[js] Add JSStringImpl box for JSString.

Change-Id: I63a2ecdf3fd2331f91632ae5b2cc51813cd44c66
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/307961
Commit-Queue: Joshua Litt <[email protected]>
Reviewed-by: Srujan Gaddam <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>

Author: joshualitt

pkg/dart2wasm/lib/class_info.dart

@@ -242,6 +242,10 @@ class ClassInfoCollector {
       cls: cls
   };
 
+  late final Set<Class> _neverMasquerades = {
+    translator.jsStringImplClass,
+  };
+
   /// Wasm field type for fields with type [_Type]. Fields of this type are
   /// added to classes for type parameters.
   ///
@@ -350,6 +354,9 @@ class ClassInfoCollector {
     translator.classForHeapType.putIfAbsent(info.struct, () => info!);
 
     ClassInfo? computeMasquerade() {
+      if (_neverMasquerades.contains(cls)) {
+        return null;
+      }
       if (info!.superInfo?.masquerade != null) {
         return info.superInfo!.masquerade;
       }

pkg/dart2wasm/lib/code_generator.dart

@@ -2585,8 +2585,10 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       return visitStringLiteral(expr, expectedType);
     }
 
-    makeListFromExpressions(node.expressions,
-        InterfaceType(translator.stringBaseClass, Nullability.nonNullable));
+    makeListFromExpressions(
+        node.expressions,
+        InterfaceType(
+            translator.coreTypes.stringClass, Nullability.nonNullable));
     return call(translator.stringInterpolate.reference);
   }
 

pkg/dart2wasm/lib/kernel_nodes.dart

@@ -12,6 +12,7 @@ mixin KernelNodes {
 
   late final LibraryIndex index = LibraryIndex(component, [
     "dart:_internal",
+    "dart:_js_types",
     "dart:async",
     "dart:collection",
     "dart:core",
@@ -23,6 +24,10 @@ mixin KernelNodes {
   // dart:_internal classes
   late final Class symbolClass = index.getClass("dart:_internal", "Symbol");
 
+  // dart:_js_types classes
+  late final Class jsStringImplClass =
+      index.getClass("dart:_js_types", "JSStringImpl");
+
   // dart:collection classes
   late final Class hashFieldBaseClass =
       index.getClass("dart:collection", "_HashFieldBase");

pkg/dart2wasm/lib/target.dart

@@ -71,6 +71,7 @@ class WasmTarget extends Target {
         'dart:_internal',
         'dart:_http',
         'dart:_js_helper',
+        'dart:_js_types',
         'dart:typed_data',
         'dart:nativewrappers',
         'dart:io',
@@ -85,13 +86,22 @@ class WasmTarget extends Target {
   @override
   List<String> get extraIndexedLibraries => const <String>[
         'dart:_js_helper',
+        'dart:_js_types',
         'dart:collection',
         'dart:typed_data',
         'dart:js_interop',
         'dart:js_util',
         'dart:_wasm',
       ];
 
+  @override
+  bool mayDefineRestrictedType(Uri uri) =>
+      uri.isScheme('dart') &&
+      (uri.path == 'core' ||
+          uri.path == 'typed_data' ||
+          uri.path == '_js_types');
+
+  @override
   bool allowPlatformPrivateLibraryAccess(Uri importer, Uri imported) =>
       super.allowPlatformPrivateLibraryAccess(importer, imported) ||
       importer.path.contains('tests/web/wasm') ||

sdk/lib/_internal/wasm/lib/core_patch.dart

@@ -32,6 +32,8 @@ import "dart:_internal" as _internal show Symbol;
 
 import 'dart:_js_helper' show JS, JSSyntaxRegExp, quoteStringForRegExp;
 
+import 'dart:_js_types' show JSStringImpl;
+
 import "dart:collection"
     show
         HashMap,
@@ -50,6 +52,8 @@ import 'dart:math' show Random;
 
 import "dart:typed_data" show Uint8List, Uint16List;
 
+import 'dart:_string_helper';
+
 import 'dart:_wasm';
 
 part "bool.dart";

sdk/lib/_internal/wasm/lib/js_helper.dart

@@ -7,8 +7,8 @@ library dart._js_helper;
 
 import 'dart:_internal';
 import 'dart:_js_annotations' as js;
+import 'dart:_js_types' as js_types;
 import 'dart:_wasm';
-import 'dart:collection';
 import 'dart:js_interop';
 import 'dart:typed_data';
 
@@ -316,7 +316,7 @@ WasmExternRef? callMethodVarArgsRaw(
     JS<WasmExternRef?>("(o, m, a) => o[m].apply(o, a)", o, method, args);
 
 String stringify(WasmExternRef? object) =>
-    JS<String>("o => stringToDartString(String(o))", object);
+    js_types.JSStringImpl(JS<WasmExternRef?>("o => String(o)", object));
 
 void promiseThen(WasmExternRef? promise, WasmExternRef? successFunc,
         WasmExternRef? failureFunc) =>
@@ -346,6 +346,8 @@ WasmExternRef? jsifyRaw(Object? object) {
     assert(functionToJSWrapper.containsKey(object),
         'Must call `allowInterop` on functions before they flow to JS');
     return functionToJSWrapper[object]!.toExternRef;
+  } else if (object is js_types.JSStringImpl) {
+    return object.toExternRef;
   } else if (object is JSValue) {
     return object.toExternRef;
   } else if (object is String) {
@@ -391,7 +393,7 @@ Object? dartifyRaw(WasmExternRef? ref) {
   } else if (isJSNumber(ref)) {
     return toDartNumber(ref);
   } else if (isJSString(ref)) {
-    return jsStringToDartString(ref);
+    return js_types.JSStringImpl.box(ref);
   } else if (isJSInt8Array(ref)) {
     return toDartInt8List(ref);
   } else if (isJSUint8Array(ref)) {

sdk/lib/_internal/wasm/lib/js_interop_patch.dart

@@ -5,6 +5,7 @@
 import 'dart:_internal' show patch;
 import 'dart:_js_helper' hide JS;
 import 'dart:_js_helper' as js_helper;
+import 'dart:_js_types' as js_types;
 import 'dart:_wasm';
 import 'dart:async' show Completer;
 import 'dart:js_interop';
@@ -330,11 +331,20 @@ extension BoolToJSBoolean on bool {
 @patch
 extension JSStringToString on JSString {
   @patch
-  String get toDart => jsStringToDartString(toExternRef);
+  String get toDart => js_types.JSStringImpl(toExternRef);
 }
 
 @patch
 extension StringToJSString on String {
   @patch
-  JSString get toJS => _box<JSString>(jsStringFromDartString(this));
+  JSString get toJS {
+    final t = this;
+    WasmExternRef? ref;
+    if (t is js_types.JSStringImpl) {
+      ref = t.toExternRef;
+    } else {
+      ref = jsStringFromDartString(this);
+    }
+    return _box<JSString>(ref);
+  }
 }