diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart b/pkg/front_end/testcases/general/bounds_type_parameters.dart
index 9f3cfa8097d..1e7873910ee 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart
@@ -2,7 +2,7 @@
 // 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.
 
-class Class<T> {}
+mixin Class<T> {}
 
 class ConcreteClass implements Class<ConcreteClass> {}
 
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.expect
index 1454709aca5..f7b07925bf3 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.expect
@@ -605,10 +605,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    : super core::Object::•()
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.transformed.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.transformed.expect
index efe11fab897..671498da8eb 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.strong.transformed.expect
@@ -605,10 +605,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    : super core::Object::•()
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline.expect
index 7608f2da31a..174bcbf515c 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline.expect
@@ -1,4 +1,4 @@
-class Class<T> {}
+mixin Class<T> {}
 
 class ConcreteClass implements Class<ConcreteClass> {}
 
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline_modelled.expect
index 216f660d66f..a925888dcee 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.textual_outline_modelled.expect
@@ -1,5 +1,3 @@
-class Class<T> {}
-
 class Class1<
     T1 extends F,
     T2 extends F<dynamic>,
@@ -95,6 +93,7 @@ extension Extension<
     S8 extends G<int>> on Class {}
 
 main() {}
+mixin Class<T> {}
 mixin Mixin1<
     T1 extends F,
     T2 extends F<dynamic>,
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.expect
index 338d3be4ab1..824f60d56fe 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.expect
@@ -605,10 +605,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    : super core::Object::•()
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.modular.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.modular.expect
index 338d3be4ab1..824f60d56fe 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.modular.expect
@@ -605,10 +605,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    : super core::Object::•()
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.outline.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.outline.expect
index 3567960df3f..1772db6bda3 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.outline.expect
@@ -514,9 +514,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.transformed.expect b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.transformed.expect
index 029483dd243..572a984b1e1 100644
--- a/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/bounds_type_parameters.dart.weak.transformed.expect
@@ -605,10 +605,7 @@ typedef F<X extends self::Class<X> = self::Class<dynamic>> = X;
 typedef Typedef1<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
 typedef Typedef2 = <T1 extends self::Class<dynamic> = dynamic, T2 extends dynamic, T3 extends self::Class<dynamic> = dynamic, T4 extends self::Class<dynamic> = dynamic, T5 extends self::ConcreteClass = dynamic, T6 extends self::Class<self::ConcreteClass> = dynamic, T7 extends core::Object = dynamic, T8 extends core::int = dynamic, S1 extends self::G<self::Class<dynamic>> = dynamic, S2 extends self::G<dynamic> = dynamic, S3 extends self::G<self::Class<dynamic>> = dynamic, S4 extends self::G<self::Class<dynamic>> = dynamic, S5 extends self::G<self::ConcreteClass> = dynamic, S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, S7 extends self::G<core::Object> = dynamic, S8 extends self::G<core::int> = dynamic>() → void;
 typedef Typedef3<unrelated T1 extends self::Class<dynamic> = dynamic, unrelated T2 extends dynamic, unrelated T3 extends self::Class<dynamic> = dynamic, unrelated T4 extends self::Class<dynamic> = dynamic, unrelated T5 extends self::ConcreteClass = dynamic, unrelated T6 extends self::Class<self::ConcreteClass> = dynamic, unrelated T7 extends core::Object = dynamic, unrelated T8 extends core::int = dynamic, unrelated S1 extends self::G<self::Class<dynamic>> = dynamic, unrelated S2 extends self::G<dynamic> = dynamic, unrelated S3 extends self::G<self::Class<dynamic>> = dynamic, unrelated S4 extends self::G<self::Class<dynamic>> = dynamic, unrelated S5 extends self::G<self::ConcreteClass> = dynamic, unrelated S6 extends self::G<self::Class<self::ConcreteClass>> = dynamic, unrelated S7 extends self::G<core::Object> = dynamic, unrelated S8 extends self::G<core::int> = dynamic> = () → void;
-class Class<T extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::Class<self::Class::T%>
-    : super core::Object::•()
-    ;
+abstract class Class<T extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
 }
 class ConcreteClass extends core::Object implements self::Class<self::ConcreteClass> {
   synthetic constructor •() → self::ConcreteClass
diff --git a/pkg/front_end/testcases/general/issue41210a.dart b/pkg/front_end/testcases/general/issue41210a.dart
index 78cfc3c9dc0..4c9c5f2c814 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart
+++ b/pkg/front_end/testcases/general/issue41210a.dart
@@ -14,17 +14,17 @@ mixin A implements Interface {
   String method(num i, {String s = "hello"}) => s;
 }
 
