UI: Support setting operator properties for `UILayout.operator_menu_enum()`

`UILayout.operator_menu_enum()` now returns the operator properties, just like
`UILayout.operator()`. This makes it possible to set options for the operator
displayed in the menu. In C it can be done through the new
`uiItemMenuEnumFullO()` or `uiItemMenuEnumFullO_ptr()`.

It's reasonable to have this, probably just a small thing never bothered to
add. D10912 could use it, the following comment can be addressed now too:
https://developer.blender.org/diffusion/B/browse/master/source/blender/editors/space_nla/nla_buttons.c$583-586

1 files changed, 39 insertions, 15 deletions

diff --git a/source/blender/editors/interface/interface_layout.c b/source/blender/editors/interface/interface_layout.c
index cf3abc9be4a..a17a527c868 100644
--- a/source/blender/editors/interface/interface_layout.c
+++ b/source/blender/editors/interface/interface_layout.c
@@ -3381,10 +3381,13 @@ typedef struct MenuItemLevel {
 
 static void menu_item_enum_opname_menu(bContext *UNUSED(C), uiLayout *layout, void *arg)
 {
-  MenuItemLevel *lvl = (MenuItemLevel *)(((uiBut *)arg)->func_argN);
+  uiBut *but = arg;
+  MenuItemLevel *lvl = but->func_argN;
+  /* Use the operator properties from the button owning the menu. */
+  IDProperty *op_props = but->opptr ? but->opptr->data : NULL;
 
   uiLayoutSetOperatorContext(layout, lvl->opcontext);
-  uiItemsEnumO(layout, lvl->opname, lvl->propname);
+  uiItemsFullEnumO(layout, lvl->opname, lvl->propname, op_props, lvl->opcontext, 0);
 
   layout->root->block->flag |= UI_BLOCK_IS_FLIP;
 
@@ -3392,12 +3395,13 @@ static void menu_item_enum_opname_menu(bContext *UNUSED(C), uiLayout *layout, vo
   UI_block_direction_set(layout->root->block, UI_DIR_DOWN);
 }
 
-void uiItemMenuEnumO_ptr(uiLayout *layout,
-                         bContext *C,
-                         wmOperatorType *ot,
-                         const char *propname,
-                         const char *name,
-                         int icon)
+void uiItemMenuEnumFullO_ptr(uiLayout *layout,
+                             bContext *C,
+                             wmOperatorType *ot,
+                             const char *propname,
+                             const char *name,
+                             int icon,
+                             PointerRNA *r_opptr)
 {
   /* Caller must check */
   BLI_assert(ot->srna != NULL);
@@ -3416,6 +3420,15 @@ void uiItemMenuEnumO_ptr(uiLayout *layout,
   lvl->opcontext = layout->root->opcontext;
 
   uiBut *but = ui_item_menu(layout, name, icon, menu_item_enum_opname_menu, NULL, lvl, NULL, true);
+  /* Use the menu button as owner for the operator properties, which will then be passed to the
+   * individual menu items. */
+  if (r_opptr) {
+    but->opptr = MEM_callocN(sizeof(PointerRNA), "uiButOpPtr");
+    WM_operator_properties_create_ptr(but->opptr, ot);
+    BLI_assert(but->opptr->data == NULL);
+    WM_operator_properties_alloc(&but->opptr, (IDProperty **)&but->opptr->data, ot->idname);
+    *r_opptr = *but->opptr;
+  }
 
   /* add hotkey here, lower UI code can't detect it */
   if ((layout->root->block->flag & UI_BLOCK_LOOP) && (ot->prop && ot->invoke)) {
@@ -3427,12 +3440,13 @@ void uiItemMenuEnumO_ptr(uiLayout *layout,
   }
 }
 
-void uiItemMenuEnumO(uiLayout *layout,
-                     bContext *C,
-                     const char *opname,
-                     const char *propname,
-                     const char *name,
-                     int icon)
+void uiItemMenuEnumFullO(uiLayout *layout,
+                         bContext *C,
+                         const char *opname,
+                         const char *propname,
+                         const char *name,
+                         int icon,
+                         PointerRNA *r_opptr)
 {
   wmOperatorType *ot = WM_operatortype_find(opname, 0); /* print error next */
 
@@ -3444,7 +3458,17 @@ void uiItemMenuEnumO(uiLayout *layout,
     return;
   }
 
-  uiItemMenuEnumO_ptr(layout, C, ot, propname, name, icon);
+  uiItemMenuEnumFullO_ptr(layout, C, ot, propname, name, icon, r_opptr);
+}
+
+void uiItemMenuEnumO(uiLayout *layout,
+                     bContext *C,
+                     const char *opname,
+                     const char *propname,
+                     const char *name,
+                     int icon)
+{
+  uiItemMenuEnumFullO(layout, C, opname, propname, name, icon, NULL);
 }
 
 static void menu_item_enum_rna_menu(bContext *UNUSED(C), uiLayout *layout, void *arg)