Fix Torchscript typing in transformer_encoder.py

[zhxchen17]

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Fixes # (issue).

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[zhxchen17]

@alexeib

I think this should fix the Torchscript compilation error introduced in https://github.com/facebookresearch/fairseq/pull/4818

meanwhile is there recommended test to run in addition to the CI tests?

[alexeib]

some tests are still failing

[zhxchen17]

some tests are still failing

@alexeib ok after some investigation, seems these build failures are introduced by PyTorch 1.13.0 version release. (which is on Oct 28)

After I install pytorch version 1.12.1 locally and rerun the tests by pytest, seems the errors from tests/test_binaries.py::TestTranslation::test_transformer_pointer_generator and tests/test_multihead_attention.py::test_xformers_single_forward_parity are gone.

failures under tests/test_plasma_utils.py::TestPlasmaView seems irrelevant:

OSError: Could not connect to socket /tmp/tmphatl4hub

I guess we could proceed with this PR and fix other issues separately?

[alexeib]

thanks for investigating @zhxchen17 . Shall we open another issue for the pytorch test breakage and reference it here?

[zhxchen17]

thanks for investigating @zhxchen17 . Shall we open another issue for the pytorch test breakage and reference it here?

sure lemme open an issue.