Fix/workaround 'convert object' messing up linked data.

'Convert To...' Object operation has very weird effect of actually
working at obdata level, not object level, which means *all* objects
(even unselected/hidden/in other scenes/...) using same obdata will be
converted to new selected type.

IMHO this is very bad behavior, but... not a bug really, so do not
change this for now.

But at least, do not do that when working on some linked data, else it
leaves Blend file in invalid (incoherent) state until next reload.

So workaround for now is to enforce the 'Keep Original' option when some
linked object/obdata is affected by the operation.

Also fixed somewhat broken usercount handling in Curve->Mesh part.

1 files changed, 14 insertions, 1 deletions

diff --git a/source/blender/editors/object/object_add.c b/source/blender/editors/object/object_add.c
index b278d6e1e87..a901560079a 100644
--- a/source/blender/editors/object/object_add.c
+++ b/source/blender/editors/object/object_add.c
@@ -1640,7 +1640,7 @@ static int convert_exec(bContext *C, wmOperator *op)
 	MetaBall *mb;
 	Mesh *me;
 	const short target = RNA_enum_get(op->ptr, "target");
-	const bool keep_original = RNA_boolean_get(op->ptr, "keep_original");
+	bool keep_original = RNA_boolean_get(op->ptr, "keep_original");
 	int a, mballConverted = 0;
 
 	/* don't forget multiple users! */
@@ -1678,6 +1678,19 @@ static int convert_exec(bContext *C, wmOperator *op)
 	{
 		for (CollectionPointerLink *link = selected_editable_bases.first; link; link = link->next) {
 			Base *base = link->ptr.data;
+			ob = base->object;
+
+			/* The way object type conversion works currently (enforcing conversion of *all* objetcs using converted
+			 * obdata, even some un-selected/hidden/inother scene ones, sounds totally bad to me.
+			 * However, changing this is more design than bugfix, not to mention convoluted code below,
+			 * so that will be for later.
+			 * But at the very least, do not do that with linked IDs! */
+			if ((ID_IS_LINKED_DATABLOCK(ob) || ID_IS_LINKED_DATABLOCK(ob->data)) && !keep_original) {
+				keep_original = true;
+				BKE_reportf(op->reports, RPT_INFO,
+				            "Converting some linked object/object data, enforcing 'Keep Original' option to True");
+			}
+
 			DAG_id_tag_update(&base->object->id, OB_RECALC_DATA);
 		}