-abstract class B implements Interface {
+mixin B implements Interface {
   String method(num i);
 }
 
 class C with A, B {} // error
 
-abstract class D implements Interface, Interface2 {}
+mixin D implements Interface, Interface2 {}
 
 class E with A, D {} // ok
 
-abstract class F implements Interface {}
+mixin F implements Interface {}
 
 class G with A, F {} // ok
 
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.strong.expect b/pkg/front_end/testcases/general/issue41210a.dart.strong.expect
index 89137302f07..6d8f74499fd 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.strong.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.strong.expect
@@ -31,10 +31,7 @@ abstract class A extends core::Object implements self::Interface /*isMixinDeclar
   method method(core::num i, {core::String s = #C1}) → core::String
     return s;
 }
-abstract class B extends core::Object implements self::Interface {
-  synthetic constructor •() → self::B
-    : super core::Object::•()
-    ;
+abstract class B extends core::Object implements self::Interface /*isMixinDeclaration*/  {
   abstract method method(core::num i) → core::String;
 }
 abstract class _C&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -55,10 +52,7 @@ class C extends self::_C&Object&A&B {
     : super self::_C&Object&A&B::•()
     ;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -80,10 +74,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue41210a.dart.textual_outline.expect
index 599fc0f1b54..a7fbb848f24 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.textual_outline.expect
@@ -9,18 +9,17 @@ abstract class Interface2 {
 mixin A implements Interface {
   String method(num i, {String s = "hello"}) => s;
 }
-
-abstract class B implements Interface {
+mixin B implements Interface {
   String method(num i);
 }
 
 class C with A, B {}
 
-abstract class D implements Interface, Interface2 {}
+mixin D implements Interface, Interface2 {}
 
