panic in Regex::regex()

[drahnr]

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /tmp/build/56ca5ece/git-pull-request-resource/../cargo/registry/src/github.com-1ecc6299db9ec823/nlprule-0.6.2/src/utils/regex.rs:78:33

thread 'stack backtrace:

<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /tmp/build/56ca5ece/git-pull-request-resource/../cargo/registry/src/github.com-1ecc6299db9ec823/nlprule-0.6.2/src/utils/regex.rs:78:33

   0:     0x560ee78bdfd0 - std::backtrace_rs::backtrace::libunwind::trace::h5e9d00f0cdf4f57e

                               at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5

   1:     0x560ee78bdfd0 - std::backtrace_rs::backtrace::trace_unsynchronized::hd5302bd66215dab9

                               at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5

There is an .unwrap on the regex.borrow() call which panics.

https://ci.spearow.io/teams/main/pipelines/cargo-spellcheck/jobs/pr-validate/builds/45

[drahnr]

A bit of context:

Rules::suggest(...) is called in parallel over a shard immutable reference to a single &Rules instance. Looking into lazycell the ordering semantics look ok from the first glance, the API usage just seems incorrect (even in their example).

If thread A calls borrow() while thread B is just about to write the value to the UnsafeCell, it will be in LOCK state, which will return a None.
The only way I can think of doing this correctly is calling borrow() repeatedly in the else case until it succeeds.

[bminixhofer]

Hi, thanks for the issue. Refreshingly, something which I couldn't have foreseen :)

I believe the easiest fix is just to replace lazycell with once_cell, which is a more well used dependency anyway and has the get_or_init API which fits our use case.

I went ahead and implemented this: #69. Can you check if this solves the problem? Binaries from the latest release should still work.

[drahnr]

Just had a peek into the once_cell crate, and there is a significant amount of non trivial synchronization logic happening, but I ran it a few times and it works consistently 🎉 - so #69 is good to go :) Thanks for the fast turnaround 👍

[drahnr]

Could you craft a release, that's the last thing pending for a cargo-spellcheck 0.8.0 which is again needed for paritytech/parity-bridges-common#832

[bminixhofer]

Sure! Release CI is running for 0.6.3 now.