From dd47ee9e25e2faff2582ea4cb1cd11efec33e2ac Mon Sep 17 00:00:00 2001
From: Jacques Lucke <jacques@blender.org>
Date: Mon, 12 May 2025 16:13:57 +0200
Subject: [PATCH] Nodes: show warning when a group output is unused

There are very rare use-cases for having multiple Group Output nodes. However,
it's something that's been supported for a long time and removing it may be a
regression for some. In practice, it's usually a mistake when someone has
multiple Group Output nodes.

This patch adds a simple warning on inactive Group Output nodes to help the user
notice this case.

Pull Request: https://projects.blender.org/blender/blender/pulls/138743
---
 .../blender/editors/space_node/node_draw.cc   |  2 +-
 source/blender/nodes/NOD_node_extra_info.hh   |  1 +
 source/blender/nodes/intern/node_common.cc    | 22 +++++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/source/blender/editors/space_node/node_draw.cc b/source/blender/editors/space_node/node_draw.cc
index cc3f3336221..32179ae04b8 100644
--- a/source/blender/editors/space_node/node_draw.cc
+++ b/source/blender/editors/space_node/node_draw.cc
@@ -3070,7 +3070,7 @@ static Vector<NodeExtraInfoRow> node_get_extra_info(const bContext &C,
   Vector<NodeExtraInfoRow> rows;
 
   if (node.typeinfo->get_extra_info) {
-    nodes::NodeExtraInfoParams params{rows, node, C};
+    nodes::NodeExtraInfoParams params{rows, *snode.edittree, node, C};
     node.typeinfo->get_extra_info(params);
   }
 
diff --git a/source/blender/nodes/NOD_node_extra_info.hh b/source/blender/nodes/NOD_node_extra_info.hh
index 10c777bd350..69c4c7ee58d 100644
--- a/source/blender/nodes/NOD_node_extra_info.hh
+++ b/source/blender/nodes/NOD_node_extra_info.hh
@@ -22,6 +22,7 @@ struct NodeExtraInfoRow {
 
 struct NodeExtraInfoParams {
   Vector<NodeExtraInfoRow> &rows;
+  const bNodeTree &tree;
   const bNode &node;
   const bContext &C;
 };
diff --git a/source/blender/nodes/intern/node_common.cc b/source/blender/nodes/intern/node_common.cc
index b0f16b81707..4f17eb656b1 100644
--- a/source/blender/nodes/intern/node_common.cc
+++ b/source/blender/nodes/intern/node_common.cc
@@ -33,10 +33,14 @@
 
 #include "NOD_common.hh"
 #include "NOD_node_declaration.hh"
+#include "NOD_node_extra_info.hh"
 #include "NOD_register.hh"
 #include "NOD_socket.hh"
 #include "NOD_socket_declarations.hh"
 #include "NOD_socket_declarations_geometry.hh"
+
+#include "UI_resources.hh"
+
 #include "node_common.h"
 #include "node_util.hh"
 
@@ -875,6 +879,23 @@ bNodeSocket *node_group_output_find_socket(bNode *node, const StringRef identifi
   return nullptr;
 }
 
+static void node_group_output_extra_info(blender::nodes::NodeExtraInfoParams &params)
+{
+  const blender::Span<const bNode *> group_output_nodes = params.tree.nodes_by_type(
+      "NodeGroupOutput");
+  if (group_output_nodes.size() <= 1) {
+    return;
+  }
+  if (params.node.flag & NODE_DO_OUTPUT) {
+    return;
+  }
+  blender::nodes::NodeExtraInfoRow row;
+  row.text = IFACE_("Unused Output");
+  row.icon = ICON_ERROR;
+  row.tooltip = TIP_("There are multiple group output nodes and this one is not active");
+  params.rows.append(std::move(row));
+}
+
 void register_node_type_group_output()
 {
   /* used for all tree types, needs dynamic allocation */
@@ -889,6 +910,7 @@ void register_node_type_group_output()
   blender::bke::node_type_size(*ntype, 140, 80, 400);
   ntype->declare = blender::nodes::group_output_declare;
   ntype->insert_link = blender::nodes::group_output_insert_link;
+  ntype->get_extra_info = node_group_output_extra_info;
 
   ntype->no_muting = true;