xcb: Use functors in QXcbConnection::checkEvent()

... to check for buffered events. This makes the code less verbose and
easier to read. Changed the filter signature to pass an event type in addition
to the actual event, for the convenience of API user. And do not pass worthless
nullptr-s to the filter.

The only reason why KeyChecker from qxcbkeyboard.cpp was not converted
to lambda expression is that the code looks suspicious - KeyChecker::m_release
default value is 'true' and I don't see where it would ever be assigned
'false' (ref. QTBUG-69679) and the code is known to be buggy (ref. QTBUG-57335).
Those issues are out-of-scope for this patch.

Change-Id: If2fdd60fbb93eb983f3c9ad616aaf04834fede9f
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>

1 files changed, 6 insertions, 8 deletions

diff --git a/src/plugins/platforms/xcb/qxcbdrag.cpp b/src/plugins/platforms/xcb/qxcbdrag.cpp
index 0d72da0701..2b8e507f30 100644
--- a/src/plugins/platforms/xcb/qxcbdrag.cpp
+++ b/src/plugins/platforms/xcb/qxcbdrag.cpp
@@ -781,12 +781,11 @@ namespace
     public:
         ClientMessageScanner(xcb_atom_t a) : atom(a) {}
         xcb_atom_t atom;
-        bool checkEvent(xcb_generic_event_t *event) const {
-            if (!event)
+        bool operator() (xcb_generic_event_t *event, int type) const {
+            if (type != XCB_CLIENT_MESSAGE)
                 return false;
-            if ((event->response_type & 0x7f) != XCB_CLIENT_MESSAGE)
-                return false;
-            return ((xcb_client_message_event_t *)event)->type == atom;
+            auto clientMessage = reinterpret_cast<xcb_client_message_event_t *>(event);
+            return clientMessage->type == atom;
         }
     };
 }
@@ -794,12 +793,11 @@ namespace
 void QXcbDrag::handlePosition(QPlatformWindow * w, const xcb_client_message_event_t *event)
 {
     xcb_client_message_event_t *lastEvent = const_cast<xcb_client_message_event_t *>(event);
-    xcb_generic_event_t *nextEvent;
     ClientMessageScanner scanner(atom(QXcbAtom::XdndPosition));
-    while ((nextEvent = connection()->checkEvent(scanner))) {
+    while (auto nextEvent = connection()->checkEvent(scanner)) {
         if (lastEvent != event)
             free(lastEvent);
-        lastEvent = (xcb_client_message_event_t *)nextEvent;
+        lastEvent = reinterpret_cast<xcb_client_message_event_t *>(nextEvent);
     }
 
     handle_xdnd_position(w, lastEvent);