[Deprecation] Softly deprecate extra-tensors wrt out_keys

ghstack-source-id: aea9814fecbab903ad22ae54903a2921f4b88c5b
Pull Request resolved: #1215

tensordict/nn/common.py

@@ -1055,7 +1055,21 @@ def _write_to_tensordict(
                     tensordict_out = TensorDict()
             else:
                 tensordict_out = tensordict
-        for _out_key, _tensor in _zip_strict(out_keys, tensors):
+        if len(tensors) > len(out_keys):
+            incipit = "There are more tensors than out_keys. "
+        elif len(out_keys) > len(tensors):
+            incipit = "There are more out_keys than tensors. "
+        else:
+            incipit = None
+        if incipit is not None:
+            warnings.warn(
+                incipit + "This is currently "
+                "allowed but it will be deprecated in v0.9. To silence this warning, "
+                "make sure the number of out_keys matches the number of outputs of the "
+                "network.",
+                category=DeprecationWarning,
+            )
+        for _out_key, _tensor in zip(out_keys, tensors):
             if _out_key != "_":
                 tensordict_out.set(_out_key, TensorDict.from_any(_tensor))
         return tensordict_out