Cleanup: Remove operator context override for drop-box operators

Drop-boxes should act on the context determined through the exact cursor
location. There should be no need to override that, basically by the
nature of how drop-boxes work.
So Campbell and I agreed on removing this.

If we wanted to support it, we'd have to restore the operator context
when drawing drop-boxes, see
https://developer.blender.org/T92501#1247581.

source/blender/editors/space_view3d/space_view3d.c

@@ -853,7 +853,6 @@ static void view3d_dropboxes(void)
   drop->draw = WM_drag_draw_item_name_fn;
   drop->draw_activate = view3d_ob_drop_draw_activate;
   drop->draw_deactivate = view3d_ob_drop_draw_deactivate;
-  drop->opcontext = WM_OP_EXEC_DEFAULT; /* Not really needed. */
 
   drop = WM_dropbox_add(lb,
                         "OBJECT_OT_transform_to_mouse",
@@ -865,7 +864,6 @@ static void view3d_dropboxes(void)
   drop->draw = WM_drag_draw_item_name_fn;
   drop->draw_activate = view3d_ob_drop_draw_activate;
   drop->draw_deactivate = view3d_ob_drop_draw_deactivate;
-  drop->opcontext = WM_OP_INVOKE_DEFAULT;
 
   WM_dropbox_add(lb,
                  "OBJECT_OT_drop_named_material",

source/blender/windowmanager/WM_types.h

@@ -1079,6 +1079,10 @@ typedef struct wmDrag {
 /**
  * Dropboxes are like keymaps, part of the screen/area/region definition.
  * Allocation and free is on startup and exit.
+ *
+ * The operator is polled and invoked with the current context (#WM_OP_INVOKE_DEFAULT), there is no
+ * way to override that (by design, since dropboxes should act on the exact mouse position). So the
+ * drop-boxes are supposed to check the required area and region context in their poll.
  */
 typedef struct wmDropBox {
   struct wmDropBox *next, *prev;
@@ -1120,10 +1124,6 @@ typedef struct wmDropBox {
   struct IDProperty *properties;
   /** RNA pointer to access properties. */
   struct PointerRNA *ptr;
-
-  /** Default invoke. */
-  short opcontext;
-
 } wmDropBox;
 
 /**

source/blender/windowmanager/intern/wm_dragdrop.c

@@ -122,7 +122,6 @@ wmDropBox *WM_dropbox_add(ListBase *lb,
   drop->cancel = cancel;
   drop->tooltip = tooltip;
   drop->ot = WM_operatortype_find(idname, 0);
-  drop->opcontext = WM_OP_INVOKE_DEFAULT;
 
   if (drop->ot == NULL) {
     MEM_freeN(drop);
@@ -324,7 +323,8 @@ static wmDropBox *dropbox_active(bContext *C,
             continue;
           }
 
-          if (WM_operator_poll_context(C, drop->ot, drop->opcontext)) {
+          const int opcontext = wm_drop_operator_context_get(drop);
+          if (WM_operator_poll_context(C, drop->ot, opcontext)) {
             return drop;
           }
 
@@ -392,10 +392,11 @@ static void wm_drop_update_active(bContext *C, wmDrag *drag, const wmEvent *even
 
 void wm_drop_prepare(bContext *C, wmDrag *drag, wmDropBox *drop)
 {
+  const int opcontext = wm_drop_operator_context_get(drop);
   /* Optionally copy drag information to operator properties. Don't call it if the
    * operator fails anyway, it might do more than just set properties (e.g.
    * typically import an asset). */
-  if (drop->copy && WM_operator_poll_context(C, drop->ot, drop->opcontext)) {
+  if (drop->copy && WM_operator_poll_context(C, drop->ot, opcontext)) {
     drop->copy(drag, drop);
   }
 
@@ -423,6 +424,16 @@ void wm_drags_check_ops(bContext *C, const wmEvent *event)
   }
 }
 
+/**
+ * The operator of a dropbox should always be executed in the context determined by the mouse
+ * coordinates. The dropbox poll should check the context area and region as needed.
+ * So this always returns #WM_OP_INVOKE_DEFAULT.
+ */
+int wm_drop_operator_context_get(const wmDropBox *UNUSED(drop))
+{
+  return WM_OP_INVOKE_DEFAULT;
+}
+
 /* ************** IDs ***************** */
 
 void WM_drag_add_local_ID(wmDrag *drag, ID *id, ID *from_parent)

source/blender/windowmanager/intern/wm_event_system.c

@@ -3063,8 +3063,9 @@ static int wm_handlers_do_intern(bContext *C, wmWindow *win, wmEvent *event, Lis
                   BLI_addtail(&single_lb, drag);
                   event->customdata = &single_lb;
 
+                  const int opcontext = wm_drop_operator_context_get(drop);
                   int op_retval = wm_operator_call_internal(
-                      C, drop->ot, drop->ptr, NULL, drop->opcontext, false, event);
+                      C, drop->ot, drop->ptr, NULL, opcontext, false, event);
                   OPERATOR_RETVAL_CHECK(op_retval);
 
                   if ((op_retval & OPERATOR_CANCELLED) && drop->cancel) {

source/blender/windowmanager/wm_event_system.h

@@ -175,6 +175,7 @@ void wm_dropbox_free(void);
 void wm_drags_exit(wmWindowManager *wm, wmWindow *win);
 void wm_drop_prepare(bContext *C, wmDrag *drag, wmDropBox *drop);
 void wm_drags_check_ops(bContext *C, const wmEvent *event);
+int wm_drop_operator_context_get(const wmDropBox *drop);
 void wm_drags_draw(bContext *C, wmWindow *win);
 
 #ifdef __cplusplus