[dart2wasm]: Unexpected type StructuralParameterType StructuralParameterType(T).

[ykmnkmi]

Got this error and don't know which as throws:

Running dart compile wasm...
  - input file name   = file:///C:/.../web/main.dart
  - output file name  = .\web\main.wasm
  - librariesSpecPath = null
  - packagesPath file = null
  - platformPath file = file:///C:/.../Dart/lib/_internal/dart2wasm_platform.dill
  - generate source maps = true
Unhandled exception:
Unexpected type StructuralParameterType StructuralParameterType(T)
#0      TypesBuilder.fromStaticType (package:vm/transformations/type_flow/types.dart:261)
#1      SummaryCollector._typeCheck (package:vm/transformations/type_flow/summary_collector.dart:1260)
#3      AsExpression.accept (package:kernel/src/ast/expressions.dart:3628)
#4      SummaryCollector._visit (package:vm/transformations/type_flow/summary_collector.dart:975)
#5      SummaryCollector.visitExpressionStatement (package:vm/transformations/type_flow/summary_collector.dart:2300)
#6      ExpressionStatement.accept (package:kernel/src/ast/statements.dart:50)
#7      SummaryCollector._visitWithoutResult (package:vm/transformations/type_flow/summary_collector.dart:978)
#8      List.forEach (dart:core-patch/growable_array.dart:417)
#9      SummaryCollector.visitBlock (package:vm/transformations/type_flow/summary_collector.dart:2251)
#10     Block.accept (package:kernel/src/ast/statements.dart:103)
#11     SummaryCollector._visitWithoutResult (package:vm/transformations/type_flow/summary_collector.dart:978)
#12     SummaryCollector.createSummary (package:vm/transformations/type_flow/summary_collector.dart:838)
#13     TypeFlowAnalysis.getSummary (package:vm/transformations/type_flow/analysis.dart:1912)
#14     _DirectInvocation._processFunction (package:vm/transformations/type_flow/analysis.dart:399)
#15     _DirectInvocation.process (package:vm/transformations/type_flow/analysis.dart:288)
#16     _WorkList.processInvocation (package:vm/transformations/type_flow/analysis.dart:1793)
#17     _WorkList.process (package:vm/transformations/type_flow/analysis.dart:1736)
#18     TypeFlowAnalysis.process (package:vm/transformations/type_flow/analysis.dart:1941)
#19     transformComponent (package:vm/transformations/type_flow/transformer.dart:122)
#20     compileToModule (package:dart2wasm/compile.dart:221)
<asynchronous suspension>
#21     generateWasm (package:dart2wasm/generate_wasm.dart:51)
<asynchronous suspension>
#22     main (file:///C:/b/s/w/ir/x/w/sdk/pkg/dart2wasm/bin/dart2wasm.dart:10)
<asynchronous suspension>

[ykmnkmi]

Dart 3.6.0 (stable) (Thu Dec 5 07:46:24 2024 -0800) on "windows_x64".

[dart-github-bot]

Summary: dart2wasm compilation fails with Unexpected type StructuralParameterType error during type checking, likely caused by a type mismatch in the user's code. The specific location is unclear.

[ykmnkmi]

Compiles with dart2js and ddc.

[mraleph]

cc @alexmarkov

[ykmnkmi]

Same with 3.6.1.

[alexmarkov]

TFA crashes as it doesn't support as checks against StructuralParameterType types.

However, I'm not sure how to create an example of such as check: StructuralParameterType is a type for a StructuralParameter which represents a type parameter in a function type, and such type parameters presumably cannot be used outside of function types. @johnniwinther @chloestefantsova Could you help me to create an example of such as check?

@ykmnkmi Could you try to reduce your app to a small example which would still crash the compiler?

[ykmnkmi]

@alexmarkov wokring on it.

[ykmnkmi]

@alexmarkov

import 'dart:js_interop';

import 'package:web/web.dart';

void main() {
  void handler<T extends Event>(Element element, T event) {
    print(element == event.currentTarget);
  }

  // throws
  // JSExportedDartFunction jsHandler = handler.toJSCaptureThis;

  // works
  JSExportedDartFunction jsHandler = handler<MouseEvent>.toJSCaptureThis;
  document.body!.addEventListener('click', jsHandler);
}

[chloestefantsova]

Chances are, it's a CFE issue. StructuralParameterTypes should not appear on their own, outside of the scope of a FunctionType's generic parameters.

I've updated the labels accordingly.