[tfa,aot,dart2wasm] Retain libraries which only have extensions and extension types

Previously, TFA-based tree shaker did not retain libraries if they have
extensions and extension types which are still used.
As a result, kernel files were incomplete and certain tools, such as
Flutter const finder failed to read kernel files after tree shaking.

This change fixes tree shaker to retain libraries when they have used
extensions and extension types.

TEST=pkg/vm/testcases/transformations/type_flow/transformer/regress_flutter160137.dart
Fixes flutter/flutter#160137

Change-Id: Iac6f3a13323d053dfab2230367dcafa2550484db
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/401481
Commit-Queue: Slava Egorov <[email protected]>
Auto-Submit: Alexander Markov <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>

Author: alexmarkov

pkg/vm/lib/transformations/type_flow/transformer.dart

@@ -998,6 +998,7 @@ class TreeShaker {
 
   void addUsedExtension(Extension node) {
     if (_usedExtensions.add(node)) {
+      _usedLibraries.add(node.enclosingLibrary);
       node.annotations = const <Expression>[];
       _pass1.transformTypeParameterList(node.typeParameters, node);
       node.onType.accept(typeVisitor);
@@ -1006,6 +1007,7 @@ class TreeShaker {
 
   void addUsedExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
     if (_usedExtensionTypeDeclarations.add(node)) {
+      _usedLibraries.add(node.enclosingLibrary);
       node.annotations = const <Expression>[];
       _pass1.transformTypeParameterList(node.typeParameters, node);
       node.declaredRepresentationType.accept(typeVisitor);

pkg/vm/testcases/transformations/type_flow/transformer/regress_flutter160137.dart

@@ -0,0 +1,30 @@
+// Copyright (c) 2024, 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.
+
+// Regression test for https://github.com/flutter/flutter/issues/160137.
+// Verifies that TFA correctly retains library if it only has an extension
+// type declaration.
+
+import 'regress_flutter160137.lib.dart';
+
+class Class {
+  void procedure() {
+    Helper helper = new Helper();
+    if (helper.instance != null) {
+      print("hello");
+    }
+  }
+}
+
+class Helper {
+  Helper();
+  MyExtensionType? get instance {
+    return null;
+  }
+}
+
+void main() {
+  Class c = new Class();
+  c.procedure();
+}

pkg/vm/testcases/transformations/type_flow/transformer/regress_flutter160137.dart.expect

@@ -0,0 +1,43 @@
+library #lib;
+import self as self;
+import "dart:core" as core;
+
+import "file:pkg/vm/testcases/transformations/type_flow/transformer/regress_flutter160137.lib.dart";
+
+class Class extends core::Object {
+  synthetic constructor •() → self::Class
+    : super core::Object::•()
+    ;
+
+  [@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+  [@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasTearOffUses:false,methodOrSetterSelectorId:1,getterSelectorId:2]
+  method procedure() → void {
+    self::Helper helper = new self::Helper::•();
+    {
+      [@vm.direct-call.metadata=#lib::Helper.instance] [@vm.inferred-type.metadata=dart.core::Null? (value: null)] helper.{self::Helper::instance}{#lib1::MyExtensionType? /* erasure=core::int? */};
+    }
+  }
+}
+class Helper extends core::Object {
+  constructor •() → self::Helper
+    : super core::Object::•()
+    ;
+
+  [@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+  [@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasNonThisUses:false,hasTearOffUses:false,getterSelectorId:3]
+  get instance() → #lib1::MyExtensionType? /* erasure=core::int? */ {
+    return null;
+  }
+}
+
+[@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+static method main() → void {
+  self::Class c = new self::Class::•();
+  [@vm.direct-call.metadata=#lib::Class.procedure] [@vm.inferred-type.metadata=!? (skip check)] c.{self::Class::procedure}(){() → void};
+}
+library regress_flutter160137.lib.dart;
+import self as self;
+import "dart:core" as core;
+
+extension type MyExtensionType(core::int foo) {
+}

pkg/vm/testcases/transformations/type_flow/transformer/regress_flutter160137.lib.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2024, 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 const MyExtensionType._(int foo) {}