Fix handling of $NIX_LINK{,_NEW} in nix-profile*.sh

[NiklasGollenstede]

Motivation

In the profile file added for non-NixOS installations of Nix, there is a warning that is to be emitted it two ($NIX_LINK{,_NEW}) profile links exist. Currently, it would never be printed.

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• [ ] agreed on idea
• [ ] agreed on implementation strategy
• [ ] tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• [ ] documentation in the manual
• [ ] documentation in the internal API docs
• [ ] code and comments are self-explanatory
• [ ] commit message explains why the change was made
• [ ] new feature or incompatible change: updated release notes

Priorities

Add :+1: to pull requests you find important.

[abathur]

@cole-h Does this look right to you? (It looks right to me on a quick read, but I'm not terribly familiar with the profile logic and I'm leery of sliding back into the problem that merited #7925.)

[iFreilicht]

@cole-h Does this look right to you? (It looks right to me on a quick read, but I'm not terribly familiar with the profile logic and I'm leery of sliding back into the problem that merited #7925.)

I'm not them, but it looks good to me as well. I don't see a way for this to regress into the issue you linked again.

[fennewald]

Any motion on this? Just noticed this issue on my own.