Reland "Add more interface and final modifiers to dart:core."

This is a reland of commit 4f8333e

Blocked on Flutter patch: flutter/engine#40175

Original change's description:
> Add more `interface` and `final` modifiers to `dart:core`.
>
> Make intent explicit for classes which are intended as interfaces,
> or which are not intended to be subclassed.
>
> Mainly classes which are pure interfaces are marked as such,
> and platform-specific classes not intended for subclassing
> are made `final`.
>
> The `final` classes includes `BigInt`, which is written to assume
> that arguments inherit its private members
> (it runs `_ensureSystemBigInt` on arguments).
>
> It also includes the `Expando`, `WeakReference` and `Finalizer` classes,
> which are just intended as stand-alone implementation classes for accessing
> platform-specific functionality.
>
> Change-Id: Ib770c265edff127a289a67fe72d15b9ff0499407
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287180
> Reviewed-by: Stephen Adams <sra@google.com>
> Commit-Queue: Lasse Nielsen <lrn@google.com>
> Reviewed-by: Aske Simon Christensen <askesc@google.com>
> Reviewed-by: Nate Bosch <nbosch@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>

CoreLibraryReviewExempt: Accepted in original CL.
Change-Id: Id713edede4228801bb097a64734be4f2187f51a9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/288206
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

Author: lrhn

CHANGELOG.md

@@ -62,13 +62,36 @@
     a shared supertype locking them to a specific name for moving backwards.
 
 - **Breaking change when migrating code to Dart 3.0**:
-  Some changes to platform libraries only affect code when it is migrated
+  Some changes to platform libraries only affect code when that code is migrated
   to language version 3.0.
-  - The `Function` type can no longer be implemented.
+  - The `Function` type can no longer be implemented, extended or mixed in.
     Since Dart 2.0 writing `implements Function` has been allowed
     for backwards compatibility, but it has not had any effect.
-    In Dart 3.0, the `Function` type is `final` and cannot be implemented
-    by class-modifier aware code.
+    In Dart 3.0, the `Function` type is `final` and cannot be subtyped,
+    preventing code from mistakenly assuming it works.
+  - The following declarations can only be implemented, not extended:
+    * `Comparable`
+    * `Exception`
+    * `Iterator`
+    * `Pattern`
+    * `Match`
+    * `RegExp`
+    * `RegExpMatch`
+    * `StackTrace`
+    * `StringSink`
+    None of these declarations contained any implementation to inherit,
+    and are marked as `interface` to signify that they are only intended
+    as interfaces.
+  - The following declarations can no longer be implemented or extended:
+    * `MapEntry`
+    * `OutOfMemoryError`
+    * `StackOverflowError`
+    * `Expando`
+    * `WeakReference`
+    * `Finalizer`
+    The `MapEntry` value class is restricted to enable later optimizations.
+    The remaining classes are tightly coupled to the platform and not
+    intended to be subclassed or implemented.
 
 [#49529]: https://github.com/dart-lang/sdk/issues/49529
 [`List.filled`]: https://api.dart.dev/stable/2.18.6/dart-core/List/List.filled.html

pkg/_fe_analyzer_shared/lib/src/util/link_implementation.dart

@@ -31,7 +31,7 @@ class LinkIterator<T> implements Iterator<T> {
 
 typedef T Transformation<S, T>(S input);
 
-class MappedLinkIterator<S, T> extends Iterator<T> {
+class MappedLinkIterator<S, T> implements Iterator<T> {
   Transformation<S, T> _transformation;
   Link<S> _link;
   T? _current;

pkg/compiler/lib/src/universe/class_set.dart

@@ -967,7 +967,7 @@ class SubtypesIterable extends IterableBase<ClassEntity> {
 }
 
 /// Iterator for the subtypes in a [ClassSet].
-class SubtypesIterator extends Iterator<ClassEntity> {
+class SubtypesIterator implements Iterator<ClassEntity> {
   final SubtypesIterable iterable;
   Iterator<ClassEntity>? elements;
   Iterator<ClassHierarchyNode>? hierarchyNodes;

pkg/compiler/test/inference/powerset_bits3_test.dart

@@ -13,19 +13,19 @@ import '../helpers/element_lookup.dart';
 import 'package:compiler/src/util/memory_compiler.dart';
 
 const String CODE = """
-class A extends Comparable {
+class A implements Comparable {
   int compareTo(x) { return 0; }
 }
-class B extends Comparable {
+class B implements Comparable {
   int compareTo(x) { return 0; }
 }
-class C extends Comparable {
+class C implements Comparable {
   int compareTo(x) { return 0; }
 }
-class D extends Comparable {
+class D implements Comparable {
   int compareTo(x) { return 0; }
 }
-class E extends Comparable {
+class E implements Comparable {
   int compareTo(x) { return 0; }
 }
 

