Initial many variant

[jonringer]

Standardize how packages which many versions or variants are constructed and exposed.

Also reduces the number of "variant aliases" needs to be defined in a scope. E.g. openssl_3_0, openssl_3_1, openssl_3_2, openssl_3_3; now there's just a openssl.v3.X which can be selected.

Rendered: https://github.com/jonringer/eeps/blob/many-variants/eeps/0005-many-variants.md

[jonringer]

If we changed .override to .overrideDeps, and changed .overrideVariant to .overridePackage, we could live in a world where you could do:

patchedCurl = let 
  newerCurl = prev.curl.overridePackage {
    version = "4.9.1";
    srcHash = "...";
    withDocs = false;
  };
  in newerCurl.overrideDeps {
    openssl = openssl.v3_2;
  };

this feels much more intuitive than:

  patchedCurl = let
    newerCurl = prev.curl.overrideAttrs (oldAttrs: {
      version = "4.9.1"
      src = fetchurl {
        url = "https:// ....";
        hash = "...";
      };
      # patches may also need to be touched
    };
    in newerCurl.override {
      openssl = openssl_3_2;
      withDocs = false;
    };

Since package toggles get lumped with version info, now there's a separation of concerns between dependencies and build time flags

[jonringer]

Hmm

  in newerCurl.overrideDeps {
    openssl = openssl.v3_2;
  };

doesn't really work if people do:

{
  openssl,
  ...
}:
... {
  buildInputs = [ openssl.v3_1 ];
}:

because the downstream usage of openssl is more opinionated