Sporadic test failure for srcloc assembly test (non-optimized)

[ehuss]

The srcloc.rs test has seen a couple sporadic failures on CI with the x86_64-gnu-nopt job.

• Revert switch of env locking to rwlock, to fix deadlock in process spawning #82877 (comment)
• Rollup of 10 pull requests #82847 (comment)

The error is that it is not always emitting all 23 errors. Sometimes I see it report anywhere from 3 to 15 errors.

I'm able to reproduce locally with rust.optimize-tests = false, and running in a loop. The failure rate isn't high, but I can repro within a few seconds.

cc @Amanieu

[Amanieu]

This doesn't seem to happen with -Ccodegen-units=1. However that doesn't make sense: all the asm!s are in a single function, there's no way they could be split over multiple codegen units, right?

[tmiasko]

AFAIK, the channel used for emitting diagnostic from codegen threads is not guaranteed to be fully drained when compilation session is aborted.

[Amanieu]

@tmiasko Is this issue considered fixed by #83328?

[tmiasko]

@Amanieu I left this open in the case there is an interest in fixing the underlying cause, if not feel free to close.