Allow running nixpkgs-vet on specific files only

[wolfgangwalther]

Being able to specify the list of files I'd like to check on the command line would allow to run it in a git pre-commit hook, only checking the files that actually changed (which should be much quicker).

We'd also need to find a way to integrate that with ratchet checks.

Extension: Support for --stdin. Although, I don't know whether that makes any sense given how nixpkgs-vet operates. At least some checks don't make sense in the context of a "virtual" file like that (?), aka they look at other existing files in relation etc.

[philiptaron]

How would you imagine that this works? Since there's no inherent mapping from file path to relevant test attributes in general, and since the information nixpkgs-vet gathers fundamentally comes through Nix expressions implemented as a nixpkgs-wide overlay (see src/eval.nix) my mental math says that it's going to need to import roughly everything.

[wolfgangwalther]

I must admit, I have no idea, yet, how nixpkgs-vet works internally. :D

So, this might very well be unworkable. I'm just thinking about the user interface right now. And in general, if such a check can be run really quickly pre-commit, that would be great, because it gives a much faster feedback cycle.

But if that's not possible, the next step would be to make it easy to run locally in full (where some of the other issues come into play).

I'm hoping that because of by-name, it could be remotely possible, though. Maybe this mode could only check by-name packages, which can be inferred from the pathname? So instead of eval'ing all packages, I'd only eval a single by-name package, because I only touched files in there.

[philiptaron]

Something with by-name is definitely the exception. We might be able to concoct a fast path there, for sure.