dart2js has incomplete support for local function type variables #42088
Description
Consider the following contrived, but small, example:
class Foo<T> {}
void main() {
<T>() => Foo<T>().runtimeType;
}The VM compiles this successfully. (You can, for example, print the local function to ensure liveness.)
On dart2js, the compiler throws:
The compiler crashed: Assertion failure: Local function type variables are not supported.
#0 failedAt (package:compiler/src/diagnostics/invariant.dart:49:3)
#1 JsToFrontendMapImpl.toBackendTypeVariable (package:compiler/src/js_model/js_world_builder.dart:712:7)
#2 JsToFrontendMapImpl.toBackendEntity (package:compiler/src/js_model/js_world_builder.dart:689:14)
#3 _TypeConverter.visitTypeVariableType (package:compiler/src/js_model/js_world_builder.dart:792:49)
#4 TypeVariableType.accept (package:compiler/src/elements/types.dart:414:15)
#5 _TypeConverter.visit (package:compiler/src/js_model/js_world_builder.dart:751:17)
#6 _TypeConverter.visitLegacyType (package:compiler/src/js_model/js_world_builder.dart:764:29)
#7 LegacyType.accept (package:compiler/src/elements/types.dart:234:15)
#8 _TypeConverter.visit (package:compiler/src/js_model/js_world_builder.dart:751:17)
#9 _TypeConverter.visitList (package:compiler/src/js_model/js_world_builder.dart:757:16)
#10 _TypeConverter.visitInterfaceType (package:compiler/src/js_model/js_world_builder.dart:786:34)
#11 InterfaceType.accept (package:compiler/src/elements/types.dart:354:15)
#12 _TypeConverter.visit (package:compiler/src/js_model/js_world_builder.dart:751:17)
#13 JsToFrontendMapImpl.toBackendType (package:compiler/src/js_model/js_world_builder.dart:683:16)
#14 JsClosedWorldBuilder._convertBackendUsage.<anonymous closure> (package:compiler/src/js_model/js_world_builder.dart:256:15)
#15 MappedIterator.moveNext (dart:_internal/iterable.dart:392:20)
#16 SetMixin.addAll (dart:collection/set.dart:57:23)
#17 new LinkedHashSet.of (dart:collection/linked_hash_set.dart:111:27)
#18 Iterable.toSet (dart:core/iterable.dart:416:21)
#19 JsClosedWorldBuilder._convertBackendUsage (package:compiler/src/js_model/js_world_builder.dart:258:8)
#20 JsClosedWorldBuilder.convertClosedWorld (package:compiler/src/js_model/js_world_builder.dart:66:9)
#21 JsBackendStrategy.createJClosedWorld (package:compiler/src/js_model/js_strategy.dart:180:52)
...
Although local type variables cannot be (globally) indexed, it should be possible to convert them from the K-model to the J-model by first ensuring the enclosing local function is converted and indexing into its type variables.
/cc @johnniwinther