dart2wasm: Failed null check at ClosureRepresentation.fieldIndexForSignature on a statically typed constructor tearoff expression #56372
Description
I get a compilation error when compiling to wasm with flutter build web --wasm --release (that I don't get with other compilation targets.) (I use a flutter command but the error happens in the dart2wasm library, so I'm posting the issue here.)
The error is:
Target dart2wasm failed: ProcessException: Process exited abnormally with exit code 64:
*NOTE*: Compilation to WasmGC is experimental.
The support may change, or be removed, with no advance notice.
Exception in ConstantExpression at [...]:70:21
Unhandled exception:
Null check operator used on a null value
Stack trace:
Details
#0 ClosureRepresentation.fieldIndexForSignature (package:dart2wasm/closures.dart:112)
#1 ConstantCreator.visitInstantiationConstant.<anonymous closure>.fillVtableEntry (package:dart2wasm/constants.dart:725)
#2 ConstantCreator.visitInstantiationConstant.<anonymous closure>.makeVtable (package:dart2wasm/constants.dart:749)
#3 ConstantCreator.visitInstantiationConstant.<anonymous closure> (package:dart2wasm/constants.dart:765)
#4 ConstantCreator.createConstant (package:dart2wasm/constants.dart:285)
#5 ConstantCreator.visitInstantiationConstant (package:dart2wasm/constants.dart:698)
#6 InstantiationConstant.accept (package:kernel/ast.dart:14209)
#7 ConstantCreator.ensureConstant (package:dart2wasm/constants.dart:252)
#8 ConstantInstantiator.defaultConstant (package:dart2wasm/constants.dart:137)
#9 ConstantVisitorDefaultMixin.visitStaticTearOffConstant (package:kernel/visitor.dart:944)
#10 InstantiationConstant.accept (package:kernel/ast.dart:14209)
#11 ConstantInstantiator.instantiate (package:dart2wasm/constants.dart:121)
#12 Constants.instantiateConstant (package:dart2wasm/constants.dart:103)
#13 CodeGenerator.visitConstantExpression (package:dart2wasm/code_generator.dart:2841)
#14 ConstantExpression.accept1 (package:kernel/ast.dart:8707)
#15 CodeGenerator.wrap (package:dart2wasm/code_generator.dart:852)
#16 CodeGenerator.visitRecordLiteral (package:dart2wasm/code_generator.dart:3086)
#17 RecordLiteral.accept1 (package:kernel/ast.dart:8490)
#18 CodeGenerator.wrap (package:dart2wasm/code_generator.dart:852)
#19 CodeGenerator.visitLet (package:dart2wasm/code_generator.dart:1669)
#20 Let.accept1 (package:kernel/ast.dart:8775)
#21 CodeGenerator.wrap (package:dart2wasm/code_generator.dart:852)
#22 CodeGenerator.visitLet (package:dart2wasm/code_generator.dart:1669)
#23 Let.accept1 (package:kernel/ast.dart:8775)
#24 CodeGenerator.wrap (package:dart2wasm/code_generator.dart:852)
#25 CodeGenerator.visitMapLiteral.<anonymous closure> (package:dart2wasm/code_generator.dart:2956)
#26 Translator.makeArray (package:dart2wasm/translator.dart:1025)
#27 CodeGenerator.makeArray (package:dart2wasm/code_generator.dart:2921)
#28 CodeGenerator.visitMapLiteral (package:dart2wasm/code_generator.dart:2949)
#29 MapLiteral.accept1 (package:kernel/ast.dart:8341)
#30 CodeGenerator.wrap (package:dart2wasm/code_generator.dart:852)
#31 CodeGenerator.visitVariableDeclaration (package:dart2wasm/code_generator.dart:1020)
#32 VariableDeclaration.accept (package:kernel/ast.dart:10791)
#33 CodeGenerator.visitStatement (package:dart2wasm/code_generator.dart:863)
#34 CodeGenerator.visitBlock (package:dart2wasm/code_generator.dart:983)
#35 Block.accept (package:kernel/ast.dart:9247)
#36 CodeGenerator.visitStatement (package:dart2wasm/code_generator.dart:863)
#37 CodeGenerator.generateBody (package:dart2wasm/code_generator.dart:557)
#38 CodeGenerator.generate (package:dart2wasm/code_generator.dart:236)
#39 Translator.translate (package:dart2wasm/translator.dart:374)
#40 compileToModule (package:dart2wasm/compile.dart:188)
<asynchronous suspension>
#41 generateWasm (package:dart2wasm/generate_wasm.dart:24)
<asynchronous suspension>
#42 main (file:///C:/b/s/w/ir/x/w/sdk/pkg/dart2wasm/bin/dart2wasm.dart:10)
<asynchronous suspension>
I've tried to write a minimal reproducible example from scratch, but I haven't succeeded, so I'll show my actual code.
