Geometry Nodes: improve debug graph for repeat zone

This makes some labels more self-explanatory in the graph generated with
`graph.to_dot()`.

source/blender/functions/FN_lazy_function_graph.hh

@@ -208,6 +208,10 @@ class Graph : NonCopyable, NonMovable {
    * Used to allocate nodes and sockets in the graph.
    */
   LinearAllocator<> allocator_;
+  /**
+   * Name of the graph for debugging purposes.
+   */
+  StringRefNull name_;
   /**
    * Contains all nodes in the graph so that it is efficient to iterate over them.
    * The first two nodes are the interface input and output nodes.
@@ -227,9 +231,11 @@ class Graph : NonCopyable, NonMovable {
   int socket_num_ = 0;
 
  public:
-  Graph();
+  Graph(StringRef name = "unkown");
   ~Graph();
 
+  StringRefNull name() const;
+
   /**
    * Get all nodes in the graph. The index in the span corresponds to #Node::index_in_graph.
    */
@@ -489,6 +495,11 @@ inline const LazyFunction &FunctionNode::function() const
 /** \name #Graph Inline Methods
  * \{ */
 
+inline StringRefNull Graph::name() const
+{
+  return name_;
+}
+
 inline Span<const Node *> Graph::nodes() const
 {
   return nodes_;

source/blender/functions/intern/lazy_function_graph.cc

@@ -10,8 +10,9 @@
 
 namespace blender::fn::lazy_function {
 
-Graph::Graph()
+Graph::Graph(const StringRef name)
 {
+  name_ = allocator_.copy_string(name);
   graph_input_node_ = allocator_.construct<InterfaceNode>().release();
   graph_output_node_ = allocator_.construct<InterfaceNode>().release();
   nodes_.append(graph_input_node_);

source/blender/functions/intern/lazy_function_graph_executor.cc

@@ -1475,6 +1475,8 @@ GraphExecutor::GraphExecutor(const Graph &graph,
       side_effect_provider_(side_effect_provider),
       node_execute_wrapper_(node_execute_wrapper)
 {
+  debug_name_ = graph.name().c_str();
+
   /* The graph executor can handle partial execution when there are still missing inputs. */
   allow_missing_requested_inputs_ = true;
 

source/blender/nodes/intern/geometry_nodes_lazy_function.cc

@@ -1860,11 +1860,11 @@ class LazyFunctionForRepeatZone : public LazyFunction {
 
     for (const int i : inputs_.index_range()) {
       const lf::Input &input = inputs_[i];
-      lf_inputs.append(&lf_graph.add_input(*input.type, input.debug_name));
+      lf_inputs.append(&lf_graph.add_input(*input.type, this->input_name(i)));
     }
     for (const int i : outputs_.index_range()) {
       const lf::Output &output = outputs_[i];
-      lf_outputs.append(&lf_graph.add_output(*output.type, output.debug_name));
+      lf_outputs.append(&lf_graph.add_output(*output.type, this->output_name(i)));
     }
 
     /* Create body nodes. */
@@ -2474,7 +2474,7 @@ struct GeometryNodesLazyFunctionBuilder {
    */
   ZoneBodyFunction &build_zone_body_function(const bNodeTreeZone &zone)
   {
-    lf::Graph &lf_body_graph = scope_.construct<lf::Graph>();
+    lf::Graph &lf_body_graph = scope_.construct<lf::Graph>("Repeat Body");
 
     BuildGraphParams graph_params{lf_body_graph};