Cleanup: Blendwrite: Move code deciding if an ID should be written out of ID callbacks.

This was not really useful, and added estra useless steps in case and ID
should not actually be written.

Further more, it prevented clearing the usercount on write, which can be
cause a false positive 'chanhged' detection in undo/redo case.

35 files changed, 687 insertions, 722 deletions

diff --git a/source/blender/blenkernel/intern/action.c b/source/blender/blenkernel/intern/action.c
index d55f023d209..981815f400a 100644
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -186,22 +186,21 @@ static void action_foreach_id(ID *id, LibraryForeachIDData *data)
 static void action_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   bAction *act = (bAction *)id;
-  if (act->id.us > 0 || BLO_write_is_undo(writer)) {
-    BLO_write_id_struct(writer, bAction, id_address, &act->id);
-    BKE_id_blend_write(writer, &act->id);
 
-    BKE_fcurve_blend_write(writer, &act->curves);
+  BLO_write_id_struct(writer, bAction, id_address, &act->id);
+  BKE_id_blend_write(writer, &act->id);
 
-    LISTBASE_FOREACH (bActionGroup *, grp, &act->groups) {
-      BLO_write_struct(writer, bActionGroup, grp);
-    }
+  BKE_fcurve_blend_write(writer, &act->curves);
 
-    LISTBASE_FOREACH (TimeMarker *, marker, &act->markers) {
-      BLO_write_struct(writer, TimeMarker, marker);
-    }
+  LISTBASE_FOREACH (bActionGroup *, grp, &act->groups) {
+    BLO_write_struct(writer, bActionGroup, grp);
+  }
 
-    BKE_previewimg_blend_write(writer, act->preview);
+  LISTBASE_FOREACH (TimeMarker *, marker, &act->markers) {
+    BLO_write_struct(writer, TimeMarker, marker);
   }
+
+  BKE_previewimg_blend_write(writer, act->preview);
 }
 
 static void action_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/armature.c b/source/blender/blenkernel/intern/armature.c
index 1f02b084534..87320c88b1b 100644
--- a/source/blender/blenkernel/intern/armature.c
+++ b/source/blender/blenkernel/intern/armature.c
@@ -212,25 +212,24 @@ static void write_bone(BlendWriter *writer, Bone *bone)
 static void armature_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   bArmature *arm = (bArmature *)id;
-  if (arm->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    arm->bonehash = NULL;
-    arm->edbo = NULL;
-    /* Must always be cleared (armatures don't have their own edit-data). */
-    arm->needs_flush_to_id = 0;
-    arm->act_edbone = NULL;
 
-    BLO_write_id_struct(writer, bArmature, id_address, &arm->id);
-    BKE_id_blend_write(writer, &arm->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  arm->bonehash = NULL;
+  arm->edbo = NULL;
+  /* Must always be cleared (armatures don't have their own edit-data). */
+  arm->needs_flush_to_id = 0;
+  arm->act_edbone = NULL;
 
-    if (arm->adt) {
-      BKE_animdata_blend_write(writer, arm->adt);
-    }
+  BLO_write_id_struct(writer, bArmature, id_address, &arm->id);
+  BKE_id_blend_write(writer, &arm->id);
 
-    /* Direct data */
-    LISTBASE_FOREACH (Bone *, bone, &arm->bonebase) {
-      write_bone(writer, bone);
-    }
+  if (arm->adt) {
+    BKE_animdata_blend_write(writer, arm->adt);
+  }
+
+  /* Direct data */
+  LISTBASE_FOREACH (Bone *, bone, &arm->bonebase) {
+    write_bone(writer, bone);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/brush.c b/source/blender/blenkernel/intern/brush.c
index 3418e37642c..7b81187be21 100644
--- a/source/blender/blenkernel/intern/brush.c
+++ b/source/blender/blenkernel/intern/brush.c
@@ -202,48 +202,47 @@ static void brush_foreach_id(ID *id, LibraryForeachIDData *data)
 static void brush_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Brush *brush = (Brush *)id;
-  if (brush->id.us > 0 || BLO_write_is_undo(writer)) {
-    BLO_write_id_struct(writer, Brush, id_address, &brush->id);
-    BKE_id_blend_write(writer, &brush->id);
 
-    if (brush->curve) {
-      BKE_curvemapping_blend_write(writer, brush->curve);
-    }
+  BLO_write_id_struct(writer, Brush, id_address, &brush->id);
+  BKE_id_blend_write(writer, &brush->id);
 
-    if (brush->gpencil_settings) {
-      BLO_write_struct(writer, BrushGpencilSettings, brush->gpencil_settings);
+  if (brush->curve) {
+    BKE_curvemapping_blend_write(writer, brush->curve);
+  }
 
-      if (brush->gpencil_settings->curve_sensitivity) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_sensitivity);
-      }
-      if (brush->gpencil_settings->curve_strength) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_strength);
-      }
-      if (brush->gpencil_settings->curve_jitter) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_jitter);
-      }
-      if (brush->gpencil_settings->curve_rand_pressure) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_pressure);
-      }
-      if (brush->gpencil_settings->curve_rand_strength) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_strength);
-      }
-      if (brush->gpencil_settings->curve_rand_uv) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_uv);
-      }
-      if (brush->gpencil_settings->curve_rand_hue) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_hue);
-      }
-      if (brush->gpencil_settings->curve_rand_saturation) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_saturation);
-      }
-      if (brush->gpencil_settings->curve_rand_value) {
-        BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_value);
-      }
+  if (brush->gpencil_settings) {
+    BLO_write_struct(writer, BrushGpencilSettings, brush->gpencil_settings);
+
+    if (brush->gpencil_settings->curve_sensitivity) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_sensitivity);
     }
-    if (brush->gradient) {
-      BLO_write_struct(writer, ColorBand, brush->gradient);
+    if (brush->gpencil_settings->curve_strength) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_strength);
     }
+    if (brush->gpencil_settings->curve_jitter) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_jitter);
+    }
+    if (brush->gpencil_settings->curve_rand_pressure) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_pressure);
+    }
+    if (brush->gpencil_settings->curve_rand_strength) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_strength);
+    }
+    if (brush->gpencil_settings->curve_rand_uv) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_uv);
+    }
+    if (brush->gpencil_settings->curve_rand_hue) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_hue);
+    }
+    if (brush->gpencil_settings->curve_rand_saturation) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_saturation);
+    }
+    if (brush->gpencil_settings->curve_rand_value) {
+      BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_value);
+    }
+  }
+  if (brush->gradient) {
+    BLO_write_struct(writer, ColorBand, brush->gradient);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/cachefile.c b/source/blender/blenkernel/intern/cachefile.c
index 8dd28c889f5..4a60564b4a1 100644
--- a/source/blender/blenkernel/intern/cachefile.c
+++ b/source/blender/blenkernel/intern/cachefile.c
@@ -97,19 +97,18 @@ static void cache_file_free_data(ID *id)
 static void cache_file_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   CacheFile *cache_file = (CacheFile *)id;
-  if (cache_file->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    BLI_listbase_clear(&cache_file->object_paths);
-    cache_file->handle = NULL;
-    memset(cache_file->handle_filepath, 0, sizeof(cache_file->handle_filepath));
-    cache_file->handle_readers = NULL;
 
-    BLO_write_id_struct(writer, CacheFile, id_address, &cache_file->id);
-    BKE_id_blend_write(writer, &cache_file->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  BLI_listbase_clear(&cache_file->object_paths);
+  cache_file->handle = NULL;
+  memset(cache_file->handle_filepath, 0, sizeof(cache_file->handle_filepath));
+  cache_file->handle_readers = NULL;
 
-    if (cache_file->adt) {
-      BKE_animdata_blend_write(writer, cache_file->adt);
-    }
+  BLO_write_id_struct(writer, CacheFile, id_address, &cache_file->id);
+  BKE_id_blend_write(writer, &cache_file->id);
+
+  if (cache_file->adt) {
+    BKE_animdata_blend_write(writer, cache_file->adt);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/camera.c b/source/blender/blenkernel/intern/camera.c
index 5172b067eba..46b079fb42e 100644
--- a/source/blender/blenkernel/intern/camera.c
+++ b/source/blender/blenkernel/intern/camera.c
@@ -122,18 +122,17 @@ static void camera_foreach_id(ID *id, LibraryForeachIDData *data)
 static void camera_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Camera *cam = (Camera *)id;
-  if (cam->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, Camera, id_address, &cam->id);
-    BKE_id_blend_write(writer, &cam->id);
 
-    if (cam->adt) {
-      BKE_animdata_blend_write(writer, cam->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Camera, id_address, &cam->id);
+  BKE_id_blend_write(writer, &cam->id);
 
-    LISTBASE_FOREACH (CameraBGImage *, bgpic, &cam->bg_images) {
-      BLO_write_struct(writer, CameraBGImage, bgpic);
-    }
+  if (cam->adt) {
+    BKE_animdata_blend_write(writer, cam->adt);
+  }
+
+  LISTBASE_FOREACH (CameraBGImage *, bgpic, &cam->bg_images) {
+    BLO_write_struct(writer, CameraBGImage, bgpic);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/collection.c b/source/blender/blenkernel/intern/collection.c
index b62e33ff564..d36e9b67d00 100644
--- a/source/blender/blenkernel/intern/collection.c
+++ b/source/blender/blenkernel/intern/collection.c
@@ -214,20 +214,19 @@ void BKE_collection_blend_write_nolib(BlendWriter *writer, Collection *collectio
 static void collection_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Collection *collection = (Collection *)id;
-  if (collection->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
-    collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE;
-    collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE_INSTANCED;
-    collection->tag = 0;
-    BLI_listbase_clear(&collection->object_cache);
-    BLI_listbase_clear(&collection->object_cache_instanced);
-    BLI_listbase_clear(&collection->parents);
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Collection, id_address, &collection->id);
+  /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
+  collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE;
+  collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE_INSTANCED;
+  collection->tag = 0;
+  BLI_listbase_clear(&collection->object_cache);
+  BLI_listbase_clear(&collection->object_cache_instanced);
+  BLI_listbase_clear(&collection->parents);
 
