nixpkgs manual: warning: lib.readPathsFromFile is deprecated

[davidak]

Describe the bug

I get this warnings when opening nix-shell for manual:

[davidak@gaming:~/code/nixpkgs/doc]$ nix-shell 
trace: lib.crossLists is deprecated, use lib.cartesianProductOfSets instead
trace: `mkStrict' is obsolete; use `mkOverride 0' instead.
trace: `lib.nixpkgsVersion` is deprecated, use `lib.version` instead!
trace: warning: lib.readPathsFromFile is deprecated, use a list instead
trace: Warning: `showVal` is deprecated and will be removed in the next release, please use `traceSeqN`
trace: lib.zip is deprecated, use lib.zipAttrsWith instead
these derivations will be built:
  /nix/store/9zz2jxwyb2abix1fy24hpdkxd3caa92j-epub.xsl.drv
  /nix/store/cd41m3dip3ygi6s2mfv066cc0jzq0x9l-xhtml.xsl.drv
  /nix/store/qcg7k535a5rs3rkf4kzz93rdcvn904s4-locations.xml.drv
  /nix/store/iwvmrda8ypzg6h4wqh90xnivmb1myf9h-nixpkgs-lib-docs.drv
  /nix/store/68v6x94cpnvnbaynch6g7ncwl7647sdv-doc-support.drv
these paths will be fetched (351.53 MiB download, 675.01 MiB unpacked)
...

It still works.

This was first mentioned in #63513 (comment)

Might get fixed by #108063

To Reproduce
Steps to reproduce the behavior:

1. Follow Contributing to this documentation

Expected behavior
no warnings

Additional context
Add any other context about the problem here.

Notify maintainers

Metadata

• system: "x86_64-linux"
• host os: Linux 5.11.2, NixOS, 21.05pre274338.102eb68ceec (Okapi)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.10
• channels(root): "home-manager-20.09, nixos-21.05pre274338.102eb68ceec, nixos-hardware, nixos-unstable-21.05pre274338.102eb68ceec"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:

[stale]

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

[ncfavier]

The warnings were re-introduced by b3792b4 (cc @infinisil).

I don't know if we should just accept this or extend the libsets with subsets like lib.path.subpath.