Fix T80626: Crash adding custom-data layers after reloading the file

Regression in a48d78ce07f4f which caused the meshes CustomData
to be written before it's layer values were updated for writing.

4 files changed, 88 insertions, 28 deletions

diff --git a/source/blender/blenkernel/BKE_customdata.h b/source/blender/blenkernel/BKE_customdata.h
index 25360d4b3fa..d21fe5afa7e 100644
--- a/source/blender/blenkernel/BKE_customdata.h
+++ b/source/blender/blenkernel/BKE_customdata.h
@@ -414,11 +414,6 @@ void CustomData_from_bmesh_block(const struct CustomData *source,
                                  void *src_block,
                                  int dest_index);
 
-void CustomData_file_write_prepare(struct CustomData *data,
-                                   struct CustomDataLayer **r_write_layers,
-                                   struct CustomDataLayer *write_layers_buff,
-                                   size_t write_layers_size);
-
 /* query info over types */
 void CustomData_file_write_info(int type, const char **r_struct_name, int *r_struct_num);
 int CustomData_sizeof(int type);
@@ -574,8 +569,14 @@ void CustomData_data_transfer(const struct MeshPairRemap *me_remap,
                               const CustomDataTransferLayerMap *laymap);
 
 /* .blend file I/O */
+void CustomData_blend_write_prepare(struct CustomData *data,
+                                   struct CustomDataLayer **r_write_layers,
+                                   struct CustomDataLayer *write_layers_buff,
+                                   size_t write_layers_size);
+
 void CustomData_blend_write(struct BlendWriter *writer,
                             struct CustomData *data,
+                            CustomDataLayer *layers,
                             int count,
                             CustomDataMask cddata_mask,
                             struct ID *id);
diff --git a/source/blender/blenkernel/intern/customdata.c b/source/blender/blenkernel/intern/customdata.c
index 5a5fb7a36df..e2adaabca33 100644
--- a/source/blender/blenkernel/intern/customdata.c
+++ b/source/blender/blenkernel/intern/customdata.c
@@ -4342,10 +4342,10 @@ void CustomData_file_write_info(int type, const char **r_struct_name, int *r_str
  * This means written typemap does not match written layers (as returned by \a r_write_layers).
  * Trivial to fix is ever needed.
  */
-void CustomData_file_write_prepare(CustomData *data,
-                                   CustomDataLayer **r_write_layers,
-                                   CustomDataLayer *write_layers_buff,
-                                   size_t write_layers_size)
+void CustomData_blend_write_prepare(CustomData *data,
+                                    CustomDataLayer **r_write_layers,
+                                    CustomDataLayer *write_layers_buff,
+                                    size_t write_layers_size)
 {
   CustomDataLayer *write_layers = write_layers_buff;
   const size_t chunk_size = (write_layers_size > 0) ? write_layers_size : CD_TEMP_CHUNK_SIZE;
@@ -5193,13 +5193,16 @@ static void write_grid_paint_mask(BlendWriter *writer, int count, GridPaintMask
   }
 }
 
-void CustomData_blend_write(
-    BlendWriter *writer, CustomData *data, int count, CustomDataMask cddata_mask, ID *id)
+/**
+ * \param layers: The layers argument assigned by #CustomData_blend_write_prepare.
+ */
+void CustomData_blend_write(BlendWriter *writer,
+                            CustomData *data,
+                            CustomDataLayer *layers,
+                            int count,
+                            CustomDataMask cddata_mask,
+                            ID *id)
 {
-  CustomDataLayer *layers = NULL;
-  CustomDataLayer layers_buff[CD_TEMP_CHUNK_SIZE];
-  CustomData_file_write_prepare(data, &layers, layers_buff, ARRAY_SIZE(layers_buff));
-
   /* write external customdata (not for undo) */
   if (data->external && !BLO_write_is_undo(writer)) {
     CustomData_external_write(data, id, cddata_mask, count, 0);
@@ -5252,10 +5255,6 @@ void CustomData_blend_write(
   if (data->external) {
     BLO_write_struct(writer, CustomDataExternal, data->external);
   }
-
-  if (!ELEM(layers, NULL, layers_buff)) {
-    MEM_freeN(layers);
-  }
 }
 
 static void blend_read_mdisps(BlendDataReader *reader, int count, MDisps *mdisps, int external)
diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index a7568bcd6ea..0e6ef50f491 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -180,6 +180,18 @@ static void mesh_blend_write(BlendWriter *writer, ID *id, const void *id_address
     memset(&mesh->fdata, 0, sizeof(mesh->fdata));
     memset(&mesh->runtime, 0, sizeof(mesh->runtime));
 
