[dev_compiler] Web: Unsupported operation: Undetermined nullability

[llfbandit]

Context: Flutter web plugin implementation interoperating with JS.

This exception is only thrown in debug mode, release mode is OK.

Package issue reference

• Dart SDK Version 3.0.5 shipped with Flutter 3.10.5

Here's the stack trace

Unhandled exception:
Unsupported operation: Undetermined nullability. Encountered while compiling file:///......./Pub/Cache/hosted/pub.dev/typings-0.0.1+1/lib/src/d/core/lib_es2015_collection_d.dart, which contains the type: InterfaceType(Object%).
lib_es2015_collection_d.dart:1
#0      ProgramCompiler._typeCompilationError (package:dev_compiler/src/kernel/compiler.dart:3355:7)
#1      ProgramCompiler._undeterminedNullabilityError (package:dev_compiler/src/kernel/compiler.dart:3352:7)
#2      ProgramCompiler._emitInterfaceType (package:dev_compiler/src/kernel/compiler.dart:3277:7)
#3      ProgramCompiler.visitInterfaceType (package:dev_compiler/src/kernel/compiler.dart:3191:7)
#4      InterfaceType.accept (package:kernel/ast.dart:12100:42)
#5      MappedListIterable.elementAt (dart:_internal/iterable.dart:415:31)
#6      MappedListIterable.elementAt (dart:_internal/iterable.dart:415:40)
#7      ListIterator.moveNext (dart:_internal/iterable.dart:344:26)
#8      InstantiatorGeneratorVisitor.splayNodes (package:dev_compiler/src/js_ast/template.dart:224:23)
#9      InstantiatorGeneratorVisitor.handleCallOrNew.<anonymous closure> (package:dev_compiler/src/js_ast/template.dart:604:22)
#10     Template.instantiate (package:dev_compiler/src/js_ast/template.dart:118:26)
#11     JsBuilder.call (package:dev_compiler/src/js_ast/builder.dart:212:21)
#12     ProgramCompiler._emitGenericClassType (package:dev_compiler/src/kernel/compiler.dart:3393:15)
#13     ProgramCompiler._emitInterfaceType (package:dev_compiler/src/kernel/compiler.dart:3256:17)
#14     ProgramCompiler.visitInterfaceType (package:dev_compiler/src/kernel/compiler.dart:3191:7)

#15     InterfaceType.accept (package:kernel/ast.dart:12100:42)
#16     ProgramCompiler._emitType (package:dev_compiler/src/kernel/compiler.dart:3076:60)
#17     ProgramCompiler._emitArgumentList (package:dev_compiler/src/kernel/compiler.dart:6223:41)
#18     ProgramCompiler._emitMethodCall (package:dev_compiler/src/kernel/compiler.dart:5326:16)
#19     ProgramCompiler.visitInstanceInvocation (package:dev_compiler/src/kernel/compiler.dart:5240:12)
#20     InstanceInvocation.accept (package:kernel/ast.dart:6128:44)
#21     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#22     ProgramCompiler._emitMethodCall (package:dev_compiler/src/kernel/compiler.dart:5325:22)
#23     ProgramCompiler.visitInstanceInvocation (package:dev_compiler/src/kernel/compiler.dart:5240:12)
#24     InstanceInvocation.accept (package:kernel/ast.dart:6128:44)
#25     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#26     ProgramCompiler.visitConditionalExpression (package:dev_compiler/src/kernel/compiler.dart:6598:21)
#27     ConditionalExpression.accept (package:kernel/ast.dart:7420:44)
#28     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#29     ProgramCompiler.visitLet (package:dev_compiler/src/kernel/compiler.dart:6996:16)
#30     Let.accept (package:kernel/ast.dart:9277:44)
#31     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#32     ProgramCompiler.visitLet (package:dev_compiler/src/kernel/compiler.dart:6995:16)
#33     Let.accept (package:kernel/ast.dart:9277:44)
#34     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#35     MappedListIterable.elementAt (dart:_internal/iterable.dart:415:31)
#36     ListIterator.moveNext (dart:_internal/iterable.dart:344:26)

