`lib.hiPrio` gets erased after calling `override` or `overrideAttrs`

[andrewhamon]

Describe the bug

lib.hiPrio and related functions update meta using simple merging.

If a package later has an override applied, though, the updated meta is discarded. This can be really surprising, particularly to those less well-versed in nix.

Steps To Reproduce

Try this in a REPL:

(pkgs.lib.hiPrio pkgs.cowsay).meta.priority
# => -10

((pkgs.lib.hiPrio pkgs.cowsay).overrideAttrs { }).meta.priority or "priority is not set"
# => "priority is not set"

# also impacts `override`
((pkgs.lib.hiPrio pkgs.cowsay).override { }).meta.priority or "priority is not set"
# => "priority is not set"

Expected behavior

Functions that "mutate" derivations should do so using overrideAttrs, so that later invocations of overrideAttrs don't discard information.

Screenshots

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Additional context

Add any other context about the problem here.

Notify maintainers

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"aarch64-darwin"`
 - host os: `Darwin 23.5.0, macOS 14.5`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.22.0`
 - nixpkgs: `/nix/store/rhg90jpryc286xn9xjy6qjiaap6pjgdc-source`

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Add a :+1: reaction to issues you find important.

[andrewhamon]

Similar issue from long ago where this is mentioned: https://github.com/NixOS/nixpkgs/issues/7425

[eclairevoyant]

Why not move the hiPrio outside the override?

[andrewhamon]

Yes, that's an easy workaround to apply, if you know what the problem is. But if you don't know already, I don't think the solution is obvious.

Do you see any downsides to adopting a merge function such as this?