Fixes nix standard derivation. (#1042)

* Adds a formatter for nix. Use `nix fmt`.

* Fixes nix standard derivation.

The standard derivation has been broken for quite some time now, but I
didn't use it, so I didn't care to fix it. Today I cared. It now builds
and is updated for the new packaging system.

default.nix

@@ -4,19 +4,38 @@
 
 let
   zig-overlay = pkgs.fetchFromGitHub {
-    owner = "arqv";
+    owner = "mitchellh";
     repo = "zig-overlay";
-    rev = "5b9504b8bff072553051d6e130727f7f5c0715c3";
-    sha256 = "NDm5qT6/qr789IhI2dsQxrR5/Mr7cXVj17x/+tl3pDE=";
+    rev = "62ca03d2ff30fb2920c5a1d8a2b6c87d1b68867b";
+    sha256 = "1xriHeSpoL4qN5xqPiQc9S9R7Qvcl3RxHwJ5FYPjLn0=";
   };
+
   gitignoreSrc = pkgs.fetchFromGitHub {
     owner = "hercules-ci";
-    repo = "gitignore";
-    rev = "c4662e662462e7bf3c2a968483478a665d00e717";
-    sha256 = "1npnx0h6bd0d7ql93ka7azhj40zgjp815fw2r6smg8ch9p7mzdlx";
+    repo = "gitignore.nix";
+    rev = "a20de23b925fd8264fd7fad6454652e142fd7f73";
+    sha256 = "8DFJjXG8zqoONA1vXtgeKXy68KdJL5UaXR8NtVMUbx8=";
   };
+
   inherit (import gitignoreSrc { inherit (pkgs) lib; }) gitignoreSource;
-  zig = (import zig-overlay { inherit pkgs system; }).master.latest;
+  zig = (import zig-overlay { inherit pkgs system; }).master;
+
+  zon = builtins.fromJSON (
+    builtins.concatStringsSep "" [
+      "{"
+      (builtins.replaceStrings [ "}, " ] [ "}" ]
+        (builtins.replaceStrings [ " ." " =" "\n" ", }" ] [ "\"" "\" :" "" "}" ]
+          (builtins.replaceStrings [ ".{" ] [ "{" ]
+            (builtins.concatStringsSep " "
+              (builtins.filter builtins.isString
+                (builtins.split "[ \n]+"
+                  (builtins.elemAt
+                    (builtins.match ".*dependencies = .[{](.*)[}].*" (builtins.readFile ./build.zig.zon))
+                    0)))))))
+    ]
+  );
+
+  cp-phase = builtins.concatStringsSep ";" (builtins.attrValues (builtins.mapAttrs (k: v: "cp -r ${builtins.fetchTarball v.url} .cache/p/${v.hash}") zon));
 in
 pkgs.stdenvNoCC.mkDerivation {
   name = "zls";
@@ -27,7 +46,8 @@ pkgs.stdenvNoCC.mkDerivation {
   dontInstall = true;
   buildPhase = ''
     mkdir -p $out
-    zig build install -Dcpu=baseline -Drelease-safe=true -Ddata_version=master --prefix $out
+    mkdir -p .cache/{p,z,tmp}
+    ${cp-phase}
+    zig build install --cache-dir $(pwd)/zig-cache --global-cache-dir $(pwd)/.cache -Dcpu=baseline -Doptimize=ReleaseSafe -Ddata_version=master --prefix $out
   '';
-  XDG_CACHE_HOME = ".cache";
 }

flake.nix

@@ -48,6 +48,7 @@
         cp-phase = builtins.concatStringsSep ";" (builtins.attrValues (builtins.mapAttrs (k: v: "cp -r ${inputs.${k}} .cache/p/${v.hash}") zon));
       in
       rec {
+        formatter = nixpkgs.legacyPackages.${system}.nixpkgs-fmt;
         packages.default = packages.zls;
         packages.zls = pkgs.stdenvNoCC.mkDerivation {
           name = "zls";