Spurious redirect from `latest` to crate page

[kpreid]

Steps to reproduce:

1. Visit https://docs.rs/cpal/latest/cpal/, which should be the documentation for cpal.
2. Get redirected to https://docs.rs/crate/cpal/latest

This only happens with latest and not with, for example, https://docs.rs/cpal/0.18.1/cpal/. I notice that the build info says that some but not all builds failed, so, as wild speculation, perhaps what is happening is that the logic to redirect away from a failed docs build is activating when it should not.

@rustbot label +C-bug +A-frontend

[rustbot]

Error: Label C-bug can only be set by Rust team members

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.

[syphar]

this is definitely weird, will investigate.

[syphar]

potentially: #3328, also likely: #3336

[syphar]

i purged the CDN for this crate, and the redirect is correct.

My guess is that there was a race between build activity & purges, and we do them in the wrong order.

[syphar]

I'll leave this open to see if there are more cases, our code looks good from the places we purge.

Only other reason could be fastly not actually processing the purge.