Spurious warning in #[allow(clippy::non_send_fields_in_send_ty)] for complex thread-safe wrapper

[alice-i-cecile]

Summary

Our unsafe implementation of Send for a wrapper type that deliberately strips out all of the !Send components of our complex collection tripped the new clippy lint. This was, in fact the entire point of the type, and why we used an unsafe impl block.

Ping @DJMcNab, the author of that PR.

Lint Name

#[allow(clippy::non_send_fields_in_send_ty)]

Reproducer

See bevyengine/bevy#3519 for the case where this lint triggered spuriously.

The existing warning on World was correct: this impl was in fact unsound, and this PR was an attempt to solve that problem.

Version

rustc 1.60.0-nightly (1bd4fdc94 2022-01-12)
binary: rustc
commit-hash: 1bd4fdc943513e1004f498bbf289279c9784fc6f
commit-date: 2022-01-12
host: x86_64-pc-windows-msvc
release: 1.60.0-nightly
LLVM version: 13.0.0

Additional Labels

No response

[xFrednet]

Thank you for the report. The lint sadly has several false positives.

There will be a 1.58.1 release to make the lint allow by default on next Thursday. (See #8045)

[Qwaz]

Thanks for sharing the spurious failures. It's still good to hear that the lint was able to prevent a soundness bug. Hope we can bring this lint back to enable-by-default in the future after solving these known false positives.