initial bits for an enum id prop

This is used to disambiguate ID property types on assignment.
A plain integer value will always create an integer ID property, so this
new type allows creating enum ID properties specifically.

@@ -431,0 +496,4 @@
+    }
+    if (!used_identifiers.add(item.identifier)) {
+      if (error_fn) {
+        std::string msg = std::string("Item identifier '") + std::string(item.identifier) +

@@ -119,0 +123,4 @@
+  char *name;
+  /* Optional description. */
+  char *description;
+  /* Unique value, generated automatically. */

@@ -1501,6 +1508,36 @@ void RNA_property_enum_items_ex(bContext *C,
                                 int *r_totitem,
                                 bool *r_free)
 {
+  if (!use_static && prop->magic != RNA_MAGIC) {

@@ -116,6 +116,26 @@ typedef struct IDPropertyUIDataID {
   char _pad[6];
 } IDPropertyUIDataID;
 
+typedef struct IDPropertyUIDataEnumItem {

@@ -682,0 +694,4 @@
+
+  IDPropertyTemplate val = {0};
+  val.i = enum_ob->value;
+  if (val.i == -1 && PyErr_Occurred()) {

@@ -432,6 +432,172 @@ static bool idprop_ui_data_update_string(IDProperty *idprop, PyObject *args, PyO
   return true;
 }
 
+static int icon_id_from_name(const char *name)

@@ -435,0 +458,4 @@
+  return false;
+}
+
+static bool try_parse_enum_item(PyObject *py_item, const int index, IDPropertyUIDataEnumItem &item)

@@ -435,0 +547,4 @@
+ */
+static bool idprop_ui_data_update_enum(IDProperty *idprop, PyObject *args, PyObject *kwargs)
+{
+  PyObject *items;

@@ -54,6 +57,7 @@ static size_t idp_size_table[] = {
     sizeof(double),    /* #IDP_DOUBLE */
     0,                 /* #IDP_IDPARRAY (no fixed size). */
     sizeof(int8_t),    /* #IDP_BOOLEAN */
+    sizeof(int),       /* #IDP_ENUM */

@@ -119,0 +223,4 @@
+                          "items",
+                          "subtype",
+                          "description",
+                          nullptr};

@@ -176,0 +300,4 @@
+          PyErr_SetString(PyExc_ValueError, msg);
+        }))
+    {
+      return false;