+    CustomDataLayer *vlayers = NULL, vlayers_buff[CD_TEMP_CHUNK_SIZE];
+    CustomDataLayer *elayers = NULL, elayers_buff[CD_TEMP_CHUNK_SIZE];
+    CustomDataLayer *flayers = NULL, flayers_buff[CD_TEMP_CHUNK_SIZE];
+    CustomDataLayer *llayers = NULL, llayers_buff[CD_TEMP_CHUNK_SIZE];
+    CustomDataLayer *players = NULL, players_buff[CD_TEMP_CHUNK_SIZE];
+
+    CustomData_blend_write_prepare(&mesh->vdata, &vlayers, vlayers_buff, ARRAY_SIZE(vlayers_buff));
+    CustomData_blend_write_prepare(&mesh->edata, &elayers, elayers_buff, ARRAY_SIZE(elayers_buff));
+    flayers = flayers_buff;
+    CustomData_blend_write_prepare(&mesh->ldata, &llayers, llayers_buff, ARRAY_SIZE(llayers_buff));
+    CustomData_blend_write_prepare(&mesh->pdata, &players, players_buff, ARRAY_SIZE(players_buff));
+
     BLO_write_id_struct(writer, Mesh, id_address, &mesh->id);
     BKE_id_blend_write(writer, &mesh->id);
 
@@ -191,12 +203,34 @@ static void mesh_blend_write(BlendWriter *writer, ID *id, const void *id_address
     BLO_write_pointer_array(writer, mesh->totcol, mesh->mat);
     BLO_write_raw(writer, sizeof(MSelect) * mesh->totselect, mesh->mselect);
 
-    CustomData_blend_write(writer, &mesh->vdata, mesh->totvert, CD_MASK_MESH.vmask, &mesh->id);
-    CustomData_blend_write(writer, &mesh->edata, mesh->totedge, CD_MASK_MESH.emask, &mesh->id);
+    CustomData_blend_write(
+        writer, &mesh->vdata, vlayers, mesh->totvert, CD_MASK_MESH.vmask, &mesh->id);
+    CustomData_blend_write(
+        writer, &mesh->edata, elayers, mesh->totedge, CD_MASK_MESH.emask, &mesh->id);
     /* fdata is really a dummy - written so slots align */
-    CustomData_blend_write(writer, &mesh->fdata, mesh->totface, CD_MASK_MESH.fmask, &mesh->id);
-    CustomData_blend_write(writer, &mesh->ldata, mesh->totloop, CD_MASK_MESH.lmask, &mesh->id);
-    CustomData_blend_write(writer, &mesh->pdata, mesh->totpoly, CD_MASK_MESH.pmask, &mesh->id);
+    CustomData_blend_write(
+        writer, &mesh->fdata, flayers, mesh->totface, CD_MASK_MESH.fmask, &mesh->id);
+    CustomData_blend_write(
+        writer, &mesh->ldata, llayers, mesh->totloop, CD_MASK_MESH.lmask, &mesh->id);
+    CustomData_blend_write(
+        writer, &mesh->pdata, players, mesh->totpoly, CD_MASK_MESH.pmask, &mesh->id);
+
+    /* Free temporary data */
+
+/* Free custom-data layers, when not assigned a buffer value. */
+#define CD_LAYERS_FREE(id) \
+  if (id && id != id##_buff) { \
+    MEM_freeN(id); \
+  } \
+  ((void)0)
+
+    CD_LAYERS_FREE(vlayers);
+    CD_LAYERS_FREE(elayers);
+    /* CD_LAYER_FREE(flayers); */ /* Never allocated. */
+    CD_LAYERS_FREE(llayers);
+    CD_LAYERS_FREE(players);
+
+#undef CD_LAYERS_FREE
   }
 }
 
