def convert_bart_checkpoint(checkpoint_path, pytorch_dump_folder_path, hf_checkpoint_name=None):
    """
    Copy/paste/tweak model's weights to our BERT structure.
    """
    if not os.path.exists(checkpoint_path):
        bart = torch.hub.load("pytorch/fairseq", checkpoint_path).eval()
    else:
        bart = load_xsum_checkpoint(checkpoint_path)

    bart.model.upgrade_state_dict(bart.model.state_dict())
    if hf_checkpoint_name is None:
        hf_checkpoint_name = checkpoint_path.replace(".", "-")
    config = BartConfig.from_pretrained(hf_checkpoint_name)
    tokens = bart.encode(SAMPLE_TEXT).unsqueeze(0)
    tokens2 = BartTokenizer.from_pretrained(hf_checkpoint_name).encode(SAMPLE_TEXT, return_tensors="pt").unsqueeze(0)
    if not torch.eq(tokens, tokens2).all():
        raise ValueError(
            f"converted tokenizer and pretrained tokenizer returned different output: {tokens} != {tokens2}"
        )

    if checkpoint_path == "bart.large.mnli":
        state_dict = bart.state_dict()
        remove_ignore_keys_(state_dict)
        state_dict["model.shared.weight"] = state_dict["model.decoder.embed_tokens.weight"]
        for src, dest in mnli_rename_keys:
            rename_key(state_dict, src, dest)
        model = BartForSequenceClassification(config).eval()
        model.load_state_dict(state_dict)
        fairseq_output = bart.predict("mnli", tokens, return_logits=True)
        new_model_outputs = model(tokens)[0]  # logits
    else:  # no classification heads to worry about
        state_dict = bart.model.state_dict()
        remove_ignore_keys_(state_dict)
        state_dict["shared.weight"] = state_dict["decoder.embed_tokens.weight"]
        fairseq_output = bart.extract_features(tokens)
        if hf_checkpoint_name == "facebook/bart-large":
            model = BartModel(config).eval()
            model.load_state_dict(state_dict)
            new_model_outputs = model(tokens).model[0]
        else:
            model = BartForConditionalGeneration(config).eval()  # an existing summarization ckpt
            model.model.load_state_dict(state_dict)
            if hasattr(model, "lm_head"):
                model.lm_head = make_linear_from_emb(model.model.shared)
            new_model_outputs = model.model(tokens)[0]

    # Check results
    if fairseq_output.shape != new_model_outputs.shape:
        raise ValueError(
            f"`fairseq_output` shape and `new_model_output` shape are different: {fairseq_output.shape=}, {new_model_outputs.shape}"
        )
    if (fairseq_output != new_model_outputs).any().item():
        raise ValueError("Some values in `fairseq_output` are different from `new_model_outputs`")
    Path(pytorch_dump_folder_path).mkdir(exist_ok=True)
    model.save_pretrained(pytorch_dump_folder_path)

    Copy/paste/tweak model's weights to our BERT structure.
    
dpkd/transformers/src/transformers/models/bart/convert_bart_original_pytorch_checkpoint_to_pytorch.py