failed to initialize cache, disabling related functionality: bitcode error

[marie-bnl]

I use comma through nix-index-database, using the NixOS module and programs.nix-index-database.comma.enable = true;.

Since quite some time ago, everytime I use comma, I get the following non-fatal error.

$ , hello
failed to initialize cache, disabling related functionality: bitcode error
Hello, world!

Comma can't save the package used so it keeps asking which one to use on every run.

I don't know what the conditions for reproducing the issue are, and I think it's not related to my configuration, but to non-deterministic aspects of my system. I believe the issue disappears on a re-installation of NixOS.

[marie-bnl]

Turns out my .local/state/comma-choices file was empty for some reason. It caused a bitcode decoding error, which prevented the creation of a cache altogether. Deleting it solved the problem.

I see three solutions:

1. Check if the file is empty in Cache::new. If it is, force the creation of a new cache.
2. On any bitcode::decode error, overwrite the file with a new cache. Dangerous as you may lose a lot of choices accumulated over time. But it does not seem like critical data, and I doubt any user will attempt to recover from a corrupted cache anyway, as it is a lot easier to just create a new one.
3. Like solution 2, but before, copy the current cache to comma-choices.old. That way if the user really cares about their cache and does want to try to recover manually, there is a choice to.
4. Replace the generic bitcode error with a message telling the user their cache is located in ~/.local/state/comma-choices and is corrupted, and that they should delete the file to solve the issue.

Solution 3 appears best to me, as it solves it for any corrupted cache and does not incur any data loss.

Note: .local/state/comma-choices has moved to .local/state/comma/choices.

[marie-bnl]

I've just figured out one case the issue happens is when your disk is full. I guess comma tries to write in the cache but does not successfully write all the data and just corrupts the file.