GLB/LUB do not handle generic functions

[jmesserly]

for example:

void main() {
  var isEven = new DateTime.now().millisecond.isEven;
  var f = isEven ? <T>(T t) => t : <U>(U t) => t;
  print(f<int>(42)); // The method '(<bottom>) → Object' is declared with 0 type parameters, but 1 type arguments were given
}

even worse:

void main() {
  var isEven = new DateTime.now().millisecond.isEven;
  var f = isEven ? <T>() => 42 : <U>() => 42;
  print(f());
}

prints the internal closure used for generic method dispatch (this function object should never be exposed to user code):

Closure: NativeJavaScriptObject from: () => {
    return 42;
  }

[jmesserly]

this was fixed, yay!

[scheglov]

This still fails.

typedef F1 = T Function<T>();
typedef F2 = U Function<U>();

main() {
  F1 a;
  F2 b;
  F1 c = a ?? b;
}

error: A value of type '() → Object' can't be assigned to a variable of type '<T>() → T'. (invalid_assignment at [test] bin/test.dart:7)

But when I change both a and b to be either F1 or F2, then their types become identical objects, and returned from getLeastUpperBound(t1, t2) as t1, which does have type parameters.

Found this while working on a change for nullability, which we don't check yet, but we get non-identical FunctionType instances, so don't take the shortcut.

[jmesserly]

Yeah, wow, _functionLeastUpperBound does not handle generic functions at all, same for GLB. (Not sure why I thought it was fixed, oops!)

[srawlins]

This appears to be fixed. Also the follow up example, when modified for null safety:

typedef F1 = T Function<T>();
typedef F2 = U Function<U>();

f(F1? a, F2, b) {
  F1 c = a ?? b;
}

is fixed.