[cfe] Report an error on optional positional or named parameters in extension type declarations

Part of https://github.com/dart-lang/sdk/issues/49731

Change-Id: I49e813f9573b2b66950e8aae572591b65b62e2ec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331260
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -10365,6 +10365,16 @@ Message _withArgumentsNamedMixinOverride(String name, String name2) {
       arguments: {'name': name, 'name2': name2});
 }
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeNamedParametersInExtensionTypeDeclaration =
+    messageNamedParametersInExtensionTypeDeclaration;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageNamedParametersInExtensionTypeDeclaration =
+    const MessageCode("NamedParametersInExtensionTypeDeclaration",
+        problemMessage:
+            r"""Extension type declarations can't have named parameters.""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeNativeClauseShouldBeAnnotation =
     messageNativeClauseShouldBeAnnotation;
@@ -11593,6 +11603,16 @@ const MessageCode messageOperatorWithTypeParameters = const MessageCode(
         r"""Types parameters aren't allowed when defining an operator.""",
     correctionMessage: r"""Try removing the type parameters.""");
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeOptionalParametersInExtensionTypeDeclaration =
+    messageOptionalParametersInExtensionTypeDeclaration;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageOptionalParametersInExtensionTypeDeclaration =
+    const MessageCode("OptionalParametersInExtensionTypeDeclaration",
+        problemMessage:
+            r"""Extension type declarations can't have optional parameters.""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<
     Message Function(

pkg/front_end/lib/src/fasta/modifier.dart

@@ -136,13 +136,18 @@ class Modifier {
   /// Method [maskContainsActualModifiers] returns `true` if the mask has any of
   /// the actual modifier bits set, and `false` otherwise.
   static bool maskContainsActualModifiers(int mask) {
-    mask &= ~(1 << mixinDeclarationMask);
-    mask &= ~(1 << hasInitializerMask);
-    mask &= ~(1 << initializingFormalMask);
-    mask &= ~(1 << declaresConstConstructorMask);
-    mask &= ~(1 << superInitializingFormalMask);
-    mask &= ~(1 << varMask);
+    mask &= ~(mixinDeclarationMask |
+        hasInitializerMask |
+        initializingFormalMask |
+        declaresConstConstructorMask |
+        superInitializingFormalMask |
+        varMask);
 
     return mask != 0;
   }
+
+  /// Sets the bit in [mask] corresponding to [requiredMask] to 0.
+  static int removeRequiredMask(int mask) {
+    return mask & ~requiredMask;
+  }
 }

pkg/front_end/lib/src/fasta/source/outline_builder.dart

@@ -1627,14 +1627,9 @@ class OutlineBuilder extends StackListenerImpl {
     bool inExtensionType =
         declarationContext == DeclarationContext.ExtensionType;
     if (formals != null) {
-      if (inExtensionType && formals.isEmpty) {
-        libraryBuilder.addProblem(
-            messageExpectedRepresentationField, charOffset, 1, uri);
-      }
-      if (inExtensionType && formals.length > 1) {
-        libraryBuilder.addProblem(
-            messageMultipleRepresentationFields, charOffset, 1, uri);
-      }
+      int requiredPositionalCount = 0;
+      int? firstNamedParameterOffset;
+      int? firstOptionalPositionalParameterOffset;
       for (int i = 0; i < formals.length; i++) {
         FormalParameterBuilder formal = formals[i];
         if (inExtensionType && formal.type is ImplicitTypeBuilder) {
@@ -1642,10 +1637,21 @@ class OutlineBuilder extends StackListenerImpl {
               formal.charOffset, formal.name.length, formal.fileUri);
         }
         if (inExtensionType &&
-            Modifier.maskContainsActualModifiers(formal.modifiers)) {
+            Modifier.maskContainsActualModifiers(
+                Modifier.removeRequiredMask(formal.modifiers))) {
           libraryBuilder.addProblem(messageRepresentationFieldModifier,
               formal.charOffset, formal.name.length, formal.fileUri);
         }
+        if (formal.isPositional) {
+          if (formal.isOptionalPositional) {
+            firstOptionalPositionalParameterOffset = formal.charOffset;
+          } else {
+            requiredPositionalCount++;
+          }
+        }
+        if (formal.isNamed) {
+          firstNamedParameterOffset = formal.charOffset;
+        }
         libraryBuilder.addPrimaryConstructorField(
             // TODO(johnniwinther): Support annotations on annotations on fields
             // defined through a primary constructor. This is not needed for
@@ -1657,6 +1663,27 @@ class OutlineBuilder extends StackListenerImpl {
             charOffset: formal.charOffset);
         formals[i] = formal.forPrimaryConstructor(libraryBuilder);
       }
+      if (inExtensionType) {
+        if (firstOptionalPositionalParameterOffset != null) {
+          libraryBuilder.addProblem(
+              messageOptionalParametersInExtensionTypeDeclaration,
+              firstOptionalPositionalParameterOffset,
+              1,
+              uri);
+        } else if (firstNamedParameterOffset != null) {
+          libraryBuilder.addProblem(
+              messageNamedParametersInExtensionTypeDeclaration,
+              firstNamedParameterOffset,
+              1,
+              uri);
+        } else if (requiredPositionalCount == 0) {
+          libraryBuilder.addProblem(
+              messageExpectedRepresentationField, charOffset, 1, uri);
+        } else if (inExtensionType && formals.length > 1) {
+          libraryBuilder.addProblem(
+              messageMultipleRepresentationFields, charOffset, 1, uri);
+        }
+      }
     }
 
