Fix/workaround: Undo erase all dyntopo changes

Memfile undo isn't compatible with sculpt or edit-mode.

This didn't work in 2.7x, so best disable memfile undo for now in
situations where it's going to loose data or crash.

2 files changed, 26 insertions, 1 deletions

diff --git a/source/blender/editors/undo/ed_undo.c b/source/blender/editors/undo/ed_undo.c
index 09de2998561..337ad1d514a 100644
--- a/source/blender/editors/undo/ed_undo.c
+++ b/source/blender/editors/undo/ed_undo.c
@@ -273,6 +273,23 @@ bool ED_undo_is_valid(const bContext *C, const char *undoname)
 	return BKE_undosys_stack_has_undo(wm->undo_stack, undoname);
 }
 
+bool ED_undo_is_memfile_compatible(const bContext *C)
+{
+	/* Some modes don't co-exist with memfile undo, disable their use: T60593
+	 * (this matches 2.7x behavior). */
+	ViewLayer *view_layer = CTX_data_view_layer(C);
+	if (view_layer != NULL) {
+		Object *obact = OBACT(view_layer);
+		if (obact != NULL) {
+			if (obact->mode & (OB_MODE_SCULPT | OB_MODE_EDIT)) {
+				return false;
+			}
+		}
+	}
+	return true;
+}
+
+
 /**
  * Ideally we wont access the stack directly,
  * this is needed for modes which handle undo themselves (bypassing #ED_undo_push).
diff --git a/source/blender/editors/undo/memfile_undo.c b/source/blender/editors/undo/memfile_undo.c
index 1560c414c42..1b0fe9a0c3d 100644
--- a/source/blender/editors/undo/memfile_undo.c
+++ b/source/blender/editors/undo/memfile_undo.c
@@ -53,13 +53,21 @@ typedef struct MemFileUndoStep {
 	MemFileUndoData *data;
 } MemFileUndoStep;
 
-static bool memfile_undosys_poll(bContext *UNUSED(C))
+static bool memfile_undosys_poll(bContext *C)
 {
 	/* other poll functions must run first, this is a catch-all. */
 
 	if ((U.uiflag & USER_GLOBALUNDO) == 0) {
 		return false;
 	}
+
+	/* Allow a single memfile undo step (the first). */
+	UndoStack *ustack = ED_undo_stack_get();
+	if ((ustack->step_active != NULL) &&
+	    (ED_undo_is_memfile_compatible(C) == false))
+	{
+		return false;
+	}
 	return true;
 }