Move logic for emitting UNSAFE_CODE for unsafe attributes to attr parsing

[JonathanBrouwer]

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Fixes #131801

This moves the emitting of UNSAFE_CODE for unsafe attributes to attr parsing.
Because it is now implemented generically for all unsafe attributes, we don't have to manually list all attributes anymore, and we can't miss adding support for new unsafe attributes in the future.

This adds support for detecting UNSAFE_CODE for the following attributes:

• #[naked] (stable attribute!)
• #[ffi_pure]
• #[ffi_const]
• #[force_target_feature]

[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

[rustbot]

r? @mati865

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[JonathanBrouwer]

@rustbot label +I-lang-nominated
@rust-lang/lang

Previously, the UNSAFE_CODE lint emitted a lint for the usage of the following unstable attributes:

• #[no_mangle]
• #[link_section]
• #[export_name]

This PR extends the lint to emit a lint for all unsafe attributes, which adds the following currently unsafe attributes:

• #[naked] (stable attribute!)
• #[ffi_pure] (unstable attribute)
• #[ffi_const] (unstable attribute)
• #[force_target_feature] (unstable attribute)

[traviscross]

Makes sense to me. Thanks @JonathanBrouwer for pushing this forward. I propose we do it:

@rfcbot fcp merge lang

One thing I'll mention is that we do use unsafe both to create and to discharge safety obligations. So far, all the unsafe attributes discharge obligations. If we both 1) ever wanted to create a safety obligation with an unsafe attribute and 2) rethink whether unsafe_code should apply to creating safety obligations (e.g., #148651, which we discussed without resolution in our meeting on 2026-01-14), then maybe this would need to get a bit more complicated. Not a problem today.

[rust-rfcbot]

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

• @joshtriplett
• @nikomatsakis
• @scottmcm
• @tmandry
• @traviscross

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

[mati865]

r=me after the fcp concludes

View changes since this review

[rust-rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[JonathanBrouwer]

@bors r=mati865 rollup

[rust-bors]

📋 This PR cannot be approved because it currently has the following labels: proposed-final-comment-period, needs-fcp, S-waiting-on-t-lang.

[JonathanBrouwer]

@bors r=mati865 rollup

[rust-bors]

📌 Commit 5681079 has been approved by mati865

It is now in the queue for this repository.

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

...............................F.................. (50/144)
.................................................. (100/144)
............................................       (144/144)

======== tests/rustdoc-gui/go-to-collapsed-elem.goml ========

[ERROR] line 40
    at `tests/rustdoc-gui/go-to-collapsed-elem.goml` line 21: Error: Node is detached from document: for command `click: "//*[@id='search']//a[@href='../test_docs/struct.Foo.html#method.must_use']"`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/struct.Foo.html?search=t_use>


<= doc-ui tests done: 143 succeeded, 1 failed, 0 filtered out

Error: ()

[JonathanBrouwer]

(spurious)