[CFE/VM] Fix mixin deleting procedure-setter because of final field

Fixes https://github.com/dart-lang/sdk/issues/63440
Tested: Tests added.
Change-Id: I0bdfd71c48ecae6094557fa4f46b8fc4b50afa73
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/506980
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>

pkg/front_end/testcases/general/issue_63440.dart

@@ -0,0 +1,16 @@
+// 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.
+
+// This has historically crashed with target vm.
+
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {
+  MA().c = 42;
+}

pkg/front_end/testcases/general/issue_63440.dart.strong.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440.dart.strong.modular.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440.dart.strong.outline.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c;
+  set c(wildcard core::int _#wc0#formal) → void
+    ;
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void
+  ;

pkg/front_end/testcases/general/issue_63440.dart.strong.transformed.expect

@@ -0,0 +1,18 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA extends core::Object implements self::M /*isEliminatedMixin*/  {
+  final field core::int c = 1;
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  set c(core::int _#wc0#formal) → void {}
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440.dart.textual_outline.expect

@@ -0,0 +1,8 @@
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {}

pkg/front_end/testcases/general/issue_63440.dart.textual_outline_modelled.expect

@@ -0,0 +1,8 @@
+class MA = Object with M;
+
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+void hello() {}

pkg/front_end/testcases/general/issue_63440_prime_1.dart

@@ -0,0 +1,16 @@
+// 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.
+
+// This has historically crashed with target vm.
+
+mixin M {
+  late final int c;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {
+  MA().c = 42;
+}

pkg/front_end/testcases/general/issue_63440_prime_1.dart.strong.expect

@@ -0,0 +1,29 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:9:12: Error: Conflicts with the implicit setter of the field 'c'.
+//   void set c(int _) {}
+//            ^
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:8:18: Context: Field 'c' with the implicit setter.
+//   late final int c;
+//                  ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  late final [setter] field core::int c;
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int value) → void
+    return super.{self::M::c} = value;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440_prime_1.dart.strong.modular.expect

@@ -0,0 +1,29 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:9:12: Error: Conflicts with the implicit setter of the field 'c'.
+//   void set c(int _) {}
+//            ^
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:8:18: Context: Field 'c' with the implicit setter.
+//   late final int c;
+//                  ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  late final [setter] field core::int c;
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int value) → void
+    return super.{self::M::c} = value;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440_prime_1.dart.strong.outline.expect

@@ -0,0 +1,28 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:9:12: Error: Conflicts with the implicit setter of the field 'c'.
+//   void set c(int _) {}
+//            ^
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:8:18: Context: Field 'c' with the implicit setter.
+//   late final int c;
+//                  ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  late final [setter] field core::int c;
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int value) → void
+    return super.{self::M::c} = value;
+}
+static method hello() → void
+  ;

pkg/front_end/testcases/general/issue_63440_prime_1.dart.strong.transformed.expect

@@ -0,0 +1,26 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:9:12: Error: Conflicts with the implicit setter of the field 'c'.
+//   void set c(int _) {}
+//            ^
+// pkg/front_end/testcases/general/issue_63440_prime_1.dart:8:18: Context: Field 'c' with the implicit setter.
+//   late final int c;
+//                  ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  late final [setter] field core::int c;
+}
+class MA extends core::Object implements self::M /*isEliminatedMixin*/  {
+  late final [setter] field core::int c;
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/general/issue_63440_prime_1.dart.textual_outline.expect

@@ -0,0 +1,8 @@
+mixin M {
+  late final int c;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {}

pkg/front_end/testcases/general/issue_63440_prime_1.dart.textual_outline_modelled.expect

