DDC is incorrectly hoisting types

[vsmenon]

The following:

class Foo {
}

class Bar {
}

typedef Type Func<S extends Foo, T>(T s);

class Baz<S extends Foo, T extends Bar> {
  Func<S, Bar> func;
}

void main() {
  dynamic baz = new Baz();
  print(baz.func);
}

fails with:

ReferenceError: S is not defined ReferenceError: S is not defined

[vsmenon]

@jmesserly @leafpetersen - can one of you take a look? If I can Func<S, Bar> to Func<S, T>, no error - looks like a bug in the hoist logic.

[jmesserly]

I can take a look. I hope it's not an instance of #30379 (because that one is showing up everywhere lately).

[jmesserly]

The reason this is broken is that S is not used in the function type, so it doesn't appear at all after the typedef has been instantiated. The function type is just (Bar) -> Type, so no free variables, and hoisting is legal. The problem is we emit it using the typedef (to preserve the name perhaps).

I'm guessing no one has hit this combo before, as unused type parameters aren't super common.

Shouldn't be too hard to fix.

[jmesserly]

https://dart-review.googlesource.com/c/sdk/+/9125