Qwen2-VL: fix rope delta calculation (#36013)

* fix rope delats calculation

* add test

* style

tests/models/qwen2_vl/test_modeling_qwen2_vl.py

@@ -284,6 +284,29 @@ class Qwen2VLModelTest(ModelTesterMixin, GenerationTesterMixin, unittest.TestCas
             image_grid_thw = torch.cat([image_grid_thw, image_grid_thw], dim=0)
             _ = model(input_ids=input_ids, pixel_values=pixel_values, image_grid_thw=image_grid_thw)
 
+    def test_forward_with_rope_deltas_cached(self):
+        """
+        Tests that Qwen2-VL computes new rope deltas every forward pass with new set of inputs.
+        Rope deltas are cached when we generate and re-used for decoding phase, byt are not reset
+        automatically after generation ends. See https://github.com/huggingface/transformers/pull/36013 for more
+        """
+        config, input_dict = self.model_tester.prepare_config_and_inputs_for_common()
+        for model_class in self.all_generative_model_classes:
+            model = model_class(config).to(torch_device)
+
+            # Generate and make sure rope_deltas are not `None`
+            self.assertTrue(model.rope_deltas is None)
+            generation_output = model.generate(
+                **input_dict, max_new_tokens=4, return_dict_in_generate=True, output_logits=True
+            )
+            self.assertTrue(model.rope_deltas is not None)
+
+            # Now if we try to do forward pass, we should get new rope logits, because cache is not passed
+            forward_output = model(**input_dict)
+            torch.testing.assert_close(
+                generation_output.logits[0], forward_output.logits[:, -1, :], rtol=1e-4, atol=1e-4
+            )
+
     @unittest.skip(reason="Feedforward chunking is not yet supported")
     def test_feed_forward_chunking(self):
         pass