#37     new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:189:27)
#38     new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
#39     new List.of (dart:core-patch/array_patch.dart:47:28)
#40     ListIterable.toList (dart:_internal/iterable.dart:214:7)
#41     ProgramCompiler._visitExpressionList (package:dev_compiler/src/kernel/compiler.dart:4195:40)
#42     ProgramCompiler.visitListLiteral (package:dev_compiler/src/kernel/compiler.dart:6833:20)
#43     ListLiteral.accept (package:kernel/ast.dart:8700:44)
#44     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#45     ProgramCompiler._emitArgumentList (package:dev_compiler/src/kernel/compiler.dart:6232:11)

#46     ProgramCompiler.visitStaticInvocation (package:dev_compiler/src/kernel/compiler.dart:6146:16)
#47     StaticInvocation.accept (package:kernel/ast.dart:7029:44)
#48     ProgramCompiler._visitExpression (package:dev_compiler/src/kernel/compiler.dart:4232:20)
#49     ProgramCompiler.visitReturnStatement (package:dev_compiler/src/kernel/compiler.dart:4794:45)
#50     ReturnStatement.accept (package:kernel/ast.dart:10786:43)
#51     ProgramCompiler._visitStatement (package:dev_compiler/src/kernel/compiler.dart:4141:20)

#52     ProgramCompiler._emitFunctionScopedBody (package:dev_compiler/src/kernel/compiler.dart:4174:18)
#53     ProgramCompiler._emitSyncFunctionBody.<anonymous closure> (package:dev_compiler/src/kernel/compiler.dart:3909:17)
#54     ProgramCompiler._withLetScope (package:dev_compiler/src/kernel/compiler.dart:2593:25)

#55     ProgramCompiler._withCurrentFunction (package:dev_compiler/src/kernel/compiler.dart:3943:18)
#56     ProgramCompiler._emitSyncFunctionBody (package:dev_compiler/src/kernel/compiler.dart:3905:17)

#57     ProgramCompiler._emitFactoryConstructor (package:dev_compiler/src/kernel/compiler.dart:2310:18)
#58     ProgramCompiler._emitJSInteropClassNonExternalMembers (package:dev_compiler/src/kernel/compiler.dart:919:23)

#59     ProgramCompiler._emitClass (package:dev_compiler/src/kernel/compiler.dart:734:31)
#60     List.forEach (dart:core-patch/growable_array.dart:416:8)
#61     ProgramCompiler._emitLibrary (package:dev_compiler/src/kernel/compiler.dart:670:23)
#62     List.forEach (dart:core-patch/growable_array.dart:416:8)

#63     ProgramCompiler.emitModule (package:dev_compiler/src/kernel/compiler.dart:479:15)
#64     IncrementalJavaScriptBundler.compile (package:frontend_server/src/javascript_bundle.dart:217:33)
#65     FrontendCompiler.writeJavaScriptBundle (package:frontend_server/frontend_server.dart:778:46)
<asynchronous suspension>
#66     FrontendCompiler.compile (package:frontend_server/frontend_server.dart:641:9)
<asynchronous suspension>

#67     listenAndCompile.<anonymous closure> (package:frontend_server/frontend_server.dart:1308:11)
<asynchronous suspension>

the Dart compiler exited unexpectedly.
Failed to compile application.

[srujzs]

Thanks for filing! Can you share with us a minimal repro of this issue?

cc @nshahan

[llfbandit]

Here's a reproducer. this is Flutter app.
This is purely default app with typings package dependency added and an attachment to foo method call to avoid tree shake on unused package.

dev_compiler_issue.zip

[jodinathan]

is there anything I could change in Typings to fix this @srujzs ?

[srujzs]

There's likely some type here that the CFE is unable to determine the nullability of correctly, which throws in DDC, so yes, but I still need to figure out what the offending code is here. I'm trying to run typings but keep coming across issues when trying to do with build_runner e.g.

