[dart2wasm] Fix @pragma('wasm:initialize-at-startup') in deferred loading scenario

The module owning the storage for the static field has to emit the
initialization code in it's start function.

Change-Id: I9089e99d6e12ea275343cebe3e456658a7c7a540
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/485480
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

pkg/dart2wasm/lib/dynamic_modules.dart

@@ -650,8 +650,9 @@ class DynamicModuleInfo {
   }
 
   void finishDynamicModule() {
-    _registerModuleRefs(
-        isSubmodule ? initFunction.body : translator.initFunction.body);
+    _registerModuleRefs(isSubmodule
+        ? initFunction.body
+        : translator.mainModule.startFunction.body);
   }
 
   void _registerModuleRefs(w.InstructionsBuilder b) {

pkg/dart2wasm/lib/globals.dart

@@ -160,15 +160,11 @@ class DartGlobals {
         final definition =
             _defineGlobalBasedField(field, fieldType, module, true, init, null);
 
-        if (module.module == translator.initFunction.enclosingModule) {
-          // We have to initialize the global field in the same module as where
-          // the field value is defined in.
-          // TODO: Once dynamic modules only compile code for the submodule and
-          // not the main module, we should turn this into an assert.
-          EagerStaticFieldInitializerCodeGenerator(
-                  translator, field, definition.global)
-              .generate(translator.initFunction.body, [], null);
-        }
+        // We have to initialize the global field in the same module as where
+        // the field value is defined in.
+        EagerStaticFieldInitializerCodeGenerator(
+                translator, field, definition.global)
+            .generate(module.startFunction.body, [], null);
 
         return definition;
       }

pkg/dart2wasm/lib/translator.dart

@@ -247,7 +247,6 @@ class Translator with KernelNodes {
   final Set<Member> membersContainingInnerFunctions = {};
   final Set<Member> membersBeingGenerated = {};
   final Map<Reference, Closures> constructorClosures = {};
-  late final w.FunctionBuilder initFunction;
   late final w.ValueType voidMarker =
       w.RefType.def(w.StructType("void"), nullable: true);
   // Lazily import FFI memory if used.
@@ -595,8 +594,6 @@ class Translator with KernelNodes {
   Map<ModuleMetadata, w.Module> translate(
       Uri Function(String moduleName)? sourceMapUrlGenerator) {
     _initModules(sourceMapUrlGenerator);
-    initFunction = mainModule.startFunction;
-
     closureLayouter.collect();
     classInfoCollector.collect();
 
@@ -637,7 +634,7 @@ class Translator with KernelNodes {
         }
       });
     }
-    _printFunction(initFunction, "init");
+    _printFunction(mainModule.startFunction, "init");
 
     // Remove empty modules.
     _outputToBuilder.removeWhere((outputModule, moduleBuilder) {

pkg/dart2wasm/test/ir_test.dart

@@ -64,6 +64,7 @@ void main(List<String> args) async {
         'pkg/dart2wasm/tool/compile_benchmark',
         for (final option in compilerOptions) '--extra-compiler-option=$option',
         '--extra-compiler-option=--no-unique-constant-names',
+        '--extra-compiler-option=--enable-experimental-wasm-interop',
         if (runFromSource) '--src',
         '--no-strip-wasm',
         '-o',

pkg/dart2wasm/test/ir_tests/deferred.init_at_startup.dart

@@ -0,0 +1,29 @@
+// Copyright (c) 2026, 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.
+//
+// functionFilter=write|read|#init
+// tableFilter=cross-module-funcs
+// globalFilter=array
+// typeFilter=NoMatch
+// compilerOption=--enable-deferred-loading
+// compilerOption=--no-minify
+
+import 'dart:_wasm';
+
+import '' deferred as D;
+
+import 'package:expect/expect.dart';
+
+void main() async {
+  await D.loadLibrary();
+
+  D.write();
+  Expect.equals('hello', D.read());
+}
+
+void write() => array[0] = 'hello';
+String read() => array[0]!;
+
+@pragma("wasm:initialize-at-startup")
+final WasmArray<String?> array = WasmArray<String?>(1);

