Fix: improve CD_ASSIGN handling when adding custom data layer

Previously, the code would incorrectly free the passed in custom data
layer even when `CD_ASSIGN` was not used. Now the function actually
supports assigning the data to the layer. This only fixes the case for
custom data layer types that only support a single layer like `CD_MEDGE`.

Informally reviewed by Hans Goudey.

1 files changed, 15 insertions, 5 deletions

diff --git a/source/blender/blenkernel/intern/customdata.cc b/source/blender/blenkernel/intern/customdata.cc
index e4405abdde8..01017466764 100644
--- a/source/blender/blenkernel/intern/customdata.cc
+++ b/source/blender/blenkernel/intern/customdata.cc
@@ -2799,11 +2799,6 @@ static CustomDataLayer *customData_add_layer__internal(CustomData *data,
   const LayerTypeInfo *typeInfo = layerType_getInfo(type);
   int flag = 0;
 
-  if (!typeInfo->defaultname && CustomData_has_layer(data, type)) {
-    MEM_SAFE_FREE(layerdata);
-    return &data->layers[CustomData_get_layer_index(data, type)];
-  }
-
   void *newlayerdata = nullptr;
   switch (alloctype) {
     case CD_SET_DEFAULT:
@@ -2856,6 +2851,21 @@ static CustomDataLayer *customData_add_layer__internal(CustomData *data,
       break;
   }
 
+  /* Some layer types only support a single layer. */
+  const bool reuse_existing_layer = !typeInfo->defaultname && CustomData_has_layer(data, type);
+  if (reuse_existing_layer) {
+    CustomDataLayer &layer = data->layers[CustomData_get_layer_index(data, type)];
+    if (layer.data != nullptr) {
+      if (typeInfo->free) {
+        typeInfo->free(layer.data, totelem, typeInfo->size);
+      }
+      MEM_SAFE_FREE(layer.data);
+    }
+    layer.data = newlayerdata;
+    layer.flag = flag;
+    return &layer;
+  }
+
   int index = data->totlayer;
   if (index >= data->maxlayer) {
     if (!customData_resize(data, CUSTOMDATA_GROW)) {