 class E with A, D {}
 
-abstract class F implements Interface {}
+mixin F implements Interface {}
 
 class G with A, F {}
 
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue41210a.dart.textual_outline_modelled.expect
index d6c9646869e..bb1aa13a79c 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.textual_outline_modelled.expect
@@ -1,11 +1,3 @@
-abstract class B implements Interface {
-  String method(num i);
-}
-
-abstract class D implements Interface, Interface2 {}
-
-abstract class F implements Interface {}
-
 abstract class Interface {
   String method(num i);
 }
@@ -24,3 +16,8 @@ main() {}
 mixin A implements Interface {
   String method(num i, {String s = "hello"}) => s;
 }
+mixin B implements Interface {
+  String method(num i);
+}
+mixin D implements Interface, Interface2 {}
+mixin F implements Interface {}
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.weak.expect b/pkg/front_end/testcases/general/issue41210a.dart.weak.expect
index 89137302f07..6d8f74499fd 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.weak.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.weak.expect
@@ -31,10 +31,7 @@ abstract class A extends core::Object implements self::Interface /*isMixinDeclar
   method method(core::num i, {core::String s = #C1}) → core::String
     return s;
 }
-abstract class B extends core::Object implements self::Interface {
-  synthetic constructor •() → self::B
-    : super core::Object::•()
-    ;
+abstract class B extends core::Object implements self::Interface /*isMixinDeclaration*/  {
   abstract method method(core::num i) → core::String;
 }
 abstract class _C&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -55,10 +52,7 @@ class C extends self::_C&Object&A&B {
     : super self::_C&Object&A&B::•()
     ;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -80,10 +74,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.weak.modular.expect b/pkg/front_end/testcases/general/issue41210a.dart.weak.modular.expect
index 89137302f07..6d8f74499fd 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.weak.modular.expect
@@ -31,10 +31,7 @@ abstract class A extends core::Object implements self::Interface /*isMixinDeclar
   method method(core::num i, {core::String s = #C1}) → core::String
     return s;
 }
-abstract class B extends core::Object implements self::Interface {
-  synthetic constructor •() → self::B
-    : super core::Object::•()
-    ;
+abstract class B extends core::Object implements self::Interface /*isMixinDeclaration*/  {
   abstract method method(core::num i) → core::String;
 }
 abstract class _C&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -55,10 +52,7 @@ class C extends self::_C&Object&A&B {
     : super self::_C&Object&A&B::•()
     ;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -80,10 +74,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue41210a.dart.weak.outline.expect
index 22ccaeebdf8..5886e447b8e 100644
--- a/pkg/front_end/testcases/general/issue41210a.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/issue41210a.dart.weak.outline.expect
@@ -29,9 +29,7 @@ abstract class A extends core::Object implements self::Interface /*isMixinDeclar
   method method(core::num i, {core::String s = "hello"}) → core::String
     ;
 }
-abstract class B extends core::Object implements self::Interface {
-  synthetic constructor •() → self::B
-    ;
+abstract class B extends core::Object implements self::Interface /*isMixinDeclaration*/  {
   abstract method method(core::num i) → core::String;
 }
 abstract class _C&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -51,9 +49,7 @@ class C extends self::_C&Object&A&B {
   synthetic constructor •() → self::C
     ;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -74,9 +70,7 @@ class E extends self::_E&Object&A&D {
   synthetic constructor •() → self::E
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart b/pkg/front_end/testcases/general/issue41210a_no_error.dart
index b838aa983b7..370da14afbb 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart
@@ -18,11 +18,11 @@ abstract class B implements Interface {
   String method(num i);
 }
 
-abstract class D implements Interface, Interface2 {}
+mixin D implements Interface, Interface2 {}
 
 class E with A, D {} // ok
 
-abstract class F implements Interface {}
+mixin F implements Interface {}
 
 class G with A, F {} // ok
 
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.expect
index 2913f38b5c1..4d9a1a696b2 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.expect
@@ -24,10 +24,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -49,10 +46,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.transformed.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.transformed.expect
index fcfe4b1f55f..3c22fab9588 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.strong.transformed.expect
@@ -24,10 +24,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A extends core::Object implements self::A /*isAnonymousMixin,isEliminatedMixin,hasConstConstructor*/  {
@@ -49,10 +46,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A extends core::Object implements self::A /*isAnonymousMixin,isEliminatedMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline.expect
index c01fb180047..eb79a0a9d0b 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline.expect
@@ -14,11 +14,11 @@ abstract class B implements Interface {
   String method(num i);
 }
 
-abstract class D implements Interface, Interface2 {}
+mixin D implements Interface, Interface2 {}
 
 class E with A, D {}
 
-abstract class F implements Interface {}
+mixin F implements Interface {}
 
 class G with A, F {}
 
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline_modelled.expect
index 801b25ed2d6..85393233537 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.textual_outline_modelled.expect
@@ -2,10 +2,6 @@ abstract class B implements Interface {
   String method(num i);
 }
 
