Other changes (discovered in test files)

[MichaReiser]

Changes to Black's formatting that seem to change but have no explicit preview feature?

• preview_percent_precedence.py
• FIXME in ignore_pyi Avoid unstable formatting in ellipsis-only body with trailing comment #8984

[dhruvmanila]

(Updated the description to link the files from the Black repository.)

[charliermarsh]

This is relevant: psf/black#3942

[MichaReiser]

This is relevant: psf/black#3942

Nice find. I assumed we implemented this correctly. I opened #8938

[MichaReiser]

preview_percent_precedence seems to be about Black removing parentheses for % operations in some case. This feels surprising because it would be the only place where black removes parentheses in sub-expressions (and what if the __mod__ operator is overloaded?).

I don't think we should implement this change to avoid potentially changing the AST.