Fix clang-format version

[ezyang]

vision is clang-formatted via the default clang-format that is apt installed in CI. This is not friendly for users who are not using the exact distro in CI. We should fix a specific clang-format version and let people download clang format binaries on whatever platform they on.

This is implemented in pytorch/pytorch in tools/clang_format_all.py and related scripts. CC @suo @SplitInfinity

[datumbox]

Thanks for reporting this @ezyang. I stumbled upon this problem myself and I agree that we need to fix it. :)

First a summary of the situation:

• PyTorch: As Edward pointed out, we use the clang_format_all.py script to check the formatting. The script is responsible for downloading the right version of clang-format based on the OS, verifies its signature and stores it locally. Then it runs the formatter on a list of permitted directories (which unfortunately are hardcoded) and returns success/failure.
• TorchVision: Here we use the run-clang-format.py to check the formatting. Unlike on PyTorch, the formatter is installed via apt on cicleci's config file.

So it looks like we have a few options:

1. Copy PyTorch's scripts here and slightly adjust them to point to the right allowlisted directory.
2. Adjust slightly TorchVision's cicleci config file to download the clang-format binary that PyTorch uses.
3. Move the formatter scripts from PyTorch to a utils project, make scripts generic and available to all projects.

It would be great to eventually do the 3rd option but perhaps it's more realistic to fix this quickly by doing 1 or 2. Thoughts?

[SplitInfinity]

clang_format_all.py was introduced when there was semi-automatic formatting internally at Facebook as part of pre-commit hooks. Shortly after, Facebook began automatically formatting code internally (in allowlisted directories) every day with an automated job that runs clang-format and commits the result. Does torchvision use the same development model as pytorch (i.e. source of truth is inside Facebook and GitHub is more of a mirror). If so, perhaps we don't need to support clang-format externally at all?

[datumbox]

@SplitInfinity Currently for TorchVision it's the opposite. GitHub is the source of truth.

[fmassa]

To complement @datumbox point, torchvision now is in a mixed state where most of the development happens in GitHub, but we do have an internal sync via ShipIt but on a separate branch than master (named fbsync).
This means that for now we are both out of sync (commits added on both sides), and we might as well have lint differences due to the automatic formatting within FB.

[fmassa]

Fixed in #2872