Simplify the credentials configuration step

nixproc/create-managed-process/agnostic/generate-docker-container.nix

@@ -73,7 +73,9 @@ let
     path = basePackages ++ path;
   };
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 
   _user = util.determineUser {
     inherit user forceDisableUserChange;

nixproc/create-managed-process/bsdrc/create-bsdrc-script.nix

@@ -228,7 +228,9 @@ let
     '';
   };
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   inherit name;

nixproc/create-managed-process/disnix/create-process-script.nix

@@ -9,7 +9,9 @@
 }:
 
 let
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   inherit name;

nixproc/create-managed-process/launchd/create-launchd-daemon.nix

@@ -88,7 +88,9 @@ let
     '';
   };
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   inherit name;

nixproc/create-managed-process/supervisord/create-supervisord-program.nix

@@ -63,7 +63,9 @@ let
       ) (builtins.attrNames properties);
   };
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   inherit name priority;

nixproc/create-managed-process/systemd/create-systemd-service.nix

@@ -100,7 +100,9 @@ let
     '';
   };
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   name = "${prefix}${name}";

nixproc/create-managed-process/sysvinit/create-sysvinit-script.nix

@@ -240,7 +240,9 @@ let
     if number < 10 then "0${toString number}"
     else toString number;
 
-  credentialsSpec = if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
+  credentialsSpec = util.createCredentialsOrNull {
+    inherit createCredentials credentials forceDisableUserChange;
+  };
 in
 stdenv.mkDerivation {
   inherit name;

nixproc/create-managed-process/util/default.nix

@@ -77,4 +77,11 @@ rec {
     in
     if user == null then invocation
     else "${su} ${user} -c ${lib.escapeShellArgs [ invocation ]}";
+
+  /*
+   * Creates credential configuration files for users and groups, or returns
+   * null if user changing was disabled.
+   */
+  createCredentialsOrNull = {createCredentials, credentials, forceDisableUserChange}:
+    if credentials == {} || forceDisableUserChange then null else createCredentials credentials;
 }

tests/webapps-agnostic-supervisord.nix

@@ -25,6 +25,11 @@ let
     exprFile = ../examples/webapps-agnostic/processes.nix;
   };
 
+  processesEnvAutoUnprivileged = import ../nixproc/create-managed-process/supervisord/build-supervisord-env.nix {
+    exprFile = ../examples/webapps-agnostic/processes.nix;
+    forceDisableUserChange = true;
+  };
+
   processesEnvAdvanced = import ../nixproc/create-managed-process/supervisord/build-supervisord-env.nix {
     exprFile = ../examples/webapps-agnostic/processes-advanced.nix;
   };
@@ -44,7 +49,16 @@ makeTest {
     {pkgs, ...}:
 
     {
-      virtualisation.pathsInNixDB = [ pkgs.stdenv ] ++ pkgs.coreutils.all ++ [ supervisordProcessEnv processesEnvForeground processesEnvDaemon processesEnvAuto processesEnvAdvanced processesEnvEmpty ];
+      virtualisation.pathsInNixDB = [ pkgs.stdenv ] ++ pkgs.coreutils.all ++ [
+        supervisordProcessEnv
+        processesEnvForeground
+        processesEnvDaemon
+        processesEnvAuto
+        processesEnvAutoUnprivileged
+        processesEnvAdvanced
+        processesEnvEmpty
+      ];
+
       virtualisation.writableStore = true;
       virtualisation.memorySize = 1024;