pizauth: fix systemd feature (#531688)

pkgs/by-name/pi/pizauth/package.nix

@@ -4,6 +4,7 @@
   fetchFromGitHub,
   stdenv,
   nix-update-script,
+  enableSystemd ? stdenv.hostPlatform.isLinux,
 }:
 
 rustPlatform.buildRustPackage (finalAttrs: {
@@ -19,17 +20,25 @@ rustPlatform.buildRustPackage (finalAttrs: {
 
   cargoHash = "sha256-pxzPcieUXE3VOyGNDaeDHUQPayRDZXpW57VWMejlZ4k=";
 
-  buildFeatures = lib.optionals stdenv.hostPlatform.isLinux [
+  buildFeatures = lib.optionals enableSystemd [
     "systemd"
   ];
 
   preConfigure = ''
     substituteInPlace lib/systemd/user/pizauth.service \
       --replace-fail /usr/bin/ ''${!outputBin}/bin/
+    # Upstream's Makefile uses target/release/pizauth as a Makefile target that
+    # the `install` target depends upon. Nixpkgs' cargoBuildHook defaults to
+    # using the explicit `--target @rustcTargetSpec@` flag, so that the
+    # executable always ends up in
+    # `target/${stdenv.hostPlatform.rust.rustcTargetSpec}/release`. To make the
+    # Makefile not run cargo build again, we use this substitution.
+    substituteInPlace Makefile \
+      --replace-fail target/release target/${stdenv.hostPlatform.rust.rustcTargetSpec}/release
   '';
 
   postInstall = ''
-    make PREFIX=$out install ${lib.optionalString stdenv.hostPlatform.isLinux "install-systemd"}
+    make PREFIX=$out install ${lib.optionalString enableSystemd "install-systemd"}
   '';
 
   passthru.updateScript = nix-update-script { extraArgs = [ "--version-regex=pizauth-(.*)" ]; };