src/transformers/models/mbart/configuration_mbart.py/MBartOnnxConfig/inputs
class MBartOnnxConfig:    def inputs(self) -> Mapping[str, Mapping[int, str]]:
        if self.task in ["default", "seq2seq-lm"]:
            common_inputs = OrderedDict(
                [
                    ("input_ids", {0: "batch", 1: "encoder_sequence"}),
                    ("attention_mask", {0: "batch", 1: "encoder_sequence"}),
                ]
            )

            if self.use_past:
                common_inputs["decoder_input_ids"] = {0: "batch"}
                common_inputs["decoder_attention_mask"] = {0: "batch", 1: "past_decoder_sequence + sequence"}
            else:
                common_inputs["decoder_input_ids"] = {0: "batch", 1: "decoder_sequence"}
                common_inputs["decoder_attention_mask"] = {0: "batch", 1: "decoder_sequence"}

            if self.use_past:
                self.fill_with_past_key_values_(common_inputs, direction="inputs")
        elif self.task == "causal-lm":
            # TODO: figure this case out.
            common_inputs = OrderedDict(
                [
                    ("input_ids", {0: "batch", 1: "encoder_sequence"}),
                    ("attention_mask", {0: "batch", 1: "encoder_sequence"}),
                ]
            )
            if self.use_past:
                num_encoder_layers, _ = self.num_layers
                for i in range(num_encoder_layers):
                    common_inputs[f"past_key_values.{i}.key"] = {0: "batch", 2: "past_sequence + sequence"}
                    common_inputs[f"past_key_values.{i}.value"] = {0: "batch", 2: "past_sequence + sequence"}
        else:
            common_inputs = OrderedDict(
                [
                    ("input_ids", {0: "batch", 1: "encoder_sequence"}),
                    ("attention_mask", {0: "batch", 1: "encoder_sequence"}),
                    ("decoder_input_ids", {0: "batch", 1: "decoder_sequence"}),
                    ("decoder_attention_mask", {0: "batch", 1: "decoder_sequence"}),
                ]
            )

        return common_inputs