style-guide: Document style editions, start 2024 style edition

[joshtriplett]

Link to a snapshot for the 2015/2018/2021 style edition.

This is a draft, because I'd like to wait for a few style guide fixes to merge
before snapshotting the 2015/2018/2021 style edition:

• style-guide: Document newline rules for assignment operators #113145
• style-guide: clean up "must"/"should"/"may" #113380
• style-guide: Clarify grammar for small patterns (not a semantic change) #113384
• style-guide: Fix chain example to match rustfmt behavior #113385
• style-guide: Expand example of combinable expressions to include arrays #113386
• style-guide: Some cleanups from the fmt-rfcs repo history #113392

I'd like to wait for these for two reasons: to make it easier to see the
differences between the 2015/2018/2021 style edition and the 2024 style
edition (without the noise of guide-wide changes), and to minimize confusion so
that bugfixes to the style guide that we include in the previous edition don't
look like they're only part of the 2024 style edition.

I've used "Miscellaneous rustfmt bugfixes" as a starting point for the list
of 2024 changes, for now. We can update that when we add more 2024 changes.

The section added in this PR can then serve as a baseline for our drafts of
2024 style edition changes.

In the meantime, I'd like to get someone from @rust-lang/style to review and
approve the text here; I'll update it with a commit hash when the above PRs
have merged.

[rustbot]

r? @yaahc

(rustbot has picked a reviewer for you, use r? to override)

[bors]

☔ The latest upstream changes (presumably #113391) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

Some changes occurred in src/doc/style-guide

cc @rust-lang/style

[joshtriplett]

OK, this is ready to merge once reviewed.

[calebcartwright]

OK, this is ready to merge once reviewed.

I thought we might have one outstanding activity to grab a couple of commits from the old repo that didn't get pulled over? If so then I definitely want to make sure we get those captured before we snapshot anything

[joshtriplett]

@calebcartwright #113392 captures all the ones I felt confident in my ability to capture accurately.

[calebcartwright]

Might be worth linking to general edition docs and the style evolution RFC, but this lgtm as is anyway.

r=me whenever/so long as #114154 gets incorporated into the 2015-2021 archived version

[joshtriplett]

I've added a link to the edition guide.

I was trying to document style editions in a self-contained way within the style guide, rather than linking out to the style edition RFC, since the RFC doesn't seem like it'd be as good at being end-user documentation. But I'm happy to expand it further, if you think there's something missing. I'd like to get the snapshot done first, though.

@bors r=calebcartwright rollup

[bors]

📌 Commit 6a0886c has been approved by calebcartwright

It is now in the queue for this repository.