Fix T88807: crash when there are multiple links between the same sockets

This commit does two things:

* Disallows creating more than one link from one socket to a multi socket input.
* Properly count links if there happen to be more than one link between the same sockets.

The new link counting should also be more efficient asymptotically.

Differential Revision: https://developer.blender.org/D11570

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_nodetree.c b/source/blender/makesrna/intern/rna_nodetree.c
index b625f0fc204..2a1ea3d6716 100644
--- a/source/blender/makesrna/intern/rna_nodetree.c
+++ b/source/blender/makesrna/intern/rna_nodetree.c
@@ -1283,6 +1283,13 @@ static bNodeLink *rna_NodeTree_link_new(bNodeTree *ntree,
     if (nodeCountSocketLinks(ntree, tosock) + 1 > nodeSocketLinkLimit(tosock)) {
       nodeRemSocketLinks(ntree, tosock);
     }
+    if (tosock->flag & SOCK_MULTI_INPUT) {
+      LISTBASE_FOREACH_MUTABLE (bNodeLink *, link, &ntree->links) {
+        if (link->fromsock == fromsock && link->tosock == tosock) {
+          nodeRemLink(ntree, link);
+        }
+      }
+    }
   }
 
   ret = nodeAddLink(ntree, fromnode, fromsock, tonode, tosock);