[dart2wasm] Avoid implicitly internalizing WasmExternRef.

CoreLibraryReviewExempt: Wasm only changes.
Change-Id: I0e0a6cddffa1c7f2d7c74779f480dd10bf509c1c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/279268
Commit-Queue: Joshua Litt <joshualitt@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>

pkg/dart2wasm/lib/intrinsics.dart

@@ -1051,6 +1051,10 @@ class Intrinsifier {
           codeGen.wrap(value, w.RefType.extern(nullable: true));
           b.extern_internalize();
           return w.RefType.any(nullable: true);
+        case "_wasmExternRefIsNull":
+          codeGen.wrap(value, w.RefType.extern(nullable: true));
+          b.ref_is_null();
+          return w.NumType.i32;
       }
     }
 
@@ -1746,6 +1750,12 @@ class Intrinsifier {
       return true;
     }
 
+    if (member.enclosingClass == translator.wasmExternRefClass &&
+        name == "nullRef") {
+      b.ref_null(w.HeapType.noextern);
+      return true;
+    }
+
     return false;
   }
 }

pkg/dart2wasm/lib/js_runtime_blob.dart

@@ -93,7 +93,7 @@ const jsRuntimeBlobPart2 = r'''
 
     // Initialize async bridge.
     asyncBridge = new WebAssembly.Function(
-        {parameters: ['externref', 'externref'], results: ['externref']},
+        {parameters: ['anyref', 'anyref'], results: ['externref']},
         dartInstance.exports.$asyncBridge,
         {promising: 'first'});
     return dartInstance;

pkg/dart2wasm/lib/js_runtime_generator.dart

@@ -120,6 +120,7 @@ class _JSLowerer extends Transformer {
   final Procedure _jsifyRawTarget;
   final Procedure _isDartFunctionWrappedTarget;
   final Procedure _wrapDartFunctionTarget;
+  final Procedure _jsObjectFromDartObjectTarget;
   final Procedure _jsValueBoxTarget;
   final Procedure _jsValueUnboxTarget;
   final Procedure _allowInteropTarget;
@@ -151,6 +152,8 @@ class _JSLowerer extends Transformer {
             .getTopLevelProcedure('dart:_js_helper', '_isDartFunctionWrapped'),
         _wrapDartFunctionTarget = _coreTypes.index
             .getTopLevelProcedure('dart:_js_helper', '_wrapDartFunction'),
+        _jsObjectFromDartObjectTarget = _coreTypes.index
+            .getTopLevelProcedure('dart:_js_helper', 'jsObjectFromDartObject'),
         _jsValueConstructor = _coreTypes.index
             .getClass('dart:_js_helper', 'JSValue')
             .constructors
@@ -606,7 +609,11 @@ class _JSLowerer extends Transformer {
                 Arguments([
                   VariableGet(v),
                   StaticInvocation(
-                      jsWrapperFunction, Arguments([VariableGet(v)])),
+                      jsWrapperFunction,
+                      Arguments([
+                        StaticInvocation(_jsObjectFromDartObjectTarget,
+                            Arguments([VariableGet(v)]))
+                      ])),
                 ], types: [
                   type
                 ])),
@@ -625,7 +632,12 @@ class _JSLowerer extends Transformer {
     return ConstructorInvocation(
         _jsValueConstructor,
         Arguments([
-          StaticInvocation(jsWrapperFunction, Arguments([argument]))
+          StaticInvocation(
+              jsWrapperFunction,
+              Arguments([
+                StaticInvocation(
+                    _jsObjectFromDartObjectTarget, Arguments([argument]))
+              ]))
         ]));
   }
 

pkg/dart2wasm/lib/translator.dart

@@ -372,7 +372,7 @@ class Translator with KernelNodes {
 
   w.DefinedFunction generateGetMain(Procedure mainFunction) {
     w.DefinedFunction getMain = m.addFunction(
-        m.addFunctionType(const [], const [w.RefType.extern(nullable: true)]));
+        m.addFunctionType(const [], const [w.RefType.any(nullable: true)]));
     constants.instantiateConstant(getMain, getMain.body,
         StaticTearOffConstant(mainFunction), getMain.type.outputs.single);
     getMain.body.end();
@@ -568,17 +568,22 @@ class Translator with KernelNodes {
   }
 
