Print nicer message when Qt xkb plugin is missing

TODO

@@ -39,8 +39,6 @@ New big features
 Improvements / minor features
 =============================
 
-- Print some meaningful message (via qInstallMsgHandler) when platform plugins
-  are missing, especially with xcb (on Arch: libxkbcommon-x11)
 - Reimplement tabbar to paint it by ourselves to look like dwb
 - Save cookies in Netscape format so it can be used by wget. (see notes)
 - Zoom with ctrl + mousewheel

qutebrowser/utils/log.py

@@ -192,6 +192,18 @@ def qt_message_handler(msg_type, context, msg):
     else:
         func = context.function
     name = 'qt' if context.category == 'default' else 'qt-' + context.category
+    if msg.splitlines()[0] == ('This application failed to start because it '
+                               'could not find or load the Qt platform plugin '
+                               '"xcb".'):
+        # Handle this message specially.
+        msg += ("\n\nOn Archlinux, this should fix the problem:\n"
+                "    pacman -S libxkbcommon-x11")
+        try:
+            import faulthandler
+        except ImportError:
+            pass
+        else:
+            faulthandler.disable()
     record = qt.makeRecord(name, level, context.file, context.line, msg, None,
                            None, func)
     qt.handle(record)