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

@@ -0,0 +1,34 @@
+(module $module0
+  (type $#Top <...>)
+  (type $Array<String> <...>)
+  (type $Array<WasmI16> <...>)
+  (type $Array<int> <...>)
+  (type $JSExternWrapper <...>)
+  (type $Object <...>)
+  (table $cross-module-funcs-0 (export "cross-module-funcs-0") 3 funcref)
+  (global $"\"1.0\"" (ref $JSExternWrapper) <...>)
+  (global $BoxedDouble._cacheKeys (mut (ref $Array<int>)) <...>)
+  (global $BoxedDouble._cacheValues (mut (ref $Array<String>)) <...>)
+  (global $JSStringImpl._stringFromCodePointBuffer (mut (ref $Array<WasmI16>)) <...>)
+  (global $_deletedDataMarker (mut (ref $#Top)) <...>)
+  (elem $cross-module-funcs-0
+    (set 2 (ref.func $"_TypeError._throwNullCheckErrorWithCurrentStack <noInline>")))
+  (func $_TypeError._throwNullCheckErrorWithCurrentStack <noInline> (result (ref none)) <...>)
+  (func $#init
+    global.get $"\"1.0\""
+    i32.const 16
+    array.new $Array<String>
+    global.set $BoxedDouble._cacheValues
+    i64.const 4607182418800017408
+    i32.const 16
+    array.new $Array<int>
+    global.set $BoxedDouble._cacheKeys
+    i32.const 2
+    array.new_default $Array<WasmI16>
+    global.set $JSStringImpl._stringFromCodePointBuffer
+    i32.const 1
+    i32.const 0
+    struct.new $Object
+    global.set $_deletedDataMarker
+  )
+)

pkg/dart2wasm/test/ir_tests/deferred.init_at_startup_module1.wat

@@ -0,0 +1,37 @@
+(module $module1
+  (type $#Top <...>)
+  (type $Array<String?> <...>)
+  (type $JSExternWrapper <...>)
+  (global $"\"hello\"" (import "module0" "global0") (ref $JSExternWrapper))
+  (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 3 funcref)
+  (global $array (mut (ref $Array<String?>))
+    (array.new_fixed $Array<String?> 0))
+  (elem $module0.cross-module-funcs-0
+    (set 0 (ref.func $write))
+    (set 1 (ref.func $read)))
+  (func $#init
+    i32.const 1
+    array.new_default $Array<String?>
+    global.set $array
+  )
+  (func $read (result (ref $JSExternWrapper))
+    block $label0 (result (ref $JSExternWrapper))
+      global.get $array
+      i32.const 0
+      array.get $Array<String?>
+      br_on_non_null $label0
+      i32.const 2
+      call_indirect (result (ref none))
+      unreachable
+    end $label0
+  )
+  (func $write (result (ref null $#Top))
+    (local $var0 (ref $JSExternWrapper))
+    global.get $array
+    i32.const 0
+    global.get $"\"hello\""
+    local.tee $var0
+    array.set $Array<String?>
+    local.get $var0
+  )
+)

tests/web/wasm/deferred_init_at_startup_test.dart

@@ -0,0 +1,24 @@
+// Copyright (c) 2026, 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 --extra-compiler-option=--enable-experimental-wasm-interop
+
+import 'dart:_wasm';
+
+import '' deferred as D;
+
+import 'package:expect/expect.dart';
+
+void main() async {
+  await D.loadLibrary();
+
+  D.write();
+  Expect.equals('hello', D.read());
+}
+
+void write() => array[0] = 'hello';
+String read() => array[0]!;
+
+@pragma("wasm:initialize-at-startup")
+final WasmArray<String?> array = WasmArray<String?>(1);