Intra-doc links should work for deref methods

[jyn514]

I tried this code:

/// [`get`]: std::vec::Vec::get
pub fn f() {}

I expected to see this happen: A link to https://doc.rust-lang.org/std/vec/struct.Vec.html#method.get

Instead, this happened: The link wasn't resolved, because get is a method on slices, not Vec itself.

[jyn514]

Note that this currently means Vec::get can't be linked to at all because of #63351.

[GuillaumeGomez]

I need to get back to the fix and understand what changes between the two.

[jyn514]

FWIW I don't think this ever worked, it just wasn't implemented.

[GuillaumeGomez]

It never did, I was referring to my PR to fix primitive discoverability.

[Manishearth]

I'm against this, Vec::get does not exist and does not work in code. I think we should maybe just bite the bullet and allow slice to exist as a string.

[jyn514]

I'm ok with saying we should fix linking to primitives instead, but it's not as simple as 'allow slice to exist as a string', see #63351 (comment).