[cfe] Allow extension types implement Object

This is a prerequisite to the implementation of
dart-lang/language#3434

Closes #53840
Part of #49731

Change-Id: Ib3bb5961cd8c4919cbc8c8ba37ac4d76fb72a3de
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/333000
Commit-Queue: Chloe Stefantsova <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: chloestefantsova

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

@@ -201,8 +201,7 @@ class SourceExtensionTypeDeclarationBuilder
             }
           } else {
             Class cls = interface.classNode;
-            if (LibraryBuilder.isObject(cls, coreLibrary) ||
-                LibraryBuilder.isFunction(cls, coreLibrary) ||
+            if (LibraryBuilder.isFunction(cls, coreLibrary) ||
                 LibraryBuilder.isRecord(cls, coreLibrary)) {
               if (aliasBuilder != null) {
                 errorMessage =

pkg/front_end/testcases/extension_types/implement_all.dart

@@ -34,7 +34,7 @@ extension type ET_Void(Null it) implements void /* Error */ {}
 
 extension type ET_Never(Never it) implements Never /* Error */ {}
 
-extension type ET_Object(Object it) implements Object /* Error */ {}
+extension type ET_Object(Object it) implements Object /* Ok */ {}
 
 extension type ET_Record(Record it) implements Record /* Error */ {}
 

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -140,7 +136,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -140,7 +136,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -140,7 +136,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -140,7 +136,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -138,7 +134,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

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

@@ -35,10 +35,6 @@ library;
 // extension type ET_Never(Never it) implements Never /* Error */ {}
 //                               ^^
 //
-// pkg/front_end/testcases/extension_types/implement_all.dart:37:48: Error: The type 'Object' can't be implemented by an extension type.
-// extension type ET_Object(Object it) implements Object /* Error */ {}
-//                                                ^
-//
 // pkg/front_end/testcases/extension_types/implement_all.dart:39:48: Error: The type 'Record' can't be implemented by an extension type.
 // extension type ET_Record(Record it) implements Record /* Error */ {}
 //                                                ^
@@ -140,7 +136,7 @@ extension type ET_Never(invalid-type it) {
   constructor • = self::ET_Never|constructor#;
   constructor tearoff • = self::ET_Never|constructor#_#new#tearOff;
 }
-extension type ET_Object(core::Object it) {
+extension type ET_Object(core::Object it) implements core::Object {
   abstract inline-class-member representation-field get it() → core::Object;
   constructor • = self::ET_Object|constructor#;
   constructor tearoff • = self::ET_Object|constructor#_#new#tearOff;

pkg/front_end/testcases/extension_types/issue53840.dart

@@ -0,0 +1,35 @@
+// 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.
+
+import 'dart:async';
+
+class A {}
+
+mixin M on A {}
+
+enum En {
+  element;
+}
+
+extension type E1(num it) implements Object {} // Ok.
+extension type E2(E1 it) implements Object {} // Ok.
+extension type E3(String? it) implements Object {} // Error.
+extension type E4(E3 it) implements Object {} // Error.
+
+extension type E5(Null it) implements void {} // Error.
+extension type E6(Null it) implements dynamic {} // Error.
+extension type E7(Null it) implements double? {} // Error.
+extension type E8(bool it) implements FutureOr<bool> {} // Error.
+extension type E9<X>(X it) implements FutureOr<X> {} // Error.
+extension type E10(void Function(int) it) implements Function {} // Error.
+extension type E11(String Function() it) implements String Function() {} // Error.
+extension type E12((int, Object?) it) implements Record {} // Error.
+extension type E13((Null, num) it) implements (Null, num) {} // Error.
+extension type E14(Null it) implements Null {} // Error.
+extension type E15<X>(X it) implements Never {} // Error.
+extension type E16(Null it) implements Never {} // Error.
+
+extension type E17(A a) implements A {} // Ok.
+extension type E18(M m) implements M {} // Ok.
+extension type E19(En en) implements En {} // Ok.