nix-env: Use pname and version attrs in -q

[jtojnar]

Previously1, we started including pname and version keys in nix-env -qa --json output (and thus in packages.json).

But those values were obtained using parseDrvName, which does not work in many cases, for example when a project does not follow Nix’s arbitrary requirement that version names have to start with a digit.

The keys are also misleading as many modern Nixpkgs packages pass identically named attributes to mkDerivation but these keys do not use those values.

Let’s fix this discrepancy by officially recognizing pname and version attributes as special and using them in the JSON output.

This will be useful for Repology as well.

[jtojnar]

Verified that this patch prints correct values in nix-env -f channel:nixos-unstable-small -qa --json:

Unstable Nix:

1901858:  "vapoursynth": {
1901859:    "name": "vapoursynth-R52",
1901860:    "pname": "vapoursynth-R52",
1901861-    "version": "",

This patch:

1904437:  "vapoursynth": {
1904438:    "name": "vapoursynth-R49",
1904439:    "pname": "vapoursynth",
1904440-    "version": "R49",

[jtojnar]

Wanted to mark this as closing https://github.com/NixOS/nixos-homepage/issues/306 but that issue disappeared (still accessible through API).

[edolstra]

I'm hesitant to modify the semantics of nix-env since it's kinda legacy at this point. The replacement (nix profile) does not use the (p)name/version attributes at all.

[jtojnar]

We still use nix-env output for packages.json which ends up being picked up by Repology. And these keys were only added recently specifically for use on Repology.

[stale]

I marked this as stale due to inactivity. → More info

[r-burns]

Still relevant

[superherointj]

@edolstra

In case this PR is not accepted (which seems so?), a replacement is needed here:
https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/make-tarball.nix#L67

How to use nix profile to replace nix-env for this use case?

With nix-env I'd list packages this way:
nix-env --query --available --meta --json

What would be the equivalent using nix profile?
nix profile list won't list it.

Maybe nix search would be better here but then (1) version is broken as well (2) doesn't provide all of meta information. #3868

[Ericson2314]

It might be prudent to generate the repology info in a way that is agnostic to nix-env and nix profile. That helps with Nix vs Nixpkgs layering.

[nixos-discourse]

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

https://discourse.nixos.org/t/nixpkgs-cli-working-group/30517/1