     libraryBuilder.beginNestedDeclaration(

pkg/front_end/messages.status

@@ -378,8 +378,8 @@ FastaUsageShort/analyzerCode: Fail
 FastaUsageShort/example: Fail
 FfiAbiSpecificIntegerInvalid/analyzerCode: Fail
 FfiAbiSpecificIntegerMappingInvalid/analyzerCode: Fail
-FfiCreateOfStructOrUnion/analyzerCode: Fail
 FfiCompoundImplementsFinalizable/analyzerCode: Fail
+FfiCreateOfStructOrUnion/analyzerCode: Fail
 FfiDartTypeMismatch/analyzerCode: Fail
 FfiEmptyStruct/analyzerCode: Fail
 FfiExceptionalReturnNull/analyzerCode: Fail
@@ -395,6 +395,7 @@ FfiFieldNoAnnotation/analyzerCode: Fail
 FfiFieldNull/analyzerCode: Fail
 FfiLeafCallMustNotReturnHandle/analyzerCode: Fail
 FfiLeafCallMustNotTakeHandle/analyzerCode: Fail
+FfiNativeCallableListenerReturnVoid/analyzerCode: Fail
 FfiNativeMustBeExternal/analyzerCode: Fail
 FfiNativeOnlyNativeFieldWrapperClassCanBePointer/analyzerCode: Fail
 FfiNativeUnexpectedNumberOfParameters/analyzerCode: Fail
@@ -402,7 +403,6 @@ FfiNativeUnexpectedNumberOfParametersWithReceiver/analyzerCode: Fail
 FfiNotStatic/analyzerCode: Fail
 FfiPackedAnnotation/analyzerCode: Fail
 FfiPackedAnnotationAlignment/analyzerCode: Fail
-FfiNativeCallableListenerReturnVoid/analyzerCode: Fail
 FfiSizeAnnotation/analyzerCode: Fail
 FfiSizeAnnotationDimensions/analyzerCode: Fail
 FfiStructAnnotation/analyzerCode: Fail
@@ -616,10 +616,10 @@ JsInteropExportMemberCollision/analyzerCode: Fail # Web compiler specific
 JsInteropExportMemberCollision/example: Fail # Web compiler specific
 JsInteropExportNoExportableMembers/analyzerCode: Fail # Web compiler specific
 JsInteropExportNoExportableMembers/example: Fail # Web compiler specific
-JsInteropExtensionTypeNotInterop/analyzerCode: Fail # Web compiler specific
-JsInteropExtensionTypeNotInterop/example: Fail # Web compiler specific
 JsInteropExtensionTypeMemberNotInterop/analyzerCode: Fail # Web compiler specific
 JsInteropExtensionTypeMemberNotInterop/example: Fail # Web compiler specific
+JsInteropExtensionTypeNotInterop/analyzerCode: Fail # Web compiler specific
+JsInteropExtensionTypeNotInterop/example: Fail # Web compiler specific
 JsInteropExtensionTypeUsedWithWrongJsAnnotation/analyzerCode: Fail # Web compiler specific
 JsInteropExtensionTypeUsedWithWrongJsAnnotation/example: Fail # Web compiler specific
 JsInteropExternalExtensionMemberOnTypeInvalid/analyzerCode: Fail # Web compiler specific
@@ -628,6 +628,8 @@ JsInteropExternalExtensionMemberWithStaticDisallowed/analyzerCode: Fail # Web co
 JsInteropExternalExtensionMemberWithStaticDisallowed/example: Fail # Web compiler specific
 JsInteropExternalMemberNotJSAnnotated/analyzerCode: Fail # Web compiler specific
 JsInteropExternalMemberNotJSAnnotated/example: Fail # Web compiler specific
+JsInteropFunctionToJSRequiresStaticType/analyzerCode: Fail # Web compiler specific
+JsInteropFunctionToJSRequiresStaticType/example: Fail # Web compiler specific
 JsInteropInvalidStaticClassMemberName/analyzerCode: Fail
