Fix T95591: Crash on drawing with measure tool with tweak fallback tool

Using press to activate the Tweak tool doesn't work well when used a
fallback tool as the drag event is often used by the current tool -
making it impossible not to select when dragging (unless the fallback
tool is disabled entirely).
Resolve this by using CLICK events when the Tweak tool is used as a
fallback.

Even though this avoids the crash, check for null-pointer de-reference
since changes to the key-map shouldn't cause operators to crash.

Note that the ability for operators to access a gizmo before it's fully
initialized is a more general problem that should be addressed, but out
of scope for a bug-fix.

Reviewed By: zeddb, JulienKaspar, Severin

Maniphest Tasks: T95591

Ref D14231

1 files changed, 20 insertions, 0 deletions

diff --git a/source/blender/editors/space_view3d/view3d_gizmo_ruler.c b/source/blender/editors/space_view3d/view3d_gizmo_ruler.c
index 1082483dcd7..adcb101bca9 100644
--- a/source/blender/editors/space_view3d/view3d_gizmo_ruler.c
+++ b/source/blender/editors/space_view3d/view3d_gizmo_ruler.c
@@ -469,6 +469,19 @@ static bool view3d_ruler_item_mousemove(const bContext *C,
   return false;
 }
 
+/**
+ * When the gizmo-group has been created immediately before running an operator
+ * to manipulate rulers, it's possible the new gizmo-group has not yet been initialized.
+ * in 3.0 this happened because left-click drag would both select and add a new ruler,
+ * significantly increasing the likelihood of this happening.
+ * Workaround this crash by checking the gizmo's custom-data has not been cleared.
+ * The key-map has also been modified not to trigger this bug, see T95591.
+ */
+static bool gizmo_ruler_check_for_operator(const wmGizmoGroup *gzgroup)
+{
+  return gzgroup->customdata != NULL;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -1308,6 +1321,10 @@ static int view3d_ruler_add_invoke(bContext *C, wmOperator *op, const wmEvent *e
   wmGizmoGroup *gzgroup = WM_gizmomap_group_find(gzmap, view3d_gzgt_ruler_id);
   const bool use_depth = (v3d->shading.type >= OB_SOLID);
 
+  if (!gizmo_ruler_check_for_operator(gzgroup)) {
+    return OPERATOR_CANCELLED;
+  }
+
   /* Create new line */
   RulerItem *ruler_item;
   ruler_item = ruler_item_add(gzgroup);
@@ -1383,6 +1400,9 @@ static int view3d_ruler_remove_invoke(bContext *C, wmOperator *op, const wmEvent
   wmGizmoMap *gzmap = region->gizmo_map;
   wmGizmoGroup *gzgroup = WM_gizmomap_group_find(gzmap, view3d_gzgt_ruler_id);
   if (gzgroup) {
+    if (!gizmo_ruler_check_for_operator(gzgroup)) {
+      return OPERATOR_CANCELLED;
+    }
     RulerInfo *ruler_info = gzgroup->customdata;
     if (ruler_info->item_active) {
       RulerItem *ruler_item = ruler_info->item_active;