Empty lines in where-clause

[stanislav-tkach]

I would expect the empty line between the T: std::fmt::Debug and T: std::fmt::Display lines to be removed by rustfmt, but it isn't:

fn foo<T>(_: T)
where
    T: std::fmt::Debug,

    T: std::fmt::Display,
{
}

At least not by the rustfmt 1.5.1-stable (69f9c33d 2022-12-12) version.

I'm sorry if it is a duplicate, but I haven't been able to find any related issues.

[ytmimi]

Thanks for reaching out! hmm odd behavior, but confirming I can reproduce this!

The style guide section on where clauses doesn't mention anything about preserving newlines, so this might just be rustfmt wanting to leave the bounds as the developer wrote them.

I did some digging and it turns out that the newlines are kept because we set preserve_newline(true) when building the ListFormatting in rewrite_bounds_on_where_clause:

rustfmt/src/items.rs

Lines 2886 to 2889 in ee2bed9

	let fmt = ListFormatting::new(shape, context.config)
	.tactic(shape_tactic)
	.trailing_separator(comma_tactic)
	.preserve_newline(true);

We can't change the current default behavior because that would be a breaking formatting change, but we could introduce a new, nightly, configuration option to allow you to configure whether or not to preserve newlines between where clause bounds.

[naosense]

looks simple, I'll take it

@rustbot claim