 JsInteropInvalidStaticClassMemberName/example: Fail
 JsInteropJSClassExtendsDartClass/analyzerCode: Fail # Web compiler specific
@@ -642,12 +644,12 @@ JsInteropNonExternalMember/analyzerCode: Fail # Web compiler specific
 JsInteropNonExternalMember/example: Fail # Web compiler specific
 JsInteropNonStaticWithStaticInteropSupertype/analyzerCode: Fail # Web compiler specific
 JsInteropNonStaticWithStaticInteropSupertype/example: Fail # Web compiler specific
+JsInteropObjectLiteralConstructorPositionalParameters/analyzerCode: Fail # Web compiler specific
+JsInteropObjectLiteralConstructorPositionalParameters/example: Fail # Web compiler specific
 JsInteropOperatorCannotBeRenamed/analyzerCode: Fail # Web compiler specific
 JsInteropOperatorCannotBeRenamed/example: Fail # Web compiler specific
 JsInteropOperatorsNotSupported/analyzerCode: Fail # Web compiler specific
 JsInteropOperatorsNotSupported/example: Fail # Web compiler specific
-JsInteropObjectLiteralConstructorPositionalParameters/analyzerCode: Fail # Web compiler specific
-JsInteropObjectLiteralConstructorPositionalParameters/example: Fail # Web compiler specific
 JsInteropStaticInteropExternalMemberWithInvalidTypeParameters/analyzerCode: Fail # Web compiler specific
 JsInteropStaticInteropExternalMemberWithInvalidTypeParameters/example: Fail # Web compiler specific
 JsInteropStaticInteropExternalTypeViolation/analyzerCode: Fail # Web compiler specific
@@ -680,8 +682,6 @@ JsInteropStaticInteropWithInvalidJsTypesSupertype/analyzerCode: Fail # Web compi
 JsInteropStaticInteropWithInvalidJsTypesSupertype/example: Fail # Web compiler specific
 JsInteropStaticInteropWithNonStaticSupertype/analyzerCode: Fail # Web compiler specific
 JsInteropStaticInteropWithNonStaticSupertype/example: Fail # Web compiler specific
-JsInteropFunctionToJSRequiresStaticType/analyzerCode: Fail # Web compiler specific
-JsInteropFunctionToJSRequiresStaticType/example: Fail # Web compiler specific
 JsInteropStrictModeForbiddenLibrary/analyzerCode: Fail # Web compiler specific
 JsInteropStrictModeForbiddenLibrary/example: Fail # Web compiler specific
 LanguageVersionInvalidInDotPackages/analyzerCode: Fail
@@ -748,6 +748,7 @@ NameNotFoundInRecordNameGet/example: Fail
 NamedFunctionExpression/example: Fail
 NamedMixinOverride/analyzerCode: Fail
 NamedMixinOverride/example: Fail
+NamedParametersInExtensionTypeDeclaration/analyzerCode: Fail
 NativeClauseShouldBeAnnotation/example: Fail
 NeverReachableSwitchDefaultError/analyzerCode: Fail
 NeverReachableSwitchDefaultError/example: Fail
@@ -868,6 +869,7 @@ OperatorParameterMismatch1/example: Fail
 OperatorParameterMismatch2/example: Fail
 OperatorWithOptionalFormals/analyzerCode: Fail
 OperatorWithOptionalFormals/example: Fail
+OptionalParametersInExtensionTypeDeclaration/analyzerCode: Fail
 OptionalSuperParameterWithoutInitializer/analyzerCode: Fail
 OptionalSuperParameterWithoutInitializer/example: Fail
 OverrideFewerNamedArguments/example: Fail

