Implement the Q1 2021 small features release in the CFE

[leafpetersen]

Implementation issue for this set of features.

See also.

cc @johnniwinther @franklinyow

[leafpetersen]

@stefantsov any updates?

[chloestefantsova]

The support for GFT in type arguments and bounds landed as https://dart-review.googlesource.com/c/sdk/+/188701.

[nshahan]

@stefantsov @eernstg
I'm seeing compile time errors for the tests that were landed for the Generic Function Types in type arguments and bounds feature. https://dart-ci.firebaseapp.com/current_results/#/filter=language/generic/generic_function_type_argument_test&showAll

Is there an experiment flag we need to turn on at this point?

[leafpetersen]

I think that test is still failing in the front ends.

[eernstg]

I think the test language/generic/generic_function_type_argument_test.dart requires that

FB<F> <: F   // That is:
S Function<S extends X Function<X>(X)>(S) <: X Function<X>(X)   // Which is not true.

So the test and the analyzer need to be adjusted.

[crelier]

@stefantsov I'm seeing an error reported by CFE on annotations:

$ out/DebugX64/dart --enable-experiment=generic-metadata tests/language/generic/generic_function_type_argument_test.dart
tests/language/generic/generic_function_type_argument_test.dart:48:2: Error: Type argument 'S Function<S extends T Function<T>(T)>(S)' doesn't conform to the bound 'T Function<T>(T)' of the type variable 'T' on 'CB'.
Try changing type arguments so that they conform to the bounds.
@CB<FB<F>>(fb)
 ^
tests/language/generic/generic_function_type_argument_test.dart:31:10: Context: This is the type variable whose bound isn't conformed to.
class CB<T extends F> {
         ^

[chloestefantsova]

@stefantsov I'm seeing an error reported by CFE on annotations:

I think that error reporting is correct, as @eernstg wrote above. The bound is T Function<T>(T), and the type argument is S Function<S extends T Function<T>(T)>(S). The type parameters in the two have different bounds, so they are incomparable: neither is a subtype of the other, and the error should be reported.

[leafpetersen]

The test needs adjustment. I'll work on getting that done.

[crelier]

I think that error reporting is correct, as @eernstg wrote above.

Sorry, I totally missed Erik's post. My comment was sitting in a draft tab for too long.
Thanks all!