clippy: add missing proc_macros aux-build declarations.

[daym]

Fix two Clippy UI tests that import the proc_macros auxiliary crate without declaring it as an aux-build dependency.

Both tests only declare:

//@aux-build:proc_macro_derive.rs

but they also contain:

extern crate proc_macros;
use proc_macros::inline_macros;

Because proc_macros.rs is not declared, ui_test does not pass an explicit --extern proc_macros=.../libproc_macros.so for these tests. The tests can still appear to work when another test has already built proc_macros.rs, because rustc then finds it through the shared -L .../tests/ui/auxiliary directory.

That fallback is racy. During a parallel Clippy UI run, the auxiliary build can leave libproc_macros.rmeta visible before libproc_macros.so is written. If one of these tests starts in that window, rustc loads metadata for a proc-macro crate but has no dylib in the crate source, then ICEs in rustc_metadata::creader with:

no dylib for a proc-macro crate

Adding //@aux-build:proc_macros.rs makes the dependency explicit, forcing ui_test to build proc_macros.rs before running the test and to pass the proc-macro dylib through --extern.

Happened to me when building rust (1.94.1 specifically) on a 64 core amd epyc.

[rustbot]

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

[rustbot]

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[daym]

Ok, opened a PR at rust-lang/rust-clippy#17406 .

Still good to record here that this problem exists starting with the rust release 1.94.1 and following (at least).

non_canonical_clone_impl.rs: bug present since rust 1.81.0. Earlier versions didnt use proc macros.

[ada4a]

I'd say let's close this one in favor of the clippy PR? To avoid wasting CI cycles