rustdoc primitve impl method anchors are not disambiguated

[brson]

The page for pointers contains impls for both *const and *mut but the links to their methods are not disambiguated by pointer type, so http://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.as_ref is used for the anchor of both as_ref methods.

[nagisa]

cc #30036

[mitaa]

This is because even though we're generating unique ids, the code that renders the methods and creates the links (render_assoc_item) does not know about the allocated id and creates a naive one itself..

render_assoc_item takes a

enum AssocItemLink<'a> {
    Anchor,
    GotoSource(DefId, &'a HashSet<String>),
}

where Anchor refers to an item on the current page and GotoSource refers to the trait pages item (used in the trait implementations section).

I think the best fix would be to change Anchor to Anchor(Option<String>) and fill it lazily with the allocated id from derive_id(..).

Relevant code is in src/librustdoc/html/render.rs.

Label as "E-easy"?

[caipre]

I'll take a look at this.