[core][graphIO] PartialSerializer: fix List/GroupAttribute link serialization

Ensure attribute input connection is serialized, even for List/GroupAttributes.
Note: while connecting GroupAttributes is not yet supported, this will benefit
this type of attribute once it is.

meshroom/core/graphIO.py

@@ -200,9 +200,13 @@ class PartialGraphSerializer(GraphSerializer):
         Serialize `attribute` (recursively for list/groups) and deal with attributes being connected
         to nodes that are not part of the partial list of nodes to serialize.
         """
-        # If the attribute is connected to a node that is not in the list of nodes to serialize,
-        # the link expression should not be serialized.
-        if attribute.isLink and attribute.getLinkParam().node not in self.nodes:
+        linkParam = attribute.getLinkParam()
+
+        if linkParam is not None:
+            # Use standard link serialization if upstream node is part of the serialization.
+            if linkParam.node in self.nodes:
+                return attribute.getExportValue()
+            # Skip link serialization otherwise.
             # If part of a list, this entry can be discarded.
             if isinstance(attribute.root, ListAttribute):
                 return None

tests/test_graphIO.py

@@ -243,6 +243,20 @@ class TestGraphPartialSerialization:
             assert compareGraphsContent(graph, graphA)
             assert compareGraphsContent(graphA, graphB)
 
+    def test_listAttributeToListAttributeConnectionIsSerialized(self):
+        graph = Graph("")
+
+        with registeredNodeTypes([NodeWithListAttributes]):
+            nodeA = graph.addNewNode(NodeWithListAttributes.__name__)
+            nodeB = graph.addNewNode(NodeWithListAttributes.__name__)
+
+            graph.addEdge(nodeA.listInput, nodeB.listInput)
+
+            otherGraph = Graph("")
+            otherGraph._deserialize(graph.serializePartial([nodeA, nodeB]))
+
+            assert otherGraph.node(nodeB.name).listInput.linkParam == otherGraph.node(nodeA.name).listInput
+
     def test_singleNodeWithInputConnectionFromNonSerializedNodeRemovesEdge(self):
         graph = Graph("")