UI: Internal support for custom UI list item drag & activate operators

For pose libraries, we need to be able to apply a pose whenever
activating (clicking) an item in the Pose Library asset view and blend
it by dragging (press & move). And since we want to allow Python scripts
to define what happens at least when activating an asset (so they can
define for example a custom "Apply" operator for preset assets), it
makes sense to just let them pass an operator name to the asset view
template. The template will be introduced in a following commit.

1 files changed, 6 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_operators.c b/source/blender/windowmanager/intern/wm_operators.c
index 485e65cf3dc..576f15731a0 100644
--- a/source/blender/windowmanager/intern/wm_operators.c
+++ b/source/blender/windowmanager/intern/wm_operators.c
@@ -604,6 +604,12 @@ void WM_operator_properties_create(PointerRNA *ptr, const char *opstring)
  * used for keymaps and macros */
 void WM_operator_properties_alloc(PointerRNA **ptr, IDProperty **properties, const char *opstring)
 {
+  IDProperty *tmp_properties = NULL;
+  /* Allow passing NULL for properties, just create the properties here then. */
+  if (properties == NULL) {
+    properties = &tmp_properties;
+  }
+
   if (*properties == NULL) {
     IDPropertyTemplate val = {0};
     *properties = IDP_New(IDP_GROUP, &val, "wmOpItemProp");