Fix T51877: Deleting a scene uses freed memory

At the moment libblock_remap_data_preprocess is using
FOREACH_SCENE_OBJECT to iterate over all the objects of the scene and
unlink them.

However we were storing a reference to the Base of the removed object.
Anyways, the loop is now sanitized so that this crash no longer happens.

Also now we have an unittest for this.

source/blender/blenkernel/intern/collection.c

@@ -565,7 +565,7 @@ void BKE_scene_collections_iterator_end(struct BLI_Iterator *iter)
 
 typedef struct SceneObjectsIteratorData {
 	GSet *visited;
-	LinkData *link;
+	LinkData *link_next;
 	BLI_Iterator scene_collection_iter;
 } SceneObjectsIteratorData;
 
@@ -609,10 +609,10 @@ static LinkData *object_base_unique(GSet *gs, LinkData *link)
 void BKE_scene_objects_iterator_next(BLI_Iterator *iter)
 {
 	SceneObjectsIteratorData *data = iter->data;
-	LinkData *link = data->link ? object_base_unique(data->visited, data->link->next) : NULL;
+	LinkData *link = data->link_next ? object_base_unique(data->visited, data->link_next) : NULL;
 
 	if (link) {
-		data->link = link;
+		data->link_next = link->next;
 		iter->current = link->data;
 	}
 	else {
@@ -624,8 +624,8 @@ void BKE_scene_objects_iterator_next(BLI_Iterator *iter)
 			/* get the first unique object of this collection */
 			LinkData *new_link = object_base_unique(data->visited, sc->objects.first);
 			if (new_link) {
-				data->link = new_link;
-				iter->current = data->link->data;
+				data->link_next = new_link->next;
+				iter->current = new_link->data;
 				return;
 			}
 			BKE_scene_collections_iterator_next(&data->scene_collection_iter);

tests/python/render_layer/CMakeLists.txt

@@ -170,4 +170,5 @@ RENDER_LAYER_TEST(scene_copy_b)
 RENDER_LAYER_TEST(scene_copy_c)
 RENDER_LAYER_TEST(scene_copy_d)
 RENDER_LAYER_TEST(scene_copy_e)
+RENDER_LAYER_TEST(scene_delete)
 RENDER_LAYER_TEST(scene_write_read)

tests/python/render_layer/test_scene_delete.py

@@ -0,0 +1,39 @@
+# ############################################################
+# Importing - Same For All Render Layer Tests
+# ############################################################
+
+import unittest
+import os
+import sys
+
+from render_layer_common import *
+
+
+# ############################################################
+# Testing
+# ############################################################
+
+class UnitTesting(RenderLayerTesting):
+    def test_scene_delete(self):
+        """
+        See if a scene can be properly deleted
+        """
+        import bpy
+
+        scene = bpy.context.scene
+        bpy.data.scenes.new('New')
+        bpy.data.scenes.remove(scene)
+
+
+# ############################################################
+# Main - Same For All Render Layer Tests
+# ############################################################
+
+if __name__ == '__main__':
+    import sys
+
+    extra_arguments = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else []
+    sys.argv = [__file__] + (sys.argv[sys.argv.index("--") + 2:] if "--" in sys.argv else [])
+
+    UnitTesting._extra_arguments = extra_arguments
+    unittest.main()