From 6b7331427bedf0458d000ea35c39a5289c45ae19 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alu=C3=ADsio=20Augusto=20Silva=20Gon=C3=A7alves?=
 <aluisio@aasg.name>
Date: Sun, 25 Apr 2021 22:16:37 -0300
Subject: [PATCH] make-job-script: Extract systemd service script builder from
 Nixpkgs

This can be used when you want to use `preStart`, `postStart`, or
`preStop` but also need to apply one of the special executable prefixes.
---
 flake.nix                                     |  1 +
 .../build-support/make-job-script/default.nix | 24 +++++++++++++++++++
 pkgs/manifest.nix                             |  1 +
 pkgs/overlay.nix                              |  2 ++
 4 files changed, 28 insertions(+)
 create mode 100644 pkgs/build-support/make-job-script/default.nix

diff --git a/flake.nix b/flake.nix
index fa197f8..fcc11b0 100644
--- a/flake.nix
+++ b/flake.nix
@@ -26,6 +26,7 @@
           # Remove packages not compatible with this system.
           (filterAttrs (attr: drv: drv ? meta.platforms -> builtins.elem system drv.meta.platforms))
         ]);
+      legacyPackages = genAttrs defaultSystems (system: (import ./. { pkgs = nixpkgs.legacyPackages.${system}; }));
       nixosModules = mapAttrs (name: path: import path) (import ./modules);
       overlays = {
         pkgs = import ./pkgs/overlay.nix;
diff --git a/pkgs/build-support/make-job-script/default.nix b/pkgs/build-support/make-job-script/default.nix
new file mode 100644
index 0000000..2362439
--- /dev/null
+++ b/pkgs/build-support/make-job-script/default.nix
@@ -0,0 +1,24 @@
+{ lib, writeTextFile, stdenv, runtimeShell }:
+let
+  inherit (lib) replaceChars;
+
+  # Taken from <nixpkgs/nixos/modules/system/boot/systemd.nix>.
+  makeJobScript = name: text:
+    let
+      scriptName = replaceChars [ "\\" "@" ] [ "-" "_" ] name;
+      out = writeTextFile {
+        name = "unit-script-${scriptName}";
+        executable = true;
+        destination = "/bin/${scriptName}";
+        text = ''
+          #!${runtimeShell} -e
+          ${text}
+        '';
+        checkPhase = ''
+          ${stdenv.shell} -n "$out/bin/${scriptName}"
+        '';
+      };
+    in
+    "${out}/bin/${scriptName}";
+in
+makeJobScript
diff --git a/pkgs/manifest.nix b/pkgs/manifest.nix
index 52efcaf..06461be 100644
--- a/pkgs/manifest.nix
+++ b/pkgs/manifest.nix
@@ -10,6 +10,7 @@
   [ "iwgtk" ]
   [ "linuxPackages" "rtl8723bu" ]
   [ "linuxPackages_latest" "rtl8723bu" ]
+  [ "makeJobScript" ]
   [ "matrix-appservice-irc" ]
   [ "prometheus-bird-exporter" ]
   [ "python3Packages" "daemonocle" ]
diff --git a/pkgs/overlay.nix b/pkgs/overlay.nix
index 56408c6..31432d7 100644
--- a/pkgs/overlay.nix
+++ b/pkgs/overlay.nix
@@ -25,6 +25,8 @@ final: prev:
   linuxPackagesFor = kernel:
     (prev.linuxPackagesFor kernel).extend (import ./os-specific/linux/kernel-packages.nix);
 
+  makeJobScript = final.callPackage ./build-support/make-job-script { };
+
   matrix-appservice-irc = final.callPackage ./servers/matrix-synapse/matrix-appservice-irc {
     nodejs = final.nodejs-12_x;
   };
-- 
2.38.5