pkg/front_end/messages.yaml

@@ -7468,3 +7468,15 @@ AwaitOfExtensionTypeNotFuture:
   script: |
     extension type E(num foo) { test(E e) async { await e; } }
   analyzerCode: AWAIT_OF_EXTENSION_TYPE_NOT_FUTURE
+
+NamedParametersInExtensionTypeDeclaration:
+  problemMessage: "Extension type declarations can't have named parameters."
+  experiments: inline-class
+  script: |
+    extension type E(int foo, {dynamic bar}) {}
+
+OptionalParametersInExtensionTypeDeclaration:
+  problemMessage: "Extension type declarations can't have optional parameters."
+  experiments: inline-class
+  script: |
+    extension type E(int foo, [dynamic bar]) {}

pkg/front_end/testcases/extension_types/issue52119.dart.strong.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 // pkg/front_end/testcases/extension_types/issue52119.dart:12:26: Error: Couldn't find constructor 'Foo.unresolved'.
 //   Foo.erroneous() : this.unresolved(); // Error
 //                          ^^^^^^^^^^

pkg/front_end/testcases/extension_types/issue52119.dart.strong.transformed.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 // pkg/front_end/testcases/extension_types/issue52119.dart:12:26: Error: Couldn't find constructor 'Foo.unresolved'.
 //   Foo.erroneous() : this.unresolved(); // Error
 //                          ^^^^^^^^^^

pkg/front_end/testcases/extension_types/issue52119.dart.weak.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 // pkg/front_end/testcases/extension_types/issue52119.dart:12:26: Error: Couldn't find constructor 'Foo.unresolved'.
 //   Foo.erroneous() : this.unresolved(); // Error
 //                          ^^^^^^^^^^

pkg/front_end/testcases/extension_types/issue52119.dart.weak.modular.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 // pkg/front_end/testcases/extension_types/issue52119.dart:12:26: Error: Couldn't find constructor 'Foo.unresolved'.
 //   Foo.erroneous() : this.unresolved(); // Error
 //                          ^^^^^^^^^^

pkg/front_end/testcases/extension_types/issue52119.dart.weak.outline.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 import self as self;
 import "dart:core" as core;
 

pkg/front_end/testcases/extension_types/issue52119.dart.weak.transformed.expect

@@ -6,10 +6,6 @@ library;
 // extension type Bar<T>._(this.i) {
 //                              ^
 //
-// pkg/front_end/testcases/extension_types/issue52119.dart:15:30: Error: Representation fields can't have modifiers.
-// extension type Bar<T>._(this.i) {
-//                              ^
-//
 // pkg/front_end/testcases/extension_types/issue52119.dart:12:26: Error: Couldn't find constructor 'Foo.unresolved'.
 //   Foo.erroneous() : this.unresolved(); // Error
 //                          ^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation.dart.strong.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 // pkg/front_end/testcases/extension_types/representation.dart:9:31: Error: Can't use 'instanceField' because it is declared more than once.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation.dart.strong.transformed.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 // pkg/front_end/testcases/extension_types/representation.dart:9:31: Error: Can't use 'instanceField' because it is declared more than once.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation.dart.weak.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 // pkg/front_end/testcases/extension_types/representation.dart:9:31: Error: Can't use 'instanceField' because it is declared more than once.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation.dart.weak.modular.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 // pkg/front_end/testcases/extension_types/representation.dart:9:31: Error: Can't use 'instanceField' because it is declared more than once.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation.dart.weak.outline.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 import self as self;
 import "dart:core" as core;
 

pkg/front_end/testcases/extension_types/representation.dart.weak.transformed.expect

