Wayland KDE: Fix abort when pasting into Firefox

Dunno why kwin uses drag and drop callbacks when pasting into Firefox on
Wayland, but then this is Wayland, so every stupid thing imaginable will
be done at least once.

Fixes #5603

docs/changelog.rst

@@ -40,6 +40,8 @@ Detailed list of changes
 
 - Fix a regression in the previous release that caused a :opt:`resize_draw_strategy` of ``static`` to not work (:iss:`5601`)
 
+- Wayland KDE: Fix abort when pasting into Firefox (:iss:`5603`)
+
 0.26.4 [2022-10-17]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

glfw/wl_window.c

@@ -1691,9 +1691,18 @@ static void primary_selection_source_canceled(void *data UNUSED, struct zwp_prim
     zwp_primary_selection_source_v1_destroy(primary_selection_source);
 }
 
+// KWin aborts if we don't define these even though they are not used for copy/paste
+static void dummy_data_source_target(void* data UNUSED, struct wl_data_source* wl_data_source UNUSED, const char* mime_type UNUSED) {
+}
+
+static void dummy_data_source_action(void* data UNUSED, struct wl_data_source* wl_data_source UNUSED, uint dnd_action UNUSED) {
+}
+
 static const struct wl_data_source_listener data_source_listener = {
     .send = _glfwSendClipboardText,
     .cancelled = data_source_canceled,
+    .target = dummy_data_source_target,
+    .action = dummy_data_source_action,
 };
 
 static const struct zwp_primary_selection_source_v1_listener primary_selection_source_listener = {