Add support for nix 2.19 path-info

[GrigorenkoPV]

Fixes #67

[utdemir]

Thanks!

[SuperSandro2000]

Tested this with the following overlay and works like a charm

    haskellPackages = prev.haskellPackages.override (oldArgs: {
      overrides = lib.composeExtensions (oldArgs.overrides or (_: _: { }))
        (hfinal: hprev: {     ■ Unused lambda argument: hfinal
          nix-tree = haskell.lib.doJailbreak (hprev.nix-tree.overrideAttrs ({ patches ? [ ], ... }: {
            patches = patches ++ [
              # nix 2.19 compatibility
              (fetchpatch {
                url = "https://github.com/utdemir/nix-tree/pull/68.patch";
                hash = "sha256-70Xo88ZWzWUYM0qxbW64kYaVwHaYkS2dQWmBGCkL0oA=";
              })
            ];
          }));
        });
    });

[lierdakil]

I'm just passing by, but IIUC this code will break the moment it encounters invalid paths, because obj2LegacyArray doesn't handle the Null value, which can happen according to https://nixos.org/manual/nix/stable/release-notes/rl-2.19.

[GrigorenkoPV]

I'm just passing by, but IIUC this code will break the moment it encounters invalid paths, because obj2LegacyArray doesn't handle the Null value, which can happen according to https://nixos.org/manual/nix/stable/release-notes/rl-2.19.

You are correct, thank you! In reality this simply resulted in a less informative error message. Not catastrophic, but not very desirable either. Anyways, I have submitted a fix #69.