@@ -17,10 +17,6 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
-// extension type Duplicate(bool instanceField, int instanceField) {} // Error
-//                         ^
-//
 // pkg/front_end/testcases/extension_types/representation.dart:9:50: Error: 'instanceField' is already declared in this scope.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                                                  ^^^^^^^^^^^^^
@@ -28,6 +24,10 @@ library;
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^
 //
+// pkg/front_end/testcases/extension_types/representation.dart:9:25: Error: Each extension type should have exactly one representation field.
+// extension type Duplicate(bool instanceField, int instanceField) {} // Error
+//                         ^
+//
 // pkg/front_end/testcases/extension_types/representation.dart:9:31: Error: Can't use 'instanceField' because it is declared more than once.
 // extension type Duplicate(bool instanceField, int instanceField) {} // Error
 //                               ^^^^^^^^^^^^^

pkg/front_end/testcases/extension_types/representation_field_error.dart

@@ -14,3 +14,9 @@ extension type E9(int foo, String bar) {} // Error.
 extension type E10(num foo, bool bar, double baz) {} // Error.
 extension type E11(bool foo,) {} // Error.
 extension type E12(bool foo = false,) {} // Error.
+extension type E13([int? foo]) {} // Error.
+extension type E14({String? foo}) {} // Error.
+extension type E15({required double foo}) {} // Error.
+extension type E16(bool foo, [dynamic bar]) {} // Error.
+extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+extension type E18(double foo, {required int bar}) {} // Error.

pkg/front_end/testcases/extension_types/representation_field_error.dart.strong.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */ {
   lowered final self::E1 /* = dynamic */ #this = foo;
   return #this;
@@ -173,12 +231,12 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
 }
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
+static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
+  return self::E6|constructor#(foo);
 static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */ {
   lowered final self::E6 /* = core::double */ #this = foo;
   return #this;
 }
-static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
-  return self::E6|constructor#(foo);
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */ {
   lowered final self::E7 /* = dynamic */ #this = foo;
   return #this;
@@ -215,7 +273,44 @@ static inline-class-member method E12|constructor#(core::bool foo = #C1) → sel
 }
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = #C2]) → self::E13 /* = core::int? */ {
+  lowered final self::E13 /* = core::int? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = #C2}) → self::E14 /* = core::String? */ {
+  lowered final self::E14 /* = core::String? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = #C2}) → self::E15 /* = core::double */ {
+  lowered final self::E15 /* = core::double */ #this = foo;
+  return #this;
+}
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = #C2]) → self::E16 /* = core::bool */ {
+  lowered final self::E16 /* = core::bool */ #this = bar;
+  return #this;
+}
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = #C2, core::String? baz = #C2}) → self::E17 /* = core::Object */ {
+  lowered final self::E17 /* = core::Object */ #this = baz;
+  return #this;
+}
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = #C2}) → self::E18 /* = core::double */ {
+  lowered final self::E18 /* = core::double */ #this = bar;
+  return #this;
+}
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);
 
 constants  {
   #C1 = false
+  #C2 = null
 }

pkg/front_end/testcases/extension_types/representation_field_error.dart.strong.transformed.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */ {
   lowered final self::E1 /* = dynamic */ #this = foo;
   return #this;
@@ -173,12 +231,12 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
 }
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
+static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
+  return self::E6|constructor#(foo);
 static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */ {
   lowered final self::E6 /* = core::double */ #this = foo;
   return #this;
 }
-static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
-  return self::E6|constructor#(foo);
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */ {
   lowered final self::E7 /* = dynamic */ #this = foo;
   return #this;
@@ -215,7 +273,44 @@ static inline-class-member method E12|constructor#(core::bool foo = #C1) → sel
 }
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = #C2]) → self::E13 /* = core::int? */ {
+  lowered final self::E13 /* = core::int? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = #C2}) → self::E14 /* = core::String? */ {
+  lowered final self::E14 /* = core::String? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = #C2}) → self::E15 /* = core::double */ {
+  lowered final self::E15 /* = core::double */ #this = foo;
+  return #this;
+}
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = #C2]) → self::E16 /* = core::bool */ {
+  lowered final self::E16 /* = core::bool */ #this = bar;
+  return #this;
+}
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = #C2, core::String? baz = #C2}) → self::E17 /* = core::Object */ {
+  lowered final self::E17 /* = core::Object */ #this = baz;
+  return #this;
+}
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = #C2}) → self::E18 /* = core::double */ {
+  lowered final self::E18 /* = core::double */ #this = bar;
+  return #this;
+}
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);
 
 constants  {
   #C1 = false
+  #C2 = null
 }

pkg/front_end/testcases/extension_types/representation_field_error.dart.textual_outline.expect

