diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart b/pkg/front_end/testcases/extension_types/issue53172.dart
new file mode 100644
index 00000000000..d600822b8d4
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart
@@ -0,0 +1,33 @@
+// Copyright (c) 2023, 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.
+
+extension type E11(num it) {
+  void foo() {}
+}
+
+extension type E12(num it) {
+  void set foo(String value) {}
+}
+
+extension type E13(num it) implements E11, E12 {} /* Error */
+
+extension type E21(bool it) {
+  void bar() {}
+}
+
+extension type E22(bool it) {
+  void bar() {}
+}
+
+extension type E23(bool it) implements E21, E22 {} /* Error */
+
+extension type E31(String it) {
+  void baz() {}
+}
+
+extension type E32(String it) implements E31 {}
+
+extension type E33(String it) implements E31 {}
+
+extension type E34(String it) implements E32, E33 {} /* Ok */
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.strong.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.strong.expect
new file mode 100644
index 00000000000..3cd63abf173
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.strong.expect
@@ -0,0 +1,160 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */ {
+  lowered final self::E11 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void {}
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */ {
+  lowered final self::E12 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void {}
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */ {
+  lowered final self::E13 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */ {
+  lowered final self::E21 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void {}
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */ {
+  lowered final self::E22 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void {}
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */ {
+  lowered final self::E23 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */ {
+  lowered final self::E31 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void {}
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */ {
+  lowered final self::E32 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */ {
+  lowered final self::E33 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */ {
+  lowered final self::E34 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.strong.transformed.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.strong.transformed.expect
new file mode 100644
index 00000000000..3cd63abf173
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.strong.transformed.expect
@@ -0,0 +1,160 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */ {
+  lowered final self::E11 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void {}
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */ {
+  lowered final self::E12 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void {}
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */ {
+  lowered final self::E13 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */ {
+  lowered final self::E21 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void {}
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */ {
+  lowered final self::E22 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void {}
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */ {
+  lowered final self::E23 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */ {
+  lowered final self::E31 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void {}
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */ {
+  lowered final self::E32 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */ {
+  lowered final self::E33 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */ {
+  lowered final self::E34 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline.expect
new file mode 100644
index 00000000000..28054d54cf5
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline.expect
@@ -0,0 +1,20 @@
+extension type E11(num it) {
+  void foo() {}
+}
+extension type E12(num it) {
+  void set foo(String value) {}
+}
+extension type E13(num it) implements E11, E12 {}
+extension type E21(bool it) {
+  void bar() {}
+}
+extension type E22(bool it) {
+  void bar() {}
+}
+extension type E23(bool it) implements E21, E22 {}
+extension type E31(String it) {
+  void baz() {}
+}
+extension type E32(String it) implements E31 {}
+extension type E33(String it) implements E31 {}
+extension type E34(String it) implements E32, E33 {}
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline_modelled.expect
new file mode 100644
index 00000000000..28054d54cf5
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.textual_outline_modelled.expect
@@ -0,0 +1,20 @@
+extension type E11(num it) {
+  void foo() {}
+}
+extension type E12(num it) {
+  void set foo(String value) {}
+}
+extension type E13(num it) implements E11, E12 {}
+extension type E21(bool it) {
+  void bar() {}
+}
+extension type E22(bool it) {
+  void bar() {}
+}
+extension type E23(bool it) implements E21, E22 {}
+extension type E31(String it) {
+  void baz() {}
+}
+extension type E32(String it) implements E31 {}
+extension type E33(String it) implements E31 {}
+extension type E34(String it) implements E32, E33 {}
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.weak.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.expect
new file mode 100644
index 00000000000..3cd63abf173
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.expect
@@ -0,0 +1,160 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */ {
+  lowered final self::E11 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void {}
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */ {
+  lowered final self::E12 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void {}
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */ {
