Analyzer doesn't report "Generic function type cannot be used as a type parameter"

[sgrekhov]

Consider the following code

dynamic forgetType(dynamic d) => d;

typedef T0 = void Function();
typedef T1 = void Function<X>();

void t0Instance() {}
void t1Instance<X>() {}

class ArgumentsBindingTest<X>  {
  ArgumentsBindingTest(X t1) {}
}

main() {
  T0 t0 = t0Instance;
  T1 t1 = t1Instance;
  new ArgumentsBindingTest<T0>(forgetType(t0)); // works
  new ArgumentsBindingTest<T1>(forgetType(t1)); // error
}

This code produces

error: generic function type '<X>() => void' not allowed as type argument of type 'ArgumentsBindingTest<<X>() => void>'
#0      _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:279:19)
#1      _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:165:12)

Why function type can be used as a type parameter, but generic function type cannot?

Dart VM version: 2.0.0-dev.63.0 (Fri Jun 15 00:42:43 2018 +0200) on "windows_x64"

[lrhn]

The class Exception doesn't cover most errors in Dart. You probably want to use Error instead (or just drop the on part of the catch and catch all thrown objects).

This does throw a TypeError, which implements Error and not Exception. I don't know why it prints badly, if you paste the code into DartPad, it prints the error message as

TypeError: Closure 't0Func': type '<T1 extends B0, T2 extends B1>(V0, V1, {V2 x2, V3 x3, V4 x4}) => U0' is not a subtype of type '<T1 extends B0, T2 extends B1>(S0, S1, {S2 x2, S3 x3, S4 x4, V4 x5}) => U1'

[sgrekhov]

@lrhn, problem is that generic function type cannot be used as a type parameter. I've rewritten the issue. Please, look at it once again

[lrhn]

That's actually expected behavior. We do not allow generic method types as type arguments.

[sgrekhov]

If this is an expected behaviour, then, there should be an error in analyzer, I think, but there isn't.

[lrhn]

There should be an error reported by analyzer, yes.