Add use statements support to #[project] attribute

[taiki-e]

This adds a feature to convert annotated imports to a projected type's imports.

For now, this works as an import for both projected type and projection trait. Now, this works as an import for projected type.

Examples

use pin_project::pin_project;

#[pin_project]
struct Foo<A> {
    #[pin]
    field: A,
}

mod bar {
    use pin_project::project;
    use super::Foo;
    use std::pin::Pin;

    #[project]
    use super::Foo;

    #[project]
    fn baz<A>(foo: Pin<&mut Foo<A>>) {
        #[project]
        let Foo { field } = foo.project();
        let _: Pin<&mut A> = field;
    }
}

[taiki-e]

I feel that if importing both the projected-type and the original type, it will not look very good.

#[project]
use super::Foo;
use super::Foo;

[taiki-e]

cc #43

[taiki-e]

bors r+

[bors]

Merge conflict

[taiki-e]

bors retry

[bors]

Build succeeded

• taiki-e.pin-project