nixos/ipfs: improve how the commandline flags are generated

Use `utils.escapeSystemdExecArgs` instead of relying on the exact way in which `toString` formats a list.
In https://github.com/NixOS/nixpkgs/pull/156706#discussion_r795867283 a suggestion was made and then implemented to replace `toString` with `concatStringsSep " "`.
@pennae then suggested to use `utils.escapeSystemdExecArgs` instead in https://github.com/NixOS/nixpkgs/pull/164846#issuecomment-1073001848.

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -467,6 +467,15 @@
           its reliance on python2.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <literal>services.ipfs.extraFlags</literal> is now escaped
+          with <literal>utils.escapeSystemdExecArgs</literal>. If you
+          rely on systemd interpolating <literal>extraFlags</literal> in
+          the service <literal>ExecStart</literal>, this will no longer
+          work.
+        </para>
+      </listitem>
       <listitem>
         <para>
           The <literal>matrix-synapse</literal> service

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -157,6 +157,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - The `mailpile` email webclient (`services.mailpile`) has been removed due to its reliance on python2.
 
+- `services.ipfs.extraFlags` is now escaped with `utils.escapeSystemdExecArgs`. If you rely on systemd interpolating `extraFlags` in the service `ExecStart`, this will no longer work.
+
 - The `matrix-synapse` service (`services.matrix-synapse`) has been converted to use the `settings` option defined in RFC42.
   This means that options that are part of your `homeserver.yaml` configuration, and that were specified at the top-level of the
   module (`services.matrix-synapse`) now need to be moved into `services.matrix-synapse.settings`. And while not all options you

nixos/modules/services/network-filesystems/ipfs.nix

@@ -1,16 +1,17 @@
-{ config, lib, pkgs, options, ... }:
+{ config, lib, pkgs, options, utils, ... }:
 with lib;
 let
   cfg = config.services.ipfs;
   opt = options.services.ipfs;
 
-  ipfsFlags = toString ([
-    (optionalString cfg.autoMount "--mount")
-    (optionalString cfg.enableGC "--enable-gc")
-    (optionalString (cfg.serviceFdlimit != null) "--manage-fdlimit=false")
-    (optionalString (cfg.defaultMode == "offline") "--offline")
-    (optionalString (cfg.defaultMode == "norouting") "--routing=none")
-  ] ++ cfg.extraFlags);
+  ipfsFlags = utils.escapeSystemdExecArgs (
+    optional cfg.autoMount "--mount" ++
+    optional cfg.enableGC "--enable-gc" ++
+    optional (cfg.serviceFdlimit != null) "--manage-fdlimit=false" ++
+    optional (cfg.defaultMode == "offline") "--offline" ++
+    optional (cfg.defaultMode == "norouting") "--routing=none" ++
+    cfg.extraFlags
+  );
 
   profile =
     if cfg.localDiscovery