Unused warning for type alias doesn't take into account inherent impls.

[cristicbz]

The following code (playground):

pub struct GenericFoo<T>(T);

type Foo = GenericFoo<u32>;

impl Foo {
    fn bar(self) -> u8 {
        0
    }
}

fn main() {    
    println!("{}", GenericFoo(0).bar());
}

results in the warning:

warning: type alias is never used: `Foo`
 --> src/main.rs:3:1
  |
3 | type Foo = GenericFoo<u32>;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

This is incorrect, since the Foo impl uses it (and it can be unwieldy to write it out otherwise).

[jsgf]

This looks like a similar case: type aliases used for trait bounds on inherent impl are not considered used: playground

#![deny(warnings)]

type FooBar<F> = <F as Foo>::Bar;

trait Foo {
    type Bar;
}

struct Blop<F>(F);

impl<F: Foo> Blop<F>
where
    FooBar<F>: Clone,
{
}

impl Foo for () {
    type Bar = ();
}

fn main() {
    let _ = Blop(());
}

[shepmaster]

Additional example:

type Inner = Box<i32>;
struct Wrapper(Inner);

fn main() {
    Wrapper(Box::new(42));
}

warning: type alias is never used: `Inner`
 --> src/main.rs:4:1
  |
4 | type Inner = Box<i32>;
  | ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

Rust 1.32.0