Fix T82388: Sculpt mode: Unexpected undo behavior.

Issue exposed by rB4c7b1766a7f1.

Main idea is that non-memfile first undo step should check into previous
memfile and tag the ID it is editing as `future_changed`.

That way, when we go back and undo to the memfile, said IDs are properly
detected as changed and re-read from the memfile.

Otherwise, undo system sees them as unchanged, and just re-use the
current data instead.

Note that currently only Sculpt mode seems affected (probably because it
is storing the mode switch itself as a Sculpt undo step instead of a
memfile one), but similar action might be needed in some other cases
too.

Maniphest Tasks: T82388

Differential Revision: https://developer.blender.org/D9510

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/editors/include/ED_undo.h b/source/blender/editors/include/ED_undo.h
index 989854872f3..7b643e7c764 100644
--- a/source/blender/editors/include/ED_undo.h
+++ b/source/blender/editors/include/ED_undo.h
@@ -87,6 +87,7 @@ void ED_undosys_type_free(void);
 
 /* memfile_undo.c */
 struct MemFile *ED_undosys_stack_memfile_get_active(struct UndoStack *ustack);
+void ED_undosys_stack_memfile_id_changed_tag(struct UndoStack *ustack, struct ID *id);
 
 #ifdef __cplusplus
 }