[Bug Report] `Errno::ENOENT: No such file or directory @ rb_sysopen - tmp/cache/packwerk/inflections` (issue with cache)

[alexevanczuk]

Description
The cache periodically (rarely) fails in our CI system with the error shown in the screenshots section.

We suspect that the packwerk cache has a race condition when forked processes are initializing the cache independently.
Namely -- after one process has bust the cache and created the cache directory, another process can then bust the cache, after which the original process may try to write the cache contents of inflections.rb. This can result in the bug:
Errno::ENOENT: No such file or directory @ rb_sysopen - tmp/cache/packwerk/inflections

To Reproduce
We are not able to reliably reproduce this bug.

Expected Behaviour
We expect the cache to not raise an error. From an implementation perspective, we expect tmp/cache/packwerk to already exist before attempting to write the cache file.

Screenshots

Version Information

• Packwerk: 2.1.0
• Ruby: 2.7.5

Additional Context
Some potential solutions we're looking at to solve this issue:

• We can initialize Cache within the parent process to ensure that the call to FileUtils.rm_fr is only run once at the start. This is what we went with in this PR: #183
• Alternatively, we can also drop the rm_fr entirely, and use a strategy that hashes based on the digest of the current inflections.

[exterm]

going to close this now that the candidate fix is released with 2.1.1. Let's reopen should the error reoccur.