shell: stop fish from having to be built every time

Drop the patch to fish source code, instead opting
to employ fish's inbuilt share/fish/vendor_conf.d
to add custom code to fish.

This is both a bit simpler, and makes it so fish does not
have to be compiled on every update to it's source / to my configuration.

packages/shell/default.nix

@@ -1,34 +1,42 @@
-# This shell setup was inspired by sioodmy. Check out his setup!
+# This shell setup was originally inspired by sioodmy.
+# Some further cool tricks, like using vendor_conf.d to avoid having
+# to build fish myself, are taken from viperml's setup.
 {pkgs, ...}: let
+  inherit (pkgs) lib;
+  inherit (lib.strings) concatStringsSep;
+  inherit (lib.attrsets) mapAttrsToList;
+
   toml = pkgs.formats.toml {};
   starship-config = import ./starship.nix;
   aliases = import ./aliases.nix {inherit pkgs;};
+  vendorConf = "share/fish/vendor_conf.d";
 
-  fishinit = import ./fishinit.nix {inherit pkgs aliasesStr;};
+  fishinit = import ./fishinit.nix {
+    inherit
+      pkgs
+      aliasesStr
+      vendorConf
+      ;
+  };
 
   aliasesStr =
     mapAttrsToList (k: v: "alias ${k}=\"${v}\"") aliases
     |> concatStringsSep "\n";
 
   packages = import ./packages.nix pkgs;
-
-  # this was taken from viperml, check out his config for this!
-  custom-fish = pkgs.fish.overrideAttrs (old: {
-    patches = [./fish-on-tmpfs.patch];
-    doCheck = false;
-    postInstall =
-      old.postInstall
-      + ''
-        echo "source ${fishinit}" >> $out/etc/fish/config.fish
-      '';
-  });
 in
   (pkgs.symlinkJoin {
     name = "fish";
-    paths = [custom-fish] ++ packages;
+    paths = [pkgs.fish] ++ packages;
     nativeBuildInputs = [pkgs.makeWrapper];
     postBuild = ''
-      wrapProgram $out/bin/fish --set STARSHIP_CONFIG "${toml.generate "starship.toml" starship-config}" \
+      wrapProgram $out/bin/fish \
+      --set STARSHIP_CONFIG "${toml.generate "starship.toml" starship-config}" \
+      --prefix XDG_DATA_DIRS : "${
+        lib.makeSearchPathOutput "out" "share" [
+          fishinit
+        ]
+      }"
     '';
   })
   .overrideAttrs (_: {