add IDP_MergeGroup(dst, src, overwrite) function,

like PyDict_Merge()

source/blender/blenkernel/BKE_idprop.h

@@ -154,6 +154,12 @@ __attribute__((nonnull))
 #endif
 ;
 
+void IDP_MergeGroup(IDProperty *dest, IDProperty *src, const int do_overwrite)
+#ifdef __GNUC__
+__attribute__((nonnull))
+#endif
+;
+
 /**
  * This function has a sanity check to make sure ID properties with the same name don't
  * get added to the group.

source/blender/blenkernel/intern/idprop.c

@@ -492,6 +492,30 @@ void IDP_ReplaceInGroup(IDProperty *group, IDProperty *prop)
 	}
 }
 
+/*
+ * If a property is missing in \a dest, add it.
+ */
+void IDP_MergeGroup(IDProperty *dest, IDProperty *src, const int do_overwrite)
+{
+	IDProperty *prop;
+
+	if (do_overwrite) {
+		for (prop = src->data.group.first; prop; prop = prop->next) {
+			IDProperty *copy = IDP_CopyProperty(prop);
+			IDP_ReplaceInGroup(dest, copy);
+		}
+	}
+	else {
+		for (prop = src->data.group.first; prop; prop = prop->next) {
+			if (IDP_GetPropertyFromGroup(dest, prop->name) == NULL) {
+				IDProperty *copy = IDP_CopyProperty(prop);
+				dest->len++;
+				BLI_addtail(&dest->data.group, copy);
+			}
+		}
+	}
+}
+
 /* returns 0 if an id property with the same name exists and it failed,
  * or 1 if it succeeded in adding to the group.*/
 int IDP_AddToGroup(IDProperty *group, IDProperty *prop)

source/blender/python/generic/idprop_py_api.c

@@ -43,10 +43,6 @@
 #include "py_capi_utils.h"
 #endif
 
-extern PyTypeObject BPy_IDArray_Type;
-extern PyTypeObject BPy_IDGroup_Iter_Type;
-extern PyTypeObject BPy_IDGroup_Type;
-
 /*********************** ID Property Main Wrapper Stuff ***************/
 
 /* ----------------------------------------------------------------------------
@@ -809,17 +805,28 @@ static PyObject *BPy_IDGroup_Update(BPy_IDProperty *self, PyObject *value)
 	PyObject *pkey, *pval;
 	Py_ssize_t i = 0;
 
-	if (!PyDict_Check(value)) {
+	if (BPy_IDGroup_Check(value)) {
+		BPy_IDProperty *other = (BPy_IDProperty *)value;
+		if (UNLIKELY(self->prop == other->prop)) {
+			Py_RETURN_NONE;
+		}
+
+		/* XXX, possible one is inside the other */
+		IDP_MergeGroup(self->prop, other->prop, TRUE);
+	}
+	else if (PyDict_Check(value)) {
+		while (PyDict_Next(value, &i, &pkey, &pval)) {
+			BPy_IDGroup_Map_SetItem(self, pkey, pval);
+			if (PyErr_Occurred()) return NULL;
+		}
+	}
+	else {
 		PyErr_Format(PyExc_TypeError,
-		             "expected a dict not a %.200s",
+		             "expected a dict or an IDPropertyGroup type, not a %.200s",
 		             Py_TYPE(value)->tp_name);
 		return NULL;
 	}
 
-	while (PyDict_Next(value, &i, &pkey, &pval)) {
-		BPy_IDGroup_Map_SetItem(self, pkey, pval);
-		if (PyErr_Occurred()) return NULL;
-	}
 
 	Py_RETURN_NONE;
 }

source/blender/python/generic/idprop_py_api.h

@@ -32,6 +32,17 @@ struct ID;
 struct IDProperty;
 struct BPy_IDGroup_Iter;
 
+extern PyTypeObject BPy_IDArray_Type;
+extern PyTypeObject BPy_IDGroup_Iter_Type;
+extern PyTypeObject BPy_IDGroup_Type;
+
+#define BPy_IDArray_Check(v)			(PyObject_TypeCheck(v, &BPy_IDArray_Type))
+#define BPy_IDArray_CheckExact(v)		(Py_TYPE(v) == &BPy_IDArray_Type)
+#define BPy_IDGroup_Iter_Check(v)		(PyObject_TypeCheck(v, &BPy_IDGroup_Iter_Type))
+#define BPy_IDGroup_Iter_CheckExact(v)	(Py_TYPE(v) == &BPy_IDGroup_Iter_Type)
+#define BPy_IDGroup_Check(v)			(PyObject_TypeCheck(v, &BPy_IDGroup_Type))
+#define BPy_IDGroup_CheckExact(v)		(Py_TYPE(v) == &BPy_IDGroup_Type)
+
 typedef struct BPy_IDProperty {
 	PyObject_VAR_HEAD
 	struct ID *id;           /* can be NULL */