The culprit of this exception, as pointed out by the error, seems to be this tearoff expression:
final Map<Type, _TypeConfig> typesConfig = {
// [...]
Habit: (
enabled: isSubtype<Habit, C>(),
typeInfo: CommitmentTypeInfo(
name: "Habit",
icon: Habit.icon_,
orderKey: DiscreteHabit.commitmentTypeInfo.orderKey,
fromMapFactory: (map) => throw UnimplementedError(),
),
editScreen: EditHabit.blank // ERROR: this is the constant expression that causes the error
),
// [...]
};I have the following typedefs:
typedef _EditPageBuilder<C extends Commitment> = Widget Function({
CompositeCommitment<C>? parentCommitment,
Function(C)? onEdited,
});
typedef _TypeConfig<C extends Commitment> = ({
bool enabled,
CommitmentTypeInfo typeInfo,
_EditPageBuilder<C> editScreen,
});The problem disappears when I set:
typedef _EditPageBuilder<C extends Commitment> = dynamic;Related code (definition of EditHabit.blank):
Details
class EditHabit<H extends Habit> extends EditCommitment<H> {
// [...]
EditHabit.blank({
super.key,
super.parentCommitment,
super.onEdited,
}) : super.blank(
commitmentTypeInfo: DiscreteHabit.commitmentTypeInfo,
titleHintText: titleHint,
);
// [...]
}
abstract class EditCommitment<C extends Commitment> extends Edit<C> {
// [...]
/// For creating a new commitment.
const EditCommitment.blank({
super.key,
required CommitmentTypeInfo commitmentTypeInfo,
required super.titleHintText,
this.parentCommitment,
super.onEdited,
}) : _commitmentTypeInfo = commitmentTypeInfo,
super.blank();
// Should be CompositeCommitment<C> but Dart forces the type parameter to be
// covariant, which is not desirable here.
final CompositeCommitment? parentCommitment;
// [...]
}
abstract class Edit<O extends CommitmentStoreObjectSnapshot>
extends ConsumerStatefulWidget {
// [...]
const Edit.blank({
super.key,
required this.titleHintText,
this.onEdited,
}) : object = null;
/// Called after the edit/creation has been successfully executed.
final Function(O)? onEdited;
// [...]
}
Surprisingly, I have other elements in the map above for which this error does not occur, in particular for EditTask.blank:
Details
class EditTask extends EditCommitment<Task> {
// [...]
const EditTask.blank({
super.parentCommitment,
super.key,
super.onEdited,
}) : super.blank(
commitmentTypeInfo: Task.commitmentTypeInfo,
titleHintText: titleHint,
);
// [...]
}I thought the difference might be in the const, but I haven't managed to make a minimal reproducible example. Maybe someone experienced with dart2wasm will be able to do so.
- Dart version and tooling diagnostic info (
dart info)
Details
#### General info
- Dart 3.4.4 (stable) (Wed Jun 12 15:54:31 2024 +0000) on "windows_x64"
- on windows / "Windows 10 Home" 10.0 (Build 22631)
- locale is en-GB
#### Project info
- sdk constraint: '^3.4.0'
- dependencies: built_collection, cloud_firestore, collection, cupertino_icons, easy_debounce, equatable, firebase_auth, firebase_core, firebase_ui_auth, firebase_ui_oauth_google, flut
ter, flutter_fancy_tree_view, flutter_local_notifications, flutter_localizations, flutter_riverpod, flutter_speed_dial, flutter_timezone, google_sign_in, intersperse, intl, meta, modal_bottom_sheet, package_info_plus, quiver, rrule_generator, skeletonizer, sliver_tools, stream_transform, timezone, url_launcher
- dev_dependencies: custom_lint, flutter_launcher_icons, flutter_lints, flutter_test, riverpod_lint, test
- elided dependencies: 2
#### Process info
| Memory | CPU | Elapsed time | Command line |
| -----: | --: | -----------: | ------------ |
| 274 MB | -- | | dart.exe |
| 30 MB | -- | | dart.exe |
| 3 MB | -- | | dart.exe |
| 476 MB | -- | | dart.exe |
| 485 MB | -- | | dart.exe |
| 94 MB | -- | | dart.exe |
| 100 MB | -- | | dart.exe |
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