fix __asdf_traverse__ for non-tagged object

asdf/_node_info.py

@@ -282,7 +282,8 @@ def from_root_node(cls, key, root_identifier, root_node, schema=None, refresh_ex
 
                     if cls.traversable(node):
                         t_node = node.__asdf_traverse__()
-                        info.set_schema_from_node(node, extension_manager)
+                        if hasattr(node, "_tag"):
+                            info.set_schema_from_node(node, extension_manager)
 
                     else:
                         t_node = node

asdf/_tests/_regtests/test_1738.py

@@ -0,0 +1,28 @@
+import asdf
+
+
+def test_info_on_non_tagged_asdf_traverse_object():
+    """
+    Calling info with a tree containing an object that implements
+    __asdf_traverse__ but does not have a _tag results in an
+    error
+
+    https://github.com/asdf-format/asdf/issues/1738
+    """
+
+    class MyContainer:
+        def __init__(self, data):
+            self.data = data
+
+        def __asdf_traverse__(self):
+            return self.data
+
+    c = MyContainer([1, 2, 3])
+    af = asdf.AsdfFile()
+    af["c"] = c
+
+    # info should not error out
+    af.info()
+
+    # and search should work with the container
+    assert af.search(type_=int).paths == ["root['c'][0]", "root['c'][1]", "root['c'][2]"]