Fix #33628, Segmentation fault after pasting a closed group of nodes into an open group. Finally now there is a proper check for pasting nodes into groups. It uses the poll_instance callback of node types to determine if a node can be added into a specific node tree. Currently this is only implemented for group nodes and does a recursive check to avoid pasting a node group into itself (on any level, also nested groups).

source/blender/editors/space_node/node_edit.c

@@ -1978,7 +1978,7 @@ static int node_clipboard_paste_exec(bContext *C, wmOperator *op)
 	bNodeLink *link;
 	int num_nodes;
 	float center[2];
-	int is_clipboard_valid;
+	int is_clipboard_valid, all_nodes_valid;
 
 	/* validate pointers in the clipboard */
 	is_clipboard_valid = BKE_node_clipboard_validate();
@@ -2000,6 +2000,17 @@ static int node_clipboard_paste_exec(bContext *C, wmOperator *op)
 		BKE_report(op->reports, RPT_WARNING, "Some nodes references could not be restored, will be left empty");
 	}
 
+	/* make sure all clipboard nodes would be valid in the target tree */
+	all_nodes_valid = TRUE;
+	for (node = clipboard_nodes_lb->first; node; node = node->next) {
+		if (!node->typeinfo->poll_instance(node, ntree)) {
+			all_nodes_valid = FALSE;
+			BKE_reportf(op->reports, RPT_ERROR, "Cannot add node %s into node tree %s", node->name, ntree->id.name+2);
+		}
+	}
+	if (!all_nodes_valid)
+		return OPERATOR_CANCELLED;
+
 	ED_preview_kill_jobs(C);
 
 	/* deselect old nodes */

source/blender/nodes/composite/nodes/node_composite_common.c

@@ -51,6 +51,7 @@ void register_node_type_cmp_group(void)
 	node_type_base_custom(&ntype, "CompositorNodeGroup", "Group", NODE_CLASS_GROUP, NODE_OPTIONS | NODE_CONST_OUTPUT);
 	ntype.type = NODE_GROUP;
 	ntype.poll = cmp_node_poll_default;
+	ntype.poll_instance = node_group_poll_instance;
 	ntype.update_internal_links = node_update_internal_links_default;
 	ntype.ext.srna = RNA_struct_find("CompositorNodeGroup");
 	BLI_assert(ntype.ext.srna != NULL);

source/blender/nodes/intern/node_common.c

@@ -89,11 +89,15 @@ const char *node_group_label(bNode *node)
 
 int node_group_poll_instance(bNode *node, bNodeTree *nodetree)
 {
-	bNodeTree *grouptree = (bNodeTree*)node->id;
-	if (grouptree)
-		return nodeGroupPoll(nodetree, grouptree);
+	if (node->typeinfo->poll(node->typeinfo, nodetree)) {
+		bNodeTree *grouptree = (bNodeTree*)node->id;
+		if (grouptree)
+			return nodeGroupPoll(nodetree, grouptree);
+		else
+			return TRUE;	/* without a linked node tree, group node is always ok */
+	}
 	else
-		return 1;
+		return FALSE;
 }
 
 int nodeGroupPoll(bNodeTree *nodetree, bNodeTree *grouptree)

source/blender/nodes/shader/nodes/node_shader_common.c

@@ -231,6 +231,7 @@ void register_node_type_sh_group(void)
 	node_type_base_custom(&ntype, "ShaderNodeGroup", "Group", NODE_CLASS_GROUP, NODE_OPTIONS | NODE_CONST_OUTPUT);
 	ntype.type = NODE_GROUP;
 	ntype.poll = sh_node_poll_default;
+	ntype.poll_instance = node_group_poll_instance;
 	ntype.update_internal_links = node_update_internal_links_default;
 	ntype.ext.srna = RNA_struct_find("ShaderNodeGroup");
 	BLI_assert(ntype.ext.srna != NULL);

source/blender/nodes/texture/nodes/node_texture_common.c

@@ -159,6 +159,7 @@ void register_node_type_tex_group(void)
 	node_type_base_custom(&ntype, "TextureNodeGroup", "Group", NODE_CLASS_GROUP, NODE_OPTIONS | NODE_CONST_OUTPUT);
 	ntype.type = NODE_GROUP;
 	ntype.poll = tex_node_poll_default;
+	ntype.poll_instance = node_group_poll_instance;
 	ntype.update_internal_links = node_update_internal_links_default;
 	ntype.ext.srna = RNA_struct_find("TextureNodeGroup");
 	BLI_assert(ntype.ext.srna != NULL);