5 files changed, 61 insertions, 9 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index 9df3d7c544d..d4bc0245a61 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -731,6 +731,8 @@ void nodeSetSocketAvailability(struct bNodeSocket *sock, bool is_available);
 
 int nodeSocketLinkLimit(const struct bNodeSocket *sock);
 
+void nodeDeclarationEnsure(struct bNodeTree *ntree, struct bNode *node);
+
 /* Node Clipboard */
 void BKE_node_clipboard_init(const struct bNodeTree *ntree);
 void BKE_node_clipboard_clear(void);
diff --git a/source/blender/blenkernel/intern/node.cc b/source/blender/blenkernel/intern/node.cc
index e6af587cbd7..61b90b44b03 100644
--- a/source/blender/blenkernel/intern/node.cc
+++ b/source/blender/blenkernel/intern/node.cc
@@ -653,6 +653,7 @@ void ntreeBlendReadData(BlendDataReader *reader, bNodeTree *ntree)
   BLO_read_list(reader, &ntree->nodes);
   LISTBASE_FOREACH (bNode *, node, &ntree->nodes) {
     node->typeinfo = nullptr;
+    node->declaration = nullptr;
 
     BLO_read_list(reader, &node->inputs);
     BLO_read_list(reader, &node->outputs);
@@ -1014,10 +1015,8 @@ IDTypeInfo IDType_ID_NT = {
 static void node_add_sockets_from_type(bNodeTree *ntree, bNode *node, bNodeType *ntype)
 {
   if (ntype->declare != nullptr) {
-    blender::nodes::NodeDeclaration node_decl;
-    blender::nodes::NodeDeclarationBuilder builder{node_decl};
-    ntype->declare(builder);
-    node_decl.build(*ntree, *node);
+    nodeDeclarationEnsure(ntree, node);
+    node->declaration->build(*ntree, *node);
     return;
   }
   bNodeSocketTemplate *sockdef;
@@ -2216,6 +2215,10 @@ bNode *BKE_node_copy_ex(bNodeTree *ntree,
   bNodeLink *link_dst, *link_src;
 
   *node_dst = *node_src;
+
+  /* Reset the declaration of the new node. */
+  node_dst->declaration = nullptr;
+
   /* can be called for nodes outside a node tree (e.g. clipboard) */
   if (ntree) {
     if (unique_name) {
@@ -3103,6 +3106,8 @@ static void node_free_node(bNodeTree *ntree, bNode *node)
     MEM_freeN(node->prop);
   }
 
+  delete node->declaration;
+
   MEM_freeN(node);
 
   if (ntree) {
@@ -3933,6 +3938,21 @@ int nodeSocketLinkLimit(const bNodeSocket *sock)
   return sock->limit;
 }
 
+/**
+ * If the node implements a `declare` function, this function makes sure that `node->declaration`
+ * is up to date.
+ */
+void nodeDeclarationEnsure(bNodeTree *UNUSED(ntree), bNode *node)
+{
+  if (node->typeinfo->declare == nullptr) {
+    return;
+  }
+
+  node->declaration = new blender::nodes::NodeDeclaration();
+  blender::nodes::NodeDeclarationBuilder builder{*node->declaration};
+  node->typeinfo->declare(builder);
+}
+
 /* ************** Node Clipboard *********** */
 
 #define USE_NODE_CB_VALIDATE
diff --git a/source/blender/makesdna/DNA_node_types.h b/source/blender/makesdna/DNA_node_types.h
index 82eabf6995c..c4cbc71762c 100644
--- a/source/blender/makesdna/DNA_node_types.h
+++ b/source/blender/makesdna/DNA_node_types.h
@@ -216,6 +216,16 @@ typedef enum eNodeSocketFlag {
   SOCK_HIDE_LABEL = (1 << 12),
 } eNodeSocketFlag;
 
+/** Workaround to forward-declare C++ type in C header. */
+#ifdef __cplusplus
+namespace blender::nodes {
+class NodeDeclaration;
+}
+using NodeDeclarationHandle = blender::nodes::NodeDeclaration;
+#else
+typedef struct NodeDeclarationHandle NodeDeclarationHandle;
+#endif
+
 /* TODO: Limit data in bNode to what we want to see saved. */
 typedef struct bNode {
   struct bNode *next, *prev, *new_node;
@@ -315,6 +325,26 @@ typedef struct bNode {
    * needs to be a float to feed GPU_uniform.
    */
   float sss_id;
+
+  /**
+   * Describes the desired interface of the node. This is run-time data only.
+   * The actual interface of the node may deviate from the declaration temporarily.
+   * It's possible to sync the actual state of the node to the desired state. Currently, this is
+   * only done when a node is created or loaded.
+   *
+   * In the future, we may want to keep more data only in the declaration, so that it does not have
+   * to be synced to other places that are stored in files. That especially applies to data that
+   * can't be edited by users directly (e.g. min/max values of sockets, tooltips, ...).
+   *
+   * The declaration of a node can be recreated at any time when it is used. Caching it here is
+   * just a bit more efficient when it is used a lot. To make sure that the cache is up-to-date,
+   * call #nodeDeclarationEnsure before using it.
+   *
+   * Currently, the declaration is the same for every node of the same type. Going forward, that is
+   * intended to change though. Especially when nodes become more dynamic with respect to how many
+   * sockets they have.
+   */
+  NodeDeclarationHandle *declaration;
 } bNode;
 
 /* node->flag */
diff --git a/source/blender/nodes/NOD_node_declaration.hh b/source/blender/nodes/NOD_node_declaration.hh
index 52f4ac291d2..7ba4ac52b86 100644
--- a/source/blender/nodes/NOD_node_declaration.hh
+++ b/source/blender/nodes/NOD_node_declaration.hh
@@ -60,6 +60,8 @@ class NodeDeclaration {
 
   Span<SocketDeclarationPtr> inputs() const;
   Span<SocketDeclarationPtr> outputs() const;
+
+  MEM_CXX_CLASS_ALLOC_FUNCS("NodeDeclaration")
 };
 
 class NodeDeclarationBuilder {
diff --git a/source/blender/nodes/intern/node_socket.cc b/source/blender/nodes/intern/node_socket.cc
index 8efd6c55459..31260f95242 100644
--- a/source/blender/nodes/intern/node_socket.cc
+++ b/source/blender/nodes/intern/node_socket.cc
@@ -269,11 +269,9 @@ void node_verify_sockets(bNodeTree *ntree, bNode *node, bool do_id_user)
     return;
   }
   if (ntype->declare != nullptr) {
-    blender::nodes::NodeDeclaration node_decl;
-    blender::nodes::NodeDeclarationBuilder builder{node_decl};
-    ntype->declare(builder);
-    if (!node_decl.matches(*node)) {
-      refresh_node(*ntree, *node, node_decl, do_id_user);
+    nodeDeclarationEnsure(ntree, node);
+    if (!node->declaration->matches(*node)) {
+      refresh_node(*ntree, *node, *node->declaration, do_id_user);
     }
     return;
   }