-abstract class D implements Interface, Interface2 {}
-
-abstract class F implements Interface {}
-
 abstract class Interface {
   String method(num i);
 }
@@ -22,3 +18,5 @@ main() {}
 mixin A implements Interface {
   String method(num i, {String s = "hello"}) => s;
 }
+mixin D implements Interface, Interface2 {}
+mixin F implements Interface {}
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.expect
index 2913f38b5c1..4d9a1a696b2 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.expect
@@ -24,10 +24,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -49,10 +46,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.modular.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.modular.expect
index 2913f38b5c1..4d9a1a696b2 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.modular.expect
@@ -24,10 +24,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -49,10 +46,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.outline.expect
index 016588f517b..65365a74b6a 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.outline.expect
@@ -21,9 +21,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
@@ -44,9 +42,7 @@ class E extends self::_E&Object&A&D {
   synthetic constructor •() → self::E
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A = core::Object with self::A /*isAnonymousMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.transformed.expect
index fcfe4b1f55f..3c22fab9588 100644
--- a/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/issue41210a_no_error.dart.weak.transformed.expect
@@ -24,10 +24,7 @@ abstract class B extends core::Object implements self::Interface {
     ;
   abstract method method(core::num i) → core::String;
 }
-abstract class D extends core::Object implements self::Interface, self::Interface2 {
-  synthetic constructor •() → self::D
-    : super core::Object::•()
-    ;
+abstract class D extends core::Object implements self::Interface, self::Interface2 /*isMixinDeclaration*/  {
   abstract forwarding-stub method method(covariant-by-declaration core::num i) → core::String;
 }
 abstract class _E&Object&A extends core::Object implements self::A /*isAnonymousMixin,isEliminatedMixin,hasConstConstructor*/  {
@@ -49,10 +46,7 @@ class E extends self::_E&Object&A&D {
     : super self::_E&Object&A&D::•()
     ;
 }
-abstract class F extends core::Object implements self::Interface {
-  synthetic constructor •() → self::F
-    : super core::Object::•()
-    ;
+abstract class F extends core::Object implements self::Interface /*isMixinDeclaration*/  {
 }
 abstract class _G&Object&A extends core::Object implements self::A /*isAnonymousMixin,isEliminatedMixin,hasConstConstructor*/  {
   const synthetic constructor •() → self::_G&Object&A
diff --git a/pkg/front_end/testcases/general/issue46389.dart b/pkg/front_end/testcases/general/issue46389.dart
index b1acb267780..e36823aa3a4 100644
--- a/pkg/front_end/testcases/general/issue46389.dart
+++ b/pkg/front_end/testcases/general/issue46389.dart
@@ -20,7 +20,7 @@ class A {
   int boz = 0;
 }
 
-abstract class B<X> {
+mixin B<X> {
   X foo(X x);
   X bar({required X x});
   void set baz(X x);
diff --git a/pkg/front_end/testcases/general/issue46389.dart.strong.expect b/pkg/front_end/testcases/general/issue46389.dart.strong.expect
index 55be1b7db8f..6be83dc4080 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.strong.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.strong.expect
@@ -19,10 +19,7 @@ class A extends core::Object {
     core::print(x.{core::Object::runtimeType}{core::Type});
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = #C1}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46389.dart.strong.transformed.expect b/pkg/front_end/testcases/general/issue46389.dart.strong.transformed.expect
index efd3846a4ea..cacc5088ac6 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.strong.transformed.expect
@@ -19,10 +19,7 @@ class A extends core::Object {
     core::print(x.{core::Object::runtimeType}{core::Type});
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = #C1}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46389.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue46389.dart.textual_outline.expect
index 8c1997d6824..f3c6337b0c3 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.textual_outline.expect
@@ -5,7 +5,7 @@ class A {
   int boz = 0;
 }
 
-abstract class B<X> {
+mixin B<X> {
   X foo(X x);
   X bar({required X x});
   void set baz(X x);
diff --git a/pkg/front_end/testcases/general/issue46389.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue46389.dart.textual_outline_modelled.expect
index 8aae48366b2..79a85d3311a 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.textual_outline_modelled.expect
@@ -1,10 +1,3 @@
-abstract class B<X> {
-  X bar({required X x});
-  X foo(X x);
-  void set baz(X x);
-  void set boz(X x);
-}
-
 class A {
   int boz = 0;
   num bar({required int x}) {}
@@ -14,5 +7,11 @@ class A {
 