-    BKE_collection_blend_write_nolib(writer, collection);
-  }
+  /* write LibData */
+  BLO_write_id_struct(writer, Collection, id_address, &collection->id);
+
+  BKE_collection_blend_write_nolib(writer, collection);
 }
 
 #ifdef USE_COLLECTION_COMPAT_28
diff --git a/source/blender/blenkernel/intern/curve.c b/source/blender/blenkernel/intern/curve.c
index c49788528a4..397838e6904 100644
--- a/source/blender/blenkernel/intern/curve.c
+++ b/source/blender/blenkernel/intern/curve.c
@@ -146,51 +146,50 @@ static void curve_foreach_id(ID *id, LibraryForeachIDData *data)
 static void curve_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Curve *cu = (Curve *)id;
-  if (cu->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    cu->editnurb = NULL;
-    cu->editfont = NULL;
-    cu->batch_cache = NULL;
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Curve, id_address, &cu->id);
-    BKE_id_blend_write(writer, &cu->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  cu->editnurb = NULL;
+  cu->editfont = NULL;
+  cu->batch_cache = NULL;
 
-    /* direct data */
-    BLO_write_pointer_array(writer, cu->totcol, cu->mat);
-    if (cu->adt) {
-      BKE_animdata_blend_write(writer, cu->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Curve, id_address, &cu->id);
+  BKE_id_blend_write(writer, &cu->id);
 
-    if (cu->vfont) {
-      BLO_write_raw(writer, cu->len + 1, cu->str);
-      BLO_write_struct_array(writer, CharInfo, cu->len_char32 + 1, cu->strinfo);
-      BLO_write_struct_array(writer, TextBox, cu->totbox, cu->tb);
+  /* direct data */
+  BLO_write_pointer_array(writer, cu->totcol, cu->mat);
+  if (cu->adt) {
+    BKE_animdata_blend_write(writer, cu->adt);
+  }
+
+  if (cu->vfont) {
+    BLO_write_raw(writer, cu->len + 1, cu->str);
+    BLO_write_struct_array(writer, CharInfo, cu->len_char32 + 1, cu->strinfo);
+    BLO_write_struct_array(writer, TextBox, cu->totbox, cu->tb);
+  }
+  else {
+    /* is also the order of reading */
+    LISTBASE_FOREACH (Nurb *, nu, &cu->nurb) {
+      BLO_write_struct(writer, Nurb, nu);
     }
-    else {
-      /* is also the order of reading */
-      LISTBASE_FOREACH (Nurb *, nu, &cu->nurb) {
-        BLO_write_struct(writer, Nurb, nu);
+    LISTBASE_FOREACH (Nurb *, nu, &cu->nurb) {
+      if (nu->type == CU_BEZIER) {
+        BLO_write_struct_array(writer, BezTriple, nu->pntsu, nu->bezt);
       }
-      LISTBASE_FOREACH (Nurb *, nu, &cu->nurb) {
-        if (nu->type == CU_BEZIER) {
-          BLO_write_struct_array(writer, BezTriple, nu->pntsu, nu->bezt);
+      else {
+        BLO_write_struct_array(writer, BPoint, nu->pntsu * nu->pntsv, nu->bp);
+        if (nu->knotsu) {
+          BLO_write_float_array(writer, KNOTSU(nu), nu->knotsu);
         }
-        else {
-          BLO_write_struct_array(writer, BPoint, nu->pntsu * nu->pntsv, nu->bp);
-          if (nu->knotsu) {
-            BLO_write_float_array(writer, KNOTSU(nu), nu->knotsu);
-          }
-          if (nu->knotsv) {
-            BLO_write_float_array(writer, KNOTSV(nu), nu->knotsv);
-          }
+        if (nu->knotsv) {
+          BLO_write_float_array(writer, KNOTSV(nu), nu->knotsv);
         }
       }
     }
+  }
 
-    if (cu->bevel_profile != NULL) {
-      BKE_curveprofile_blend_write(writer, cu->bevel_profile);
-    }
+  if (cu->bevel_profile != NULL) {
+    BKE_curveprofile_blend_write(writer, cu->bevel_profile);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/font.c b/source/blender/blenkernel/intern/font.c
index 72add476bfe..c1765967238 100644
--- a/source/blender/blenkernel/intern/font.c
+++ b/source/blender/blenkernel/intern/font.c
@@ -126,23 +126,22 @@ static void vfont_blend_write(BlendWriter *writer, ID *id, const void *id_addres
 {
   VFont *vf = (VFont *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (vf->id.us > 0 || is_undo) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    vf->data = NULL;
-    vf->temp_pf = NULL;
-
-    /* Do not store packed files in case this is a library override ID. */
-    if (ID_IS_OVERRIDE_LIBRARY(vf) && !is_undo) {
-      vf->packedfile = NULL;
-    }
 
-    /* write LibData */
-    BLO_write_id_struct(writer, VFont, id_address, &vf->id);
-    BKE_id_blend_write(writer, &vf->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  vf->data = NULL;
+  vf->temp_pf = NULL;
 
-    /* direct data */
-    BKE_packedfile_blend_write(writer, vf->packedfile);
+  /* Do not store packed files in case this is a library override ID. */
+  if (ID_IS_OVERRIDE_LIBRARY(vf) && !is_undo) {
+    vf->packedfile = NULL;
   }
+
+  /* write LibData */
+  BLO_write_id_struct(writer, VFont, id_address, &vf->id);
+  BKE_id_blend_write(writer, &vf->id);
+
+  /* direct data */
+  BKE_packedfile_blend_write(writer, vf->packedfile);
 }
 
 static void vfont_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/gpencil.c b/source/blender/blenkernel/intern/gpencil.c
index f566e18fb2f..9cdb7395925 100644
--- a/source/blender/blenkernel/intern/gpencil.c
+++ b/source/blender/blenkernel/intern/gpencil.c
@@ -150,47 +150,46 @@ static void greasepencil_foreach_id(ID *id, LibraryForeachIDData *data)
 static void greasepencil_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   bGPdata *gpd = (bGPdata *)id;
-  if (gpd->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
-    /* XXX not sure why the whole run-time data is not cleared in reading code,
-     * for now mimicking it here. */
-    gpd->runtime.sbuffer = NULL;
-    gpd->runtime.sbuffer_used = 0;
-    gpd->runtime.sbuffer_size = 0;
-    gpd->runtime.tot_cp_points = 0;
 
-    /* write gpd data block to file */
-    BLO_write_id_struct(writer, bGPdata, id_address, &gpd->id);
-    BKE_id_blend_write(writer, &gpd->id);
+  /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
+  /* XXX not sure why the whole run-time data is not cleared in reading code,
+   * for now mimicking it here. */
+  gpd->runtime.sbuffer = NULL;
+  gpd->runtime.sbuffer_used = 0;
+  gpd->runtime.sbuffer_size = 0;
+  gpd->runtime.tot_cp_points = 0;
 
-    if (gpd->adt) {
-      BKE_animdata_blend_write(writer, gpd->adt);
-    }
+  /* write gpd data block to file */
+  BLO_write_id_struct(writer, bGPdata, id_address, &gpd->id);
+  BKE_id_blend_write(writer, &gpd->id);
 
-    BKE_defbase_blend_write(writer, &gpd->vertex_group_names);
+  if (gpd->adt) {
+    BKE_animdata_blend_write(writer, gpd->adt);
+  }
 
-    BLO_write_pointer_array(writer, gpd->totcol, gpd->mat);
+  BKE_defbase_blend_write(writer, &gpd->vertex_group_names);
 
