From a6b83617e9de01c3a4719770f88fc0ad2933e55a Mon Sep 17 00:00:00 2001
From: Iliya Katueshenock <Moder>
Date: Mon, 17 Oct 2022 12:00:09 +0200
Subject: Fix T101705: crash when connecting reroute to multi-input socket

Differential Revision: https://developer.blender.org/D16203
---
 source/blender/blenkernel/BKE_node.h     |  6 ++++++
 source/blender/blenkernel/intern/node.cc | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

(limited to 'source/blender/blenkernel')

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index b1b4045370c..ecf7a556459 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -792,6 +792,12 @@ void nodeChainIterBackwards(const bNodeTree *ntree,
  */
 void nodeParentsIter(bNode *node, bool (*callback)(bNode *, void *), void *userdata);
 
+/**
+ * A dangling reroute node is a reroute node that does *not* have a "data source", i.e. no
+ * non-reroute node is connected to its input.
+ */
+bool nodeIsDanglingReroute(const struct bNodeTree *ntree, const struct bNode *node);
+
 struct bNodeLink *nodeFindLink(struct bNodeTree *ntree,
                                const struct bNodeSocket *from,
                                const struct bNodeSocket *to);
diff --git a/source/blender/blenkernel/intern/node.cc b/source/blender/blenkernel/intern/node.cc
index 654eb06a781..8028f990c42 100644
--- a/source/blender/blenkernel/intern/node.cc
+++ b/source/blender/blenkernel/intern/node.cc
@@ -2157,6 +2157,38 @@ void nodeParentsIter(bNode *node, bool (*callback)(bNode *, void *), void *userd
   }
 }
 
+bool nodeIsDanglingReroute(const bNodeTree *ntree, const bNode *node)
+{
+  ntree->ensure_topology_cache();
+  BLI_assert(blender::bke::node_tree_runtime::topology_cache_is_available(*ntree));
+  BLI_assert(!ntree->has_available_link_cycle());
+
+  const bNode *iter_node = node;
+  if (!iter_node->is_reroute()) {
+    return false;
+  }
+
+  while (true) {
+    const blender::Span<const bNodeLink *> links =
+        iter_node->input_socket(0).directly_linked_links();
+    BLI_assert(links.size() <= 1);
+    if (links.is_empty()) {
+      return true;
+    }
+    const bNodeLink &link = *links[0];
+    if (!link.is_available()) {
+      return false;
+    }
+    if (link.is_muted()) {
+      return false;
+    }
+    iter_node = link.fromnode;
+    if (!iter_node->is_reroute()) {
+      return false;
+    }
+  }
+}
+
 /* ************** Add stuff ********** */
 
 void nodeUniqueName(bNodeTree *ntree, bNode *node)
-- 
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