 class C extends A with B<num> {}
 
+mixin B<X> {
+  X bar({required X x});
+  X foo(X x);
+  void set baz(X x);
+  void set boz(X x);
+}
 throws(void Function() f) {}
 void main() {}
diff --git a/pkg/front_end/testcases/general/issue46389.dart.weak.expect b/pkg/front_end/testcases/general/issue46389.dart.weak.expect
index 55be1b7db8f..6be83dc4080 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.weak.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.weak.expect
@@ -19,10 +19,7 @@ class A extends core::Object {
     core::print(x.{core::Object::runtimeType}{core::Type});
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = #C1}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46389.dart.weak.modular.expect b/pkg/front_end/testcases/general/issue46389.dart.weak.modular.expect
index 55be1b7db8f..6be83dc4080 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.weak.modular.expect
@@ -19,10 +19,7 @@ class A extends core::Object {
     core::print(x.{core::Object::runtimeType}{core::Type});
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = #C1}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46389.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue46389.dart.weak.outline.expect
index bb955ac3080..99737af15e1 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.weak.outline.expect
@@ -13,9 +13,7 @@ class A extends core::Object {
   set baz(core::int x) → void
     ;
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = null}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46389.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue46389.dart.weak.transformed.expect
index efd3846a4ea..cacc5088ac6 100644
--- a/pkg/front_end/testcases/general/issue46389.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/issue46389.dart.weak.transformed.expect
@@ -19,10 +19,7 @@ class A extends core::Object {
     core::print(x.{core::Object::runtimeType}{core::Type});
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
   abstract method bar({required covariant-by-class self::B::X% x = #C1}) → self::B::X%;
   abstract set baz(covariant-by-class self::B::X% x) → void;
diff --git a/pkg/front_end/testcases/general/issue46390.dart b/pkg/front_end/testcases/general/issue46390.dart
index 305717eabe8..bd4a660c019 100644
--- a/pkg/front_end/testcases/general/issue46390.dart
+++ b/pkg/front_end/testcases/general/issue46390.dart
@@ -9,7 +9,7 @@ class A {
   }
 }
 
-abstract class B<X> {
+mixin B<X> {
   X foo(X x);
 }
 
diff --git a/pkg/front_end/testcases/general/issue46390.dart.strong.expect b/pkg/front_end/testcases/general/issue46390.dart.strong.expect
index 8c3187233dc..3a8a87df5a7 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.strong.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.strong.expect
@@ -11,10 +11,7 @@ class A extends core::Object {
     return 1.1;
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B = self::A with self::B<core::num> /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/general/issue46390.dart.strong.transformed.expect b/pkg/front_end/testcases/general/issue46390.dart.strong.transformed.expect
index 6447989dc03..7e75b73f986 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.strong.transformed.expect
@@ -11,10 +11,7 @@ class A extends core::Object {
     return 1.1;
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B extends self::A implements self::B<core::num> /*isAnonymousMixin,isEliminatedMixin*/  {
diff --git a/pkg/front_end/testcases/general/issue46390.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue46390.dart.textual_outline.expect
index 554317fa363..85132be948e 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.textual_outline.expect
@@ -2,7 +2,7 @@ class A {
   num foo(num n) {}
 }
 
-abstract class B<X> {
+mixin B<X> {
   X foo(X x);
 }
 
diff --git a/pkg/front_end/testcases/general/issue46390.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue46390.dart.textual_outline_modelled.expect
index 77cbaa09449..085a94f32f1 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.textual_outline_modelled.expect
@@ -1,11 +1,10 @@
-abstract class B<X> {
-  X foo(X x);
-}
-
 class A {
   num foo(num n) {}
 }
 