log

srujzs-macbookpro:typingsissue srujzs$ dart run build_runner build
Building package executable... (6.6s)
Built build_runner:build_runner.
[INFO] Generating build script completed, took 412ms
[WARNING] ../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/project.dart:61:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class ExternalInteropModule {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/project.dart:77:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class ExternalInteropProject {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/library.dart:149:19: Error: The setter 'external' isn't defined for the class 'FieldBuilder'.
 - 'FieldBuilder' is from 'package:code_builder/src/specs/field.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/field.dart').
Try correcting the name to the name of an existing setter, or defining a setter or field named 'external'.
                ..external = true
                  ^^^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/library.dart:171:23: Error: The setter 'external' isn't defined for the class 'FieldBuilder'.
 - 'FieldBuilder' is from 'package:code_builder/src/specs/field.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/field.dart').
Try correcting the name to the name of an existing setter, or defining a setter or field named 'external'.
                    ..external = true
                      ^^^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/property.dart:61:13: Error: The setter 'external' isn't defined for the class 'FieldBuilder'.
 - 'FieldBuilder' is from 'package:code_builder/src/specs/field.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/field.dart').
Try correcting the name to the name of an existing setter, or defining a setter or field named 'external'.
          ..external = true;
            ^^^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:4:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataCtor {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:10:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataIndex {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:22:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataCall {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:28:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataStruct {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:80:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataTypeRef {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/metadata/struct.dart:88:1: Error: This requires the experimental 'inline-class' language feature to be enabled.
Try passing the '--enable-experiment=inline-class' command line option.
inline class MetadataStructMember {
^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/method.dart:266:19: Error: The getter 'namedParameters' isn't defined for the class 'RecordTypeBuilder'.
 - 'RecordTypeBuilder' is from 'package:code_builder/src/specs/type_record.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/type_record.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'namedParameters'.
                b.namedParameters['\$${index + start}'] = element.express;
                  ^^^^^^^^^^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/method.dart:266:67: Error: The getter 'express' isn't defined for the class 'Method'.
 - 'Method' is from 'package:code_builder/src/specs/method.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/method.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'express'.
                b.namedParameters['\$${index + start}'] = element.express;
                                                                  ^^^^^^^
../../.pub-cache/hosted/pub.dev/ts2dart-0.0.2/lib/src/ast/types/tuple.dart:41:11: Error: The getter 'parameters' isn't defined for the class 'RecordTypeBuilder'.
 - 'RecordTypeBuilder' is from 'package:code_builder/src/specs/type_record.dart' ('../../.pub-cache/hosted/pub.dev/code_builder-4.5.0/lib/src/specs/type_record.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'parameters'.
        b.parameters.add(type.ref());
          ^^^^^^^^^^
[INFO] Precompiling build script... completed, took 1.1s
[SEVERE] Failed to precompile build script .dart_tool/build/entrypoint/build.dart.

Any idea where I'm going wrong in trying to use the package?

[jodinathan]

I use inline classes in ts2dart I guess it changed to extension types or something like that.
Try with SDK 3.0.7

[srujzs]

Hmm I don't think the migration to extension types is the issue, we haven't removed support for the inline class syntax yet either. Trying it with SDK 3.0.7 still produces the same error for me.

Are you running this with something besides build_runner? I'm avoiding using Flutter to do this as it adds some extra step to use a custom Dart SDK and debug.

[jodinathan]

You need to clean things up when changing the SDK, please try

rm -Rf .dart_tool
dart pub get
./run.sh

[srujzs]

Couldn't get that to work but ended up debugging using a local Flutter engine. The failure is at: https://github.com/jodinathan/typings/blob/e8e231c7905af52bc24538fe4ea17486e81cbc4d/typings/lib/src/d/core/lib.es2015.collection.d.dart#L265

A simple repro for the undetermined nullability error:

class WeakMap<K extends Object, V> {
  WeakMap(List<(K, V)> entries) {
    entries.map((i) => [i.$1, i.$2]);
  }
}

void main() {}

The fix seems to be just add an explicit <Object?> to the list within the map function (at least in the simple repro). Weirdly enough, removing the extends Object also fixes this.

cc @johnniwinther

[nshahan]

@srujzs You are a hero for finding the offending line of code! Thank you!

It looks like the issue arrises from combining values with the types K extends Object and V into the same list. The inferred type argument of the list creates the intersection Object% (undetermined nullability). Should it be inferred as Object? instead?

You can trigger the same issue with an even smaller repro:

fn<T extends Object, S>(T t, S s) => [t, s];

void main() {}

cc @stereotype441