-    /* write grease-pencil layers to file */
-    BLO_write_struct_list(writer, bGPDlayer, &gpd->layers);
-    LISTBASE_FOREACH (bGPDlayer *, gpl, &gpd->layers) {
-      /* Write mask list. */
-      BLO_write_struct_list(writer, bGPDlayer_Mask, &gpl->mask_layers);
-      /* write this layer's frames to file */
-      BLO_write_struct_list(writer, bGPDframe, &gpl->frames);
-      LISTBASE_FOREACH (bGPDframe *, gpf, &gpl->frames) {
-        /* write strokes */
-        BLO_write_struct_list(writer, bGPDstroke, &gpf->strokes);
-        LISTBASE_FOREACH (bGPDstroke *, gps, &gpf->strokes) {
-          BLO_write_struct_array(writer, bGPDspoint, gps->totpoints, gps->points);
-          BLO_write_struct_array(writer, bGPDtriangle, gps->tot_triangles, gps->triangles);
-          BKE_defvert_blend_write(writer, gps->totpoints, gps->dvert);
-          if (gps->editcurve != NULL) {
-            bGPDcurve *gpc = gps->editcurve;
-            BLO_write_struct(writer, bGPDcurve, gpc);
-            BLO_write_struct_array(
-                writer, bGPDcurve_point, gpc->tot_curve_points, gpc->curve_points);
-          }
+  BLO_write_pointer_array(writer, gpd->totcol, gpd->mat);
+
+  /* write grease-pencil layers to file */
+  BLO_write_struct_list(writer, bGPDlayer, &gpd->layers);
+  LISTBASE_FOREACH (bGPDlayer *, gpl, &gpd->layers) {
+    /* Write mask list. */
+    BLO_write_struct_list(writer, bGPDlayer_Mask, &gpl->mask_layers);
+    /* write this layer's frames to file */
+    BLO_write_struct_list(writer, bGPDframe, &gpl->frames);
+    LISTBASE_FOREACH (bGPDframe *, gpf, &gpl->frames) {
+      /* write strokes */
+      BLO_write_struct_list(writer, bGPDstroke, &gpf->strokes);
+      LISTBASE_FOREACH (bGPDstroke *, gps, &gpf->strokes) {
+        BLO_write_struct_array(writer, bGPDspoint, gps->totpoints, gps->points);
+        BLO_write_struct_array(writer, bGPDtriangle, gps->tot_triangles, gps->triangles);
+        BKE_defvert_blend_write(writer, gps->totpoints, gps->dvert);
+        if (gps->editcurve != NULL) {
+          bGPDcurve *gpc = gps->editcurve;
+          BLO_write_struct(writer, bGPDcurve, gpc);
+          BLO_write_struct_array(
+              writer, bGPDcurve_point, gpc->tot_curve_points, gpc->curve_points);
         }
       }
     }
diff --git a/source/blender/blenkernel/intern/hair.c b/source/blender/blenkernel/intern/hair.c
index 2894d6daf23..af7cc0acb57 100644
--- a/source/blender/blenkernel/intern/hair.c
+++ b/source/blender/blenkernel/intern/hair.c
@@ -114,32 +114,31 @@ static void hair_foreach_id(ID *id, LibraryForeachIDData *data)
 static void hair_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Hair *hair = (Hair *)id;
-  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, 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);
-    }
+  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, 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);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/image.c b/source/blender/blenkernel/intern/image.c
index d2ab54de697..de9f2a5a656 100644
--- a/source/blender/blenkernel/intern/image.c
+++ b/source/blender/blenkernel/intern/image.c
@@ -229,44 +229,43 @@ static void image_blend_write(BlendWriter *writer, ID *id, const void *id_addres
 {
   Image *ima = (Image *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (ima->id.us > 0 || is_undo) {
-    ImagePackedFile *imapf;
 
-    BLI_assert(ima->packedfile == NULL);
-    /* Do not store packed files in case this is a library override ID. */
-    if (ID_IS_OVERRIDE_LIBRARY(ima) && !is_undo) {
-      BLI_listbase_clear(&ima->packedfiles);
-    }
-    else {
-      /* Some trickery to keep forward compatibility of packed images. */
-      if (ima->packedfiles.first != NULL) {
-        imapf = ima->packedfiles.first;
-        ima->packedfile = imapf->packedfile;
-      }
+  ImagePackedFile *imapf;
+
+  BLI_assert(ima->packedfile == NULL);
+  /* Do not store packed files in case this is a library override ID. */
+  if (ID_IS_OVERRIDE_LIBRARY(ima) && !is_undo) {
+    BLI_listbase_clear(&ima->packedfiles);
+  }
+  else {
+    /* Some trickery to keep forward compatibility of packed images. */
+    if (ima->packedfiles.first != NULL) {
+      imapf = ima->packedfiles.first;
+      ima->packedfile = imapf->packedfile;
     }
+  }
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Image, id_address, &ima->id);
-    BKE_id_blend_write(writer, &ima->id);
+  /* write LibData */
+  BLO_write_id_struct(writer, Image, id_address, &ima->id);
+  BKE_id_blend_write(writer, &ima->id);
 
-    for (imapf = ima->packedfiles.first; imapf; imapf = imapf->next) {
-      BLO_write_struct(writer, ImagePackedFile, imapf);
-      BKE_packedfile_blend_write(writer, imapf->packedfile);
-    }
+  for (imapf = ima->packedfiles.first; imapf; imapf = imapf->next) {
+    BLO_write_struct(writer, ImagePackedFile, imapf);
+    BKE_packedfile_blend_write(writer, imapf->packedfile);
+  }
 
-    BKE_previewimg_blend_write(writer, ima->preview);
+  BKE_previewimg_blend_write(writer, ima->preview);
 
-    LISTBASE_FOREACH (ImageView *, iv, &ima->views) {
-      BLO_write_struct(writer, ImageView, iv);
-    }
-    BLO_write_struct(writer, Stereo3dFormat, ima->stereo3d_format);
+  LISTBASE_FOREACH (ImageView *, iv, &ima->views) {
+    BLO_write_struct(writer, ImageView, iv);
+  }
+  BLO_write_struct(writer, Stereo3dFormat, ima->stereo3d_format);
 
-    BLO_write_struct_list(writer, ImageTile, &ima->tiles);
+  BLO_write_struct_list(writer, ImageTile, &ima->tiles);
 
-    ima->packedfile = NULL;
+  ima->packedfile = NULL;
 
-    BLO_write_struct_list(writer, RenderSlot, &ima->renderslots);
-  }
+  BLO_write_struct_list(writer, RenderSlot, &ima->renderslots);
 }
 
 static void image_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/key.c b/source/blender/blenkernel/intern/key.c
index 724216bee6c..b59f51c36f7 100644
--- a/source/blender/blenkernel/intern/key.c
+++ b/source/blender/blenkernel/intern/key.c
@@ -114,27 +114,26 @@ static void shapekey_blend_write(BlendWriter *writer, ID *id, const void *id_add
 {
   Key *key = (Key *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (key->id.us > 0 || is_undo) {
-    /* write LibData */
-    BLO_write_id_struct(writer, Key, id_address, &key->id);
-    BKE_id_blend_write(writer, &key->id);
-
-    if (key->adt) {
-      BKE_animdata_blend_write(writer, key->adt);
-    }
-
-    /* direct data */
-    LISTBASE_FOREACH (KeyBlock *, kb, &key->block) {
-      KeyBlock tmp_kb = *kb;
-      /* Do not store actual geometry data in case this is a library override ID. */
-      if (ID_IS_OVERRIDE_LIBRARY(key) && !is_undo) {
-        tmp_kb.totelem = 0;
-        tmp_kb.data = NULL;
-      }
-      BLO_write_struct_at_address(writer, KeyBlock, kb, &tmp_kb);
-      if (tmp_kb.data != NULL) {
-        BLO_write_raw(writer, tmp_kb.totelem * key->elemsize, tmp_kb.data);
-      }
+
+  /* write LibData */
+  BLO_write_id_struct(writer, Key, id_address, &key->id);
+  BKE_id_blend_write(writer, &key->id);
+
+  if (key->adt) {
+    BKE_animdata_blend_write(writer, key->adt);
+  }
+
+  /* direct data */
+  LISTBASE_FOREACH (KeyBlock *, kb, &key->block) {
+    KeyBlock tmp_kb = *kb;
+    /* Do not store actual geometry data in case this is a library override ID. */
+    if (ID_IS_OVERRIDE_LIBRARY(key) && !is_undo) {
+      tmp_kb.totelem = 0;
+      tmp_kb.data = NULL;
+    }
+    BLO_write_struct_at_address(writer, KeyBlock, kb, &tmp_kb);
+    if (tmp_kb.data != NULL) {
+      BLO_write_raw(writer, tmp_kb.totelem * key->elemsize, tmp_kb.data);
     }
   }
 }
diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index 9875d776d33..e804f32e5a6 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -137,26 +137,25 @@ static void lattice_foreach_id(ID *id, LibraryForeachIDData *data)
 static void lattice_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Lattice *lt = (Lattice *)id;
-  if (lt->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    lt->editlatt = NULL;
-    lt->batch_cache = NULL;
-
-    /* write LibData */
-    BLO_write_id_struct(writer, Lattice, id_address, &lt->id);
-    BKE_id_blend_write(writer, &lt->id);
-
-    /* write animdata */
-    if (lt->adt) {
-      BKE_animdata_blend_write(writer, lt->adt);
-    }
 
-    /* direct data */
-    BLO_write_struct_array(writer, BPoint, lt->pntsu * lt->pntsv * lt->pntsw, lt->def);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  lt->editlatt = NULL;
+  lt->batch_cache = NULL;
+
+  /* write LibData */
+  BLO_write_id_struct(writer, Lattice, id_address, &lt->id);
+  BKE_id_blend_write(writer, &lt->id);
 
-    BKE_defbase_blend_write(writer, &lt->vertex_group_names);
-    BKE_defvert_blend_write(writer, lt->pntsu * lt->pntsv * lt->pntsw, lt->dvert);
+  /* write animdata */
+  if (lt->adt) {
+    BKE_animdata_blend_write(writer, lt->adt);
   }
+
+  /* direct data */
+  BLO_write_struct_array(writer, BPoint, lt->pntsu * lt->pntsv * lt->pntsw, lt->def);
+
+  BKE_defbase_blend_write(writer, &lt->vertex_group_names);
+  BKE_defvert_blend_write(writer, lt->pntsu * lt->pntsv * lt->pntsw, lt->dvert);
 }
 
 static void lattice_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/light.c b/source/blender/blenkernel/intern/light.c
index d91d80ac683..c2b71b85973 100644
--- a/source/blender/blenkernel/intern/light.c
+++ b/source/blender/blenkernel/intern/light.c
@@ -136,27 +136,26 @@ static void light_foreach_id(ID *id, LibraryForeachIDData *data)
 static void light_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Light *la = (Light *)id;
-  if (la->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, Light, id_address, &la->id);
-    BKE_id_blend_write(writer, &la->id);
 
