Switch to new node group interfaces and deprecate old DNA and API.
This completes support for panels in node drawing and in node group
interface declarations in particular.

The new node group interface DNA and RNA code has been added in parts
1 and 2 (#110885, #110952) but has not be enabled yet. This commit
completes the integration by
* enabling the new RNA API
* using the new API in UI
* read/write new interfaces from blend files
* add versioning for backward compatibility
* add forward-compatible writing code to reconstruct old interfaces

All places accessing node group interface declarations should now be
using the new API. A runtime cache has been added that allows simple
linear access to socket inputs and outputs even when a panel hierarchy
is used.

Old DNA has been deprecated and should only be accessed for versioning
(inputs/outputs renamed to inputs_legacy/outputs_legacy to catch
errors). Versioning code ensures both backward and forward
compatibility of existing files.

The API for old interfaces is removed. The new API is very similar but
is defined on the `ntree.interface` instead of the `ntree` directly.
Breaking change notifications and detailed instructions for migrating
will be added.

A python test has been added for the node group API functions. This
includes new functionality such as creating panels and moving items
between different levels.

@@ -55,0 +66,4 @@
+        layout.prop(self, "randomize")
+
+    def init_socket(self, node, socket, data_path):
+        print("I am doing the socket thing")

@@ -219,0 +223,4 @@
+   * node tree hasn't been drawn yet. In the node tree's "world space" (the same as
+   * #bNode::runtime::totr).
+   */
+  float2 location;

@@ -206,1 +201,3 @@
-
+  ntree_dst->tree_interface.copy_data(ntree_src->tree_interface, flag);
+  /* Legacy inputs/outputs lists may contain unmanaged pointers, don't copy these. */
+  BLI_listbase_clear(&ntree_dst->inputs_legacy);

@@ -301,1 +296,3 @@
-    MEM_freeN(sock);
+  ntree->tree_interface.free_data();
+  /* Free legacy interface data */
+  LISTBASE_FOREACH_MUTABLE (bNodeSocket *, socket, &ntree->inputs_legacy) {

@@ -473,1 +469,4 @@
 
+namespace blender::bke::forward_compat {
+
+static void write_node_socket_interface(BlendWriter *writer, bNodeSocket *sock)

@@ -3936,3 +3870,3 @@
 
 static void update_socket_declarations(ListBase *sockets,
-                                       Span<blender::nodes::SocketDeclarationPtr> declarations)
+                                       Span<blender::nodes::SocketDeclaration *> declarations)

@@ -29,3 +29,2 @@
   bNodeTreeRuntime &tree_runtime = *ntree.runtime;
-  tree_runtime.interface_inputs = ntree.inputs;
-  tree_runtime.interface_outputs = ntree.outputs;
+  tree_runtime.interface_cache.rebuild(const_cast<bNodeTreeInterface &>(ntree.tree_interface));

@@ -577,2 +607,4 @@
     FOREACH_NODETREE_END;
 
+    /* Convert old socket lists into new interface items. */
+    FOREACH_NODETREE_BEGIN (bmain, ntree, id) {

@@ -0,0 +156,4 @@
+  std::unique_ptr<TreeViewItemDropTarget> create_drop_target() override;
+
+ private:
+  bNodeTree &nodetree_;

@@ -1564,3 +1581,3 @@
   GPU_matrix_push();
 
-  /* The draw manager is used to draw the backdrop image. */
+  /* The draw manager is used to draw the

@@ -462,0 +489,4 @@
+  /* Parent panel stack with count of items still to be added. */
+  struct PanelUpdate {
+    int remaining_items;
+    bool is_collapsed;

@@ -1629,6 +1753,130 @@ static void node_draw_sockets(const View2D &v2d,
   }

@@ -896,2 +915,4 @@
   RNA_def_property_clear_flag(prop, PROP_EDITABLE);
   RNA_def_property_ui_text(prop, "Items", "Items in the node panel");
+
+  prop = RNA_def_property(srna, "is_child_panel_allowed", PROP_BOOLEAN, PROP_NONE);

@@ -935,3 +960,3 @@
                       "Socket Type",
                       "Type of socket generated on nodes");
-  /* Note: itemf callback works for the function parameter, it does not require a data pointer. */
+  /* Note: itemf callback works for the function parameter, it does not require a data pointer.

