bspwm: add alwaysResetDesktops (#2785)

If set to true, desktops configured in `monitors` will be reset every time
the config is run.

If set to false, desktops will only be configured the first time the config is run.
This is useful if you want to dynamically add desktops and you don't want them
to be destroyed if you re-run `bspwmrc`.

modules/services/window-managers/bspwm/default.nix

@@ -10,7 +10,19 @@ let
     builtins.replaceStrings upperChars (map (c: "_${c}") lowerChars);
 
   formatMonitor = monitor: desktops:
+    let
+      resetDesktops =
         "bspc monitor ${escapeShellArg monitor} -d ${escapeShellArgs desktops}";
+      defaultDesktopName =
+        "Desktop"; # https://github.com/baskerville/bspwm/blob/master/src/desktop.h
+    in if cfg.alwaysResetDesktops then
+      resetDesktops
+    else ''
+      if [[ $(bspc query --desktops --names --monitor ${
+        escapeShellArg monitor
+      }) == ${defaultDesktopName} ]]; then
+        ${resetDesktops}
+      fi'';
 
   formatValue = v:
     if isList v then

modules/services/window-managers/bspwm/options.nix

@@ -185,6 +185,19 @@ in {
       example = { "HDMI-0" = [ "web" "terminal" "III" "IV" ]; };
     };
 
+    alwaysResetDesktops = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        If set to <literal>true</literal>, desktops configured in <option>monitors</option> will be reset
+        every time the config is run.
+
+        If set to <literal>false</literal>, desktops will only be configured the first time the config is run.
+        This is useful if you want to dynamically add desktops and you don't want them to be destroyed if you
+        re-run <literal>bspwmrc</literal>.
+      '';
+    };
+
     rules = mkOption {
       type = types.attrsOf rule;
       default = { };

tests/modules/services/window-managers/bspwm/bspwmrc

@@ -1,4 +1,6 @@
-bspc monitor 'focused' -d 'desktop 1' 'd'\''esk top'
+if [[ $(bspc query --desktops --names --monitor 'focused') == Desktop ]]; then
+  bspc monitor 'focused' -d 'desktop 1' 'd'\''esk top'
+fi
 
 bspc config 'border_width' '2'
 bspc config 'external_rules_command' '/path/to/external rules command'

tests/modules/services/window-managers/bspwm/configuration.nix

@@ -8,6 +8,7 @@ with lib;
       enable = true;
       monitors.focused =
         [ "desktop 1" "d'esk top" ]; # pathological desktop names
+      alwaysResetDesktops = false;
       settings = {
         border_width = 2;
         split_ratio = 0.52;