@@ -10,3 +10,9 @@ extension type E9(int foo, String bar) {}
 extension type E10(num foo, bool bar, double baz) {}
 extension type E11(bool foo,) {}
 extension type E12(bool foo = false,) {}
+extension type E13([int? foo]) {}
+extension type E14({String? foo}) {}
+extension type E15({required double foo}) {}
+extension type E16(bool foo, [dynamic bar]) {}
+extension type E17(Object foo, {num? bar, String? baz}) {}
+extension type E18(double foo, {required int bar}) {}

pkg/front_end/testcases/extension_types/representation_field_error.dart.textual_outline_modelled.expect

@@ -2,6 +2,12 @@ extension type E1(var foo) {}
 extension type E10(num foo, bool bar, double baz) {}
 extension type E11(bool foo,) {}
 extension type E12(bool foo = false,) {}
+extension type E13([int? foo]) {}
+extension type E14({String? foo}) {}
+extension type E15({required double foo}) {}
+extension type E16(bool foo, [dynamic bar]) {}
+extension type E17(Object foo, {num? bar, String? baz}) {}
+extension type E18(double foo, {required int bar}) {}
 extension type E2(final foo) {}
 extension type E3(final String foo) {}
 extension type E4(covariant num foo) {}

pkg/front_end/testcases/extension_types/representation_field_error.dart.weak.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */ {
   lowered final self::E1 /* = dynamic */ #this = foo;
   return #this;
@@ -173,12 +231,12 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
 }
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
+static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
+  return self::E6|constructor#(foo);
 static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */ {
   lowered final self::E6 /* = core::double */ #this = foo;
   return #this;
 }
-static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
-  return self::E6|constructor#(foo);
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */ {
   lowered final self::E7 /* = dynamic */ #this = foo;
   return #this;
@@ -215,7 +273,44 @@ static inline-class-member method E12|constructor#(core::bool foo = #C1) → sel
 }
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = #C2]) → self::E13 /* = core::int? */ {
+  lowered final self::E13 /* = core::int? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = #C2}) → self::E14 /* = core::String? */ {
+  lowered final self::E14 /* = core::String? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = #C2}) → self::E15 /* = core::double */ {
+  lowered final self::E15 /* = core::double */ #this = foo;
+  return #this;
+}
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = #C2]) → self::E16 /* = core::bool */ {
+  lowered final self::E16 /* = core::bool */ #this = bar;
+  return #this;
+}
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = #C2, core::String? baz = #C2}) → self::E17 /* = core::Object */ {
+  lowered final self::E17 /* = core::Object */ #this = baz;
+  return #this;
+}
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = #C2}) → self::E18 /* = core::double */ {
+  lowered final self::E18 /* = core::double */ #this = bar;
+  return #this;
+}
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);
 
 constants  {
   #C1 = false
+  #C2 = null
 }

pkg/front_end/testcases/extension_types/representation_field_error.dart.weak.modular.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */ {
   lowered final self::E1 /* = dynamic */ #this = foo;
   return #this;
@@ -173,12 +231,12 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
 }
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
+static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
+  return self::E6|constructor#(foo);
 static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */ {
   lowered final self::E6 /* = core::double */ #this = foo;
   return #this;
 }
-static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
-  return self::E6|constructor#(foo);
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */ {
   lowered final self::E7 /* = dynamic */ #this = foo;
   return #this;
@@ -215,7 +273,44 @@ static inline-class-member method E12|constructor#(core::bool foo = #C1) → sel
 }
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = #C2]) → self::E13 /* = core::int? */ {
+  lowered final self::E13 /* = core::int? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = #C2}) → self::E14 /* = core::String? */ {
+  lowered final self::E14 /* = core::String? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = #C2}) → self::E15 /* = core::double */ {
+  lowered final self::E15 /* = core::double */ #this = foo;
+  return #this;
+}
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = #C2]) → self::E16 /* = core::bool */ {
+  lowered final self::E16 /* = core::bool */ #this = bar;
+  return #this;
+}
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = #C2, core::String? baz = #C2}) → self::E17 /* = core::Object */ {
+  lowered final self::E17 /* = core::Object */ #this = baz;
+  return #this;
+}
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = #C2}) → self::E18 /* = core::double */ {
+  lowered final self::E18 /* = core::double */ #this = bar;
+  return #this;
+}
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);
 
