> an if let expression over an RWLock assumed (reasonably, but incorrectly) in its else branch that the lock had been released. Instant and virulently contagious deadlock.
They may have upgraded by now, their source links to a thread from a year ago, prior to the 2024 edition, which may be when they encountered that particular bug.
I believe this behavior is changing in the 2024 edition: https://doc.rust-lang.org/edition-guide/rust-2024/temporary-...