pkg/front_end/testcases/incremental/issue_32366.yaml

@@ -8,7 +8,7 @@ worlds:
   - entry: main.dart
     sources:
       main.dart: |
-        abstract class AIterator extends Iterator {
+        abstract class AIterator implements Iterator {
         }
         class Foo {
           final a;
@@ -25,7 +25,7 @@ worlds:
     errors: true
     sources:
       main.dart: |
-        abstract class BIterator extends Iterator {
+        abstract class BIterator implements Iterator {
         }
         class Foo {
           final a kjsdf ksjdf ;

pkg/front_end/testcases/incremental/issue_32366.yaml.world.1.expect

@@ -1,9 +1,9 @@
 main = main::main;
 library from "org-dartlang-test:///main.dart" as main {
 
-  abstract class AIterator extends dart.core::Iterator<dynamic> {
+  abstract class AIterator extends dart.core::Object implements dart.core::Iterator<dynamic> {
     synthetic constructor •() → main::AIterator
-      : super dart.core::Iterator::•()
+      : super dart.core::Object::•()
       ;
   }
   class Foo extends dart.core::Object {

pkg/front_end/testcases/incremental/issue_32366.yaml.world.2.expect

@@ -30,9 +30,9 @@ library from "org-dartlang-test:///main.dart" as main {
 //            ^
 //
 
-  abstract class BIterator extends dart.core::Iterator<dynamic> {
+  abstract class BIterator extends dart.core::Object implements dart.core::Iterator<dynamic> {
     synthetic constructor •() → main::BIterator
-      : super dart.core::Iterator::•()
+      : super dart.core::Object::•()
       ;
   }
   class Foo extends dart.core::Object {

pkg/front_end/testcases/inference/try_catch_promotion.dart

@@ -11,7 +11,7 @@ class C {}
 
 class D extends C {}
 
-class E extends StackTrace {}
+class E implements StackTrace {}
 
 void test(void f()) {
   try {

pkg/front_end/testcases/inference/try_catch_promotion.dart.strong.expect

@@ -29,19 +29,19 @@ class D extends self::C {
     : super self::C::•()
     ;
 }
-class E extends core::StackTrace {
+class E extends core::Object implements core::StackTrace {
   synthetic constructor •() → self::E*
-    : super core::StackTrace::•()
+    : super core::Object::•()
     ;
   abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic; -> core::Object::noSuchMethod
-  abstract member-signature method toString() → core::String*; -> core::StackTrace::toString
   abstract member-signature get _identityHashCode() → core::int*; -> core::Object::_identityHashCode
   abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → core::bool*; -> core::Object::_instanceOf
   abstract member-signature method _simpleInstanceOf(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOf
   abstract member-signature method _simpleInstanceOfTrue(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOfTrue
   abstract member-signature method _simpleInstanceOfFalse(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOfFalse
   abstract member-signature operator ==(dynamic other) → core::bool*; -> core::Object::==
   abstract member-signature get hashCode() → core::int*; -> core::Object::hashCode
+  abstract member-signature method toString() → core::String*; -> core::Object::toString
   abstract member-signature get runtimeType() → core::Type*; -> core::Object::runtimeType
 }
 static method test(() →* void f) → void {

pkg/front_end/testcases/inference/try_catch_promotion.dart.strong.transformed.expect

@@ -29,19 +29,19 @@ class D extends self::C {
     : super self::C::•()
     ;
 }
-class E extends core::StackTrace {
+class E extends core::Object implements core::StackTrace {
   synthetic constructor •() → self::E*
-    : super core::StackTrace::•()
+    : super core::Object::•()
     ;
   abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic; -> core::Object::noSuchMethod
-  abstract member-signature method toString() → core::String*; -> core::StackTrace::toString
   abstract member-signature get _identityHashCode() → core::int*; -> core::Object::_identityHashCode
   abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → core::bool*; -> core::Object::_instanceOf
   abstract member-signature method _simpleInstanceOf(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOf
   abstract member-signature method _simpleInstanceOfTrue(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOfTrue
   abstract member-signature method _simpleInstanceOfFalse(dynamic type) → core::bool*; -> core::Object::_simpleInstanceOfFalse
   abstract member-signature operator ==(dynamic other) → core::bool*; -> core::Object::==
   abstract member-signature get hashCode() → core::int*; -> core::Object::hashCode
+  abstract member-signature method toString() → core::String*; -> core::Object::toString
   abstract member-signature get runtimeType() → core::Type*; -> core::Object::runtimeType
 }
 static method test(() →* void f) → void {