Bounds in for<...> are ignored

[jhjourdan]

When writing for<'a : 'b> fn(...) -> ..., the constraint 'a : 'b is completely ignored by borrowcheck.

This makes it possible to write the following function, which is weird:

fn g<'b>(f : for<'c : 'b> fn(&'c mut i32) -> &'b mut i32) -> &'b mut i32 {
    let f2 : for<'c> fn(&'c mut i32) -> &'b mut i32 =
      f ; // WTF, we are dropping the constraint 'c : 'b ?
}

[eddyb]

cc @nikomatsakis

[petrochenkov]

Same as #23051

[eddyb]

@petrochenkov Ahh I tried looking for an existing issue but I couldn't (wrong keywords used), thanks!

[jhjourdan]

Ah, indeed. Sorry for the noise. Closing.