"Remove this semicolon" lint for return values and closures

[alexcrichton]

Right now it looks like we don't handle closures when printing out the "consider removing this semicolon" help message (but we do handle functions!). It'd be kinda cool if we could handle closures as well (or maybe any block statement in general?

fn foo(_: || -> bool) {}

fn main() {
    foo(|| { true; });
}

[steveklabnik]

Traige, updated code:

fn foo(_: Fn() -> bool) {}

fn main() {
        foo(|| { true; });
}

No change on status though.

[pmarcelll]

It seems to be fixed, for this code:

fn foo<F: Fn() -> bool>(_: F) {}

fn main() {
        foo(|| { true; });
}

the output is:

error[E0308]: mismatched types
 --> <anon>:4:16
  |
4 |         foo(|| { true; });
  |                ^^^^^^^^^ expected bool, found ()
  |
  = note: expected type `bool`
             found type `()`
help: consider removing this semicolon:
 --> <anon>:4:22
  |
4 |         foo(|| { true; });
  |                      ^

error: aborting due to previous error

[Mark-Simulacrum]

Closing in favor of collective issue for this general problem: #41897.