-    if (la->adt) {
-      BKE_animdata_blend_write(writer, la->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Light, id_address, &la->id);
+  BKE_id_blend_write(writer, &la->id);
 
-    if (la->curfalloff) {
-      BKE_curvemapping_blend_write(writer, la->curfalloff);
-    }
+  if (la->adt) {
+    BKE_animdata_blend_write(writer, la->adt);
+  }
 
-    /* Node-tree is integral part of lights, no libdata. */
-    if (la->nodetree) {
-      BLO_write_struct(writer, bNodeTree, la->nodetree);
-      ntreeBlendWrite(writer, la->nodetree);
-    }
+  if (la->curfalloff) {
+    BKE_curvemapping_blend_write(writer, la->curfalloff);
+  }
 
-    BKE_previewimg_blend_write(writer, la->preview);
+  /* Node-tree is integral part of lights, no libdata. */
+  if (la->nodetree) {
+    BLO_write_struct(writer, bNodeTree, la->nodetree);
+    ntreeBlendWrite(writer, la->nodetree);
   }
+
+  BKE_previewimg_blend_write(writer, la->preview);
 }
 
 static void light_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/lightprobe.c b/source/blender/blenkernel/intern/lightprobe.c
index b09aed82921..15733af8ef0 100644
--- a/source/blender/blenkernel/intern/lightprobe.c
+++ b/source/blender/blenkernel/intern/lightprobe.c
@@ -60,14 +60,13 @@ static void lightprobe_foreach_id(ID *id, LibraryForeachIDData *data)
 static void lightprobe_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   LightProbe *prb = (LightProbe *)id;
-  if (prb->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, LightProbe, id_address, &prb->id);
-    BKE_id_blend_write(writer, &prb->id);
-
-    if (prb->adt) {
-      BKE_animdata_blend_write(writer, prb->adt);
-    }
+
+  /* write LibData */
+  BLO_write_id_struct(writer, LightProbe, id_address, &prb->id);
+  BKE_id_blend_write(writer, &prb->id);
+
+  if (prb->adt) {
+    BKE_animdata_blend_write(writer, prb->adt);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/linestyle.c b/source/blender/blenkernel/intern/linestyle.c
index 26d9ab7a8c7..19030fca38b 100644
--- a/source/blender/blenkernel/intern/linestyle.c
+++ b/source/blender/blenkernel/intern/linestyle.c
@@ -457,28 +457,27 @@ static void write_linestyle_geometry_modifiers(BlendWriter *writer, ListBase *mo
 static void linestyle_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   FreestyleLineStyle *linestyle = (FreestyleLineStyle *)id;
-  if (linestyle->id.us > 0 || BLO_write_is_undo(writer)) {
-    BLO_write_id_struct(writer, FreestyleLineStyle, id_address, &linestyle->id);
-    BKE_id_blend_write(writer, &linestyle->id);
 
-    if (linestyle->adt) {
-      BKE_animdata_blend_write(writer, linestyle->adt);
-    }
+  BLO_write_id_struct(writer, FreestyleLineStyle, id_address, &linestyle->id);
+  BKE_id_blend_write(writer, &linestyle->id);
 
-    write_linestyle_color_modifiers(writer, &linestyle->color_modifiers);
-    write_linestyle_alpha_modifiers(writer, &linestyle->alpha_modifiers);
-    write_linestyle_thickness_modifiers(writer, &linestyle->thickness_modifiers);
-    write_linestyle_geometry_modifiers(writer, &linestyle->geometry_modifiers);
-    for (int a = 0; a < MAX_MTEX; a++) {
-      if (linestyle->mtex[a]) {
-        BLO_write_struct(writer, MTex, linestyle->mtex[a]);
-      }
-    }
-    if (linestyle->nodetree) {
-      BLO_write_struct(writer, bNodeTree, linestyle->nodetree);
-      ntreeBlendWrite(writer, linestyle->nodetree);
+  if (linestyle->adt) {
+    BKE_animdata_blend_write(writer, linestyle->adt);
+  }
+
+  write_linestyle_color_modifiers(writer, &linestyle->color_modifiers);
+  write_linestyle_alpha_modifiers(writer, &linestyle->alpha_modifiers);
+  write_linestyle_thickness_modifiers(writer, &linestyle->thickness_modifiers);
+  write_linestyle_geometry_modifiers(writer, &linestyle->geometry_modifiers);
+  for (int a = 0; a < MAX_MTEX; a++) {
+    if (linestyle->mtex[a]) {
+      BLO_write_struct(writer, MTex, linestyle->mtex[a]);
     }
   }
+  if (linestyle->nodetree) {
+    BLO_write_struct(writer, bNodeTree, linestyle->nodetree);
+    ntreeBlendWrite(writer, linestyle->nodetree);
+  }
 }
 
 static void direct_link_linestyle_color_modifier(BlendDataReader *reader,
diff --git a/source/blender/blenkernel/intern/mask.c b/source/blender/blenkernel/intern/mask.c
index f40d1db60ff..a93fcb6e8e0 100644
--- a/source/blender/blenkernel/intern/mask.c
+++ b/source/blender/blenkernel/intern/mask.c
@@ -101,48 +101,47 @@ static void mask_foreach_id(ID *id, LibraryForeachIDData *data)
 static void mask_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Mask *mask = (Mask *)id;
-  if (mask->id.us > 0 || BLO_write_is_undo(writer)) {
-    MaskLayer *masklay;
 
-    BLO_write_id_struct(writer, Mask, id_address, &mask->id);
-    BKE_id_blend_write(writer, &mask->id);
+  MaskLayer *masklay;
 
-    if (mask->adt) {
-      BKE_animdata_blend_write(writer, mask->adt);
-    }
+  BLO_write_id_struct(writer, Mask, id_address, &mask->id);
+  BKE_id_blend_write(writer, &mask->id);
 
-    for (masklay = mask->masklayers.first; masklay; masklay = masklay->next) {
-      MaskSpline *spline;
-      MaskLayerShape *masklay_shape;
+  if (mask->adt) {
+    BKE_animdata_blend_write(writer, mask->adt);
+  }
 
-      BLO_write_struct(writer, MaskLayer, masklay);
+  for (masklay = mask->masklayers.first; masklay; masklay = masklay->next) {
+    MaskSpline *spline;
+    MaskLayerShape *masklay_shape;
 
-      for (spline = masklay->splines.first; spline; spline = spline->next) {
-        int i;
+    BLO_write_struct(writer, MaskLayer, masklay);
 
-        void *points_deform = spline->points_deform;
-        spline->points_deform = NULL;
+    for (spline = masklay->splines.first; spline; spline = spline->next) {
+      int i;
 
-        BLO_write_struct(writer, MaskSpline, spline);
-        BLO_write_struct_array(writer, MaskSplinePoint, spline->tot_point, spline->points);
+      void *points_deform = spline->points_deform;
+      spline->points_deform = NULL;
 
-        spline->points_deform = points_deform;
+      BLO_write_struct(writer, MaskSpline, spline);
+      BLO_write_struct_array(writer, MaskSplinePoint, spline->tot_point, spline->points);
 
-        for (i = 0; i < spline->tot_point; i++) {
-          MaskSplinePoint *point = &spline->points[i];
+      spline->points_deform = points_deform;
 
-          if (point->tot_uw) {
-            BLO_write_struct_array(writer, MaskSplinePointUW, point->tot_uw, point->uw);
-          }
+      for (i = 0; i < spline->tot_point; i++) {
+        MaskSplinePoint *point = &spline->points[i];
+
+        if (point->tot_uw) {
+          BLO_write_struct_array(writer, MaskSplinePointUW, point->tot_uw, point->uw);
         }
       }
+    }
 
-      for (masklay_shape = masklay->splines_shapes.first; masklay_shape;
-           masklay_shape = masklay_shape->next) {
-        BLO_write_struct(writer, MaskLayerShape, masklay_shape);
-        BLO_write_float_array(
-            writer, masklay_shape->tot_vert * MASK_OBJECT_SHAPE_ELEM_SIZE, masklay_shape->data);
-      }
+    for (masklay_shape = masklay->splines_shapes.first; masklay_shape;
+         masklay_shape = masklay_shape->next) {
+      BLO_write_struct(writer, MaskLayerShape, masklay_shape);
+      BLO_write_float_array(
+          writer, masklay_shape->tot_vert * MASK_OBJECT_SHAPE_ELEM_SIZE, masklay_shape->data);
     }
   }
 }
diff --git a/source/blender/blenkernel/intern/material.c b/source/blender/blenkernel/intern/material.c
index ca57038f1c4..13b5bca5638 100644
--- a/source/blender/blenkernel/intern/material.c
+++ b/source/blender/blenkernel/intern/material.c
@@ -179,31 +179,30 @@ static void material_foreach_id(ID *id, LibraryForeachIDData *data)
 static void material_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Material *ma = (Material *)id;
-  if (ma->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    ma->texpaintslot = NULL;
-    BLI_listbase_clear(&ma->gpumaterial);
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Material, id_address, &ma->id);
-    BKE_id_blend_write(writer, &ma->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  ma->texpaintslot = NULL;
+  BLI_listbase_clear(&ma->gpumaterial);
 
