Bors sometimes gets stuck, doesn't process the queue any more

[RalfJung]

This does not happen often but it happens regularly:

• Jan 2022, Dec 2022: https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/bors.20stuck
• Mar 2023: https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/bors.20stuck.3F.20.282023-03-28.29
• May 2023: https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/bors.20doesn't.20start.20builds.20on.20rust-analyzer

[RalfJung]

Happening again since last night.

[RalfJung]

It was a libc PR again: rust-lang/libc#3034.

Last time it was rust-lang/libc#3137.

What's going on with libc that it is causing these issues? Cc @Mark-Simulacrum @JohnTitor

[RalfJung]

@Mark-Simulacrum previously suspected it might have to do with a master branch rename. @JohnTitor when did the libc repo rename its default branch from master to main?

[JohnTitor]

I didn't rename it actually, it was changed some time ago before I knew it. Looking at rust-lang/libc@07f7c83, @joshtriplett did it, I guess?

[RalfJung]

Ah, that seems fairly recent though. So it surely cannot explain the trouble last year.

But it might be that all the trouble this year is due to that rename -- whenever a PR created before the rename gets merged, or something like that?