[dart2wasm] Use dynamic invocations to call closures when dynamic modules are enabled.

Running with dynamic modules means that closure invocation shapes cannot be statically known. A closure can flow between any modules and can then be invoked with a shape that's unknown to the module that defines the closure.

Given this, our 2 options are to generate code for every invocation shape or invoke the closure as if we don't know it's shape (dynamic invocation).

The former would scale exponentially relative to the number of named parameters so is not practical.

The latter generates slower, bigger code but is the more practical of the 2.

Change-Id: I5e3613d23662e5b2213fdaa725642678fe26e43a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/421920
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>

Author: natebiggs

pkg/dart2wasm/lib/closures.dart

@@ -200,7 +200,14 @@ class ClosureLayouter extends RecursiveVisitor {
   final Translator translator;
   final Map<TreeNode, ProcedureAttributesMetadata> procedureAttributeMetadata;
 
-  List<List<ClosureRepresentationsForParameterCount>> representations = [];
+  late final List<List<ClosureRepresentationsForParameterCount>>
+      representations;
+
+  // Dynamic modules invoke closures dynamically so they use the base structs
+  // in all cases. Therefore, We only need one global copy of the
+  // ClosureRepresentation for generic and one for non-generic functions.
+  ClosureRepresentation? _dynamicModuleRepresentation;
+  ClosureRepresentation? _dynamicModuleGenericRepresentation;
 
   Set<Constant> visitedConstants = Set.identity();
 
@@ -356,6 +363,12 @@ class ClosureLayouter extends RecursiveVisitor {
                 .mapping;
 
   void collect() {
+    // Dynamic module enabled builds use dynamic call entry points for all
+    // closure invocations so we don't need to generate any representation
+    // info.
+    if (translator.dynamicModuleSupportEnabled) return;
+    representations = [];
+
     translator.component.accept(this);
     computeClusters();
   }
@@ -391,6 +404,14 @@ class ClosureLayouter extends RecursiveVisitor {
   /// `names` should be sorted.
   ClosureRepresentation? getClosureRepresentation(
       int typeCount, int positionalCount, List<String> names) {
+    if (translator.dynamicModuleSupportEnabled) {
+      if (typeCount == 0) {
+        return _dynamicModuleRepresentation ??=
+            _createRepresentation(typeCount, 0, const [], null, null, const []);
+      }
+      return _dynamicModuleGenericRepresentation ??=
+          _createRepresentation(typeCount, 0, const [], null, null, const []);
+    }
     final representations =
         _representationsForCounts(typeCount, positionalCount);
     if (representations.withoutNamed == null) {
@@ -423,8 +444,6 @@ class ClosureLayouter extends RecursiveVisitor {
       ClosureRepresentation? parent,
       Map<NameCombination, int>? indexOfCombination,
       Iterable<int> paramCounts) {
-    // TODO(natebiggs): Add logic to allow for changing signatures in a dynamic
-    // module.
     List<String> nameTags = ["$typeCount", "$positionalCount", ...names];
     String vtableName = ["#Vtable", ...nameTags].join("-");
     String closureName = ["#Closure", ...nameTags].join("-");
@@ -505,6 +524,9 @@ class ClosureLayouter extends RecursiveVisitor {
       // generation, after the imports have been added.
 
       representation._instantiationTrampolinesGenerator = (module) {
+        // Dynamic modules do not have any trampolines, only a dynamic call
+        // entry point.
+        if (translator.dynamicModuleSupportEnabled) return const [];
         List<w.BaseFunction> instantiationTrampolines = [
           ...?parent?._instantiationTrampolinesForModule(module)
         ];

pkg/dart2wasm/lib/code_generator.dart

@@ -2454,7 +2454,8 @@ abstract class AstCodeGenerator
         intrinsifier.generateFunctionCallIntrinsic(node);
     if (intrinsicResult != null) return intrinsicResult;
 
