Fix #145103: incorrect socket usage for built-in menu sockets

The socket usage of built-in menu sockets did not take into account if any of the
outputs of the node were actually used.

Pull Request: https://projects.blender.org/blender/blender/pulls/145162

source/blender/nodes/NOD_socket_usage_inference.hh

@@ -89,6 +89,13 @@ class InputSocketUsageParams {
    */
   InferenceValue get_input(StringRef identifier) const;
 
+  /**
+   * Returns true if any output is known to be used or false if no output is used. std::nullopt is
+   * returned if it's not known yet if any output is used. In this case, the caller should return
+   * early, it will be checked again once new information about output usages becomes available.
+   */
+  std::optional<bool> any_output_is_used() const;
+
   /**
    * Utility for the case when the socket depends on a specific menu input to have a certain value.
    */

source/blender/nodes/intern/node_declaration.cc

@@ -823,6 +823,17 @@ BaseSocketDeclarationBuilder &BaseSocketDeclarationBuilder::usage_by_single_menu
   this->usage_inference([menu_value](const socket_usage_inference::InputSocketUsageParams &params)
                             -> std::optional<bool> {
     const bNodeSocket &socket = find_single_menu_input(params.node);
+    if (const std::optional<bool> any_output_used = params.any_output_is_used()) {
+      if (!*any_output_used) {
+        /* If no output is used, none if the inputs is used either. */
+        return false;
+      }
+    }
+    else {
+      /* It's not known if any output is used yet. This function will be called again once new
+       * information about output usages is available. */
+      return std::nullopt;
+    }
     return params.menu_input_may_be(socket.identifier, menu_value);
   });
   return *this;

source/blender/nodes/intern/socket_usage_inference.cc

@@ -1553,6 +1553,28 @@ InferenceValue InputSocketUsageParams::get_input(const StringRef identifier) con
   return inferencer_.get_socket_value(input_socket);
 }
 
+std::optional<bool> InputSocketUsageParams::any_output_is_used() const
+{
+  const bNodeSocket *first_missing = nullptr;
+  for (const bNodeSocket *output_socket : this->node.output_sockets()) {
+    if (const std::optional<bool> is_used = inferencer_.all_socket_usages_.lookup_try(
+            {compute_context_, output_socket}))
+    {
+      if (*is_used) {
+        return true;
+      }
+    }
+    else {
+      first_missing = output_socket;
+    }
+  }
+  if (first_missing) {
+    inferencer_.push_usage_task({compute_context_, first_missing});
+    return std::nullopt;
+  }
+  return false;
+}
+
 bool InputSocketUsageParams::menu_input_may_be(const StringRef identifier,
                                                const int enum_value) const
 {