Factor out `StoreDirConfig`

[Ericson2314]

This takes out a bunch of non-virtual methods which only depend on the store dir.

I didn't move the implementation to a store-dir-config.cc because they were already split in two locations (path.cc and store-api.cc), and also because, I must admit, it will cause me grief later with more merge conflicts.

More progress on #5729.

depends on #6258 depends on #6237

[edolstra]

I'm not really in favor of splitting things just because we can... Is there a specific use case for splitting off StoreDirConfig? (E.g. is there a plausible scenario where we have a StoreDirConfig that isn't a Store?)

[Ericson2314]

Yes there is, https://github.com/NixOS/nix/pull/6237 which depends on this. I could pass a whole store there, but that that is somewhat sketchy from a caching perspective. If I just pass StoreDirConfig, it is more clear that the cache key does have something to do with the store dir, but no other store information.

[Ericson2314]

This was working in Clang, but not GCC, due to that bug @thufschmitt ran into when first making StoreConfig. Hopefully I can fix soon.

[Ericson2314]

Actually it's a double free instead. #6258 came from my attempts debugging this over the weekend. I rebase this on top, but still no dice.

[Ericson2314]

I built with clang and the double free went away. Ugh!

[edolstra]

Yes there is, https://github.com/NixOS/nix/pull/6237 which depends on this.

That's a bit of a circular motivation, because I'm not sure what the reason for #6237 is...

[Ericson2314]

Err the motivation of #6237 is simply to use StorePath where possible to demonstrate the invariant that the item in question is in fact a store path, as we have done many times before, e.g. your recent #6198.

[edolstra]

Ah thanks, yeah that makes sense!

[Ericson2314]

@edolstra Yay! I was hoping the core change just got lost in there. I flipped the dependencies around so now this depends on that:

1. In #6237 We share Store with the eval cache a bit more, which is sketchy re purity lest we accidentally use the store for something other than printing and parsing, but I suppose fine for now as eval contexts already have a store.
2. This PR will limit the use of Store in the eval cache, in addition to making StoreDirConfig. I assume there are many more instances where we could similarly do the same. (We could even make EvalState just have a StoreDirConfig which is downcasted for things like IFD, a la what we did with LogStore and GcStore.)

If you are not yet convinced by this, but #6237 now sounds good, hopefully this new approach is an improvement.

[Ericson2314]

Still not sure how to fix this, but in the most recent commit found a bunch of locations that can be made StoreDirConfig instead of Store.

[dpulls[bot]]

:tada: All dependencies have been resolved !

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-11-10-nix-team-meeting-minutes-102/35379/1

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-11-27-nix-team-meeting-minutes-107/36112/1

[github-actions[bot]]

Backport failed for 2.18-maintenance, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin 2.18-maintenance
git worktree add -d .worktree/backport-6236-to-2.18-maintenance origin/2.18-maintenance
cd .worktree/backport-6236-to-2.18-maintenance
git switch --create backport-6236-to-2.18-maintenance
git cherry-pick -x e97ac09abeab44fa3d10eb539f0b3d51f8575798 dde1d863388617b3a63db808c125f274c86a3222

[github-actions[bot]]

Successfully created backport PR for 2.19-maintenance:

• #9561

[github-actions[bot]]

Backport failed for 2.18-maintenance, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin 2.18-maintenance
git worktree add -d .worktree/backport-6236-to-2.18-maintenance origin/2.18-maintenance
cd .worktree/backport-6236-to-2.18-maintenance
git switch --create backport-6236-to-2.18-maintenance
git cherry-pick -x e97ac09abeab44fa3d10eb539f0b3d51f8575798 dde1d863388617b3a63db808c125f274c86a3222

[github-actions[bot]]

Git push to origin failed for 2.19-maintenance with exitcode 1