-    if (ma->adt) {
-      BKE_animdata_blend_write(writer, ma->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Material, id_address, &ma->id);
+  BKE_id_blend_write(writer, &ma->id);
 
-    /* nodetree is integral part of material, no libdata */
-    if (ma->nodetree) {
-      BLO_write_struct(writer, bNodeTree, ma->nodetree);
-      ntreeBlendWrite(writer, ma->nodetree);
-    }
+  if (ma->adt) {
+    BKE_animdata_blend_write(writer, ma->adt);
+  }
 
-    BKE_previewimg_blend_write(writer, ma->preview);
+  /* nodetree is integral part of material, no libdata */
+  if (ma->nodetree) {
+    BLO_write_struct(writer, bNodeTree, ma->nodetree);
+    ntreeBlendWrite(writer, ma->nodetree);
+  }
 
-    /* grease pencil settings */
-    if (ma->gp_style) {
-      BLO_write_struct(writer, MaterialGPencilStyle, ma->gp_style);
-    }
+  BKE_previewimg_blend_write(writer, ma->preview);
+
+  /* grease pencil settings */
+  if (ma->gp_style) {
+    BLO_write_struct(writer, MaterialGPencilStyle, ma->gp_style);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/mball.c b/source/blender/blenkernel/intern/mball.c
index d6b189d484b..45cf0f17840 100644
--- a/source/blender/blenkernel/intern/mball.c
+++ b/source/blender/blenkernel/intern/mball.c
@@ -119,28 +119,27 @@ static void metaball_foreach_id(ID *id, LibraryForeachIDData *data)
 static void metaball_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   MetaBall *mb = (MetaBall *)id;
-  if (mb->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    BLI_listbase_clear(&mb->disp);
-    mb->editelems = NULL;
-    /* Must always be cleared (meta's don't have their own edit-data). */
-    mb->needs_flush_to_id = 0;
-    mb->lastelem = NULL;
-    mb->batch_cache = NULL;
-
-    /* write LibData */
-    BLO_write_id_struct(writer, MetaBall, id_address, &mb->id);
-    BKE_id_blend_write(writer, &mb->id);
-
-    /* direct data */
-    BLO_write_pointer_array(writer, mb->totcol, mb->mat);
-    if (mb->adt) {
-      BKE_animdata_blend_write(writer, mb->adt);
-    }
 
-    LISTBASE_FOREACH (MetaElem *, ml, &mb->elems) {
-      BLO_write_struct(writer, MetaElem, ml);
-    }
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  BLI_listbase_clear(&mb->disp);
+  mb->editelems = NULL;
+  /* Must always be cleared (meta's don't have their own edit-data). */
+  mb->needs_flush_to_id = 0;
+  mb->lastelem = NULL;
+  mb->batch_cache = NULL;
+
+  /* write LibData */
+  BLO_write_id_struct(writer, MetaBall, id_address, &mb->id);
+  BKE_id_blend_write(writer, &mb->id);
+
+  /* direct data */
+  BLO_write_pointer_array(writer, mb->totcol, mb->mat);
+  if (mb->adt) {
+    BKE_animdata_blend_write(writer, mb->adt);
+  }
+
+  LISTBASE_FOREACH (MetaElem *, ml, &mb->elems) {
+    BLO_write_struct(writer, MetaElem, ml);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index e99670fc488..8257e54c618 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -179,95 +179,90 @@ static void mesh_blend_write(BlendWriter *writer, ID *id, const void *id_address
 {
   Mesh *mesh = (Mesh *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (mesh->id.us > 0 || is_undo) {
-    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];
-
-    /* cache only - don't write */
-    mesh->mface = NULL;
-    mesh->totface = 0;
-    memset(&mesh->fdata, 0, sizeof(mesh->fdata));
-    memset(&mesh->runtime, 0, sizeof(mesh->runtime));
-    flayers = flayers_buff;
-
-    /* Do not store actual geometry data in case this is a library override ID. */
-    if (ID_IS_OVERRIDE_LIBRARY(mesh) && !is_undo) {
-      mesh->mvert = NULL;
-      mesh->totvert = 0;
-      memset(&mesh->vdata, 0, sizeof(mesh->vdata));
-      vlayers = vlayers_buff;
-
-      mesh->medge = NULL;
-      mesh->totedge = 0;
-      memset(&mesh->edata, 0, sizeof(mesh->edata));
-      elayers = elayers_buff;
-
-      mesh->mloop = NULL;
-      mesh->totloop = 0;
-      memset(&mesh->ldata, 0, sizeof(mesh->ldata));
-      llayers = llayers_buff;
-
-      mesh->mpoly = NULL;
-      mesh->totpoly = 0;
-      memset(&mesh->pdata, 0, sizeof(mesh->pdata));
-      players = players_buff;
-    }
-    else {
-      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));
-      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);
+  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];
 
-    /* direct data */
-    if (mesh->adt) {
-      BKE_animdata_blend_write(writer, mesh->adt);
-    }
+  /* cache only - don't write */
+  mesh->mface = NULL;
+  mesh->totface = 0;
+  memset(&mesh->fdata, 0, sizeof(mesh->fdata));
+  memset(&mesh->runtime, 0, sizeof(mesh->runtime));
+  flayers = flayers_buff;
+
+  /* Do not store actual geometry data in case this is a library override ID. */
+  if (ID_IS_OVERRIDE_LIBRARY(mesh) && !is_undo) {
+    mesh->mvert = NULL;
+    mesh->totvert = 0;
+    memset(&mesh->vdata, 0, sizeof(mesh->vdata));
+    vlayers = vlayers_buff;
+
+    mesh->medge = NULL;
+    mesh->totedge = 0;
+    memset(&mesh->edata, 0, sizeof(mesh->edata));
+    elayers = elayers_buff;
+
+    mesh->mloop = NULL;
+    mesh->totloop = 0;
+    memset(&mesh->ldata, 0, sizeof(mesh->ldata));
+    llayers = llayers_buff;
+
+    mesh->mpoly = NULL;
+    mesh->totpoly = 0;
+    memset(&mesh->pdata, 0, sizeof(mesh->pdata));
+    players = players_buff;
+  }
+  else {
+    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));
+    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);
 
-    BKE_defbase_blend_write(writer, &mesh->vertex_group_names);
+  /* direct data */
+  if (mesh->adt) {
+    BKE_animdata_blend_write(writer, mesh->adt);
+  }
+
+  BKE_defbase_blend_write(writer, &mesh->vertex_group_names);
 
-    BLO_write_pointer_array(writer, mesh->totcol, mesh->mat);
-    BLO_write_raw(writer, sizeof(MSelect) * mesh->totselect, mesh->mselect);
+  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, 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, 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);
+  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, 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 temporary data */
 
-/* Free custom-data layers, when not assigned a buffer value. */
+  /* 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);
+  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
-  }
 }
 
 static void mesh_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/movieclip.c b/source/blender/blenkernel/intern/movieclip.c
index f32b0c434c1..e507252307b 100644
--- a/source/blender/blenkernel/intern/movieclip.c
+++ b/source/blender/blenkernel/intern/movieclip.c
@@ -206,36 +206,35 @@ static void write_movieReconstruction(BlendWriter *writer,
 static void movieclip_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   MovieClip *clip = (MovieClip *)id;
-  if (clip->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    clip->anim = NULL;
-    clip->tracking_context = NULL;
-    clip->tracking.stats = NULL;
 
-    MovieTracking *tracking = &clip->tracking;
-    MovieTrackingObject *object;
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  clip->anim = NULL;
+  clip->tracking_context = NULL;
+  clip->tracking.stats = NULL;
 
-    BLO_write_id_struct(writer, MovieClip, id_address, &clip->id);
-    BKE_id_blend_write(writer, &clip->id);
+  MovieTracking *tracking = &clip->tracking;
+  MovieTrackingObject *object;
 
-    if (clip->adt) {
-      BKE_animdata_blend_write(writer, clip->adt);
-    }
+  BLO_write_id_struct(writer, MovieClip, id_address, &clip->id);
+  BKE_id_blend_write(writer, &clip->id);
+
+  if (clip->adt) {
+    BKE_animdata_blend_write(writer, clip->adt);
+  }
 
-    write_movieTracks(writer, &tracking->tracks);
-    write_moviePlaneTracks(writer, &tracking->plane_tracks);
-    write_movieReconstruction(writer, &tracking->reconstruction);
+  write_movieTracks(writer, &tracking->tracks);
+  write_moviePlaneTracks(writer, &tracking->plane_tracks);
+  write_movieReconstruction(writer, &tracking->reconstruction);
 
-    object = tracking->objects.first;
-    while (object) {
-      BLO_write_struct(writer, MovieTrackingObject, object);
+  object = tracking->objects.first;
+  while (object) {
+    BLO_write_struct(writer, MovieTrackingObject, object);
 
-      write_movieTracks(writer, &object->tracks);
-      write_moviePlaneTracks(writer, &object->plane_tracks);
-      write_movieReconstruction(writer, &object->reconstruction);
+    write_movieTracks(writer, &object->tracks);
+    write_moviePlaneTracks(writer, &object->plane_tracks);
+    write_movieReconstruction(writer, &object->reconstruction);
 