 class C extends A with B<num> {}
 
+mixin B<X> {
+  X foo(X x);
+}
 void main() {}
diff --git a/pkg/front_end/testcases/general/issue46390.dart.weak.expect b/pkg/front_end/testcases/general/issue46390.dart.weak.expect
index 8c3187233dc..3a8a87df5a7 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.weak.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.weak.expect
@@ -11,10 +11,7 @@ class A extends core::Object {
     return 1.1;
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B = self::A with self::B<core::num> /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/general/issue46390.dart.weak.modular.expect b/pkg/front_end/testcases/general/issue46390.dart.weak.modular.expect
index 8c3187233dc..3a8a87df5a7 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.weak.modular.expect
@@ -11,10 +11,7 @@ class A extends core::Object {
     return 1.1;
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B = self::A with self::B<core::num> /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/general/issue46390.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue46390.dart.weak.outline.expect
index d2a9f014541..7e1aba7d9c8 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.weak.outline.expect
@@ -8,9 +8,7 @@ class A extends core::Object {
   method foo(core::num n) → core::num
     ;
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B = self::A with self::B<core::num> /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/general/issue46390.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue46390.dart.weak.transformed.expect
index 6447989dc03..7e75b73f986 100644
--- a/pkg/front_end/testcases/general/issue46390.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/issue46390.dart.weak.transformed.expect
@@ -11,10 +11,7 @@ class A extends core::Object {
     return 1.1;
   }
 }
-abstract class B<X extends core::Object? = dynamic> extends core::Object {
-  synthetic constructor •() → self::B<self::B::X%>
-    : super core::Object::•()
-    ;
+abstract class B<X extends core::Object? = dynamic> extends core::Object /*isMixinDeclaration*/  {
   abstract method foo(covariant-by-class self::B::X% x) → self::B::X%;
 }
 abstract class _C&A&B extends self::A implements self::B<core::num> /*isAnonymousMixin,isEliminatedMixin*/  {
diff --git a/pkg/front_end/testcases/incremental/changing_modules_13.yaml b/pkg/front_end/testcases/incremental/changing_modules_13.yaml
index d0c5a04e823..1e07ae6f6f5 100644
--- a/pkg/front_end/testcases/incremental/changing_modules_13.yaml
+++ b/pkg/front_end/testcases/incremental/changing_modules_13.yaml
@@ -10,8 +10,8 @@ modules:
   module:
     module/a.dart: |
       class A { }
-      class B { }
-      class C { }
+      mixin B { }
+      mixin C { }
       class AB = A with B;
     module/.dart_tool/package_config.json: |
       {
diff --git a/pkg/front_end/testcases/incremental/changing_modules_13.yaml.world.1.expect b/pkg/front_end/testcases/incremental/changing_modules_13.yaml.world.1.expect
index dc9475d2091..8e18cac8e47 100644
--- a/pkg/front_end/testcases/incremental/changing_modules_13.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/changing_modules_13.yaml.world.1.expect
@@ -16,15 +16,9 @@ library from "package:module/a.dart" as a {
       : super dart.core::Object::•()
       ;
   }
-  class B extends dart.core::Object {
-    synthetic constructor •() → a::B
-      : super dart.core::Object::•()
-      ;
+  abstract class B extends dart.core::Object /*isMixinDeclaration*/  {
   }
-  class C extends dart.core::Object {
-    synthetic constructor •() → a::C
-      : super dart.core::Object::•()
-      ;
+  abstract class C extends dart.core::Object /*isMixinDeclaration*/  {
   }
   class AB = a::A with a::B {
     synthetic constructor •() → a::AB
diff --git a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml
index 7ecf89033f7..adaef283596 100644
--- a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml
+++ b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml
@@ -11,7 +11,7 @@ worlds:
     sources:
       main.dart: |
         import "lib.dart";
-        class B {}
+        mixin B {}
         class C = A with B;
       lib.dart: |
         class A {
diff --git a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.1.expect b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.1.expect
index 8290d7d1a11..7e8c5654438 100644
--- a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.1.expect
@@ -12,10 +12,7 @@ library from "org-dartlang-test:///main.dart" as main {
 
   import "org-dartlang-test:///lib.dart";
 
-  class B extends dart.core::Object {
-    synthetic constructor •() → main::B
-      : super dart.core::Object::•()
-      ;
+  abstract class B extends dart.core::Object /*isMixinDeclaration*/  {
   }
   class C extends lib::A implements main::B /*isEliminatedMixin*/  {
     synthetic constructor •([dart.core::int? a = #C1]) → main::C
diff --git a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.2.expect b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.2.expect
index 8290d7d1a11..7e8c5654438 100644
--- a/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/initializer_implicit_null.yaml.world.2.expect
@@ -12,10 +12,7 @@ library from "org-dartlang-test:///main.dart" as main {
 
   import "org-dartlang-test:///lib.dart";
 