@@ -0,0 +1,8 @@
+class MA = Object with M;
+
+mixin M {
+  late final int c;
+  void set c(int _) {}
+}
+
+void hello() {}

pkg/front_end/testcases/none/issue_63440.dart

@@ -0,0 +1,16 @@
+// 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.
+
+// This has historically crashed with target vm, but not target none.
+
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {
+  MA().c = 42;
+}

pkg/front_end/testcases/none/issue_63440.dart.strong.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/none/issue_63440.dart.strong.modular.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/none/issue_63440.dart.strong.outline.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c;
+  set c(wildcard core::int _#wc0#formal) → void
+    ;
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void
+  ;

pkg/front_end/testcases/none/issue_63440.dart.strong.transformed.expect

@@ -0,0 +1,20 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+abstract class M extends core::Object /*isMixinDeclaration*/  {
+  final field core::int c = 1;
+  set c(wildcard core::int _#wc0#formal) → void {}
+}
+class MA = core::Object with self::M {
+  synthetic constructor •() → self::MA
+    : super core::Object::•()
+    ;
+  synthetic mixin-super-stub get c() → core::int
+    return super.{self::M::c};
+  synthetic mixin-super-stub set c(core::int _#wc0#formal) → void
+    return super.{self::M::c} = _#wc0#formal;
+}
+static method hello() → void {
+  new self::MA::•().{self::MA::c} = 42;
+}

pkg/front_end/testcases/none/issue_63440.dart.textual_outline.expect

@@ -0,0 +1,8 @@
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+class MA = Object with M;
+
+void hello() {}

pkg/front_end/testcases/none/issue_63440.dart.textual_outline_modelled.expect

@@ -0,0 +1,8 @@
+class MA = Object with M;
+
+mixin M {
+  final c = 1;
+  void set c(int _) {}
+}
+
+void hello() {}

pkg/front_end/testcases/strong.status

@@ -121,6 +121,9 @@ nnbd/platform_definite_assignment/main: SemiFuzzFailure
 nnbd/platform_nonnullable_fields/main: SemiFuzzFailure
 nnbd/platform_optional_parameters/main: SemiFuzzFailure
 
+# Unclear exactly what is going on here - but target none isn't super important.
+none/issue_63440: SemiFuzzFailure
+
 # UNSORTED ONES:
 constructor_tearoffs/explicit_instantiation: SemiFuzzFailure
 enhanced_parts/deferred_siblings: SemiFuzzFailure

pkg/vm/lib/modular/transformations/mixin_full_resolution.dart

@@ -157,14 +157,16 @@ class MixinFullResolution {
         Reference? getterReference = indexedClass?.lookupGetterReference(
           field.name,
         );
-        Reference? setterReference = indexedClass?.lookupSetterReference(
-          field.name,
-        );
+        // We only use any given setter reference if it belongs to the field.
+        Reference? setterReference = field.hasSetter
+            ? indexedClass?.lookupSetterReference(field.name)
+            : null;
+
         if (getterReference == null) {
           getterReference = nonSetters[field.name]?.reference;
           getterReference?.canonicalName?.unbind();
         }
-        if (setterReference == null) {
+        if (setterReference == null && field.hasSetter) {
           setterReference = setters[field.name]?.reference;
           setterReference?.canonicalName?.unbind();
         }
@@ -174,12 +176,15 @@ class MixinFullResolution {
           getterReference,
           setterReference,
         );
-        Procedure? setter = setters[field.name];
-        if (setter != null) {
-          setters.remove(field.name);
-          Variable parameter = setter.function.positionalParameters.first;
-          clone.isCovariantByDeclaration = parameter.isCovariantByDeclaration;
-          clone.isCovariantByClass = parameter.isCovariantByClass;
+        if (field.hasSetter) {
+          // Only remove a setter with this name if it belongs to the field.
+          Procedure? setter = setters[field.name];
+          if (setter != null) {
+            setters.remove(field.name);
+            Variable parameter = setter.function.positionalParameters.first;
+            clone.isCovariantByDeclaration = parameter.isCovariantByDeclaration;
+            clone.isCovariantByClass = parameter.isCovariantByClass;
+          }
         }
         nonSetters.remove(field.name);
         class_.addField(clone);