fix: into_iterator not completed on Vec<{unknown}>

[iDawer]

Fixes #10297

[lnicola]

Ah, I didn't manage to write a test here.

Should we do the same thing in autoderef?

[iDawer]

Actually there are more: impls_future, impls_fnonce, impls_trait. Do we need tests for them? Let me see if there are trivial tests

[iDawer]

I couldn't reproduce this in tests but RA definetely fails on it (hir::Type::autoderef fixed):

struct Foo<T>;
struct Bar;
trait Trait {
    fn quux(&self) {}
}
impl<T> core::ops::Deref for Foo<T> {
    type Target = Bar;
    fn deref(&self) -> &Self::Target;
}
impl Trait for Bar {}
fn main() {
    let x: Foo<_>;
    x.$0
    // missing `quux` method in completions
}

---

I had tried to fix impls_trait but Chalk started panicking on the next example. This needs some elaboration.

struct Vec<T>;
impl<T> IntoIterator for Vec<T> {
    type Item = ();
    type IntoIter = ();
    fn into_iter(self);
}
fn main() {
    let x: Vec<_>;
    x.$0;
    // missing postfix completion "for"
}

Leave this and others for next time?

[flodiebold]

bors d+

[bors]

✌️ iDawer can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[iDawer]

bors r+

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)

[iDawer]

This PR caused regression in nightly #10396 (fixed by #10399)