Dart2js crash on local function type variables.

[lrhn]

I received the error

Unexpected compile error.

--- Command "dart2js" (took 01.000144s):
DART_CONFIGURATION=ReleaseX64 out/ReleaseX64/dart-sdk/bin/dart compile js -Dtest_runner.configuration=dart2js-linux-chrome --sound-null-safety --test-mode --packages=.dart_tool/package_config.json tests/corelib/iterable_extension_test.dart --sound-null-safety --out=out/ReleaseX64/generated_compilations/dart2js-linux-chrome/tests_corelib_iterable_extension_test/iterable_extension_test.js

exit code:
253

stdout:
Info: Compiling with sound null safety.
The compiler crashed: Assertion failure: Local function type variables are not supported.
#0      failedAt (package:compiler/src/diagnostics/invariant.dart:39:3)
#1      JsToFrontendMapImpl.toBackendTypeVariable (package:compiler/src/js_model/js_world_builder.dart:586:9)
...

when trying to run a new test.
It's only test code, not the code being tested, so I'll pre-approve the failure for now.

It's coming from js_world_builder.dart:

  TypeVariableEntity? toBackendTypeVariable(TypeVariableEntity typeVariable) {
    if (typeVariable is KLocalTypeVariable) {
      if (_closureData == null) {
        failedAt(
            typeVariable, "Local function type variables are not supported.");
      }

but if it's reachable from user code, then it's a bug.

[sigmundch]

Thanks @lrhn - seems like dart2js has never added support for type variables on local functions. While I agree that should be fixed, it would be a shame to not have test coverage in dart2js for your new changes because of this (especially since your feature doesn't relate to this issue). In the meantime, would you consider a small refactor on the test to avoid this feature? I'll comment on your CL as well.

[lrhn]

Are we sure it doesn't support local generic functions at all. The tests/language/generic/local_functions_test.dart test works, as far as I can see.
I can write simple generic local functions directly too. A little commenting in/out suggests that the problem is in the testIndexed function, which has a recursive generic local function. That might be the trigger, so moving just that one might be sufficient. (Still, make sure we have an issue tracking the fixing of that.)

But I'll rewrite the test and see if it helps.

[sigmundch]

Sorry, you are right, I just jumped to conclusions too quickly by looking at the error message above.

[sigmundch]

mmm... I was not able to repro the crash after I patched your CL locally. Do you know if it is still failing on your CL?

[sigmundch]

Ah, never mind - I saw most closures were still around and I didn't notice that you did hoist testRec. Putting that one back in the method reintroduces the crash.

[sigmundch]

It appears the issue is directly related to records. Here is a minimal repro:

void main() {
  void f<T>(T value, (int, T) record) {
    (0, value) == record;
  }

  f("a", (0, "a"));
}

Which crashes with the following error:

The compiler crashed: Assertion failure: Local function type variables are not supported.
#0      failedAt (package:compiler/src/diagnostics/invariant.dart:39:3)
#1      JsToFrontendMapImpl.toBackendTypeVariable (package:compiler/src/js_model/js_world_builder.dart:586:9)
#2      JsToFrontendMapImpl.toBackendEntity (package:compiler/src/js_model/js_world_builder.dart:556:14)
#3      _TypeConverter.visitTypeVariableType (package:compiler/src/js_model/js_world_builder.dart:679:36)
#4      TypeVariableType.accept (package:compiler/src/elements/types.dart:499:15)
#5      _TypeConverter.visit (package:compiler/src/js_model/js_world_builder.dart:632:17)
#6      _TypeConverter.visitList (package:compiler/src/js_model/js_world_builder.dart:638:16)
#7      _TypeConverter.visitRecordType (package:compiler/src/js_model/js_world_builder.dart:672:46)
#8      RecordType.accept (package:compiler/src/elements/types.dart:440:15)
#9      _TypeConverter.visit (package:compiler/src/js_model/js_world_builder.dart:632:17)
#10     JsToFrontendMapImpl.toBackendType (package:compiler/src/js_model/js_world_builder.dart:550:16)
#11     MappedIterator.moveNext (dart:_internal/iterable.dart:393:20)
#12     JsToFrontendMap.toBackendTypeSet (package:compiler/src/js_model/js_to_frontend_map.dart:35:36)
#13     JClosedWorldBuilder.convertClosedWorld (package:compiler/src/js_model/js_world_builder.dart:150:13)
#14     JsBackendStrategy.createJClosedWorld (package:compiler/src/js_model/js_strategy.dart:188:52)
#15     Compiler.closeResolution (package:compiler/src/compiler.dart:815:25)
#16     Compiler.computeClosedWorld (package:compiler/src/compiler.dart:387:9)
#17     Compiler.produceClosedWorld (package:compiler/src/compiler.dart:629:11)
#18     Compiler.runSequentialPhases (package:compiler/src/compiler.dart:756:15)
<asynchronous suspension>
#19     Compiler.runInternal.<anonymous closure> (package:compiler/src/compiler.dart:319:7)
<asynchronous suspension>
#20     Compiler.runInternal (package:compiler/src/compiler.dart:318:5)
<asynchronous suspension>
#21     Compiler.run.<anonymous closure> (package:compiler/src/compiler.dart:239:11)
<asynchronous suspension>
#22     main (package:compiler/src/dart2js.dart:1474:3)
<asynchronous suspension>

[sigmundch]

cc @rakudrama

[sigmundch]

It appears related to the creation of the inner record. Here is an even simpler repro:

void main() {
  Object? f<T>(T value) => (0, value);
  f("a");
}

[sigmundch]

I marked this as P1 for our team, since it's a crasher, but I don't consider this a blocker for the milestone. Feel free to move it out of the milestone as we approach the deadline.