@@ -1872,2 +1872,4 @@
     return;
   }
+
+  ntree->ensure_topology_cache();

@@ -88,3 +88,3 @@
 
   bool supports_renaming() const override;
-  bool rename(StringRefNull new_name) override;
+  bool rename(const bContext &C, StringRefNull new_name) override;

@@ -876,3 +863,1 @@
-
-
-class NodeTreeInterfacePanel(Panel):
+class NODE_PT_node_tree_declaration(Panel):

@@ -876,3 +863,1 @@
-
-
-class NodeTreeInterfacePanel(Panel):
+class NODE_PT_node_tree_declaration(Panel):

@@ -204,6 +204,8 @@ static AnonymousAttributeInferencingResult analyse_anonymous_attribute_usages(
 {
   BLI_assert(!tree.has_available_link_cycle());
 
+  const bNodeTreeInterfaceCache &cache = tree.interface_cache();

@@ -850,1 +855,4 @@
 {
+  /* Are child panels allowed? */
+  BLI_assert(item.item_type != NODE_INTERFACE_PANEL ||
+             (flag & NODE_INTERFACE_PANEL_ALLOW_CHILD_PANELS));

@@ -107,2 +116,4 @@
   /* UI name of the panel. */
   char *name;
+  char *description;
+  /* eNodeTreeInterfacePanelFlag */

@@ -281,1 +296,3 @@
-  bNodeTreeInterfacePanel *add_panel(blender::StringRefNull name, bNodeTreeInterfacePanel *parent);
+  bNodeTreeInterfacePanel *add_panel(blender::StringRefNull name,
+                                     blender::StringRefNull description,
+                                     const NodeTreeInterfacePanelFlag flag,

@@ -309,0 +319,4 @@
+
+typedef struct bNodePanelState {
+  /* Unique identifier for validating state against panels in node declaration. */
+  short uid;

@@ -423,0 +457,4 @@
+    MEM_SAFE_FREE(new_socket->default_attribute_name);
+    new_socket->default_attribute_name = BLI_strdup_null(socket->default_attribute_name);
+
+    node_socket_copy_default_value_data(

@@ -1031,3 +1028,2 @@
   for (bNode *node : nodes_to_move) {
-    for (bNodeSocket *input_socket : node->input_sockets()) {
-      for (bNodeLink *link : input_socket->directly_linked_links()) {
+    for (bNodeSocket *output_socket : node->output_sockets()) {

@@ -545,6 +548,12 @@ inline blender::Span<bNestedNodeRef> bNodeTree::nested_node_refs_span() const
   return {this->nested_node_refs, this->nested_node_refs_num};
 }
 
+inline const blender::bke::bNodeTreeInterfaceCache &bNodeTree::interface_cache() const

@@ -1001,0 +910,4 @@
+            if active_item.item_type == 'SOCKET':
+                layout.prop(active_item, "socket_type", text="Type")
+                layout.prop(active_item, "description")
+                layout.prop(active_item, "in_out", text="Input/Output Type")

@@ -46,6 +46,8 @@
 #include "ANIM_armature_iter.hh"
 #include "ANIM_bone_collections.h"
 
+#include "NOD_socket.hh"

@@ -583,6 +585,77 @@ static void version_replace_principled_hair_model(bNodeTree *ntree)
   }
 }
 
+static void legacy_socket_move_to_interface(bNodeTreeInterfaceItem *&new_item_ptr,

@@ -586,0 +646,4 @@
+{
+  /* Clear legacy sockets after conversion.
+   * Internal data pointers have been moved or freed already. */
+  LISTBASE_FOREACH_MUTABLE (bNodeSocket *, sock, &ntree->inputs_legacy) {

@@ -1879,6 +1879,7 @@ void DepsgraphNodeBuilder::build_nodetree(bNodeTree *ntree)
   if (built_map_.checkIsBuiltAndTag(ntree)) {
     return;
   }
+

@@ -575,6 +623,44 @@ static void rna_NodeTreeInterfaceItems_move_to_parent(ID *id,
 
 /* ******** Node Socket Subtypes ******** */
 
+static const EnumPropertyItem *rna_subtype_filter_itemf(const blender::Set<int> subtypes,

@@ -16,3 +16,2 @@
     group = bpy.data.node_groups.new(name, 'GeometryNodeTree')
-    group.inputs.new('NodeSocketGeometry', data_("Geometry"))
-    group.outputs.new('NodeSocketGeometry', data_("Geometry"))
+    group.interface.new_socket(data_("Geometry"), in_out={'INPUT'}, socket_type='NodeSocketGeometry')

@@ -263,0 +310,4 @@
+        if active_item:
+            # Insert into active panel if possible, otherwise insert after active item.
+            if active_item.item_type == 'PANEL' and item.item_type != 'PANEL':
+                interface.move_to_parent(item, active_item, len(active_item.interface_items))

@@ -736,0 +748,4 @@
+          break;
+        }
+        if (items[test_pos]->item_type != NODE_INTERFACE_PANEL) {
+          /* Found valid position, insert after the last socket item */

@@ -586,0 +613,4 @@
+  legacy_socket.prop = nullptr;
+
+  /* Unused data */
+  MEM_delete(legacy_socket.runtime);

@@ -914,6 +971,29 @@ void blo_do_versions_400(FileData *fd, Library * /*lib*/, Main *bmain)
     }
   }
 
+  if (!MAIN_VERSION_FILE_ATLEAST(bmain, 400, 18)) {