Compiler crashes when compiling to WASM

[Schwusch]

When compiling to WASM on MacOS Sonoma 14.3, the Dart compiler crashes.
Complete log:

flutter build web --wasm

┌─ Experimental feature ───────────────────────────────┐
│   WebAssembly compilation is experimental.           │
│   See https://flutter.dev/wasm for more information. │
└──────────────────────────────────────────────────────┘

Target dart2js failed: ProcessException: Process exited abnormally with exit code 253:
lib/file_system_access/platform_file.dart:34:20:
Internal Error: Unknown external method j:method(FilePickerOptions|constructor#)
  external factory FilePickerOptions({
                   ^
The compiler is broken.

When compiling the above element, the compiler crashed. It is not
possible to tell if this is caused by a problem in your program or
not. Regardless, the compiler should not crash.

The Dart team would greatly appreciate if you would take a moment to
report this problem at http://dartbug.com/new.

Please include the following information:

* the name and version of your operating system,

* the Dart SDK build number (3.4.0-148.0.dev), and

* the entire message you see here (including the full stack trace
  below as well as the source location above).

The compiler crashed: Assertion failure: Unknown external method j:method(FilePickerOptions|constructor#)
#0      failedAt (package:compiler/src/diagnostics/invariant.dart:39:3)
#1      KernelSsaGraphBuilder._buildExternalFunctionNode (package:compiler/src/ssa/builder.dart:1820:5)
#2      KernelSsaGraphBuilder.build.<anonymous closure> (package:compiler/src/ssa/builder.dart:440:15)
#3      DiagnosticReporter.withCurrentElement (package:compiler/src/diagnostics/diagnostic_listener.dart:154:15)
#4      KernelSsaGraphBuilder.build (package:compiler/src/ssa/builder.dart:428:21)
#5      KernelSsaBuilder.build.<anonymous closure> (package:compiler/src/js_model/js_strategy.dart:525:22)
#6      CompilerTask.measure (package:compiler/src/common/tasks.dart:66:51)
#7      KernelSsaBuilder.build (package:compiler/src/js_model/js_strategy.dart:507:18)
#8      SsaBuilderTask.build (package:compiler/src/ssa/ssa.dart:365:21)
#9      SsaFunctionCompiler.compile (package:compiler/src/ssa/ssa.dart:99:28)
#10     OnDemandCodegenResults.getCodegenResults (package:compiler/src/common/codegen.dart:409:30)
#11     JsBackendStrategy.generateCode (package:compiler/src/js_model/js_strategy.dart:331:43)
#12     KernelCodegenWorkItem.run (package:compiler/src/js_model/js_strategy.dart:466:29)
#13     Compiler.emptyQueue.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:compiler/src/compiler.dart:756:70)
#14     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#15     Compiler.emptyQueue.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:compiler/src/compiler.dart:756:32)
#16     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#17     Compiler.emptyQueue.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:compiler/src/compiler.dart:754:28)
#18     DiagnosticReporter.withCurrentElement (package:compiler/src/diagnostics/diagnostic_listener.dart:154:15)
#19     Compiler.emptyQueue.<anonymous closure>.<anonymous closure> (package:compiler/src/compiler.dart:752:18)
#20     CodegenEnqueuer._forEach (package:compiler/src/js_backend/enqueuer.dart:267:12)
#21     CodegenEnqueuer.forEach (package:compiler/src/js_backend/enqueuer.dart:283:5)
#22     Compiler.emptyQueue.<anonymous closure> (package:compiler/src/compiler.dart:748:16)
#23     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#24     Compiler.emptyQueue (package:compiler/src/compiler.dart:747:14)
#25     Compiler.processQueue.<anonymous closure> (package:compiler/src/compiler.dart:771:7)
#26     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#27     Compiler.processQueue (package:compiler/src/compiler.dart:765:14)
#28     Compiler.runCodegenEnqueuer (package:compiler/src/compiler.dart:472:5)
#29     Compiler.runSequentialPhases (package:compiler/src/compiler.dart:684:27)
<asynchronous suspension>
#30     Compiler.runInternal.<anonymous closure> (package:compiler/src/compiler.dart:315:7)
<asynchronous suspension>
#31     Compiler.runInternal (package:compiler/src/compiler.dart:314:5)
<asynchronous suspension>
