bspwm: add alwaysResetDesktops

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

@@ -10,7 +10,19 @@ let
     builtins.replaceStrings upperChars (map (c: "_${c}") lowerChars);
 
   formatMonitor = monitor: desktops:
-    "bspc monitor ${escapeShellArg monitor} -d ${escapeShellArgs 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;