+  lowered final self::E13 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */ {
+  lowered final self::E21 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void {}
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */ {
+  lowered final self::E22 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void {}
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */ {
+  lowered final self::E23 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */ {
+  lowered final self::E31 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void {}
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */ {
+  lowered final self::E32 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */ {
+  lowered final self::E33 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */ {
+  lowered final self::E34 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.weak.modular.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.modular.expect
new file mode 100644
index 00000000000..3cd63abf173
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.modular.expect
@@ -0,0 +1,160 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */ {
+  lowered final self::E11 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void {}
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */ {
+  lowered final self::E12 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void {}
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */ {
+  lowered final self::E13 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */ {
+  lowered final self::E21 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void {}
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */ {
+  lowered final self::E22 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void {}
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */ {
+  lowered final self::E23 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */ {
+  lowered final self::E31 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void {}
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */ {
+  lowered final self::E32 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */ {
+  lowered final self::E33 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */ {
+  lowered final self::E34 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.weak.outline.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.outline.expect
new file mode 100644
index 00000000000..2a4c4972ccc
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.outline.expect
@@ -0,0 +1,145 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */
+  ;
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void
+  ;
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */
+  ;
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void
+  ;
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */
+  ;
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */
+  ;
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void
+  ;
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */
+  ;
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void
+  ;
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */
+  ;
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */
+  ;
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void
+  ;
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */
+  ;
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */
+  ;
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */
+  ;
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);
diff --git a/pkg/front_end/testcases/extension_types/issue53172.dart.weak.transformed.expect b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.transformed.expect
new file mode 100644
index 00000000000..3cd63abf173
--- /dev/null
+++ b/pkg/front_end/testcases/extension_types/issue53172.dart.weak.transformed.expect
@@ -0,0 +1,160 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:13:16: Error: Can't inherit members that conflict with each other.
+// extension type E13(num it) implements E11, E12 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:6:8: Context: This is one inherited member.
+//   void foo() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:10:12: Context: This is the other inherited member.
+//   void set foo(String value) {}
+//            ^^^
+//
+// pkg/front_end/testcases/extension_types/issue53172.dart:23:16: Error: The extension type 'E23' can't inherit the member 'bar' from more than one extension type.
+// Try declaring a member 'bar' in 'E23' to resolve the conflict.
+// extension type E23(bool it) implements E21, E22 {} /* Error */
+//                ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:16:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+// pkg/front_end/testcases/extension_types/issue53172.dart:20:8: Context: This is one of the inherited extension type members.
+//   void bar() {}
+//        ^^^
+//
+import self as self;
+import "dart:core" as core;
+
+extension type E11(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  method foo = self::E11|foo;
+  method tearoff foo = self::E11|get#foo;
+  constructor • = self::E11|constructor#;
+  constructor tearoff • = self::E11|constructor#_#new#tearOff;
+}
+extension type E12(core::num it) {
+  abstract extension-type-member representation-field get it() → core::num;
+  set foo = self::E12|set#foo;
+  constructor • = self::E12|constructor#;
+  constructor tearoff • = self::E12|constructor#_#new#tearOff;
+}
+extension type E13(core::num it) implements self::E11 /* = core::num */, self::E12 /* = core::num */ {
+  abstract extension-type-member representation-field get it() → core::num;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E21(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E21|bar;
+  method tearoff bar = self::E21|get#bar;
+  constructor • = self::E21|constructor#;
