nix: splice the package properly (#234)

Use callPackage on the wrapper as well. Fixes #232.

That change also breaks the public interface a bit to keep things
simple.

default.nix

@@ -4,5 +4,5 @@
 }:
 {
   lib = import ./nix/lib.nix { inherit nixpkgs; };
+  system-manager = pkgs.callPackage ./package.nix { };
 }
-// import ./packages.nix { inherit pkgs; }

flake.nix

@@ -34,21 +34,17 @@
     {
       lib = import ./nix/lib.nix { inherit nixpkgs; };
 
-      # The unwrapped version takes nix from the PATH, it will fail if nix
-      # cannot be found.
-      # The wrapped version has a reference to the nix store path, so nix is
-      # part of its runtime closure.
       packages = eachSystem (
         { pkgs, system }:
-        import ./packages.nix { inherit pkgs; }
-        // {
-          default = self.packages.${system}.system-manager;
+        {
+          default = pkgs.callPackage ./package.nix { };
         }
       );
 
       overlays = {
-        packages = final: _prev: import ./packages.nix { pkgs = final; };
-        default = self.overlays.packages;
+        default = final: _prev: {
+          system-manager = final.callPackage ./package.nix { };
+        };
       };
 
       # Only useful for quick tests
@@ -70,7 +66,7 @@
           (eachSystem (
             { system, ... }:
             {
-              system-manager = self.packages.${system}.system-manager;
+              system-manager = self.packages.${system}.default;
             }
           ))
           {

nix/lib.nix

@@ -61,9 +61,7 @@ let
               };
               # Pass the wrapped system-manager binary down
               # TODO: Use nixpkgs version by default.
-              inherit (import ../packages.nix { inherit pkgs; })
-                system-manager
-                ;
+              system-manager = pkgs.callPackage ../package.nix { };
             };
           };
 

package.nix

@@ -1,18 +1,19 @@
 {
-  pkgs ? import <nixpkgs> { },
-  lib ? pkgs.lib,
-}:
-let
-  cargoManifest = (pkgs.lib.importTOML ./Cargo.toml).package;
-  system-manager-unwrapped = pkgs.callPackage (
-    {
+  lib,
+
   rustPlatform,
+  cargo,
   dbus,
   pkg-config,
   nix,
   clippy,
+
+  runCommand,
+  makeBinaryWrapper,
 }:
-    rustPlatform.buildRustPackage {
+let
+  cargoManifest = (lib.importTOML ./Cargo.toml).package;
+  system-manager-unwrapped = rustPlatform.buildRustPackage {
       pname = "system-manager";
       version = cargoManifest.version;
       src = lib.fileset.toSource {
@@ -37,27 +38,29 @@ let
       ];
 
       preCheck = ''
-        ${lib.getExe pkgs.cargo} clippy
+        ${lib.getExe cargo} clippy
 
         # Stop the Nix command from trying to create /nix/var/nix/profiles.
         #
         # https://nix.dev/manual/nix/2.24/command-ref/new-cli/nix3-profile#profiles
         export NIX_STATE_DIR=$TMPDIR
       '';
-    }
-  ) { };
+    };
 in
+    runCommand "system-manager"
       {
-  inherit system-manager-unwrapped;
-  system-manager =
-    pkgs.runCommand "system-manager"
-      {
-        nativeBuildInputs = [ pkgs.pkgsBuildHost.makeBinaryWrapper ];
+        nativeBuildInputs = [ makeBinaryWrapper ];
+        passthru = {
+          # The unwrapped version takes nix from the PATH, it will fail if nix
+          # cannot be found.
+          # The wrapped version has a reference to the nix store path, so nix is
+          # part of its runtime closure.
+          unwrapped = system-manager-unwrapped;
+        };
       }
       ''
         makeWrapper \
           ${system-manager-unwrapped}/bin/system-manager \
           $out/bin/system-manager \
-          --prefix PATH : ${lib.makeBinPath [ pkgs.nix ]}
-      '';
-}
+          --prefix PATH : ${lib.makeBinPath [ nix ]}
+      ''