 constants  {
   #C1 = false
+  #C2 = null
 }

pkg/front_end/testcases/extension_types/representation_field_error.dart.weak.outline.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */
   ;
 static inline-class-member method E1|constructor#_#new#tearOff(dynamic foo) → self::E1 /* = dynamic */
@@ -163,10 +221,10 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
   ;
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
-static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */
-  ;
 static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
   return self::E6|constructor#(foo);
+static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */
+  ;
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */
   ;
 static inline-class-member method E7|constructor#_#new#tearOff(dynamic foo) → self::E7 /* = dynamic */
@@ -191,3 +249,27 @@ static inline-class-member method E12|constructor#(has-declared-initializer core
   ;
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = null]) → self::E13 /* = core::int? */
+  ;
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = null}) → self::E14 /* = core::String? */
+  ;
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = null}) → self::E15 /* = core::double */
+  ;
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = null]) → self::E16 /* = core::bool */
+  ;
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = null, core::String? baz = null}) → self::E17 /* = core::Object */
+  ;
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = null}) → self::E18 /* = core::double */
+  ;
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);

pkg/front_end/testcases/extension_types/representation_field_error.dart.weak.transformed.expect

@@ -78,6 +78,30 @@ library;
 // extension type E12(bool foo = false,) {} // Error.
 //                                    ^
 //
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:17:26: Error: Extension type declarations can't have optional parameters.
+// extension type E13([int? foo]) {} // Error.
+//                          ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:18:29: Error: Extension type declarations can't have named parameters.
+// extension type E14({String? foo}) {} // Error.
+//                             ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:19:37: Error: Extension type declarations can't have named parameters.
+// extension type E15({required double foo}) {} // Error.
+//                                     ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:20:39: Error: Extension type declarations can't have optional parameters.
+// extension type E16(bool foo, [dynamic bar]) {} // Error.
+//                                       ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:21:51: Error: Extension type declarations can't have named parameters.
+// extension type E17(Object foo, {num? bar, String? baz}) {} // Error.
+//                                                   ^
+//
+// pkg/front_end/testcases/extension_types/representation_field_error.dart:22:46: Error: Extension type declarations can't have named parameters.
+// extension type E18(double foo, {required int bar}) {} // Error.
+//                                              ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -143,6 +167,40 @@ extension type E12(core::bool foo) {
   constructor • = self::E12|constructor#;
   constructor tearoff • = self::E12|constructor#_#new#tearOff;
 }
+extension type E13(core::int? foo) {
+  abstract inline-class-member representation-field get foo() → core::int?;
+  constructor • = self::E13|constructor#;
+  constructor tearoff • = self::E13|constructor#_#new#tearOff;
+}
+extension type E14(core::String? foo) {
+  abstract inline-class-member representation-field get foo() → core::String?;
+  constructor • = self::E14|constructor#;
+  constructor tearoff • = self::E14|constructor#_#new#tearOff;
+}
+extension type E15(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  constructor • = self::E15|constructor#;
+  constructor tearoff • = self::E15|constructor#_#new#tearOff;
+}
+extension type E16(core::bool foo) {
+  abstract inline-class-member representation-field get foo() → core::bool;
+  abstract inline-class-member representation-field get bar() → dynamic;
+  constructor • = self::E16|constructor#;
+  constructor tearoff • = self::E16|constructor#_#new#tearOff;
