internal: remove dead #[allow] attributes

[weiscadence]

Each of these 20 #[allow(..)] attributes suppresses a lint that no longer
fires at that site, so the attribute currently has no effect. The change is
purely subtractive — 20 deletions, no statement, signature or behaviour change.

How they were found

1. Rewrote every #[allow(..)] under crates/ to #[expect(..)] and collected
   unfulfilled_lint_expectations.
2. Discarded every diagnostic whose span came from a macro expansion. Those are
   not dead: the suppression is still needed by other expansions of the same
   macro. This was the large majority (134 of 153 sites).
3. Confirmed each remaining candidate by actually deleting the attribute and
   rebuilding.

Step 3 was not redundant. One candidate that step 1 reported as unfulfilled —
#[allow(unused_mut)] in crates/hir-def/src/expr_store/lower/path.rs — makes
unused_mut fire when removed, because that binding is only mutated under
#[cfg(test)]. It is left untouched here. An unfulfilled expectation is not by
itself proof that an allow is dead.

Verification

• cargo check --workspace --all-targets — clean, no diagnostics.
• Same under CI's RUSTFLAGS="-W unreachable-pub --cfg no_salsa_async_drops".
• Cargo.lock is deliberately untouched. (It does churn locally on a pristine
  checkout too — salsa-macros — so that is unrelated to this change.)

Not covered

I could not build the in-rust-tree feature (needs a nightly toolchain), so
these were not checked under it. As far as I can tell CI only builds that
feature for proc-macro-srv, proc-macro-srv-cli and proc-macro-api, none of
which are touched here — but flagging it rather than implying coverage I don't
have.

Happy to split this per-crate if that is easier to review.

[ChayimFriedman2]

Please note that our AI policy disallows using AI to write GitHub comments, including PR descriptions.

[ChayimFriedman2]

Please switch all other allows to expects, or a comment explaining why they can't be.

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[ChayimFriedman2]

Please remove this comment as well.

[ChayimFriedman2]

This is incorrect, the #[deprecated] was just lost during the Salsa transition, we should add it back.

[ChayimFriedman2]

Here too.

[weiscadence]

infer.rs - I removed the comment

eager.rs + lib.rs - you’re right they aren’t dead but your fix doesn’t compile. #[salsa::tracked] expand the method into a trait impl. I tried both attribute orders and got the same error. So the depreciation wasn’t dropped by oversight in the salsa transition, it stopped being expressable.

rustc rejects it:
“error: #[deprecated] attribute cannot be used on trait methods in impl blocks”

There is a workaround:

rename the tracked query to macro_arg_ and put #[deprecated] on a thin wrapper. The same _-suffix pattern already in cli/flags.rs. I confirmed it compiles and that the warning genuinely fires (stripped the allow back out and the deprecation warning appeared). But it renames a salsa query so do you want that or leave those two allows deleted?

Allow-expect - for the whole codebase or just the touched files? 134 of 153 allow sites sit inside macro expansions where expect breaks because other expansions of the same macro still need the suppression.

[ChayimFriedman2]

eager.rs + lib.rs - you’re right they aren’t dead but your fix doesn’t compile. #[salsa::tracked] expand the method into a trait impl. I tried both attribute orders and got the same error. So the depreciation wasn’t dropped by oversight in the salsa transition, it stopped being expressable.

Ugh. Okay then I guess a comment above the function to not remove it will be enough, you don't need to insert an inner function.

Allow-expect - for the whole codebase or just the touched files? 134 of 153 allow sites sit inside macro expansions where expect breaks because other expansions of the same macro still need the suppression.

For the whole codebases, but only outside of macros. You can do that in a separate PR if you want.

Please also squash.

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