Tests started on PR before the previous one actually merged

[huonw]

https://github.com/rust-lang/rust/pull/21605 was merged (https://github.com/rust-lang/rust/commit/c4db18b899d98aa7181b2f2b38e8230c7de42428) on top of https://github.com/rust-lang/rust/commit/458a6a2f6e9dfb6ed3d76f14418ff1f2f5e97f86, but it should've been merged on top of https://github.com/rust-lang/rust/commit/47621db62cf9ffa82624576059b6af5e54d935a5 (which has https://github.com/rust-lang/rust/commit/458a6a2f6e9dfb6ed3d76f14418ff1f2f5e97f86 as a parent too).

It seems like maybe tests started on #21605 before the previous merge was register properly?

[barosl]

Oh, right... GitHub sometimes lags, and the GitHub API isn't completely synchronous, therefore such bad thing can happen, especially when GitHub is under high load.

Hmm, I'm not sure what to do to fix this. Maybe inserting time.sleep() before each fast-forwarding? In that case, how much time should Homu wait?

[huonw]

Is it possible to maybe detect that the parent of the current merge is the merge commit of the previous PR?

[huonw]

(And, if it isn't the right commit, wait a few seconds and try again?)