WM: warn when event's have repeat set for non keyboard events

Also add docs to event and keymap item flag.

source/blender/makesdna/DNA_windowmanager_types.h

@@ -383,6 +383,19 @@ enum {
   KMI_EXPANDED = (1 << 1),
   KMI_USER_MODIFIED = (1 << 2),
   KMI_UPDATE = (1 << 3),
+  /**
+   * When set, ignore events with #wmEvent.is_repeat enabled.
+   *
+   * \note this flag isn't cleared when editing/loading the key-map items,
+   * so it may be set in cases which don't make sense (modifier-keys or mouse-motion for example).
+   *
+   * Knowing if an event may repeat is something set at the operating-systems event handling level
+   * so rely on #wmEvent.is_repeat being false non keyboard events instead of checking if this
+   * flag makes sense.
+   *
+   * Only used when: `ISKEYBOARD(kmi->type) || (kmi->type == KM_TEXTINPUT)`
+   * as mouse, 3d-mouse, timer... etc never repeat.
+   */
   KMI_REPEAT_IGNORE = (1 << 4),
 };
 

source/blender/windowmanager/WM_types.h

@@ -559,7 +559,12 @@ typedef struct wmEvent {
   /** From ghost, fallback if utf8 isn't set. */
   char ascii;
 
-  /** Generated by auto-repeat. */
+  /**
+   * Generated by auto-repeat, note that this must only ever be set for keyboard events
+   * where `ISKEYBOARD(event->type) == true`.
+   *
+   * See #KMI_REPEAT_IGNORE for details on how key-map handling uses this.
+   */
   char is_repeat;
 
   /** Previous state, used for double click and the 'click'. */

source/blender/windowmanager/intern/wm_event_system.c

@@ -155,6 +155,15 @@ wmEvent *WM_event_add_simulate(wmWindow *win, const wmEvent *event_to_add)
 
 void wm_event_free(wmEvent *event)
 {
+#ifndef NDEBUG
+  /* Don't use assert here because it's fairly harmless in most cases,
+   * more an issue of correctness, something we should avoid in general. */
+  if (event->is_repeat && !ISKEYBOARD(event->type)) {
+    printf("%s: 'is_repeat=true' for non-keyboard event, this should not happen.\n", __func__);
+    WM_event_print(event);
+  }
+#endif
+
   if (event->customdata) {
     if (event->customdatafree) {
       /* Note: pointer to listbase struct elsewhere. */