Clean up doc_alias feature

[GuillaumeGomez]

From this comment: #50146 (comment)

Still remaining the .replace().

[GuillaumeGomez]

Actually, the " character has a meaning in the search (for "exact" search). But instead of just removing it, maybe we should instead emit an error when we encounter it. What do you think @ollie27 ?

[ollie27]

Actually, the " character has a meaning in the search (for "exact" search).

That doesn't work for #[doc(alias = "...")] though, maybe it should?

But instead of just removing it, maybe we should instead emit an error when we encounter it.

It would make sense to restrict allowed characters because even whitespace is allowed at the moment which seems questionable.

[Mark-Simulacrum]

It sounds like we need to make sure this lands before we branch beta or so?

[GuillaumeGomez]

Let's forbid ", whitespaces and tabs in the the doc alias then.

[Mark-Simulacrum]

Can we avoid ad-hoc rules and say something like "must be a rust identifier"?

[GuillaumeGomez]

Even better! Great suggestion @Mark-Simulacrum !

[GuillaumeGomez]

Just thought about it, but it cannot be the case @Mark-Simulacrum : we allow things like "*" or "+" (for the traits for example), so it cannot be ident only. I'll stick to the listed characters above.

[Mark-Simulacrum]

The documentation (https://doc.rust-lang.org/nightly/rustdoc/advanced-features.html?highlight=alias#add-aliases-for-an-item-in-documentation-search) has no mention of that -- can you elaborate?

[GuillaumeGomez]

Doc aliases can be something else than a rust identifier. For example, you can look for & or + in the std docs, and you'll see aliases results.

[Mark-Simulacrum]

Ah, I see what you mean. Okay, then I agree that we need more than just Rust identifiers, and it might be reasonable to just allow as you suggest -- everything except whitespace and quotes. I'm a bit worried that'll hurt us in terms of how expansive it is but it's probably fine.