Diagnose failure of crate-level #![expect()] in the project, then replace #![allow()] with #![expect()]

[richchurcher]

Relevant PR:

• Allow to expect (adopted) #15301 (review)

Relevant issue:

• Swap most uses of allow in lints to expect #15059

The problem

We've been trying to replace allow with expect, which is often (but not always) used in the context of the lint missing_docs. CI failures occur when --all-targets is specified. Our current CI does this:

cargo clippy --workspace --all-targets --all-features -- -Dwarnings

This results in linter failures such as:

It further seems that:

• omitting --all-targets allows CI to pass, and
• #[expect()] (non-crate-level) directives pass

For now, #![expect()] has been avoided in favour of #![allow()], but it'd be great to use #![expect()] at crate level if we can make it work smoothly using --all-targets.

[alice-i-cecile]

I've asked about this on Zulipe here. I think this may be a Rust bug TBH.

[richchurcher]

It's not all crate-level uses of expect either. unsafe_code seems to work 🤔