Disallow writing `path` input to lock file

[roberth]

Is your feature request related to a problem?

Host paths are not reproducible, so they're not a good source for flake inputs.

• partitions: incompatible with flakes as inputs that use flake-parts hercules-ci/flake-parts#252 (comment)

Proposed solution

Disallow writing path input to lock file. Throw an error.
Maybe have a flag --allow-unreproducible-local-path-input for the use case where users are testing something locally and they can't pass --override-input for whatever reason (getFlake, non-interactive Nix use, direnv, not-great CLIs, etc).

Alternative solutions

Additional context

May also solve

• Untracked files excluded from flake even with "path:" input #11930

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

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[nixos-discourse]

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

https://discourse.nixos.org/t/2024-12-04-nix-team-meeting-minutes-200/57005/1

[Enzime]

Subflakes write path inputs to lock file, but they're relative paths instead of store paths like hercules-ci/flake-parts#252 (comment)

{
  "locked": {
    "lastModified": 1,
    "narHash": "sha256-GQi2Zqvsm80KrZEsq+zb2lt+eHRFTZt8aPXzOiCWLPI=",
    "path": "overlays/nix",
    "type": "path"
  },
  "original": {
    "path": "overlays/nix",
    "type": "path"
  }
}

Will this change conflict with #10089?

[edolstra]

@Enzime Regardless of whether we disallow absolute paths in lock files, we will keep relative paths for subflakes.