Fix T99873: Store named attribute node cannot write to vertex groups

Since fd5e5dac89, the node would remove the attribute before
adding it again, which lost the vertex group status of an attribute,
meaning they were written as arbitrary attributes.

Now, the node first tries to write to attributes with the same domain
and data-type, which covers the vertex group case. Then it falls back
to removing the attribute and adding it again. Even that can fail
though, so I added an error message to make that a bit clearer.

Differential Revision: https://developer.blender.org/D15514

source/blender/nodes/geometry/nodes/node_geo_store_named_attribute.cc

@@ -1,8 +1,12 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include <atomic>
+
 #include "UI_interface.h"
 #include "UI_resources.h"
 
+#include "RNA_enum_types.h"
+
 #include "NOD_socket_search_link.hh"
 
 #include "BKE_type_conversions.hh"
@@ -85,7 +89,8 @@ static void node_gather_link_searches(GatherLinkSearchOpParams &params)
 static void try_capture_field_on_geometry(GeometryComponent &component,
                                           const StringRef name,
                                           const eAttrDomain domain,
-                                          const GField &field)
+                                          const GField &field,
+                                          std::atomic<bool> &failure)
 {
   const int domain_size = component.attribute_domain_size(domain);
   if (domain_size == 0) {
@@ -100,7 +105,7 @@ static void try_capture_field_on_geometry(GeometryComponent &component,
   const eCustomDataType data_type = bke::cpp_type_to_custom_data_type(type);
 
   /* Could avoid allocating a new buffer if:
-   * - We are writing to an attribute that exists already.
+   * - We are writing to an attribute that exists already with the correct domain and type.
    * - The field does not depend on that attribute (we can't easily check for that yet). */
   void *buffer = MEM_mallocN(type.size() * domain_size, __func__);
 
@@ -108,25 +113,27 @@ static void try_capture_field_on_geometry(GeometryComponent &component,
   evaluator.add_with_destination(field, GMutableSpan{type, buffer, domain_size});
   evaluator.evaluate();
 
-  attributes.remove(name);
-  if (attributes.contains(name)) {
-    GAttributeWriter write_attribute = attributes.lookup_for_write(name);
-    if (write_attribute && write_attribute.domain == domain &&
-        write_attribute.varray.type() == type) {
-      write_attribute.varray.set_all(buffer);
-      write_attribute.finish();
-    }
-    else {
-      /* Cannot change type of built-in attribute. */
-    }
-    type.destruct_n(buffer, domain_size);
-    MEM_freeN(buffer);
-  }
-  else {
-    if (!attributes.add(name, domain, data_type, bke::AttributeInitMove{buffer})) {
+  if (GAttributeWriter attribute = attributes.lookup_for_write(name)) {
+    if (attribute.domain == domain && attribute.varray.type() == type) {
+      attribute.varray.set_all(buffer);
+      attribute.finish();
+      type.destruct_n(buffer, domain_size);
       MEM_freeN(buffer);
+      return;
     }
   }
+
+  if (attributes.remove(name)) {
+    if (attributes.add(name, domain, data_type, bke::AttributeInitMove{buffer})) {
+      return;
+    }
+  }
+
+  /* If the name corresponds to a builtin attribute, removing the attribute might fail if
+   * it's required, and adding the attribute might fail if the domain or type is incorrect. */
+  type.destruct_n(buffer, domain_size);
+  MEM_freeN(buffer);
+  failure = true;
 }
 
 static void node_geo_exec(GeoNodeExecParams params)
@@ -177,12 +184,14 @@ static void node_geo_exec(GeoNodeExecParams params)
       break;
   }
 
+  std::atomic<bool> failure = false;
+
   /* Run on the instances component separately to only affect the top level of instances. */
   if (domain == ATTR_DOMAIN_INSTANCE) {
     if (geometry_set.has_instances()) {
       GeometryComponent &component = geometry_set.get_component_for_write(
           GEO_COMPONENT_TYPE_INSTANCES);
-      try_capture_field_on_geometry(component, name, domain, field);
+      try_capture_field_on_geometry(component, name, domain, field, failure);
     }
   }
   else {
@@ -191,12 +200,26 @@ static void node_geo_exec(GeoNodeExecParams params)
            {GEO_COMPONENT_TYPE_MESH, GEO_COMPONENT_TYPE_POINT_CLOUD, GEO_COMPONENT_TYPE_CURVE}) {
         if (geometry_set.has(type)) {
           GeometryComponent &component = geometry_set.get_component_for_write(type);
-          try_capture_field_on_geometry(component, name, domain, field);
+          try_capture_field_on_geometry(component, name, domain, field, failure);
         }
       }
     });
   }
 
+  if (failure) {
+    const char *domain_name = nullptr;
+    RNA_enum_name_from_value(rna_enum_attribute_domain_items, domain, &domain_name);
+    const char *type_name = nullptr;
+    RNA_enum_name_from_value(rna_enum_attribute_type_items, data_type, &type_name);
+    char *message = BLI_sprintfN(
+        TIP_("Failed to write to attribute \"%s\" with domain \"%s\" and type \"%s\""),
+        name.c_str(),
+        TIP_(domain_name),
+        TIP_(type_name));
+    params.error_message_add(NodeWarningType::Warning, message);
+    MEM_freeN(message);
+  }
+
   params.set_output("Geometry", std::move(geometry_set));
 }