[dart2wasm] Fix JS callback wrappers invoked in deferred modules.

The generated callback wrappers were referring to exported functions via
'dartInstance.exports' which is always the main module. But in order to
avoid bloating the main module we put some of these JS exports into
submodules.

So the wrapper must be fetched from the correct module that defines the
wrapped function. In order to facilitate this we give each module a
self-reference that it can then pass up to the JS wrapper as an
externref.

Change-Id: Id2514de2c13d38a0cee1f6c935e45a9ef826f805
Fixes: #62094
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/464820
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

pkg/dart2wasm/lib/intrinsics.dart

@@ -401,6 +401,10 @@ class Intrinsifier {
       op == '_le_u' ||
       op == '_lt_u';
 
+  final Map<w.ModuleBuilder, w.ImportedFunction> _thisModuleGlobals = {};
+  late final w.FunctionType _thisModuleType = translator.typesBuilder
+      .defineFunction(const [], const [w.RefType.extern(nullable: false)]);
+
   Intrinsifier(this.codeGen);
 
   /// Generate inline code for an [InstanceGet] if the member is an inlined
@@ -835,6 +839,18 @@ class Intrinsifier {
       }
     }
 
+    if (target.enclosingLibrary.name == 'dart._js_helper') {
+      if (target.name.text == 'thisModule') {
+        final resultType = w.RefType.extern(nullable: false);
+        final func = _thisModuleGlobals.putIfAbsent(b.moduleBuilder, () {
+          return b.moduleBuilder.functions
+              .import("\$moduleHelpers", "this", _thisModuleType);
+        });
+        b.call(func);
+        return resultType;
+      }
+    }
+
     return null;
   }
 

pkg/dart2wasm/lib/js/callback_specializer.dart

@@ -234,10 +234,10 @@ class CallbackSpecializer {
     String argumentsLength =
         captureThis ? 'arguments.length + 1' : 'arguments.length';
     String dartArguments = 'f,$argumentsLength';
-    String jsMethodParams = 'f';
+    String jsMethodParams = '(module,f)';
     if (needsCastClosure) {
       dartArguments = '$dartArguments,castClosure';
-      jsMethodParams = '($jsMethodParams,castClosure)';
+      jsMethodParams = '(module,f,castClosure)';
     }
     if (captureThis) dartArguments = '$dartArguments,this';
     if (jsParameters.isNotEmpty) {
@@ -251,6 +251,9 @@ class CallbackSpecializer {
         'dart2wasm.$jsMethodName',
         FunctionNode(null,
             positionalParameters: [
+              VariableDeclaration('thisModule',
+                  type: _util.nonNullableWasmExternRefType,
+                  isSynthesized: true),
               VariableDeclaration('dartFunction',
                   type: _util.nonNullableWasmExternRefType,
                   isSynthesized: true),
@@ -271,7 +274,7 @@ class CallbackSpecializer {
         dartProcedure,
         jsMethodName,
         "$jsMethodParams => finalizeWrapper(f, function($jsWrapperParams) {"
-        " return dartInstance.exports.${functionTrampoline.name.text}($dartArguments) "
+        " return module.exports.${functionTrampoline.name.text}($dartArguments) "
         "})");
 
     return (dartProcedure, functionTrampoline);
@@ -356,6 +359,7 @@ class CallbackSpecializer {
         StaticInvocation(
             jsWrapperFunction,
             Arguments([
+              StaticGet(_util.thisModuleGetter),
               StaticInvocation(
                   _util.jsObjectFromDartObjectTarget, Arguments([argument])),
               if (castClosure != null)

pkg/dart2wasm/lib/js/runtime_blob.dart

@@ -119,6 +119,7 @@ class CompiledApp {
       ...additionalImports,
       <<MODULE_LOADING_IMPORT>>
       <<JS_POLYFILL_IMPORT>>
+      "$moduleHelpers": {"this": () => dartInstance},
     });
 
