systemd: Add functions.escapeSystemdExecArg[s]

This makes it available outside the NixOS `utils` context.

nixos/lib/utils.nix

@@ -119,31 +119,7 @@ let
         )
       );
 
-    # Quotes an argument for use in Exec* service lines.
-    # systemd accepts "-quoted strings with escape sequences, toJSON produces
-    # a subset of these.
-    # Additionally we escape % to disallow expansion of % specifiers. Any lone ;
-    # in the input will be turned it ";" and thus lose its special meaning.
-    # Every $ is escaped to $$, this makes it unnecessary to disable environment
-    # substitution for the directive.
-    escapeSystemdExecArg =
-      arg:
-      let
-        s =
-          if isPath arg then
-            "${arg}"
-          else if isString arg then
-            arg
-          else if isInt arg || isFloat arg || isDerivation arg then
-            toString arg
-          else
-            throw "escapeSystemdExecArg only allows strings, paths, numbers and derivations";
-      in
-      replaceStrings [ "%" "$" ] [ "%%" "$$" ] (toJSON s);
-
-    # Quotes a list of arguments into a single string for use in a Exec*
-    # line.
-    escapeSystemdExecArgs = concatMapStringsSep " " escapeSystemdExecArg;
+    inherit (config.systemd.package.functions) escapeSystemdExecArg escapeSystemdExecArgs;
 
     # Returns a system path for a given shell package
     toShellPath =

pkgs/os-specific/linux/systemd/default.nix

@@ -897,6 +897,11 @@ stdenv.mkDerivation (finalAttrs: {
     # needed - and therefore `interfaceVersion` should be incremented.
     interfaceVersion = 2;
 
+    functions = import ./functions/default.nix {
+      inherit lib;
+      systemd = finalAttrs.finalPackage;
+    };
+
     inherit
       withBootloader
       withCryptsetup
@@ -1022,6 +1027,12 @@ stdenv.mkDerivation (finalAttrs: {
           pkgsCross.${systemString}.systemd;
 
         pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
+
+        functions = import ./functions/test.nix {
+          inherit lib;
+          systemd = finalAttrs.finalPackage;
+          ok = buildPackages.emptyFile;
+        };
       };
   };
 

pkgs/os-specific/linux/systemd/functions/default.nix

@@ -0,0 +1,55 @@
+/**
+  Build the `systemd.functions` library (where `systemd` is the package)
+*/
+{ lib, systemd }:
+let
+  inherit (lib)
+    concatMapStringsSep
+    isDerivation
+    isFloat
+    isInt
+    isPath
+    isString
+    replaceStrings
+    ;
+  inherit (builtins)
+    toJSON
+    ;
+
+  /**
+    Quotes an argument for use in `Exec*` service lines.
+    Additionally we escape `%` to disallow expansion of `%` specifiers. Any lone `;`
+    in the input will be turned into `";"` and thus lose its special meaning.
+    Every `$` is escaped to `$$`, this makes it unnecessary to disable environment
+    substitution for the directive.
+  */
+  escapeSystemdExecArg =
+    arg:
+    let
+      s =
+        if isPath arg then
+          "${arg}"
+        else if isString arg then
+          arg
+        else if isInt arg || isFloat arg || isDerivation arg then
+          toString arg
+        else
+          throw "escapeSystemdExecArg only allows strings, paths, numbers and derivations";
+    in
+    # systemd accepts "-quoted strings with escape sequences, toJSON produces
+    # a subset of these.
+    replaceStrings [ "%" "$" ] [ "%%" "$$" ] (toJSON s);
+
+  /**
+    Quotes a list of arguments into a single string for use in a Exec* line.
+  */
+  escapeSystemdExecArgs = concatMapStringsSep " " escapeSystemdExecArg;
+in
+# Instead of requiring v2, we can make this library conditional on the version as needed.
+assert systemd.interfaceVersion == 2;
+{
+  inherit
+    escapeSystemdExecArg
+    escapeSystemdExecArgs
+    ;
+}

pkgs/os-specific/linux/systemd/functions/test.nix

@@ -0,0 +1,23 @@
+{
+  lib,
+  systemd,
+  ok,
+}:
+
+# This function is also tested in nixosTests.systemd-escaping
+assert systemd.functions.escapeSystemdExecArg "hi" == ''"hi"'';
+assert systemd.functions.escapeSystemdExecArg "hi there" == ''"hi there"'';
+assert systemd.functions.escapeSystemdExecArg ''"hi there"'' == ''"\"hi there\""'';
+assert systemd.functions.escapeSystemdExecArg ''"%$'' == ''"\"%%$$"'';
+assert
+  systemd.functions.escapeSystemdExecArgs [
+    "hi"
+    "there"
+  ] == ''"hi" "there"'';
+assert
+  systemd.functions.escapeSystemdExecArgs [
+    "hi"
+    "%"
+    "there"
+  ] == ''"hi" "%%" "there"'';
+ok