Expose source information to Nix

[sepointon]

I'd like to put provenance information in a couple of places ('generated from revision $FOO in repository $BAR', that sort of thing). It'd be handy if npins would provide source information somewhere alongside the actually fetched sources - just exposing it to Nix would be sufficient, because I can then massage it in to whatever form's needed.

I don't quite know what this would look like - would user code be expected to deal with the various different shapes of source information (as, e.g., a tarball doesn't have a rev associated with it, but a Git checkout does)? Though, presumably, users could hard-code which shapes they're using for which sources, and change them if they change the pins. There'd also be some concern about how this would be effectively exposing a new API surface, with associated backwards/forwards compatibility considerations (so, e.g., I don't think it'd make sense to just drop in raw entries from sources.json, but rather some cleaned-up stable format).

[andir]

So we probably would need a string representation of each pin type that is exposed (or even assembled) as a nix attribute on a source?

I kind of like the idea of providing that information within builds. I regulary do that myself in some hacky ways… not so often that I thought about it as a feature, but that might be a good idea.

[sepointon]

I wasn't thinking about stringifying everything, but something like an attrset so that user code could put it together in whichever way they wanted - in the Git case, for example, repo URL and rev would probably be the keys, and, if you're outputting HTML, the the URL could go in to a HTML <a href=...> and the rev gets wrapped in <code>.

[piegamesde]

Could this be prototyped outside of the npins code base by hacking together something that parses the sources.json?