     return new InstantiatedApp(this, dartInstance);
@@ -196,11 +197,13 @@ final moduleLoadingHelperTemplate = Template(r'''
           const module = await ((source instanceof Response)
               ? WebAssembly.compileStreaming(source, builtins)
               : WebAssembly.compile(source, builtins));
-          await WebAssembly.instantiate(module, {
+          let moduleInstance;
+          moduleInstance = await WebAssembly.instantiate(module, {
             ...baseImports,
             ...additionalImports,
             <<JS_POLYFILL_IMPORT>>
             "<<MAIN_MODULE_NAME>>": dartInstance.exports,
+            "$moduleHelpers": {"this": () => moduleInstance},
           });
         }
         const promises = [];
@@ -218,11 +221,13 @@ final moduleLoadingHelperTemplate = Template(r'''
           const module = await ((source instanceof Response)
               ? WebAssembly.compileStreaming(source, this.builtins)
               : WebAssembly.compile(source, this.builtins));
-          await WebAssembly.instantiate(module, {
+          let moduleInstance;
+          moduleInstance = await WebAssembly.instantiate(module, {
             ...baseImports,
             ...additionalImports,
             <<JS_POLYFILL_IMPORT>>
             "<<MAIN_MODULE_NAME>>": dartInstance.exports,
+            "$moduleHelpers": {"this": () => moduleInstance},
           });
         }
       },
@@ -231,14 +236,16 @@ final moduleLoadingHelperTemplate = Template(r'''
           throw "No implementation of loadDynamicModule provided.";
         }
         const [source, jsModule] = await loadDynamicModule(wasmUri, jsUri);
+        let moduleInstance;
         const module = await ((source instanceof Response)
             ? WebAssembly.compileStreaming(source, this.builtins)
             : WebAssembly.compile(source, this.builtins));
-        const loadedModule = await WebAssembly.instantiate(module, {
+        moduleInstance = await WebAssembly.instantiate(module, {
           "<<MAIN_MODULE_NAME>>": dartInstance.exports,
+            "$moduleHelpers": {"this": () => moduleInstance},
           ...jsModule.imports(finalizeWrapper),
         });
-        return loadedModule.exports.$invokeEntryPoint;
+        return moduleInstance.exports.$invokeEntryPoint;
       },
     };
 ''');

pkg/dart2wasm/lib/js/util.dart

@@ -68,6 +68,7 @@ class CoreTypesUtil {
   final Procedure jsifyJSArrayBufferImpl; // JS ByteBuffer
   final Procedure jsArrayBufferFromDartByteBuffer; // Wasm ByteBuffer
   final Procedure jsifyFunction;
+  final Procedure thisModuleGetter;
 
   // Classes used in type tests for the converters.
   final Class jsInt8ArrayImplClass;
@@ -268,6 +269,8 @@ class CoreTypesUtil {
             'dart:_js_helper', 'jsArrayBufferFromDartByteBuffer'),
         jsifyFunction = coreTypes.index
             .getTopLevelProcedure('dart:_js_helper', 'jsifyFunction'),
+        thisModuleGetter = coreTypes.index
+            .getTopLevelProcedure('dart:_js_helper', 'get:thisModule'),
         jsInt8ArrayImplClass =
             coreTypes.index.getClass('dart:_js_types', 'JSInt8ArrayImpl'),
         jsUint8ArrayImplClass =

pkg/dart2wasm/test/ir_tests/deferred.constant.wat

@@ -6,12 +6,12 @@
     (field $field0 i32)
     (field $field1 (mut i32))
     (field $fun (ref $#Closure-0-1)))))
-  (type $type234 <...>)
-  (type $type237 <...>)
-  (type $type240 <...>)
-  (table $static1-0 (export "static1-0") 1 (ref null $type240))
-  (table $static2-0 (export "static2-0") 1 (ref null $type234))
-  (table $static3-0 (export "static3-0") 1 (ref null $type237))
+  (type $type236 <...>)
+  (type $type239 <...>)
+  (type $type242 <...>)
+  (table $static1-0 (export "static1-0") 1 (ref null $type242))
+  (table $static2-0 (export "static2-0") 1 (ref null $type236))
+  (table $static3-0 (export "static3-0") 1 (ref null $type239))
   (func $print (param $var0 (ref null $#Top)) (result (ref null $#Top)) <...>)
   (func $"modMainUseH0 <noInline>"
     i64.const 0

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

@@ -716,3 +716,6 @@ external T JS<T>(
   arg18,
   arg19,
 ]);
+
+@pragma("wasm:intrinsic")
+external WasmExternRef get thisModule;

tests/web/wasm/deferred_loading_js_callback_helper.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2025, 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:js_interop';
+
+int closureCalled = 0;
+JSFunction? func;
+void Function()? clos;
+
+void deferredMain() {
+  void closure() {
+    closureCalled++;
+  }
+
+  final jsClosure = closure.toJS;
+  jsClosure.callAsFunction();
+  clos = closure;
+  func = jsClosure;
+}

tests/web/wasm/deferred_loading_js_callback_test.dart

@@ -0,0 +1,26 @@
+// Copyright (c) 2025, 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.
+
+// dart2wasmOptions=--enable-deferred-loading
+
+import 'dart:js_interop';
+
+import 'package:async_helper/async_helper.dart';
+import 'package:expect/expect.dart';
+
+import 'deferred_loading_js_callback_helper.dart' deferred as D;
+
+main() async {
+  asyncStart();
+  await D.loadLibrary();
+  Expect.equals(D.closureCalled, 0);
+  D.deferredMain();
+  Expect.equals(D.closureCalled, 1);
+  D.func!.callAsFunction();
+  Expect.equals(D.closureCalled, 2);
+  final jsClosure = D.clos!.toJS;
+  jsClosure.callAsFunction();
+  Expect.equals(D.closureCalled, 3);
+  asyncEnd();
+}