-    if (node.kind == FunctionAccessKind.Function) {
+    if (node.kind == FunctionAccessKind.Function ||
+        translator.dynamicModuleSupportEnabled) {
       // Type of function is `Function`, without the argument types.
       return visitDynamicInvocation(
           DynamicInvocation(DynamicAccessKind.Dynamic, node.receiver, node.name,

pkg/dart2wasm/lib/dispatch_table.dart

@@ -424,6 +424,9 @@ class DispatchTable {
   void serialize(DataSerializer sink) {
     sink.writeList(_selectorInfo.values, (s) => s.serialize(sink));
     sink.writeList(_table, (r) => sink.writeNullable(r, sink.writeReference));
+    // Preserve call selectors for closure calls which are handled dynamically.
+    final callSelectors = _dynamicGetters['call']!;
+    sink.writeList(callSelectors, (s) => sink.writeInt(s.id));
   }
 
   factory DispatchTable.deserialize(DataDeserializer source) {
@@ -433,11 +436,20 @@ class DispatchTable {
         source.readList(() => SelectorInfo.deserialize(source, dispatchTable));
     final table = source
         .readList(() => source.readNullable(() => source.readReference()));
+    final callSelectorIds = source.readList(source.readInt);
 
     for (final selector in selectors) {
       dispatchTable._selectorInfo[selector.id] = selector;
     }
     dispatchTable._table = table;
+
+    // Preserve call selectors for closure calls which are handled dynamically.
+    final callSelectors = <SelectorInfo>{};
+    for (final selectorId in callSelectorIds) {
+      callSelectors.add(dispatchTable._selectorInfo[selectorId]!);
+    }
+    dispatchTable._dynamicGetters['call'] = callSelectors;
+
     return dispatchTable;
   }
 

pkg/dart2wasm/lib/dynamic_forwarders.dart

@@ -77,7 +77,9 @@ class Forwarder {
   Forwarder._(Translator translator, this._kind, this.memberName,
       w.ModuleBuilder module)
       : function = module.functions.define(_kind.functionType(translator),
-            "$_kind forwarder for '$memberName'");
+            "$_kind forwarder for '$memberName'"),
+        assert(!translator.isDynamicModule ||
+            (memberName == 'call' && _kind == _ForwarderKind.Getter));
 
   void _generateCode(Translator translator) {
     switch (_kind) {
@@ -478,10 +480,8 @@ class Forwarder {
       }
     }
 
-    final getterSelectors =
-        translator.dispatchTable.dynamicGetterSelectors(memberName);
     final getterValueLocal = b.addLocal(translator.topInfo.nullableType);
-    for (final selector in getterSelectors) {
+    void handleGetterSelector(SelectorInfo selector) {
       for (final (:range, :target)
           in selector.targets(unchecked: false).targetRanges) {
         for (int classId = range.start; classId <= range.end; ++classId) {
@@ -569,6 +569,21 @@ class Forwarder {
       }
     }
 
+    final getterSelectors =
+        translator.dispatchTable.dynamicGetterSelectors(memberName);
+    for (final selector in getterSelectors) {
+      handleGetterSelector(selector);
+    }
+
+    final dynamicMainModuleGetterSelectors = translator
+        .dynamicMainModuleDispatchTable
+        ?.dynamicGetterSelectors(memberName);
+    if (dynamicMainModuleGetterSelectors != null) {
+      for (final selector in dynamicMainModuleGetterSelectors) {
+        handleGetterSelector(selector);
+      }
+    }
+
     b.end(); // noSuchMethodBlock
 
