x) {
+//     ^
+// [analyzer] unspecified
+// [cfe] Enum constructors are constant so all fields must be final.
+
+  a(0)
+}
+
+enum E2() {
+//     ^
+// [analyzer] unspecified
+// [cfe] Enum constructors are constant so all fields must be final.
+  a;
+
+  int x = 0;
+}

tests/language/primary_constructors/syntax/final_formal_parameter_error_test.dart

@@ -19,10 +19,7 @@ class C {
   // [cfe] unspecified
 }
 
-enum E(var int x) {
-  //           ^
-  // [analyzer] unspecified
-  // [cfe] unspecified
+enum E(final int x) {
   e(1);
   void method1(final int x) {}
   //           ^

tests/language/primary_constructors/syntax/header_syntax_test.dart

@@ -33,20 +33,14 @@ class CSuperParameters(final int x, super.y) extends C1;
 // Named parameters (regular and required).
 class CNamedParameters({final int x = 1, required var int y});
 
-enum EnumNamedParameters({final int x = 1, required var int y}) {
-  //                                                        ^
-  // [analyzer] unspecified
-  // [cfe] unspecified
+enum EnumNamedParameters({final int x = 1, required final int y}) {
   e(x: 2, y: 3), f(y: 3);
 }
 
 // Optional parameters.
 class COptionalParameters([final int x = 1, var int y = 2]);
 
-enum EnumOptionalParameters([final int x = 1, var int y = 2]) {
-  //                                                  ^
-  // [analyzer] unspecified
-  // [cfe] unspecified
+enum EnumOptionalParameters([final int x = 1, final int y = 2]) {
   e(3, 4), f(3), g();
 }