Emit errors/warns on some wrong uses of rustdoc attributes

[LeSeulArtichaut]

This PR adds a few diagnostics:

• error if conflicting #[doc(inline)]/#[doc(no_inline)] are found
• introduce the invalid_doc_attributes lint (warn-by-default) which triggers:
  • if a crate-level attribute is used on a non-crate item
  • if #[doc(inline)]/#[doc(no_inline)] is used on a non-use item

The code could probably be improved but I wanted to get feedback first. Also, some of those changes could be considered breaking changes, so I don't know what the procedure would be? And finally, for the warnings, they are currently hard warnings, maybe it would be better to introduce a lint? (EDIT: introduced the invalid_doc_attributes lint)

Closes #80275.
r? @jyn514

[jyn514]

I think this should probably go through FCP - I'll take a look at the code first so the review isn't intermingled with the policy change.

[jyn514]

Left a few comments, and I think it would be helpful for @estebank to take a look if you have time.

[GuillaumeGomez]

Also, it could be interesting to add a macro like https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/macro.struct_span_err.html for warnings (but without error code).

[jyn514]

Also, it could be interesting to add a macro like https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/macro.struct_span_err.html for warnings (but without error code).

I think that's https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html#method.struct_span_lint_hir.

[jyn514]

I don't have time to look at this.

r? @Manishearth

[Manishearth]

Overall looks great, would love to have more doc comments

[LeSeulArtichaut]

@Manishearth Added a few doc comments in a separate commit. Let me know if you'd want anything else documented.

[Manishearth]

@bors r+

thanks!

[bors]

📌 Commit 6e8d0db has been approved by Manishearth

[bors]

⌛ Testing commit 6e8d0db with merge ac17b18a35f83579e5f75a8da8a7756f4abc9b17...

[bors]

💔 Test failed - checks-actions

[LeSeulArtichaut]

This is the only case of invalid #[doc(inline)]/#[doc(no_inline)] I found in std::{os,sys} so we should be good now

[Manishearth]

@bors r+

[bors]

📌 Commit 804ab9f has been approved by Manishearth

[bors]

⌛ Testing commit 804ab9f with merge fe62c6e...

[bors]

☀️ Test successful - checks-actions
Approved by: Manishearth
Pushing fe62c6e to master...