Local no-index repositories cache leads to bad UX

[andreabedini]

Describe the bug

It's documented that, when using local no-index repositories.

cabal-install creates a .cache file, and will aggressively use its contents if it exists. Therefore if you change the contents of the directory, remember to wipe the cache too.

but cabal-install offers no warning or message about this leaving the user staring, confused, at a solver failure. See for example #9133.

Expected behavior

Cabal should either

1. Provide a better caching mechanism, detecting changes to the local repository.
2. Remnind the user that it will only look at the cache file and that the user should manually delete the cache file if the repository has changed.

[danse]

Regarding #9133, i think i built the one failing package like the others. Maybe i rebuilt it, i do not think i changed the version. When i was inspecting the sdist dirs, i thought that the noindex.cache and the tar.gz files were both outcomes of cabal v2-install. Maybe, if it is not too expensive, could be worth always regenerating the noindex.cache when the command succeeds

[taimoorzaeem]

@ulysses4ever I would like to work on this issue. Could you kindly assign it to me? Let me know if there any updates to this issue.

[ulysses4ever]

hey @taimoorzaeem! I assigned you, thanks for volunteering!

Adding a warning is hard to get wrong, so please go on and open a PR so that we can see how it goes. We'll probably need a test and/or QA notes.

@andreabedini who opened this ticket may be a better mentor for this but I'll see what I can do if no one else pops up.

Also, it'd be great to actually fix this issue and add a proper cache invalidation via "file monitors". While not very complicated, perhaps, that would require more hacking... In the meantime, adding a warning seems like a noble feat.

[andreabedini]

@taimoorzaeem It's been a while since I opened this but feel free to reach out to me if you want to have a look together.