-      object = object->next;
-    }
+    object = object->next;
   }
 }
 
diff --git a/source/blender/blenkernel/intern/node.cc b/source/blender/blenkernel/intern/node.cc
index bd22f049a8b..2a0e05a2616 100644
--- a/source/blender/blenkernel/intern/node.cc
+++ b/source/blender/blenkernel/intern/node.cc
@@ -606,19 +606,18 @@ void ntreeBlendWrite(BlendWriter *writer, bNodeTree *ntree)
 static void ntree_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   bNodeTree *ntree = (bNodeTree *)id;
-  if (ntree->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    ntree->init = 0; /* to set callbacks and force setting types */
-    ntree->is_updating = false;
-    ntree->typeinfo = nullptr;
-    ntree->interface_type = nullptr;
-    ntree->progress = nullptr;
-    ntree->execdata = nullptr;
 
-    BLO_write_id_struct(writer, bNodeTree, id_address, &ntree->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  ntree->init = 0; /* to set callbacks and force setting types */
+  ntree->is_updating = false;
+  ntree->typeinfo = nullptr;
+  ntree->interface_type = nullptr;
+  ntree->progress = nullptr;
+  ntree->execdata = nullptr;
 
-    ntreeBlendWrite(writer, ntree);
-  }
+  BLO_write_id_struct(writer, bNodeTree, id_address, &ntree->id);
+
+  ntreeBlendWrite(writer, ntree);
 }
 
 static void direct_link_node_socket(BlendDataReader *reader, bNodeSocket *sock)
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 86db4b6ace8..1c08a46adc3 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -523,74 +523,72 @@ static void object_blend_write(BlendWriter *writer, ID *id, const void *id_addre
   Object *ob = (Object *)id;
 
   const bool is_undo = BLO_write_is_undo(writer);
-  if (ob->id.us > 0 || is_undo) {
-    /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
-    BKE_object_runtime_reset(ob);
 
-    if (is_undo) {
-      /* For undo we stay in object mode during undo presses, so keep edit-mode disabled on save as
-       * well, can help reducing false detection of changed data-blocks. */
-      ob->mode &= ~OB_MODE_EDIT;
-    }
+  /* Clean up, important in undo case to reduce false detection of changed data-blocks. */
+  BKE_object_runtime_reset(ob);
+
+  if (is_undo) {
+    /* For undo we stay in object mode during undo presses, so keep edit-mode disabled on save as
+     * well, can help reducing false detection of changed data-blocks. */
+    ob->mode &= ~OB_MODE_EDIT;
+  }
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Object, id_address, &ob->id);
-    BKE_id_blend_write(writer, &ob->id);
+  /* write LibData */
+  BLO_write_id_struct(writer, Object, id_address, &ob->id);
+  BKE_id_blend_write(writer, &ob->id);
 
-    if (ob->adt) {
-      BKE_animdata_blend_write(writer, ob->adt);
-    }
+  if (ob->adt) {
+    BKE_animdata_blend_write(writer, ob->adt);
+  }
 
-    /* direct data */
-    BLO_write_pointer_array(writer, ob->totcol, ob->mat);
-    BLO_write_raw(writer, sizeof(char) * ob->totcol, ob->matbits);
+  /* direct data */
+  BLO_write_pointer_array(writer, ob->totcol, ob->mat);
+  BLO_write_raw(writer, sizeof(char) * ob->totcol, ob->matbits);
 
-    bArmature *arm = NULL;
-    if (ob->type == OB_ARMATURE) {
-      arm = ob->data;
-      if (arm && ob->pose && arm->act_bone) {
-        BLI_strncpy(
-            ob->pose->proxy_act_bone, arm->act_bone->name, sizeof(ob->pose->proxy_act_bone));
-      }
+  bArmature *arm = NULL;
+  if (ob->type == OB_ARMATURE) {
+    arm = ob->data;
+    if (arm && ob->pose && arm->act_bone) {
+      BLI_strncpy(ob->pose->proxy_act_bone, arm->act_bone->name, sizeof(ob->pose->proxy_act_bone));
     }
+  }
 
-    BKE_pose_blend_write(writer, ob->pose, arm);
-    write_fmaps(writer, &ob->fmaps);
-    BKE_constraint_blend_write(writer, &ob->constraints);
-    animviz_motionpath_blend_write(writer, ob->mpath);
+  BKE_pose_blend_write(writer, ob->pose, arm);
+  write_fmaps(writer, &ob->fmaps);
+  BKE_constraint_blend_write(writer, &ob->constraints);
+  animviz_motionpath_blend_write(writer, ob->mpath);
 
-    BLO_write_struct(writer, PartDeflect, ob->pd);
-    if (ob->soft) {
-      /* Set deprecated pointers to prevent crashes of older Blenders */
-      ob->soft->pointcache = ob->soft->shared->pointcache;
-      ob->soft->ptcaches = ob->soft->shared->ptcaches;
-      BLO_write_struct(writer, SoftBody, ob->soft);
-      BLO_write_struct(writer, SoftBody_Shared, ob->soft->shared);
-      BKE_ptcache_blend_write(writer, &(ob->soft->shared->ptcaches));
-      BLO_write_struct(writer, EffectorWeights, ob->soft->effector_weights);
-    }
+  BLO_write_struct(writer, PartDeflect, ob->pd);
+  if (ob->soft) {
+    /* Set deprecated pointers to prevent crashes of older Blenders */
+    ob->soft->pointcache = ob->soft->shared->pointcache;
+    ob->soft->ptcaches = ob->soft->shared->ptcaches;
+    BLO_write_struct(writer, SoftBody, ob->soft);
+    BLO_write_struct(writer, SoftBody_Shared, ob->soft->shared);
+    BKE_ptcache_blend_write(writer, &(ob->soft->shared->ptcaches));
+    BLO_write_struct(writer, EffectorWeights, ob->soft->effector_weights);
+  }
 
-    if (ob->rigidbody_object) {
-      /* TODO: if any extra data is added to handle duplis, will need separate function then */
-      BLO_write_struct(writer, RigidBodyOb, ob->rigidbody_object);
-    }
-    if (ob->rigidbody_constraint) {
-      BLO_write_struct(writer, RigidBodyCon, ob->rigidbody_constraint);
-    }
+  if (ob->rigidbody_object) {
+    /* TODO: if any extra data is added to handle duplis, will need separate function then */
+    BLO_write_struct(writer, RigidBodyOb, ob->rigidbody_object);
+  }
+  if (ob->rigidbody_constraint) {
+    BLO_write_struct(writer, RigidBodyCon, ob->rigidbody_constraint);
+  }
 
-    if (ob->type == OB_EMPTY && ob->empty_drawtype == OB_EMPTY_IMAGE) {
-      BLO_write_struct(writer, ImageUser, ob->iuser);
-    }
+  if (ob->type == OB_EMPTY && ob->empty_drawtype == OB_EMPTY_IMAGE) {
+    BLO_write_struct(writer, ImageUser, ob->iuser);
+  }
 
-    BKE_particle_system_blend_write(writer, &ob->particlesystem);
-    BKE_modifier_blend_write(writer, &ob->modifiers);
-    BKE_gpencil_modifier_blend_write(writer, &ob->greasepencil_modifiers);
-    BKE_shaderfx_blend_write(writer, &ob->shader_fx);
+  BKE_particle_system_blend_write(writer, &ob->particlesystem);
+  BKE_modifier_blend_write(writer, &ob->modifiers);
+  BKE_gpencil_modifier_blend_write(writer, &ob->greasepencil_modifiers);
+  BKE_shaderfx_blend_write(writer, &ob->shader_fx);
 
-    BLO_write_struct_list(writer, LinkData, &ob->pc_ids);
+  BLO_write_struct_list(writer, LinkData, &ob->pc_ids);
 
-    BKE_previewimg_blend_write(writer, ob->preview);
-  }
+  BKE_previewimg_blend_write(writer, ob->preview);
 }
 
 /* XXX deprecated - old animation system */
diff --git a/source/blender/blenkernel/intern/paint.c b/source/blender/blenkernel/intern/paint.c
index a1fa6aae1ce..d6030941c6d 100644
--- a/source/blender/blenkernel/intern/paint.c
+++ b/source/blender/blenkernel/intern/paint.c
@@ -108,14 +108,13 @@ static void palette_free_data(ID *id)
 static void palette_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Palette *palette = (Palette *)id;
-  if (palette->id.us > 0 || BLO_write_is_undo(writer)) {
-    PaletteColor *color;
-    BLO_write_id_struct(writer, Palette, id_address, &palette->id);
-    BKE_id_blend_write(writer, &palette->id);
 
-    for (color = palette->colors.first; color; color = color->next) {
-      BLO_write_struct(writer, PaletteColor, color);
-    }
+  PaletteColor *color;
+  BLO_write_id_struct(writer, Palette, id_address, &palette->id);
+  BKE_id_blend_write(writer, &palette->id);
+
+  for (color = palette->colors.first; color; color = color->next) {
+    BLO_write_struct(writer, PaletteColor, color);
   }
 }
 
@@ -187,12 +186,11 @@ static void paint_curve_free_data(ID *id)
 static void paint_curve_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   PaintCurve *pc = (PaintCurve *)id;
-  if (pc->id.us > 0 || BLO_write_is_undo(writer)) {
-    BLO_write_id_struct(writer, PaintCurve, id_address, &pc->id);
-    BKE_id_blend_write(writer, &pc->id);
 
-    BLO_write_struct_array(writer, PaintCurvePoint, pc->tot_points, pc->points);
-  }
+  BLO_write_id_struct(writer, PaintCurve, id_address, &pc->id);
+  BKE_id_blend_write(writer, &pc->id);
+
+  BLO_write_struct_array(writer, PaintCurvePoint, pc->tot_points, pc->points);
 }
 
 static void paint_curve_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index cc8a051eceb..29849c69b6f 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -255,60 +255,59 @@ static void write_boid_state(BlendWriter *writer, BoidState *state)
 static void particle_settings_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   ParticleSettings *part = (ParticleSettings *)id;
-  if (part->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, ParticleSettings, id_address, &part->id);
-    BKE_id_blend_write(writer, &part->id);
 
