Allow leading | anywhere we allow or-patterns

[joshtriplett]

See #54883 (comment) for details.

Filing this issue to check lang-team consensus on this: do we want to allow leading | everywhere we allow or-patterns?

[joshtriplett]

@rfcbot merge

[rfcbot]

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

• @cramertj
• @joshtriplett
• @nikomatsakis
• @pnkfelix
• @scottmcm
• @withoutboats

No concerns currently listed.

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!

See this document for info about what commands tagged team members can give me.

[scottmcm]

Somehow to me they feel a little weirder in something like matches!(foo, | Bar(_) | Baz(_)), but regardless I think allowing them is the right thing to do for consistency and the overall grammar.

[joshtriplett]

@scottmcm In that use case, they'd likely look like this:

    matches!(
        some_long_expression,
        | SomeLongPattern
        | SomeOtherLongPattern
    )

[nikomatsakis]

@rfcbot reviewed

[joshtriplett]

Checking box for boats per rust-lang/team#526 .

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