Allow text generation for ProphetNetForCausalLM (huggingface#9707)

* Moved ProphetNetForCausalLM's parent initialization after config update

* Added unit tests for generation for ProphetNetForCausalLM

src/transformers/models/prophetnet/modeling_prophetnet.py

@@ -1883,11 +1883,11 @@ def get_decoder(self):
 )
 class ProphetNetForCausalLM(ProphetNetPreTrainedModel):
     def __init__(self, config):
-        super().__init__(config)
         # set config for CLM
         config = copy.deepcopy(config)
         config.is_decoder = True
         config.is_encoder_decoder = False
+        super().__init__(config)
         self.prophetnet = ProphetNetDecoderWrapper(config)
 
         self.padding_idx = config.pad_token_id

tests/test_modeling_prophetnet.py

@@ -302,6 +302,24 @@ def create_and_check_generate_with_past_key_value_states(
         output_with_past_cache = model.generate(input_ids[:1], num_beams=2, max_length=5, do_sample=True)
         self.parent.assertTrue(torch.all(output_with_past_cache == output_without_past_cache))
 
+    def create_and_check_decoder_generate_with_past_key_value_states(
+        self,
+        config,
+        input_ids,
+        decoder_input_ids,
+        attention_mask,
+        decoder_attention_mask,
+        lm_labels,
+    ):
+        model = ProphetNetForCausalLM(config=config).to(torch_device).eval()
+        torch.manual_seed(0)
+        output_without_past_cache = model.generate(
+            input_ids[:1], num_beams=2, max_length=10, do_sample=True, use_cache=False
+        )
+        torch.manual_seed(0)
+        output_with_past_cache = model.generate(input_ids[:1], num_beams=2, max_length=10, do_sample=True)
+        self.parent.assertTrue(torch.all(output_with_past_cache == output_without_past_cache))
+
     def create_and_check_model_fp16_forward(
         self,
         config,
@@ -911,6 +929,10 @@ def test_decoder_model_generate(self):
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_generate_with_past_key_value_states(*config_and_inputs)
 
+    def test_encoder_decoder_model_generate(self):
+        config_and_inputs = self.model_tester.prepare_config_and_inputs()
+        self.model_tester.create_and_check_decoder_generate_with_past_key_value_states(*config_and_inputs)
+
     def test_attn_mask_model(self):
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.check_model_with_attn_mask(*config_and_inputs)