     // Unable to find a matching member, call `noSuchMethod`

pkg/dart2wasm/lib/dynamic_modules.dart

@@ -491,14 +491,16 @@ class DynamicModuleInfo {
 
     for (final lib in translator.component.libraries) {
       for (final member in lib.members) {
-        if (!member.isDynamicModuleCallable(translator.coreTypes)) continue;
-        collectCallableReferences(member);
+        if (member.isDynamicModuleCallable(translator.coreTypes)) {
+          collectCallableReferences(member);
+        }
       }
 
       for (final cls in lib.classes) {
         for (final member in cls.members) {
-          if (!member.isDynamicModuleCallable(translator.coreTypes)) continue;
-          collectCallableReferences(member);
+          if (member.isDynamicModuleCallable(translator.coreTypes)) {
+            collectCallableReferences(member);
+          }
         }
       }
     }

pkg/dart2wasm/lib/translator.dart

@@ -836,6 +836,15 @@ class Translator with KernelNodes {
       return topInfo.typeWithNullability(nullable);
     }
     if (type is FunctionType) {
+      if (dynamicModuleSupportEnabled) {
+        // The closure representation is based on the available closure
+        // definitions and invocations seen in the program. For dynamic modules,
+        // this can differ from one module to another. So use the less specific
+        // closure base class everywhere. Usages will get downcast to the
+        // appropriate closure type.
+        return w.RefType.def(closureLayouter.closureBaseStruct,
+            nullable: nullable);
+      }
       ClosureRepresentation? representation =
           closureLayouter.getClosureRepresentation(
               type.typeParameters.length,
@@ -1095,11 +1104,13 @@ class Translator with KernelNodes {
           representation.instantiationTypeHashFunctionForModule(ib.module));
       ib.ref_func(representation.instantiationFunctionForModule(ib.module));
     }
-    for (int posArgCount = 0; posArgCount <= positionalCount; posArgCount++) {
-      fillVtableEntry(ib, posArgCount, const []);
-    }
-    for (NameCombination nameCombination in representation.nameCombinations) {
-      fillVtableEntry(ib, positionalCount, nameCombination.names);
+    if (!dynamicModuleSupportEnabled) {
+      for (int posArgCount = 0; posArgCount <= positionalCount; posArgCount++) {
+        fillVtableEntry(ib, posArgCount, const []);
+      }
+      for (NameCombination nameCombination in representation.nameCombinations) {
+        fillVtableEntry(ib, positionalCount, nameCombination.names);
+      }
     }
     ib.struct_new(representation.vtableStruct);
     ib.end();

pkg/dynamic_modules/test/data/closure_shapes/dynamic_interface.yaml

@@ -0,0 +1,10 @@
+# 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.
+callable:
+  - library: 'shared/shared.dart'
+  - library: 'dart:core'
+    class: ['int', 'num', 'Object']
+  - library: 'dart:core'
+    class: 'pragma'
+    member: '_'

pkg/dynamic_modules/test/data/closure_shapes/main.dart

@@ -0,0 +1,17 @@
+// 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 '../../common/testing.dart' as helper;
+import 'package:expect/expect.dart';
+
+import 'shared/shared.dart';
+
+/// A dynamic module is allowed to extend a class in the dynamic interface and
+/// override its members.
+void main() async {
+  final c = (await helper.load('entry1.dart')) as int Function(int, int);
+  Expect.equals(1, c1(0));
+  Expect.equals(49, c(0, 0));
+  helper.done();
+}

pkg/dynamic_modules/test/data/closure_shapes/modules/entry1.dart

@@ -0,0 +1,15 @@
+// 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 '../shared/shared.dart';
+
+int f3(int i, int j) =>
+    c1(i) +
+    c2(i, j: i + 10) +
+    c2(j, k: j + 10) +
+    c2(i, j: j + 10, k: j + 10) +
+    3;
+
+@pragma('dyn-module:entry-point')
+Object? dynamicModuleEntrypoint() => f3;

pkg/dynamic_modules/test/data/closure_shapes/shared/shared.dart

@@ -0,0 +1,9 @@
+// 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.
+
+int f1(int i) => i + 1;
+int f2(int i, {int j = 2, int k = 3}) => i + j + k;
+
+final c1 = f1;
+final c2 = f2;