"Generate Deref impl" should abbreviate std::ops::Deref if already in scope

[jonas-schievink]

use std::ops::Deref;

struct S {
    target$0: u8,
}

Applying the "Generate Deref impl using target" assist generates this:

impl std::ops::Deref for S {
    type Target = u8;

    fn deref(&self) -> &Self::Target {
        &self.target
    }
}

The std::ops::Deref is unnecessarily qualified here, just Deref would be enough. We have code that can automatically do this, should just be a matter of calling that.

[jhgg]

What's the code? Happy to make this fix!

[Veykril]

https://github.com/rust-lang/rust-analyzer/blob/master/crates/hir/src/lib.rs#L569-L585
Should be what you need here (you'll first want to fetch Deref via FamousDefs, then fetch a path via one of those)