[Twisted-Python] Black enabled in trunk

[Glyph]

> On Sep 13, 2020, at 11:45 PM, Tom Most <twm at freecog.net> wrote:
> 
> Hi all,
> 
> Craig and I have been working to land a switch to The Black Coding Style <https://black.readthedocs.io/en/stable/the_black_code_style.html>. It's in! The tree has been reformatted <https://github.com/twisted/twisted/commit/bc96c774be6e307e8e3e4d39780d37b045d0973a>. Some notable changes:

Happy to hear we're making progress on this!  I'm the tiniest bit grumpy that this went forward without having the follow-up work already landed or ready-to-land simultaneously — my experience suggests that the fact that this is now complete means that neither you nor Craig will ever contribute to Twisted, or in fact ever answer your email, ever again — but if we can get it all landed promptly I will be over the moon :-).

> * 3-2-1 blank lines are replaced by PEP 8 style 2-1-1.
> * String syntax uses "double quotes".
> 
> Run this command to exclude the formatting from git blame <https://github.com/twisted/twisted/blob/trunk/.git-blame-ignore-revs>:
> 
>     git config blame.ignoreRevsFile .git-blame-ignore-revs
> 
> There are two new Tox testenvs. To check style:
> 
>     tox -e black
> 
> To adjust the formatting:
> 
>     tox -e black-reformat
> 
> The formatting is checked by a new GitHub Actions lint built.

Could we possibly use something like this:

https://github.com/cclauss/autoblack <https://github.com/cclauss/autoblack>

to just do the formatting rather than "check" if it's correct?  PR templates are all well and good but the best checklist item is the one that's already checked off...

> There is some follow-up work planned:
> 
> * Many PRs have conflicts (more on this below).
> * Various wiki pages need updates. I've done a few, but there are probably more.
> * The coding standard should be updated <https://twistedmatrix.com/trac/ticket/9957#ticket>.
> * The PR template needs an update <https://twistedmatrix.com/trac/ticket/9956#ticket>.
> * A few examples need reformatting <https://tm.tl/#9952> (they weren't formatted because they fail to lint).
> 
> Inevitably, changes like this cause conflicts. For small PRs it's easiest to merge forward and then run tox -e black-reformat. For larger ones it can help to apply formatting before merge. To do this:
> 
> * Run black on the files your branch changes (be sure to use Black 20.8b1, not an older version)
> * Commit the result, like `git commit -am "Fade to black"`
> * Add that commit to .git-blame-ignore-revs to avoid polluting git blame.
> * Merge forward. You can ignore formatting while performing the merge.
> * Then run `tox -e black-reformat` to ensure you are in sync. Commit any changes it generates.

Can we please get this bulleted list in the form of a tool that people can run against a PR, so we don't need everyone to write their own bespoke shell script for fixing up their Twisted PRs?  This is the thing I'm the most worried about - I'd like to have it done automatically because I'm seriously worried about work in progress getting abandoned because somebody backs themselves into a corner with an apparently intractable mega-conflict by not knowing how to properly use Git to apply this sort of modification.

-g
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