   /// Translate a Dart type as it should appear on parameters and returns of
-  /// imported and exported functions. The only reference types allowed here
-  /// for JS interop are `externref` and `funcref`.
-  ///
+  /// imported and exported functions. All wasm types are allowed on the interop
+  /// boundary, but in order to be compatible with the `--closed-world` mode of
+  /// Binaryen, we coerce all reference types to abstract reference types
+  /// (`anyref`, `funcref` or `externref`).
   /// This function can be called before the class info is built.
   w.ValueType translateExternalType(DartType type) {
+    bool isPotentiallyNullable = type.isPotentiallyNullable;
     if (type is InterfaceType) {
       Class cls = type.classNode;
       if (cls == wasmFuncRefClass || cls == wasmFunctionClass) {
-        return w.RefType.func(nullable: true);
+        return w.RefType.func(nullable: isPotentiallyNullable);
       }
-      if (!type.isPotentiallyNullable) {
+      if (cls == wasmExternRefClass) {
+        return w.RefType.extern(nullable: isPotentiallyNullable);
+      }
+      if (!isPotentiallyNullable) {
         w.StorageType? builtin = builtinTypes[cls];
         if (builtin != null && builtin.isPrimitive) {
           return builtin as w.ValueType;
@@ -588,7 +593,9 @@ class Translator with KernelNodes {
         }
       }
     }
-    return w.RefType.extern(nullable: true);
+    // TODO(joshualitt): We'd like to use the potential nullability here too,
+    // but unfortunately this seems to break things.
+    return w.RefType.any(nullable: true);
   }
 
   w.DefinedGlobal makeFunctionRef(w.BaseFunction f) {
@@ -773,16 +780,6 @@ class Translator with KernelNodes {
       }
     }
 
-    bool fromIsExtern = from.isSubtypeOf(w.RefType.extern(nullable: true));
-    bool toIsExtern = to.isSubtypeOf(w.RefType.extern(nullable: true));
-    if (fromIsExtern && !toIsExtern) {
-      b.extern_internalize();
-      from = w.RefType.any(nullable: from.nullable);
-    }
-    if (!fromIsExtern && toIsExtern) {
-      to = w.RefType.any(nullable: to.nullable);
-    }
-
     if (!from.isSubtypeOf(to)) {
       if (from is w.RefType && to is w.RefType) {
         if (from.withNullability(false).isSubtypeOf(to)) {
@@ -813,10 +810,6 @@ class Translator with KernelNodes {
         throw "Conversion between non-reference types";
       }
     }
-
-    if (!fromIsExtern && toIsExtern) {
-      b.extern_externalize();
-    }
   }
 
   w.FunctionType signatureFor(Reference target) {

pkg/wasm_builder/lib/src/types.dart

@@ -147,7 +147,7 @@ class RefType extends ValueType {
   const RefType.common({required bool nullable})
       : this._(HeapType.common, nullable);
 
-  /// A (possibly nullable) reference to the `any` heap type.
+  /// A (possibly nullable) reference to the `extern` heap type.
   const RefType.extern({required bool nullable})
       : this._(HeapType.extern, nullable);
 

sdk/lib/_internal/wasm/lib/async_patch.dart

@@ -70,7 +70,7 @@ void _callAsyncBridge(WasmStructRef args, Completer<Object?> completer) =>
         "(args, completer) => asyncBridge(args, completer)", args, completer);
 
 @pragma("wasm:export", "\$asyncBridge")
-WasmAnyRef? _asyncBridge(
+WasmExternRef? _asyncBridge(
     WasmExternRef? stack, WasmStructRef args, Completer<Object?> completer) {
   try {
     Object? result = _asyncBridge2(args, stack);
@@ -112,7 +112,7 @@ Object? _awaitHelper(Object? operand, WasmExternRef? stack) {
 
