python3: set an explicit high priority

[ianthehenry]

Currently there are multiple derivations named python3, none of which have an explicit meta.priority. This means that nix-env -i python3 will give a different result than nix-env -iA nixpkgs.python3, and nix-env -u is not useful when you have nixpkgs.python3 installed.

So we explicitly raise the priority of nixpkgs.python3, so that nix-env -i python3 will no longer try to install an alpha version of python3 just because it has a higher version number.

Motivation for this change

Fixes #126036

Things done

• Fits CONTRIBUTING.md.

I verified this change by using nix-env -qa:

$ nix-env -qa python3 --json -f . | jq '.[] |= .meta.priority'   {
  "python310": null,
  "python36": null,
  "python36Full": null,
  "python37Full": null,
  "python37": null,
  "gnuradio3_8Packages.python": -10,
  "python38": null,
  "python38Full": null,
  "python3Full": -10,
  "sourcehut.python": -10,
  "python39": null,
  "python39Full": null
}

Which does not include python3 because it's identical to sourcehut.python3, but can be confirmed separately:

$ nix-env -qaA python3 --json -f . | jq '.[] |= .meta.priority'
{
  "python3": -10
}

[r-rmcgibbo]

Result of nixpkgs-review pr 126038 at 259b3b5 run on x86_64-linux 1

14 packages built successfully:

• bottles
• esphome
• kodiPackages.steam-launcher
• lutris
• nixopsUnstable
• octavePackages.symbolic
• platformio
• playonlinux
• protontricks
• steam
• steam-run
• steam-run-native
• steam-tui
• steamcmd

---

Result of nixpkgs-review pr 126038 at 259b3b5 run on aarch64-linux 1

1 package built successfully:

• nixopsUnstable

[FRidh]

I don't think we should be doing this. Yes, it resolves the issue for python3, but there are others out there as well. "It is known" that nix-env -i should not be used.

[ianthehenry]

After looking through other derivations with the same problem, I have to agree. I happened to run into the issue with python3, but this same problem affects bash, ruby, sqlite, and over a hundred other top-level packages. I don't think python3 is any more likely to be installed by a new user than one of those, and I certainly don't want to change all of them...