xorg.libX11: use the absolute path of libXcursor.so.1

[zanculmarktum]

Motivation for this change

#24137

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[pbogdan]

Does this actually work for you? IIRC the issue is that libXcursor itself depends on libX11 so it can't be fed as an input / dependency to the latter without forming a cycle and triggering an infinite recursion.

[zanculmarktum]

Yes, although only tested through my configuration.nix using https://gitlab.com/zanc/overlays.

[pbogdan]

Hmm, I haven't looked at the overlay but as is libX11 doesn't evaluate on this branch:

$ nix-instantiate -A xorg.libX11                                                                                                                                    
error: --- EvalError ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- nix-instantiate
at: (18:19) in file: /nix/store/nvmqjsr9nh3vy7w2p6bqqmrjs17q5dfc-nix-3.0pre20200829_f156513/share/nix/corepkgs/derivation.nix

    17|       value = commonAttrs // {
    18|         outPath = builtins.getAttr outputName strict;
      |                   ^
    19|         drvPath = strict.drvPath;

infinite recursion encountered
(use '--show-trace' to show detailed location information)

(presumably due to the cycle) and ofborg seems to agree.

[zanculmarktum]

Further test shows that my overlays work because I used the following:

final: prev:
{
  xorg = prev.xorg // {
    libX11 = prev.xorg.libX11.overrideAttrs (oldAttrs: {
      postPatch = (oldAttrs.postPatch or "") + ''
        substituteInPlace src/CrGlCur.c --replace "libXcursor.so.1" "${final.xorg.libXcursor}/lib/libXcursor.so.1"
      '';
    });
  };
}

instead of:

final: prev:
{
  xorg = prev.xorg.overrideScope' (self: super: {
    libX11 = super.libX11.overrideAttrs (oldAttrs: {
      postPatch = (oldAttrs.postPatch or "") + ''
        substituteInPlace src/CrGlCur.c --replace "libXcursor.so.1" "${self.libXcursor}/lib/libXcursor.so.1"
      '';
    });
  });
}

The latter gave me infinite recursion.