Fix brace_style="PreferSameLine" with trailing_comma="Vertical" results

[hirasawayuki]

Fixes #2321

• Fixed trailing comma did not disappear when configured brace_style="PreferSameLine" and trailing_comma="Vertical".
• Fixed test case.

Example

When brace_style="PreferSameLine" and trailing_comma="Vertical" configured, the results would be as in the following example:

before

fn lorem<S, T>(lorem: S, ipsum: T)
where
    S: Add + Sub,
    T: Mul + Div, { // ← trailing comma is not removed from the bound
    // body
}

after

fn lorem<S, T>(lorem: S, ipsum: T)
where
    S: Add + Sub,
    T: Mul + Div {
    // body
}

[ytmimi]

Thanks for your first contribution to rustfmt 🎉

I try and get around to reviewing this in the coming days!

[ytmimi]

Typically changing existing tests is not something we want to do and is usually a sign that the change needs to be version gated to prevent breaking formatting changes. However brace_style is an unstable option so the version gate might not be necessary in this case

[hirasawayuki]

I'll do it if I have to! 👍

[ytmimi]

Can we also include a where clause with with a single bound. I like that you've included tests with trailing_comma: Always and trailing_comma: Vertical. Could you also expand the tests to include the other combinations of brace_style

[hirasawayuki]

Thank you for the review. I added test case for brace_style AlwaysNextLine and SameLineWhere pattern.

[ytmimi]

Thank you for including those additional test cases! I'll have some time later this week to give this a more thorough review 😁

[ytmimi]

Looking at this output, I'd actually expect there to be a trailing comma after T: Mul + Div, since the where clause bounds were formatted vertically.

[ytmimi]

Maybe I don't understand the brace_style config fully, but with an option like SameLineWhere I'd expect this to format with the opening brace on the same line as the last where clause bound. Do you think the current behavior is correct?

[ytmimi]

Where clauses can appear in other contexts besides function definitions. Can we also add some examples with enum / struct definitions, and impl blocks to highlight how brace_style interacts with trailing_comma for those other language constructs?

Also including some tests with a single where clause bound (e.g. just S: Add + Sub) would also be helpful to highlight the difference between how a list of bounds VS a single bound is formatted.

[gentoid]

It looks like there's no activity last months. Is it ok, if I pick up the baton?

[ytmimi]

@gentoid thanks for asking to get involved! You're more than welcome to open up a PR that builds off of this one, but I want to be mindful or your time and say that this is a fairly low priority issue and is unlikely to be reviewed any time soon.

[gentoid]

Ok, great.

is unlikely to be reviewed any time soon.

That's fine.

Thanks!