Use the overlay from the nix flake

flake.lock

@@ -4,14 +4,14 @@
             "inputs": {
                 "nixpkgs": {
                     "inputs": {},
-                    "narHash": "sha256-HGlE2VNbdEjCP76hWAS72kHBlMWhpvqWo58Obg1Vy6s=",
-                    "originalUri": "nixpkgs",
-                    "uri": "github:edolstra/nixpkgs/13e1bce51f4aebdf3db58ce8c4a93e904a272bff"
+                    "narHash": "sha256-ltGlDPfwicH/u4orj1n4JXgRsA+jvKQsGnekObi0TV4=",
+                    "originalUri": "nixpkgs/release-19.03",
+                    "uri": "github:edolstra/nixpkgs/9a593b575e4044f9aff939b512e7cb1cf1e76a65"
                 }
             },
-            "narHash": "sha256-bzSMXhxVX5awBSTO4v6Fe0dd1igEMVFskJ5RKSSJ+/4=",
+            "narHash": "sha256-m89j1BztPNjhdaDBj3Uolc11qRagbo+kpJwSsc/vbkA=",
             "originalUri": "nix",
-            "uri": "github:NixOS/nix/aeb7148afd56b228604b79373a45793d36d660a3"
+            "uri": "github:NixOS/nix/a323b7826c1104a6404c5fdfd4a824a0d5598618"
         },
         "nixpkgs": {
             "inputs": {},

flake.nix

@@ -10,14 +10,9 @@
 
       version = "${builtins.readFile ./version}.${builtins.substring 0 8 self.lastModified}.${self.shortRev}";
 
-      # FIXME: use nix overlay?
-      nix' = nix.hydraJobs.build.x86_64-linux // {
-        perl-bindings = nix.hydraJobs.perlBindings.x86_64-linux;
-      };
-
       pkgs = import nixpkgs {
         system = "x86_64-linux";
-        overlays = [ self.overlay ];
+        overlays = [ self.overlay nix.overlay ];
       };
 
       # NixOS configuration used for VM tests.
@@ -94,8 +89,8 @@
                 TextDiff
                 TextTable
                 XMLSimple
-                nix'
-                nix'.perl-bindings
+                final.nix
+                final.nix.perl-bindings
                 git
                 boehmgc
               ];
@@ -111,14 +106,14 @@
             [ makeWrapper autoconf automake libtool unzip nukeReferences pkgconfig sqlite libpqxx
               gitAndTools.topGit mercurial darcs subversion bazaar openssl bzip2 libxslt
               guile # optional, for Guile + Guix support
-              perlDeps perl nix'
+              perlDeps perl final.nix
               postgresql95 # for running the tests
               boost
               nlohmann_json
             ];
 
           hydraPath = lib.makeBinPath (
-            [ sqlite subversion openssh nix' coreutils findutils pixz
+            [ sqlite subversion openssh final.nix coreutils findutils pixz
               gzip bzip2 lzma gnutar unzip git gitAndTools.topGit mercurial darcs gnused bazaar
             ] ++ lib.optionals stdenv.isLinux [ rpm dpkg cdrkit ] );
 
@@ -151,7 +146,7 @@
                     --prefix PATH ':' $out/bin:$hydraPath \
                     --set HYDRA_RELEASE ${version} \
                     --set HYDRA_HOME $out/libexec/hydra \
-                    --set NIX_RELEASE ${nix'.name or "unknown"}
+                    --set NIX_RELEASE ${final.nix.name or "unknown"}
             done
           '';
 
@@ -282,8 +277,7 @@
 
       nixosModules.hydra = {
         imports = [ ./hydra-module.nix ];
-        nixpkgs.overlays = [ self.overlay ];
-        nix.package = nix';
+        nixpkgs.overlays = [ self.overlay nix.overlay ];
       };
 
       nixosModules.hydraTest = {