-  class B extends dart.core::Object {
-    synthetic constructor •() → main::B
-      : super dart.core::Object::•()
-      ;
+  abstract class B extends dart.core::Object /*isMixinDeclaration*/  {
   }
   class C extends lib::A implements main::B /*isEliminatedMixin*/  {
     synthetic constructor •([dart.core::int? a = #C1]) → main::C
diff --git a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml
index a3faeafbeaa..59dbe7c3275 100644
--- a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml
+++ b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml
@@ -12,7 +12,7 @@ worlds:
           void method(covariant int i) {}
         }
 
-        class Mixin {
+        mixin Mixin {
           void method(num i) {}
         }
 
diff --git a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.1.expect b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.1.expect
index ac9787d3fa0..aadb190a8b5 100644
--- a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.1.expect
@@ -15,10 +15,7 @@ library from "org-dartlang-test:///main_lib1.dart" as mai2 {
       ;
     method method(covariant-by-declaration dart.core::int i) → void {}
   }
-  class Mixin extends dart.core::Object {
-    synthetic constructor •() → mai2::Mixin
-      : super dart.core::Object::•()
-      ;
+  abstract class Mixin extends dart.core::Object /*isMixinDeclaration*/  {
     method method(dart.core::num i) → void {}
   }
   abstract class _Class&SuperClass&Mixin = mai2::SuperClass with mai2::Mixin /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.2.expect b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.2.expect
index a1687b3a1d6..c6a2520809b 100644
--- a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.2.expect
@@ -16,10 +16,7 @@ library from "org-dartlang-test:///main_lib1.dart" as mai2 {
       ;
     method method(covariant-by-declaration dart.core::int i) → void {}
   }
-  class Mixin extends dart.core::Object {
-    synthetic constructor •() → mai2::Mixin
-      : super dart.core::Object::•()
-      ;
+  abstract class Mixin extends dart.core::Object /*isMixinDeclaration*/  {
     method method(dart.core::num i) → void {}
   }
   abstract class _Class&SuperClass&Mixin = mai2::SuperClass with mai2::Mixin /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.3.expect b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.3.expect
index ac9787d3fa0..aadb190a8b5 100644
--- a/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.3.expect
+++ b/pkg/front_end/testcases/incremental/mixin_application_declares.yaml.world.3.expect
@@ -15,10 +15,7 @@ library from "org-dartlang-test:///main_lib1.dart" as mai2 {
       ;
     method method(covariant-by-declaration dart.core::int i) → void {}
   }
-  class Mixin extends dart.core::Object {
-    synthetic constructor •() → mai2::Mixin
-      : super dart.core::Object::•()
-      ;
+  abstract class Mixin extends dart.core::Object /*isMixinDeclaration*/  {
     method method(dart.core::num i) → void {}
   }
   abstract class _Class&SuperClass&Mixin = mai2::SuperClass with mai2::Mixin /*isAnonymousMixin*/  {
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml
index 36da71a6da6..dba0a67680c 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml
+++ b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml
@@ -13,7 +13,7 @@ worlds:
         class A extends Object with B {
           foo() {}
         }
-        class B {
+        mixin B {
           bar() {}
         }
     expectedLibraryCount: 1
@@ -27,7 +27,7 @@ worlds:
         class A extends Object with B {
           foo() {}
         }
-        class B {
+        mixin B {
           bar() {}
         }
     expectedLibraryCount: 1
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.1.expect b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.1.expect
index b7af66b6388..1b5f52c032b 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.1.expect
@@ -13,10 +13,7 @@ library from "org-dartlang-test:///main.dart" as main {
       ;
     method foo() → dynamic {}
   }
-  class B extends dart.core::Object {
-    synthetic constructor •() → main::B
-      : super dart.core::Object::•()
-      ;
+  abstract class B extends dart.core::Object /*isMixinDeclaration*/  {
     method bar() → dynamic {}
   }
 }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.2.expect b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.2.expect
index b7af66b6388..1b5f52c032b 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_23.yaml.world.2.expect
@@ -13,10 +13,7 @@ library from "org-dartlang-test:///main.dart" as main {
       ;
     method foo() → dynamic {}
   }
-  class B extends dart.core::Object {
-    synthetic constructor •() → main::B
-      : super dart.core::Object::•()
-      ;
+  abstract class B extends dart.core::Object /*isMixinDeclaration*/  {
     method bar() → dynamic {}
   }
 }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml
index 146b71dbfd4..c69e62b3cae 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml
+++ b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml
@@ -12,7 +12,7 @@ worlds:
       main.dart: |
         import 'libA.dart';
 
