style-guide: Add try blocks

[ia0]

The tracking issue for try_blocks is #31436.
The tracking issue for try_blocks_heterogeneous is #149488.

I'm not sure if this should be in nightly.md instead.

See #t-lang > try blocks @ 💬 for context.

Also there doesn't seem to be any style guide about "overflowed expressions". If there were, then any decision on rust-lang/rustfmt#6799 would be relevant to document.

[rustbot]

Some changes occurred in src/doc/style-guide

cc @rust-lang/style

[rustbot]

r? @calebcartwright

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Use r? to explicitly pick a reviewer

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The reviewer was selected based on:

• Owners of files modified in this PR: style-team
• style-team expanded to calebcartwright, joshtriplett, traviscross
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[ia0]

@rustbot label +I-style-nominated

Nominating as per requested in #149488 (comment)

[joshtriplett]

This now looks right to me, and I'd be happy to see it merged, modulo that we need to figure out how to handle unstable bits (or wait for it to be stabilized with a final syntax).

[joshtriplett]

@rfcbot merge style
@rfcbot concern wait-for-final-syntax-or-handle-as-nightly

[rust-rfcbot]

Team member @joshtriplett has proposed to merge this. The next step is review by the rest of the tagged team members:

• @calebcartwright
• @joshtriplett
• @traviscross

Concerns:

• wait-for-final-syntax-or-handle-as-nightly (style-guide: Add try blocks #152311 (comment))

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

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[joshtriplett]

We should also respond to rust-lang/rustfmt#6799 .