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index a9c92719a33..7b089ec0f8f 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -3263,17 +3263,31 @@ static void write_workspace(BlendWriter *writer, WorkSpace *workspace, const voi
 static void write_hair(BlendWriter *writer, Hair *hair, const void *id_address)
 {
   if (hair->id.us > 0 || BLO_write_is_undo(writer)) {
+    CustomDataLayer *players = NULL, players_buff[CD_TEMP_CHUNK_SIZE];
+    CustomDataLayer *clayers = NULL, clayers_buff[CD_TEMP_CHUNK_SIZE];
+    CustomData_blend_write_prepare(&hair->pdata, &players, players_buff, ARRAY_SIZE(players_buff));
+    CustomData_blend_write_prepare(&hair->cdata, &clayers, clayers_buff, ARRAY_SIZE(clayers_buff));
+
     /* Write LibData */
     BLO_write_id_struct(writer, Hair, id_address, &hair->id);
     BKE_id_blend_write(writer, &hair->id);
 
     /* Direct data */
-    CustomData_blend_write(writer, &hair->pdata, hair->totpoint, CD_MASK_ALL, &hair->id);
-    CustomData_blend_write(writer, &hair->cdata, hair->totcurve, CD_MASK_ALL, &hair->id);
+    CustomData_blend_write(writer, &hair->pdata, players, hair->totpoint, CD_MASK_ALL, &hair->id);
+    CustomData_blend_write(writer, &hair->cdata, clayers, hair->totcurve, CD_MASK_ALL, &hair->id);
+
     BLO_write_pointer_array(writer, hair->totcol, hair->mat);
     if (hair->adt) {
       BKE_animdata_blend_write(writer, hair->adt);
     }
+
+    /* Remove temporary data. */
+    if (players && players != players_buff) {
+      MEM_freeN(players);
+    }
+    if (clayers && clayers != clayers_buff) {
+      MEM_freeN(clayers);
+    }
   }
 }
 
@@ -3281,7 +3295,7 @@ static void write_pointcloud(BlendWriter *writer, PointCloud *pointcloud, const
 {
   if (pointcloud->id.us > 0 || BLO_write_is_undo(writer)) {
     CustomDataLayer *players = NULL, players_buff[CD_TEMP_CHUNK_SIZE];
-    CustomData_file_write_prepare(
+    CustomData_blend_write_prepare(
         &pointcloud->pdata, &players, players_buff, ARRAY_SIZE(players_buff));
 
     /* Write LibData */
@@ -3290,7 +3304,8 @@ static void write_pointcloud(BlendWriter *writer, PointCloud *pointcloud, const
 
     /* Direct data */
     CustomData_blend_write(
-        writer, &pointcloud->pdata, pointcloud->totpoint, CD_MASK_ALL, &pointcloud->id);
+        writer, &pointcloud->pdata, players, pointcloud->totpoint, CD_MASK_ALL, &pointcloud->id);
+
     BLO_write_pointer_array(writer, pointcloud->totcol, pointcloud->mat);
     if (pointcloud->adt) {
       BKE_animdata_blend_write(writer, pointcloud->adt);
@@ -3349,13 +3364,24 @@ static void write_simulation(BlendWriter *writer, Simulation *simulation, const
       /* TODO: Decentralize this part. */
       if (STREQ(state->type, SIM_TYPE_NAME_PARTICLE_SIMULATION)) {
         ParticleSimulationState *particle_state = (ParticleSimulationState *)state;
+
+        CustomDataLayer *players = NULL, players_buff[CD_TEMP_CHUNK_SIZE];
+        CustomData_blend_write_prepare(
+            &particle_state->attributes, &players, players_buff, ARRAY_SIZE(players_buff));
+
         BLO_write_struct(writer, ParticleSimulationState, particle_state);
 
         CustomData_blend_write(writer,
                                &particle_state->attributes,
+                               players,
                                particle_state->tot_particles,
                                CD_MASK_ALL,
                                &simulation->id);
+
+        /* Remove temporary data. */
+        if (players && players != players_buff) {
+          MEM_freeN(players);
+        }
       }
       else if (STREQ(state->type, SIM_TYPE_NAME_PARTICLE_MESH_EMITTER)) {
         ParticleMeshEmitterSimulationState *emitter_state = (ParticleMeshEmitterSimulationState *)