Move go & ruby dependencies into go-packages.nix & ruby-packages.nix

[matthewbauer]

Issue description

Right now, we have lots of deps.nix (for go) & gemset.nix (for ruby). This takes up a lot of space and there appears to be at least some duplication. For instance "github.com/gorilla/websocket" is listed 14 times:

https://github.com/NixOS/nixpkgs/search?q=github.com%2Fgorilla%2Fwebsocket&unscoped_q=github.com%2Fgorilla%2Fwebsocket

Would it be possible to merge these into a ruby-packages.nix & go-packages.nix? We can keep the applications as their own files, but ideally we could avoid the duplication in the depencies.

[FRidh]

As with the packaging of most languages, a package lists it's abstract dependencies, and a resolver is used to generate a set of concrete dependencies. With this approach, it's quite common applications may use different versions of dependencies. While we can handle one part easily with our store paths, the question is how to store the names, versions, urls and hashes of these packages.

With the lock file approach, one typically generates an expression containing all dependencies, per package. Now, we could have an index listing all combinations of names and versions, but these tend to get way too big. Therefore, I think we need to find a generic way to generate sets per package, and then be able to join them in order to reduce maintenance in case patches are needed.

For that to happen, packages that require these types of dependencies, should declare so. We could then have an update script that, e.g., finds all Go applications, generates their dependency sets, and merges them.

I think it makes sense to generate a Nix expression for every application, however, we should have a way of joining expressions.

Related thread on generated data in Nixpkgs: #15480

[stale]

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