 Object? _futurePromise(WasmExternRef? stack, Future<Object?> future) =>
     JS<Object?>("""new WebAssembly.Function(
-            {parameters: ['externref', 'externref'], results: ['externref']},
+            {parameters: ['externref', 'anyref'], results: ['anyref']},
             function(future) {
                 return new Promise(function (resolve, reject) {
                     dartInstance.exports.\$awaitCallback(future, resolve);

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

@@ -80,7 +80,7 @@ extension ObjectToJS on Object {
 }
 
 // For now both `null` and `undefined` in JS map to `null` in Dart.
-bool isDartNull(WasmExternRef? ref) => ref == null || isJSUndefined(ref);
+bool isDartNull(WasmExternRef? ref) => ref.isNull || isJSUndefined(ref);
 
 // Extensions for [JSArray] and [JSObject].
 // TODO(joshualitt): Rewrite using JS types.
@@ -328,7 +328,7 @@ WasmExternRef? jsArrayBufferFromDartByteBuffer(ByteBuffer buffer) {
 
 WasmExternRef? jsifyRaw(Object? object) {
   if (object == null) {
-    return null;
+    return WasmExternRef.nullRef;
   } else if (object is bool) {
     return toJSBoolean(object);
   } else if (object is Function) {
@@ -370,10 +370,10 @@ WasmExternRef? jsifyRaw(Object? object) {
   }
 }
 
-bool isWasmGCStruct(WasmExternRef ref) => ref.internalize().isObject;
+bool isWasmGCStruct(WasmExternRef? ref) => ref.internalize()?.isObject ?? false;
 
 Object? dartifyRaw(WasmExternRef? ref) {
-  if (ref == null) {
+  if (ref.isNull) {
     return null;
   } else if (isJSUndefined(ref)) {
     // TODO(joshualitt): Introduce a `JSUndefined` type.
@@ -413,7 +413,7 @@ Object? dartifyRaw(WasmExternRef? ref) {
   } else if (isWasmGCStruct(ref)) {
     return jsObjectToDartObject(ref);
   } else {
-    return JSValue(ref);
+    return JSValue.box(ref);
   }
 }
 

sdk/lib/wasm/wasm_types.dart

@@ -46,10 +46,15 @@ extension ExternalizeNullable on WasmAnyRef? {
 /// The Wasm `externref` type.
 @pragma("wasm:entry-point")
 class WasmExternRef extends _WasmBase {
+  // To avoid conflating the null externref with Dart's null, we provide a
+  // special getter for the null externref.
+  external static WasmExternRef? get nullRef;
+
   WasmAnyRef internalize() => _internalizeNonNullable(this);
 }
 
 extension InternalizeNullable on WasmExternRef? {
+  bool get isNull => _wasmExternRefIsNull(this);
   WasmAnyRef? internalize() => _internalizeNullable(this);
 }
 
@@ -57,6 +62,7 @@ external WasmExternRef _externalizeNonNullable(WasmAnyRef ref);
 external WasmExternRef? _externalizeNullable(WasmAnyRef? ref);
 external WasmAnyRef _internalizeNonNullable(WasmExternRef ref);
 external WasmAnyRef? _internalizeNullable(WasmExternRef? ref);
+external bool _wasmExternRefIsNull(WasmExternRef? ref);
 
 /// The Wasm `funcref` type.
 @pragma("wasm:entry-point")

tests/web/wasm/wasm_types_test.dart

@@ -32,7 +32,7 @@ test() {
   Object dartObject1 = "1";
   Object dartObject2 = true;
   Object dartObject3 = Object();
-  WasmAnyRef jsObject1 = createObject(null)!.internalize();
+  WasmAnyRef jsObject1 = createObject(WasmExternRef.nullRef)!.internalize();
 
   // A JS object is not a Dart object.
   Expect.isFalse(jsObject1.isObject);
@@ -86,7 +86,8 @@ test() {
 
   // Create a typed function reference from an import and call it.
   var createObjectFun = WasmFunction.fromFunction(createObject);
-  WasmAnyRef jsObject3 = createObjectFun.call(null).internalize()!;
+  WasmAnyRef jsObject3 =
+      createObjectFun.call(WasmExternRef.nullRef).internalize()!;
   Expect.isFalse(jsObject3.isObject);
 
   Expect.equals(3, funCount);