nut: patch nutshutdown to set a default for NUT_CONFPATH

The way we build the package results in the binaries being hardcoded to
look for $out/etc/ups.conf instead of /etc/nut/ups.conf (where the
module places the file). This results in `upsdrvctl` failing to dispatch
shutdown commands (since it cannot find the configuration) and prevents
a primary monitor from cutting power to the appropriate UPS.

Note that we cannot use `--sysconfdir=/etc/nut` as a configure flag
since that results in the install phase trying to install directly into
/etc/nut which predictably fails in the sandbox.

pkgs/applications/misc/nut/default.nix

@@ -30,6 +30,13 @@ stdenv.mkDerivation rec {
   };
 
   patches = [
+    # This patch injects a default value for NUT_CONFPATH into the nutshutdown script
+    # since the way we build the package results in the binaries being hardcoded to check
+    # $out/etc/ups.conf instead of /etc/nut/ups.conf (where the module places the file).
+    # We also cannot use `--sysconfdir=/etc/nut` since that results in the install phase
+    # trying to install directly into /etc/nut which predictably fails
+    ./nutshutdown-conf-default.patch
+
     (substituteAll {
       src = ./hardcode-paths.patch;
       avahi = "${avahi}/lib";

pkgs/applications/misc/nut/nutshutdown-conf-default.patch

@@ -0,0 +1,10 @@
+diff --git a/scripts/systemd/nutshutdown.in b/scripts/systemd/nutshutdown.in
+index ace2485b3..9dee869bb 100755
+--- a/scripts/systemd/nutshutdown.in
++++ b/scripts/systemd/nutshutdown.in
+@@ -1,4 +1,5 @@
+ #!/bin/sh
++export NUT_CONFPATH="${NUT_CONFPATH-/etc/nut}"
+ 
+ # This script requires both nut-server (drivers)
+ # and nut-client (upsmon) to be present locally