+}
+extension type E17(core::Object foo) {
+  abstract inline-class-member representation-field get foo() → core::Object;
+  abstract inline-class-member representation-field get bar() → core::num?;
+  abstract inline-class-member representation-field get baz() → core::String?;
+  constructor • = self::E17|constructor#;
+  constructor tearoff • = self::E17|constructor#_#new#tearOff;
+}
+extension type E18(core::double foo) {
+  abstract inline-class-member representation-field get foo() → core::double;
+  abstract inline-class-member representation-field get bar() → core::int;
+  constructor • = self::E18|constructor#;
+  constructor tearoff • = self::E18|constructor#_#new#tearOff;
+}
 static inline-class-member method E1|constructor#(dynamic foo) → self::E1 /* = dynamic */ {
   lowered final self::E1 /* = dynamic */ #this = foo;
   return #this;
@@ -173,12 +231,12 @@ static inline-class-member method E5|constructor#(core::bool foo) → self::E5 /
 }
 static inline-class-member method E5|constructor#_#new#tearOff(core::bool foo) → self::E5 /* = core::bool */
   return self::E5|constructor#(foo);
+static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
+  return self::E6|constructor#(foo);
 static inline-class-member method E6|constructor#(covariant-by-declaration final core::double foo) → self::E6 /* = core::double */ {
   lowered final self::E6 /* = core::double */ #this = foo;
   return #this;
 }
-static inline-class-member method E6|constructor#_#new#tearOff(core::double foo) → self::E6 /* = core::double */
-  return self::E6|constructor#(foo);
 static inline-class-member method E7|constructor#(dynamic foo) → self::E7 /* = dynamic */ {
   lowered final self::E7 /* = dynamic */ #this = foo;
   return #this;
@@ -215,7 +273,44 @@ static inline-class-member method E12|constructor#(core::bool foo = #C1) → sel
 }
 static inline-class-member method E12|constructor#_#new#tearOff(has-declared-initializer core::bool foo) → self::E12 /* = core::bool */
   return self::E12|constructor#(foo);
+static inline-class-member method E13|constructor#([core::int? foo = #C2]) → self::E13 /* = core::int? */ {
+  lowered final self::E13 /* = core::int? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E13|constructor#_#new#tearOff([core::int? foo]) → self::E13 /* = core::int? */
+  return self::E13|constructor#(foo);
+static inline-class-member method E14|constructor#({core::String? foo = #C2}) → self::E14 /* = core::String? */ {
+  lowered final self::E14 /* = core::String? */ #this = foo;
+  return #this;
+}
+static inline-class-member method E14|constructor#_#new#tearOff({core::String? foo}) → self::E14 /* = core::String? */
+  return self::E14|constructor#(foo: foo);
+static inline-class-member method E15|constructor#({required core::double foo = #C2}) → self::E15 /* = core::double */ {
+  lowered final self::E15 /* = core::double */ #this = foo;
+  return #this;
+}
+static inline-class-member method E15|constructor#_#new#tearOff({required core::double foo}) → self::E15 /* = core::double */
+  return self::E15|constructor#(foo: foo);
+static inline-class-member method E16|constructor#(core::bool foo, [dynamic bar = #C2]) → self::E16 /* = core::bool */ {
+  lowered final self::E16 /* = core::bool */ #this = bar;
+  return #this;
+}
+static inline-class-member method E16|constructor#_#new#tearOff(core::bool foo, [dynamic bar]) → self::E16 /* = core::bool */
+  return self::E16|constructor#(foo, bar);
+static inline-class-member method E17|constructor#(core::Object foo, {core::num? bar = #C2, core::String? baz = #C2}) → self::E17 /* = core::Object */ {
+  lowered final self::E17 /* = core::Object */ #this = baz;
+  return #this;
+}
+static inline-class-member method E17|constructor#_#new#tearOff(core::Object foo, {core::num? bar, core::String? baz}) → self::E17 /* = core::Object */
+  return self::E17|constructor#(foo, bar: bar, baz: baz);
+static inline-class-member method E18|constructor#(core::double foo, {required core::int bar = #C2}) → self::E18 /* = core::double */ {
+  lowered final self::E18 /* = core::double */ #this = bar;
+  return #this;
+}
+static inline-class-member method E18|constructor#_#new#tearOff(core::double foo, {required core::int bar}) → self::E18 /* = core::double */
+  return self::E18|constructor#(foo, bar: bar);
 
 constants  {
   #C1 = false
+  #C2 = null
 }