xworkspaces: Deal with disappearing windows

Because the X server is asynchronous, there is no guarantee that after
reading _NET_CLIENT_LIST, all windows still exist.
For that reason we need to handle XCB_WINDOW errors appropriately.

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `format-offset` being ignored ([`#2643`](https://github.com/polybar/polybar/pull/2643))
 - Negative struts (`margin-bottom`, `margin-top`) being ignored ([`#2642`](https://github.com/polybar/polybar/issues/2642), [`#2644`](https://github.com/polybar/polybar/pull/2644))
 - Positioning in awesomeWM ([`#2651`](https://github.com/polybar/polybar/pull/2651))
+- `internal/xworkspaces`: The module sometimes crashed polybar when windows were closed. ([`#2655`](https://github.com/polybar/polybar/pull/2655))
 
 ## [3.6.1] - 2022-03-05
 ### Build

src/modules/xworkspaces.cpp

@@ -138,8 +138,18 @@ namespace modules {
 
     for (auto&& client : newclients) {
       if (m_clients.count(client) == 0) {
-        // new client: listen for changes (wm_hint or desktop)
-        m_connection.ensure_event_mask(client, XCB_EVENT_MASK_PROPERTY_CHANGE);
+        try {
+          // new client: listen for changes (wm_hint or desktop)
+          m_connection.ensure_event_mask(client, XCB_EVENT_MASK_PROPERTY_CHANGE);
+        } catch (const xpp::x::error::window& e) {
+          /*
+           * The "new client" may have already disappeared between reading the
+           * client list and setting the event mask.
+           * This is not a severe issue and it will eventually correct itself
+           * when a new _NET_CLIENT_LIST value is set.
+           */
+          m_log.info("%s: New client window no longer exists, ignoring...");
+        }
       }
     }