-    if (part->adt) {
-      BKE_animdata_blend_write(writer, part->adt);
-    }
-    BLO_write_struct(writer, PartDeflect, part->pd);
-    BLO_write_struct(writer, PartDeflect, part->pd2);
-    BLO_write_struct(writer, EffectorWeights, part->effector_weights);
+  /* write LibData */
+  BLO_write_id_struct(writer, ParticleSettings, id_address, &part->id);
+  BKE_id_blend_write(writer, &part->id);
 
-    if (part->clumpcurve) {
-      BKE_curvemapping_blend_write(writer, part->clumpcurve);
-    }
-    if (part->roughcurve) {
-      BKE_curvemapping_blend_write(writer, part->roughcurve);
-    }
-    if (part->twistcurve) {
-      BKE_curvemapping_blend_write(writer, part->twistcurve);
-    }
+  if (part->adt) {
+    BKE_animdata_blend_write(writer, part->adt);
+  }
+  BLO_write_struct(writer, PartDeflect, part->pd);
+  BLO_write_struct(writer, PartDeflect, part->pd2);
+  BLO_write_struct(writer, EffectorWeights, part->effector_weights);
 
-    LISTBASE_FOREACH (ParticleDupliWeight *, dw, &part->instance_weights) {
-      /* update indices, but only if dw->ob is set (can be NULL after loading e.g.) */
-      if (dw->ob != NULL) {
-        dw->index = 0;
-        if (part->instance_collection) { /* can be NULL if lining fails or set to None */
-          FOREACH_COLLECTION_OBJECT_RECURSIVE_BEGIN (part->instance_collection, object) {
-            if (object == dw->ob) {
-              break;
-            }
-            dw->index++;
+  if (part->clumpcurve) {
+    BKE_curvemapping_blend_write(writer, part->clumpcurve);
+  }
+  if (part->roughcurve) {
+    BKE_curvemapping_blend_write(writer, part->roughcurve);
+  }
+  if (part->twistcurve) {
+    BKE_curvemapping_blend_write(writer, part->twistcurve);
+  }
+
+  LISTBASE_FOREACH (ParticleDupliWeight *, dw, &part->instance_weights) {
+    /* update indices, but only if dw->ob is set (can be NULL after loading e.g.) */
+    if (dw->ob != NULL) {
+      dw->index = 0;
+      if (part->instance_collection) { /* can be NULL if lining fails or set to None */
+        FOREACH_COLLECTION_OBJECT_RECURSIVE_BEGIN (part->instance_collection, object) {
+          if (object == dw->ob) {
+            break;
           }
-          FOREACH_COLLECTION_OBJECT_RECURSIVE_END;
+          dw->index++;
         }
+        FOREACH_COLLECTION_OBJECT_RECURSIVE_END;
       }
-      BLO_write_struct(writer, ParticleDupliWeight, dw);
     }
+    BLO_write_struct(writer, ParticleDupliWeight, dw);
+  }
 
-    if (part->boids && part->phystype == PART_PHYS_BOIDS) {
-      BLO_write_struct(writer, BoidSettings, part->boids);
+  if (part->boids && part->phystype == PART_PHYS_BOIDS) {
+    BLO_write_struct(writer, BoidSettings, part->boids);
 
-      LISTBASE_FOREACH (BoidState *, state, &part->boids->states) {
-        write_boid_state(writer, state);
-      }
-    }
-    if (part->fluid && part->phystype == PART_PHYS_FLUID) {
-      BLO_write_struct(writer, SPHFluidSettings, part->fluid);
+    LISTBASE_FOREACH (BoidState *, state, &part->boids->states) {
+      write_boid_state(writer, state);
     }
+  }
+  if (part->fluid && part->phystype == PART_PHYS_FLUID) {
+    BLO_write_struct(writer, SPHFluidSettings, part->fluid);
+  }
 
-    for (int a = 0; a < MAX_MTEX; a++) {
-      if (part->mtex[a]) {
-        BLO_write_struct(writer, MTex, part->mtex[a]);
-      }
+  for (int a = 0; a < MAX_MTEX; a++) {
+    if (part->mtex[a]) {
+      BLO_write_struct(writer, MTex, part->mtex[a]);
     }
   }
 }
diff --git a/source/blender/blenkernel/intern/pointcloud.cc b/source/blender/blenkernel/intern/pointcloud.cc
index d9a7a376e2e..837a772607f 100644
--- a/source/blender/blenkernel/intern/pointcloud.cc
+++ b/source/blender/blenkernel/intern/pointcloud.cc
@@ -112,28 +112,27 @@ static void pointcloud_foreach_id(ID *id, LibraryForeachIDData *data)
 static void pointcloud_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   PointCloud *pointcloud = (PointCloud *)id;
-  if (pointcloud->id.us > 0 || BLO_write_is_undo(writer)) {
-    CustomDataLayer *players = nullptr, players_buff[CD_TEMP_CHUNK_SIZE];
-    CustomData_blend_write_prepare(
-        &pointcloud->pdata, &players, players_buff, ARRAY_SIZE(players_buff));
-
-    /* Write LibData */
-    BLO_write_id_struct(writer, PointCloud, id_address, &pointcloud->id);
-    BKE_id_blend_write(writer, &pointcloud->id);
-
-    /* Direct data */
-    CustomData_blend_write(
-        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);
-    }
 
-    /* Remove temporary data. */
-    if (players && players != players_buff) {
-      MEM_freeN(players);
-    }
+  CustomDataLayer *players = nullptr, players_buff[CD_TEMP_CHUNK_SIZE];
+  CustomData_blend_write_prepare(
+      &pointcloud->pdata, &players, players_buff, ARRAY_SIZE(players_buff));
+
+  /* Write LibData */
+  BLO_write_id_struct(writer, PointCloud, id_address, &pointcloud->id);
+  BKE_id_blend_write(writer, &pointcloud->id);
+
+  /* Direct data */
+  CustomData_blend_write(
+      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);
+  }
+
+  /* Remove temporary data. */
+  if (players && players != players_buff) {
+    MEM_freeN(players);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/screen.c b/source/blender/blenkernel/intern/screen.c
index e44c5a6b40e..1e725a6afc4 100644
--- a/source/blender/blenkernel/intern/screen.c
+++ b/source/blender/blenkernel/intern/screen.c
@@ -255,18 +255,16 @@ static void screen_foreach_id(ID *id, LibraryForeachIDData *data)
 static void screen_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   bScreen *screen = (bScreen *)id;
-  /* Screens are reference counted, only saved if used by a workspace. */
-  if (screen->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    /* in 2.50+ files, the file identifier for screens is patched, forward compatibility */
-    BLO_write_struct_at_address_with_filecode(writer, ID_SCRN, bScreen, id_address, screen);
-    BKE_id_blend_write(writer, &screen->id);
 
-    BKE_previewimg_blend_write(writer, screen->preview);
+  /* write LibData */
+  /* in 2.50+ files, the file identifier for screens is patched, forward compatibility */
+  BLO_write_struct_at_address_with_filecode(writer, ID_SCRN, bScreen, id_address, screen);
+  BKE_id_blend_write(writer, &screen->id);
 
-    /* direct data */
-    BKE_screen_area_map_blend_write(writer, AREAMAP_FROM_SCREEN(screen));
-  }
+  BKE_previewimg_blend_write(writer, screen->preview);
+
+  /* direct data */
+  BKE_screen_area_map_blend_write(writer, AREAMAP_FROM_SCREEN(screen));
 }
 
 /* Cannot use IDTypeInfo callback yet, because of the return value. */
diff --git a/source/blender/blenkernel/intern/simulation.cc b/source/blender/blenkernel/intern/simulation.cc
index 216563b860d..5aac29c19a7 100644
--- a/source/blender/blenkernel/intern/simulation.cc
+++ b/source/blender/blenkernel/intern/simulation.cc
@@ -114,19 +114,18 @@ static void simulation_foreach_id(ID *id, LibraryForeachIDData *data)
 static void simulation_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Simulation *simulation = (Simulation *)id;
-  if (simulation->id.us > 0 || BLO_write_is_undo(writer)) {
-    BLO_write_id_struct(writer, Simulation, id_address, &simulation->id);
-    BKE_id_blend_write(writer, &simulation->id);
-
-    if (simulation->adt) {
-      BKE_animdata_blend_write(writer, simulation->adt);
-    }
-
-    /* nodetree is integral part of simulation, no libdata */
-    if (simulation->nodetree) {
-      BLO_write_struct(writer, bNodeTree, simulation->nodetree);
-      ntreeBlendWrite(writer, simulation->nodetree);
-    }
+
+  BLO_write_id_struct(writer, Simulation, id_address, &simulation->id);
+  BKE_id_blend_write(writer, &simulation->id);
+
+  if (simulation->adt) {
+    BKE_animdata_blend_write(writer, simulation->adt);
+  }
+
+  /* nodetree is integral part of simulation, no libdata */
+  if (simulation->nodetree) {
+    BLO_write_struct(writer, bNodeTree, simulation->nodetree);
+    ntreeBlendWrite(writer, simulation->nodetree);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/sound.c b/source/blender/blenkernel/intern/sound.c
index 8730d2758e6..c61fa793367 100644
--- a/source/blender/blenkernel/intern/sound.c
+++ b/source/blender/blenkernel/intern/sound.c
@@ -137,24 +137,23 @@ static void sound_blend_write(BlendWriter *writer, ID *id, const void *id_addres
 {
   bSound *sound = (bSound *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (sound->id.us > 0 || is_undo) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    sound->tags = 0;
-    sound->handle = NULL;
-    sound->playback_handle = NULL;
-    sound->spinlock = NULL;
 
