Implement preMountHook & postMountHook

These options previously existed but had no effect. Now they are
implemented. They only affect mount during disko’s filesystem creation,
not during any later mounts.

Adding test case to existing “complex” example and test mostly because
couldn’t think of any better place to put it.

example/complex.nix

@@ -110,6 +110,9 @@
               mountOptions = [
                 "defaults"
               ];
+              postMountHook = ''
+                touch /mnt/ext4_on_lvm/file-from-postMountHook
+              '';
             };
           };
           raid1 = {

lib/default.nix

@@ -238,12 +238,19 @@ let
         description = "Creation script";
       };
 
-    mkMountOption = { default, ... }@attrs:
+    mkMountOption = { config, options, default }@attrs:
       lib.mkOption {
         internal = true;
         readOnly = true;
         type = diskoLib.jsonType;
-        default = attrs.default;
+        default = lib.mapAttrsRecursive (name: value: if builtins.isString value then ''
+          (
+            ${diskoLib.indent (diskoLib.defineHookVariables { inherit options; })}
+            ${config.preMountHook}
+            ${diskoLib.indent value}
+            ${config.postMountHook}
+          )
+        '' else value) attrs.default;
         description = "Mount script";
       };
 

tests/complex.nix

@@ -20,6 +20,9 @@ diskoLib.testLib.makeDiskoTest {
     machine.succeed("mountpoint /zfs_legacy_fs");
     machine.succeed("mountpoint /ext4onzfs");
     machine.succeed("mountpoint /ext4_on_lvm");
+
+
+    machine.succeed("test -e /ext4_on_lvm/file-from-postMountHook");
   '';
   extraInstallerConfig = {
     boot.kernelModules = [ "dm-raid" "dm-mirror" ];