Fix #136563: Crash clicking on a light after it has been deleted

Failure to refresh the highlighted gizmo meant that clicking
on a highlighted gizmo would attempt to activate it even though
it's poll function failed - which crashed in this case.

Resolve the common-case by ensuring a call to refresh the gizmo-map
causes the event system to re-evaluate the highlighted gizmo,
even if the cursor doesn't move.

Since it's still possible the call to "refresh" the gizmo is missed,
gizmo_tweak_invoke now checks the gizmo-groups poll succeeds with an
assert and early return if it doesn't. This would have prevented the
crash although the highlighted-gizmo still won't be reset - causing
the cursor to display as if it's over a gizmo until it's moved.

source/blender/windowmanager/gizmo/intern/wm_gizmo_group.cc

@@ -572,8 +572,16 @@ static wmOperatorStatus gizmo_tweak_invoke(bContext *C, wmOperator *op, const wm
 
   if (!gz) {
     /* #wm_handlers_do_intern shouldn't let this happen. */
-    BLI_assert_unreachable();
-    return (OPERATOR_CANCELLED | OPERATOR_PASS_THROUGH);
+    BLI_assert_msg(false, "the gizmo should never be null, this is a bug!");
+    return OPERATOR_CANCELLED | OPERATOR_PASS_THROUGH;
+  }
+
+  if (!WM_gizmo_group_type_poll(C, gz->parent_gzgroup->type)) {
+    /* The event-system should prevent this from happening, see: #137146.
+     * May be caused by the context changing without tagging #wmGizmoMap::tag_highlight_pending,
+     * typically via #WM_gizmomap_tag_refresh. */
+    BLI_assert_msg(false, "the gizmo-group's poll should always succeed, this is a bug!");
+    return OPERATOR_CANCELLED | OPERATOR_PASS_THROUGH;
   }
 
   const int highlight_part_init = gz->highlight_part;

source/blender/windowmanager/gizmo/intern/wm_gizmo_intern.hh

@@ -107,6 +107,9 @@ struct wmGizmoMap {
   /** When set, one of the items in 'groups' has #wmGizmoGroup.tag_remove set. */
   bool tag_remove_group;
 
+  /** When set, the event system re-calculates highlight even without cursor motion. */
+  bool tag_highlight_pending;
+
   /**
    * \brief Gizmo map runtime context
    *

source/blender/windowmanager/gizmo/intern/wm_gizmo_map.cc

@@ -314,6 +314,9 @@ void WM_gizmomap_tag_refresh_drawstep(wmGizmoMap *gzmap, const eWM_GizmoFlagMapD
   BLI_assert(uint(drawstep) < WM_GIZMOMAP_DRAWSTEP_MAX);
   if (gzmap) {
     gzmap->update_flag[drawstep] |= (GIZMOMAP_IS_PREPARE_DRAW | GIZMOMAP_IS_REFRESH_CALLBACK);
+    /* This could be split out into a separate tagging function,
+     * in practice both when refreshing the highlight should also be updated. */
+    gzmap->tag_highlight_pending = true;
   }
 }
 
@@ -323,6 +326,8 @@ void WM_gizmomap_tag_refresh(wmGizmoMap *gzmap)
     for (int i = 0; i < WM_GIZMOMAP_DRAWSTEP_MAX; i++) {
       gzmap->update_flag[i] |= (GIZMOMAP_IS_PREPARE_DRAW | GIZMOMAP_IS_REFRESH_CALLBACK);
     }
+    /* See code-comment for #WM_gizmomap_tag_refresh_drawstep. */
+    gzmap->tag_highlight_pending = true;
   }
 }
 
@@ -739,6 +744,15 @@ static wmGizmo *gizmo_find_intersected_3d(bContext *C,
   return result;
 }
 
+bool wm_gizmomap_highlight_pending(const wmGizmoMap *gzmap)
+{
+  return gzmap->tag_highlight_pending;
+}
+bool wm_gizmomap_highlight_handled(wmGizmoMap *gzmap)
+{
+  return gzmap->tag_highlight_pending = false;
+}
+
 wmGizmo *wm_gizmomap_highlight_find(wmGizmoMap *gzmap,
                                     bContext *C,
                                     const wmEvent *event,

source/blender/windowmanager/gizmo/wm_gizmo_wmapi.hh

@@ -78,6 +78,8 @@ void wm_gizmomaps_handled_modal_update(bContext *C, wmEvent *event, wmEventHandl
 void wm_gizmomap_handler_context_op(bContext *C, wmEventHandler_Op *handler);
 void wm_gizmomap_handler_context_gizmo(bContext *C, wmEventHandler_Gizmo *handler);
 
+bool wm_gizmomap_highlight_pending(const wmGizmoMap *gzmap);
+bool wm_gizmomap_highlight_handled(wmGizmoMap *gzmap);
 /**
  * Try to find a gizmo under the mouse position. 2D intersections have priority over
  * 3D ones (could check for smallest screen-space distance but not needed right now).

source/blender/windowmanager/intern/wm_event_system.cc

@@ -3270,6 +3270,12 @@ static eHandlerActionFlag wm_handlers_do_gizmo_handler(bContext *C,
     }
   }
 
+  if (prev.gz_modal == nullptr) {
+    if (handle_highlight == false && wm_gizmomap_highlight_pending(gzmap)) {
+      handle_highlight = true;
+    }
+  }
+
   if (handle_highlight) {
     int part = -1;
     gz = wm_gizmomap_highlight_find(gzmap, C, event, &part);
@@ -3288,6 +3294,8 @@ static eHandlerActionFlag wm_handlers_do_gizmo_handler(bContext *C,
         }
       }
     }
+
+    wm_gizmomap_highlight_handled(gzmap);
   }
 
   /* Don't use from now on. */