Meta: Add trailing-whitespace and end-of-file-fixer to pre-commit config

[lysnikolaou]

I was trying to remove all trailing whitespace from PEP 750 and noticed that we currently do not have trailing-whitespace and end-of-file-fixer in our pre-commit config. I think it makes sense to include these. From the pre-commit-hooks README:

end-of-file-fixer: Makes sure files end in a newline and only a newline.

trailing-whitespace
Trims trailing whitespace.

• To preserve Markdown hard linebreaks
  use args: [--markdown-linebreak-ext=md] (or other extensions used
  by your markdownfiles). If for some reason you want to treat all files
  as markdown, use --markdown-linebreak-ext=*.
• By default, this hook trims all whitespace from the ends of lines.
  To specify a custom set of characters to trim instead, use args: [--chars,"<chars to trim>"].

Do people have objections?

[hugovk]

Fine by me. It will affect 243 files, better to do them in one go to avoid over-spamming.

Are there any other similar rules we should add at the same time?

243 files

#       modified:  [1] .github/PULL_REQUEST_TEMPLATE/Mark a PEP Final.md
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[lysnikolaou]

I tried opening a PR this morning and 54 reviewers were added because of CODEOWNERS. Do we think that's acceptable?

[AA-Turner]

Can we exclude those files from the hook? Then only new PEPs will be affected.

[lysnikolaou]

Not sure how to do that without having to enumerate all of the files currently in the repo. If anyone has any ideas for this, I'd be happy to do it.

[hugovk]

I tried opening a PR for this this morning and 54 reviewers were added because of CODEOWNERS. Do we think that's acceptable?

For a one-off with a quick merge, I think it's okay. We get worse on mistake PRs quite regularly!

Can we exclude those files from the hook? Then only new PEPs will be affected.

The exclude is a regex: https://pre-commit.com/#pre-commit-configyaml---hooks

Exclude something like ^peps/pep-[03][0-6].* and take the hit on the 7xx series?

[lysnikolaou]

The exclude is a regex: pre-commit.com#pre-commit-configyaml---hooks

Exclude something like ^peps/pep-[03][0-6].* and take the hit on the 7xx series?

Right! This takes it down to 19 requested reviews. Should we go ahead and do that?

[AA-Turner]

Oops sorry, missed this - I opened #4078 as an illustration of what I meant but it is pretty much just replicating Hugo's point. An alternative would be to enumerate every number, which wouldn't be too painful.

[JelleZijlstra]

For a one-off with a quick merge, I think it's okay. We get worse on mistake PRs quite regularly!

A workaround we sometimes use is to keep the PR in draft until it's ready, then quickly take it out of draft and merge it. Everyone will still get a notification, but they'll see the PR is already merged and they won't have to review it.

[AA-Turner]

Now merged, and also updated check-peps to reject the headers we've removed so that we don't regress.