+  constructor tearoff • = self::E21|constructor#_#new#tearOff;
+}
+extension type E22(core::bool it) {
+  abstract extension-type-member representation-field get it() → core::bool;
+  method bar = self::E22|bar;
+  method tearoff bar = self::E22|get#bar;
+  constructor • = self::E22|constructor#;
+  constructor tearoff • = self::E22|constructor#_#new#tearOff;
+}
+extension type E23(core::bool it) implements self::E21 /* = core::bool */, self::E22 /* = core::bool */ {
+  abstract extension-type-member representation-field get it() → core::bool;
+  constructor • = self::E23|constructor#;
+  constructor tearoff • = self::E23|constructor#_#new#tearOff;
+}
+extension type E31(core::String it) {
+  abstract extension-type-member representation-field get it() → core::String;
+  method baz = self::E31|baz;
+  method tearoff baz = self::E31|get#baz;
+  constructor • = self::E31|constructor#;
+  constructor tearoff • = self::E31|constructor#_#new#tearOff;
+}
+extension type E32(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E32|constructor#;
+  constructor tearoff • = self::E32|constructor#_#new#tearOff;
+}
+extension type E33(core::String it) implements self::E31 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E33|constructor#;
+  constructor tearoff • = self::E33|constructor#_#new#tearOff;
+}
+extension type E34(core::String it) implements self::E32 /* = core::String */, self::E33 /* = core::String */ {
+  abstract extension-type-member representation-field get it() → core::String;
+  constructor • = self::E34|constructor#;
+  constructor tearoff • = self::E34|constructor#_#new#tearOff;
+}
+static extension-type-member method E11|constructor#(core::num it) → self::E11 /* = core::num */ {
+  lowered final self::E11 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E11|constructor#_#new#tearOff(core::num it) → self::E11 /* = core::num */
+  return self::E11|constructor#(it);
+static extension-type-member method E11|foo(lowered final self::E11 /* = core::num */ #this) → void {}
+static extension-type-member method E11|get#foo(lowered final self::E11 /* = core::num */ #this) → () → void
+  return () → void => self::E11|foo(#this);
+static extension-type-member method E12|constructor#(core::num it) → self::E12 /* = core::num */ {
+  lowered final self::E12 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E12|constructor#_#new#tearOff(core::num it) → self::E12 /* = core::num */
+  return self::E12|constructor#(it);
+static extension-type-member method E12|set#foo(lowered final self::E12 /* = core::num */ #this, core::String value) → void {}
+static extension-type-member method E13|constructor#(core::num it) → self::E13 /* = core::num */ {
+  lowered final self::E13 /* = core::num */ #this = it;
+  return #this;
+}
+static extension-type-member method E13|constructor#_#new#tearOff(core::num it) → self::E13 /* = core::num */
+  return self::E13|constructor#(it);
+static extension-type-member method E21|constructor#(core::bool it) → self::E21 /* = core::bool */ {
+  lowered final self::E21 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E21|constructor#_#new#tearOff(core::bool it) → self::E21 /* = core::bool */
+  return self::E21|constructor#(it);
+static extension-type-member method E21|bar(lowered final self::E21 /* = core::bool */ #this) → void {}
+static extension-type-member method E21|get#bar(lowered final self::E21 /* = core::bool */ #this) → () → void
+  return () → void => self::E21|bar(#this);
+static extension-type-member method E22|constructor#(core::bool it) → self::E22 /* = core::bool */ {
+  lowered final self::E22 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E22|constructor#_#new#tearOff(core::bool it) → self::E22 /* = core::bool */
+  return self::E22|constructor#(it);
+static extension-type-member method E22|bar(lowered final self::E22 /* = core::bool */ #this) → void {}
+static extension-type-member method E22|get#bar(lowered final self::E22 /* = core::bool */ #this) → () → void
+  return () → void => self::E22|bar(#this);
+static extension-type-member method E23|constructor#(core::bool it) → self::E23 /* = core::bool */ {
+  lowered final self::E23 /* = core::bool */ #this = it;
+  return #this;
+}
+static extension-type-member method E23|constructor#_#new#tearOff(core::bool it) → self::E23 /* = core::bool */
+  return self::E23|constructor#(it);
+static extension-type-member method E31|constructor#(core::String it) → self::E31 /* = core::String */ {
+  lowered final self::E31 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E31|constructor#_#new#tearOff(core::String it) → self::E31 /* = core::String */
+  return self::E31|constructor#(it);
+static extension-type-member method E31|baz(lowered final self::E31 /* = core::String */ #this) → void {}
+static extension-type-member method E31|get#baz(lowered final self::E31 /* = core::String */ #this) → () → void
+  return () → void => self::E31|baz(#this);
+static extension-type-member method E32|constructor#(core::String it) → self::E32 /* = core::String */ {
+  lowered final self::E32 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E32|constructor#_#new#tearOff(core::String it) → self::E32 /* = core::String */
+  return self::E32|constructor#(it);
+static extension-type-member method E33|constructor#(core::String it) → self::E33 /* = core::String */ {
+  lowered final self::E33 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E33|constructor#_#new#tearOff(core::String it) → self::E33 /* = core::String */
+  return self::E33|constructor#(it);
+static extension-type-member method E34|constructor#(core::String it) → self::E34 /* = core::String */ {
+  lowered final self::E34 /* = core::String */ #this = it;
+  return #this;
+}
+static extension-type-member method E34|constructor#_#new#tearOff(core::String it) → self::E34 /* = core::String */
+  return self::E34|constructor#(it);