#32     Compiler.run.<anonymous closure> (package:compiler/src/compiler.dart:235:11)
<asynchronous suspension>
#33     compile.<anonymous closure> (package:compiler/compiler_api.dart:256:30)
<asynchronous suspension>
#34     compile.compilationDone (package:compiler/src/dart2js.dart:730:3)
<asynchronous suspension>
#35     main (package:compiler/src/dart2js.dart:1240:3)
<asynchronous suspension>
  Command: /Users/jonathanbocker/fvm/versions/master/bin/cache/dart-sdk/bin/dart --disable-dart-dev /Users/jonathanbocker/fvm/versions/master/bin/cache/dart-sdk/bin/snapshots/dart2js.dart.snapshot
  --platform-binaries=/Users/jonathanbocker/fvm/versions/master/bin/cache/flutter_web_sdk/kernel --invoker=flutter_tool -Ddart.vm.product=true
  -DFLUTTER_WEB_CANVASKIT_URL=https://www.gstatic.com/flutter-canvaskit/dd530f1556dfe22c6fc3549a1e8342fadde7302c/ -DFLUTTER_WEB_AUTO_DETECT=false -DFLUTTER_WEB_USE_SKIA=true --native-null-assertions
  --no-source-maps -O4 -o /Users/jonathanbocker/development/vdu/app/.dart_tool/flutter_build/886e40a1726ba7845dc07d95e6513162/main.dart.js
  /Users/jonathanbocker/development/vdu/app/.dart_tool/flutter_build/886e40a1726ba7845dc07d95e6513162/app.dill
#0      RunResult.throwException (package:flutter_tools/src/base/process.dart:127:5)
#1      _DefaultProcessUtils.run (package:flutter_tools/src/base/process.dart:326:19)
<asynchronous suspension>
#2      Dart2JSTarget.build (package:flutter_tools/src/build_system/targets/web.dart:195:5)
<asynchronous suspension>
#3      _BuildInstance._invokeInternal (package:flutter_tools/src/build_system/build_system.dart:875:9)
<asynchronous suspension>
#4      Future.wait.<anonymous closure> (dart:async/future.dart:524:21)
<asynchronous suspension>
#5      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:813:32)
<asynchronous suspension>
#6      Future.wait.<anonymous closure> (dart:async/future.dart:524:21)
<asynchronous suspension>
#7      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:813:32)
<asynchronous suspension>
#8      FlutterBuildSystem.build (package:flutter_tools/src/build_system/build_system.dart:642:16)
<asynchronous suspension>
#9      WebBuilder.buildWeb (package:flutter_tools/src/web/compile.dart:91:34)
<asynchronous suspension>
#10     BuildWebCommand.runCommand (package:flutter_tools/src/commands/build_web.dart:237:5)
<asynchronous suspension>
#11     FlutterCommand.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command.dart:1394:27)
<asynchronous suspension>
#12     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:153:19)
<asynchronous suspension>
#13     CommandRunner.runCommand (package:args/command_runner.dart:212:13)
<asynchronous suspension>
#14     FlutterCommandRunner.runCommand.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:360:9)
<asynchronous suspension>
#15     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:153:19)
<asynchronous suspension>
#16     FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:300:5)
<asynchronous suspension>
#17     run.<anonymous closure>.<anonymous closure> (package:flutter_tools/runner.dart:119:9)
<asynchronous suspension>
#18     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:153:19)
<asynchronous suspension>
#19     main (package:flutter_tools/executable.dart:94:3)
<asynchronous suspension>

Compiling lib/main.dart for the Web...                             60.7s
Error: Failed to compile application for the Web.

[Schwusch]

The code in question is:

import 'dart:js_interop';
import 'package:web/web.dart';

extension WindowExtensions on Window {
  external JSPromise<JSArray<FileSystemFileHandle>?> showOpenFilePicker(
      FilePickerOptions options);
}

@JS()
extension type FilePickerOptions._(JSObject _) implements JSAny {
  external factory FilePickerOptions({
    String? id,
    JSArray<FileType>? types,
  });
}

@JS()
extension type FileType._(JSObject _) implements JSAny {
  external factory FileType({
    String? description,
    required JSAny accept,
  });
}

[Schwusch]

Found workaround here: #54801

Adding this on top makes the error go away:

@JS()
library;

[srujzs]

Duplicate of #54801 .

Looks like you found the workaround before I could respond. :) Also documented here under object literal constructors: https://dart.dev/interop/js-interop/usage#interop-type-members and should be fixed in 3.4.