From ccf0d22e92ccd3148326477a3e807261c3e9537c Mon Sep 17 00:00:00 2001
From: Bastien Montagne <bastien@blender.org>
Date: Tue, 7 Jun 2022 15:29:01 +0200
Subject: [PATCH] Fix T98626: Mesh Deform modifier stops working on a linked
 collection upon undo.

Regression from rBb66368f3fd9c, we still need to store all data on undo
writes, since overrides are not re-applied after undo/redo.
---
 source/blender/modifiers/intern/MOD_correctivesmooth.c | 3 ++-
 source/blender/modifiers/intern/MOD_laplaciandeform.c  | 3 ++-
 source/blender/modifiers/intern/MOD_meshdeform.c       | 3 ++-
 source/blender/modifiers/intern/MOD_surfacedeform.c    | 3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/source/blender/modifiers/intern/MOD_correctivesmooth.c b/source/blender/modifiers/intern/MOD_correctivesmooth.c
index 8b6c306dae8..3698f4403a1 100644
--- a/source/blender/modifiers/intern/MOD_correctivesmooth.c
+++ b/source/blender/modifiers/intern/MOD_correctivesmooth.c
@@ -801,8 +801,9 @@ static void panelRegister(ARegionType *region_type)
 static void blendWrite(BlendWriter *writer, const ID *id_owner, const ModifierData *md)
 {
   CorrectiveSmoothModifierData csmd = *(const CorrectiveSmoothModifierData *)md;
+  const bool is_undo = BLO_write_is_undo(writer);
 
-  if (ID_IS_OVERRIDE_LIBRARY(id_owner)) {
+  if (ID_IS_OVERRIDE_LIBRARY(id_owner) && !is_undo) {
     BLI_assert(!ID_IS_LINKED(id_owner));
     const bool is_local = (md->flag & eModifierFlag_OverrideLibrary_Local) != 0;
     if (!is_local) {
diff --git a/source/blender/modifiers/intern/MOD_laplaciandeform.c b/source/blender/modifiers/intern/MOD_laplaciandeform.c
index 06ded1c4488..a22f4b35e0d 100644
--- a/source/blender/modifiers/intern/MOD_laplaciandeform.c
+++ b/source/blender/modifiers/intern/MOD_laplaciandeform.c
@@ -846,8 +846,9 @@ static void panelRegister(ARegionType *region_type)
 static void blendWrite(BlendWriter *writer, const ID *id_owner, const ModifierData *md)
 {
   LaplacianDeformModifierData lmd = *(const LaplacianDeformModifierData *)md;
+  const bool is_undo = BLO_write_is_undo(writer);
 
-  if (ID_IS_OVERRIDE_LIBRARY(id_owner)) {
+  if (ID_IS_OVERRIDE_LIBRARY(id_owner) && !is_undo) {
     BLI_assert(!ID_IS_LINKED(id_owner));
     const bool is_local = (md->flag & eModifierFlag_OverrideLibrary_Local) != 0;
     if (!is_local) {
diff --git a/source/blender/modifiers/intern/MOD_meshdeform.c b/source/blender/modifiers/intern/MOD_meshdeform.c
index 0cff85d30ec..5dac31ac1df 100644
--- a/source/blender/modifiers/intern/MOD_meshdeform.c
+++ b/source/blender/modifiers/intern/MOD_meshdeform.c
@@ -584,8 +584,9 @@ static void panelRegister(ARegionType *region_type)
 static void blendWrite(BlendWriter *writer, const ID *id_owner, const ModifierData *md)
 {
   MeshDeformModifierData mmd = *(const MeshDeformModifierData *)md;
+  const bool is_undo = BLO_write_is_undo(writer);
 
-  if (ID_IS_OVERRIDE_LIBRARY(id_owner)) {
+  if (ID_IS_OVERRIDE_LIBRARY(id_owner) && !is_undo) {
     BLI_assert(!ID_IS_LINKED(id_owner));
     const bool is_local = (md->flag & eModifierFlag_OverrideLibrary_Local) != 0;
     if (!is_local) {
diff --git a/source/blender/modifiers/intern/MOD_surfacedeform.c b/source/blender/modifiers/intern/MOD_surfacedeform.c
index 9b0012e3890..20cc9b2392f 100644
--- a/source/blender/modifiers/intern/MOD_surfacedeform.c
+++ b/source/blender/modifiers/intern/MOD_surfacedeform.c
@@ -1672,8 +1672,9 @@ static void panelRegister(ARegionType *region_type)
 static void blendWrite(BlendWriter *writer, const ID *id_owner, const ModifierData *md)
 {
   SurfaceDeformModifierData smd = *(const SurfaceDeformModifierData *)md;
+  const bool is_undo = BLO_write_is_undo(writer);
 
-  if (ID_IS_OVERRIDE_LIBRARY(id_owner)) {
+  if (ID_IS_OVERRIDE_LIBRARY(id_owner) && !is_undo) {
     BLI_assert(!ID_IS_LINKED(id_owner));
     const bool is_local = (md->flag & eModifierFlag_OverrideLibrary_Local) != 0;
     if (!is_local) {