Encoder-Decoder: add informative exception when the decoder is not compatible (#23426)

src/transformers/models/encoder_decoder/modeling_encoder_decoder.py

@@ -16,6 +16,7 @@
 
 
 import gc
+import inspect
 import os
 import tempfile
 import warnings
@@ -245,6 +246,13 @@ class EncoderDecoderModel(PreTrainedModel):
                 f"The encoder {self.encoder} should not have a LM Head. Please use a model without LM Head"
             )
 
+        decoder_signature = set(inspect.signature(self.decoder.forward).parameters.keys())
+        if "encoder_hidden_states" not in decoder_signature:
+            raise ValueError(
+                "The selected decoder is not prepared for the encoder hidden states to be passed. Please see the "
+                "following discussion on GitHub: https://github.com/huggingface/transformers/issues/23350"
+            )
+
         # tie encoder, decoder weights if config set accordingly
         self.tie_weights()
 

src/transformers/models/encoder_decoder/modeling_tf_encoder_decoder.py

@@ -14,7 +14,7 @@
 # limitations under the License.
 """ Classes to support TF Encoder-Decoder architectures"""
 
-
+import inspect
 import re
 import warnings
 from typing import Optional, Tuple, Union
@@ -266,6 +266,13 @@ class TFEncoderDecoderModel(TFPreTrainedModel, TFCausalLanguageModelingLoss):
                 f"The encoder {self.encoder} should not have a LM Head. Please use a model without LM Head"
             )
 
+        decoder_signature = set(inspect.signature(self.decoder.call).parameters.keys())
+        if "encoder_hidden_states" not in decoder_signature:
+            raise ValueError(
+                "The selected decoder is not prepared for the encoder hidden states to be passed. Please see the "
+                "following discussion on GitHub: https://github.com/huggingface/transformers/issues/23350"
+            )
+
     @property
     def dummy_inputs(self):
         """