-    /* Do not store packed files in case this is a library override ID. */
-    if (ID_IS_OVERRIDE_LIBRARY(sound) && !is_undo) {
-      sound->packedfile = NULL;
-    }
-
-    /* write LibData */
-    BLO_write_id_struct(writer, bSound, id_address, &sound->id);
-    BKE_id_blend_write(writer, &sound->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  sound->tags = 0;
+  sound->handle = NULL;
+  sound->playback_handle = NULL;
+  sound->spinlock = NULL;
 
-    BKE_packedfile_blend_write(writer, sound->packedfile);
+  /* Do not store packed files in case this is a library override ID. */
+  if (ID_IS_OVERRIDE_LIBRARY(sound) && !is_undo) {
+    sound->packedfile = NULL;
   }
+
+  /* write LibData */
+  BLO_write_id_struct(writer, bSound, id_address, &sound->id);
+  BKE_id_blend_write(writer, &sound->id);
+
+  BKE_packedfile_blend_write(writer, sound->packedfile);
 }
 
 static void sound_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/speaker.c b/source/blender/blenkernel/intern/speaker.c
index af9b2268879..4b10522c375 100644
--- a/source/blender/blenkernel/intern/speaker.c
+++ b/source/blender/blenkernel/intern/speaker.c
@@ -56,14 +56,13 @@ static void speaker_foreach_id(ID *id, LibraryForeachIDData *data)
 static void speaker_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Speaker *spk = (Speaker *)id;
-  if (spk->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, Speaker, id_address, &spk->id);
-    BKE_id_blend_write(writer, &spk->id);
-
-    if (spk->adt) {
-      BKE_animdata_blend_write(writer, spk->adt);
-    }
+
+  /* write LibData */
+  BLO_write_id_struct(writer, Speaker, id_address, &spk->id);
+  BKE_id_blend_write(writer, &spk->id);
+
+  if (spk->adt) {
+    BKE_animdata_blend_write(writer, spk->adt);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/text.c b/source/blender/blenkernel/intern/text.c
index 6048e823abb..275cf0d4c38 100644
--- a/source/blender/blenkernel/intern/text.c
+++ b/source/blender/blenkernel/intern/text.c
@@ -171,9 +171,6 @@ static void text_free_data(ID *id)
 
 static void text_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
-  if (id->us < 1 && !BLO_write_is_undo(writer)) {
-    return;
-  }
   Text *text = (Text *)id;
 
   /* NOTE: we are clearing local temp data here, *not* the flag in the actual 'real' ID. */
diff --git a/source/blender/blenkernel/intern/texture.c b/source/blender/blenkernel/intern/texture.c
index beb92495d16..228e6fffdf7 100644
--- a/source/blender/blenkernel/intern/texture.c
+++ b/source/blender/blenkernel/intern/texture.c
@@ -150,28 +150,27 @@ static void texture_foreach_id(ID *id, LibraryForeachIDData *data)
 static void texture_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   Tex *tex = (Tex *)id;
-  if (tex->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* write LibData */
-    BLO_write_id_struct(writer, Tex, id_address, &tex->id);
-    BKE_id_blend_write(writer, &tex->id);
 
-    if (tex->adt) {
-      BKE_animdata_blend_write(writer, tex->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Tex, id_address, &tex->id);
+  BKE_id_blend_write(writer, &tex->id);
 
-    /* direct data */
-    if (tex->coba) {
-      BLO_write_struct(writer, ColorBand, tex->coba);
-    }
+  if (tex->adt) {
+    BKE_animdata_blend_write(writer, tex->adt);
+  }
 
-    /* nodetree is integral part of texture, no libdata */
-    if (tex->nodetree) {
-      BLO_write_struct(writer, bNodeTree, tex->nodetree);
-      ntreeBlendWrite(writer, tex->nodetree);
-    }
+  /* direct data */
+  if (tex->coba) {
+    BLO_write_struct(writer, ColorBand, tex->coba);
+  }
 
-    BKE_previewimg_blend_write(writer, tex->preview);
+  /* nodetree is integral part of texture, no libdata */
+  if (tex->nodetree) {
+    BLO_write_struct(writer, bNodeTree, tex->nodetree);
+    ntreeBlendWrite(writer, tex->nodetree);
   }
+
+  BKE_previewimg_blend_write(writer, tex->preview);
 }
 
 static void texture_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/volume.cc b/source/blender/blenkernel/intern/volume.cc
index b28d17df814..69452d6896f 100644
--- a/source/blender/blenkernel/intern/volume.cc
+++ b/source/blender/blenkernel/intern/volume.cc
@@ -578,27 +578,26 @@ static void volume_blend_write(BlendWriter *writer, ID *id, const void *id_addre
 {
   Volume *volume = (Volume *)id;
   const bool is_undo = BLO_write_is_undo(writer);
-  if (volume->id.us > 0 || is_undo) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    volume->runtime.grids = nullptr;
 
-    /* Do not store packed files in case this is a library override ID. */
-    if (ID_IS_OVERRIDE_LIBRARY(volume) && !is_undo) {
-      volume->packedfile = nullptr;
-    }
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  volume->runtime.grids = nullptr;
 
-    /* write LibData */
-    BLO_write_id_struct(writer, Volume, id_address, &volume->id);
-    BKE_id_blend_write(writer, &volume->id);
+  /* Do not store packed files in case this is a library override ID. */
+  if (ID_IS_OVERRIDE_LIBRARY(volume) && !is_undo) {
+    volume->packedfile = nullptr;
+  }
 
-    /* direct data */
-    BLO_write_pointer_array(writer, volume->totcol, volume->mat);
-    if (volume->adt) {
-      BKE_animdata_blend_write(writer, volume->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, Volume, id_address, &volume->id);
+  BKE_id_blend_write(writer, &volume->id);
 
-    BKE_packedfile_blend_write(writer, volume->packedfile);
+  /* direct data */
+  BLO_write_pointer_array(writer, volume->totcol, volume->mat);
+  if (volume->adt) {
+    BKE_animdata_blend_write(writer, volume->adt);
   }
+
+  BKE_packedfile_blend_write(writer, volume->packedfile);
 }
 
 static void volume_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenkernel/intern/world.c b/source/blender/blenkernel/intern/world.c
index e889d8af1d5..4abe1ff0f20 100644
--- a/source/blender/blenkernel/intern/world.c
+++ b/source/blender/blenkernel/intern/world.c
@@ -138,26 +138,25 @@ static void world_foreach_id(ID *id, LibraryForeachIDData *data)
 static void world_blend_write(BlendWriter *writer, ID *id, const void *id_address)
 {
   World *wrld = (World *)id;
-  if (wrld->id.us > 0 || BLO_write_is_undo(writer)) {
-    /* Clean up, important in undo case to reduce false detection of changed datablocks. */
-    BLI_listbase_clear(&wrld->gpumaterial);
 
-    /* write LibData */
-    BLO_write_id_struct(writer, World, id_address, &wrld->id);
-    BKE_id_blend_write(writer, &wrld->id);
+  /* Clean up, important in undo case to reduce false detection of changed datablocks. */
+  BLI_listbase_clear(&wrld->gpumaterial);
 
-    if (wrld->adt) {
-      BKE_animdata_blend_write(writer, wrld->adt);
-    }
+  /* write LibData */
+  BLO_write_id_struct(writer, World, id_address, &wrld->id);
+  BKE_id_blend_write(writer, &wrld->id);
 
-    /* nodetree is integral part of world, no libdata */
-    if (wrld->nodetree) {
-      BLO_write_struct(writer, bNodeTree, wrld->nodetree);
-      ntreeBlendWrite(writer, wrld->nodetree);
-    }
+  if (wrld->adt) {
+    BKE_animdata_blend_write(writer, wrld->adt);
+  }
 
-    BKE_previewimg_blend_write(writer, wrld->preview);
+  /* nodetree is integral part of world, no libdata */
+  if (wrld->nodetree) {
+    BLO_write_struct(writer, bNodeTree, wrld->nodetree);
+    ntreeBlendWrite(writer, wrld->nodetree);
   }
+
+  BKE_previewimg_blend_write(writer, wrld->preview);
 }
 
 static void world_blend_read_data(BlendDataReader *reader, ID *id)
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 225548f3832..337279ae84b 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -982,6 +982,14 @@ static bool write_file_handle(Main *mainvar,
         BLI_assert(
             (id->tag & (LIB_TAG_NO_MAIN | LIB_TAG_NO_USER_REFCOUNT | LIB_TAG_NOT_ALLOCATED)) == 0);
 
+        /* We only write unused IDs in undo case.
+         * NOTE: All Scenes, WindowManagers and WorkSpaces should always be written to disk, so
+         * their usercount should never be NULL currently. */
+        if (id->us == 0 && !wd->use_memfile) {
+          BLI_assert(!ELEM(GS(id->name), ID_SCE, ID_WM, ID_WS));
+          continue;
+        }
+
         const bool do_override = !ELEM(override_storage, NULL, bmain) &&
                                  ID_IS_OVERRIDE_LIBRARY_REAL(id);