[SR-12484] Make trailing comma behavior configurable (again)

[apple]

[SR-12484] Make trailing comma behavior configurable (again)

[swift-ci]

Comment by Jeremy Saklad (JIRA)

I think it is also important to consider the primary purpose of trailing commas: making version control diffing cleaner.

I think the default behavior should be thus:

1. Trailing commas are not used when an array or dictionary literal has one line

2. Trailing commas are always used when an array or dictionary literal spans multiple lines with one item per line

3. Array and dictionary literals that span multiple lines have one item per line

That’s just my personal opinion, of course. Each of those rules should be independently configurable.

[beccadax]

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