-        class Foo {
+        mixin Foo {
           method() {
             print("A");
           }
@@ -35,7 +35,7 @@ worlds:
       main.dart: |
         import 'libA.dart';
 
-        class Foo {
+        mixin Foo {
           method() {
             print("B");
           }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.1.expect b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.1.expect
index 39a5dbb22f3..979f1e53114 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.1.expect
@@ -24,10 +24,7 @@ library from "org-dartlang-test:///main.dart" as main {
 
   import "org-dartlang-test:///libA.dart";
 
-  class Foo extends dart.core::Object {
-    synthetic constructor •() → main::Foo
-      : super dart.core::Object::•()
-      ;
+  abstract class Foo extends dart.core::Object /*isMixinDeclaration*/  {
     method method() → dynamic {
       dart.core::print("A");
     }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.2.expect b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.2.expect
index d7d471ae7df..75abd1c5c81 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_4.yaml.world.2.expect
@@ -24,10 +24,7 @@ library from "org-dartlang-test:///main.dart" as main {
 
   import "org-dartlang-test:///libA.dart";
 
-  class Foo extends dart.core::Object {
-    synthetic constructor •() → main::Foo
-      : super dart.core::Object::•()
-      ;
+  abstract class Foo extends dart.core::Object /*isMixinDeclaration*/  {
     method method() → dynamic {
       dart.core::print("B");
     }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml
index 63120f7ba2e..ccec9debf44 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml
+++ b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml
@@ -15,7 +15,7 @@ worlds:
         part 'part.dart';
       part.dart: |
         part of 'main.dart';
-        class Foo {
+        mixin Foo {
           method() {
             print("A");
           }
@@ -37,7 +37,7 @@ worlds:
     sources:
       part.dart: |
         part of 'main.dart';
-        class Foo {
+        mixin Foo {
           method() {
             print("B");
           }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.1.expect b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.1.expect
index 3d7bb8a565b..2d82194083f 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.1.expect
@@ -25,10 +25,7 @@ library from "org-dartlang-test:///main.dart" as main {
   import "org-dartlang-test:///lib.dart";
 
   part part.dart;
-  class Foo extends dart.core::Object { // from org-dartlang-test:///part.dart
-    synthetic constructor •() → main::Foo
-      : super dart.core::Object::•()
-      ;
+  abstract class Foo extends dart.core::Object /*isMixinDeclaration*/  { // from org-dartlang-test:///part.dart
     method method() → dynamic {
       dart.core::print("A");
     }
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.2.expect b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.2.expect
index c9aba5f2633..0c1bac06094 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_52.yaml.world.2.expect
@@ -25,10 +25,7 @@ library from "org-dartlang-test:///main.dart" as main {
   import "org-dartlang-test:///lib.dart";
 
   part part.dart;
-  class Foo extends dart.core::Object { // from org-dartlang-test:///part.dart
-    synthetic constructor •() → main::Foo
-      : super dart.core::Object::•()
-      ;
+  abstract class Foo extends dart.core::Object /*isMixinDeclaration*/  { // from org-dartlang-test:///part.dart
     method method() → dynamic {
       dart.core::print("B");
     }