5796 derive attribute is not wrapped if it's exactly max length

[IVIURRAY]

#5796

This is not the prettiest solution but there is a assumption that once we enter write_list for list.rs we always subtract the separator from the width. This is causing the bug to occur here. As the line exceeds that max width by 1 and this subtraction makes the formatter think it is equal.

So the item_str we get back is actually greater than the width so I do a check for this and format it again but this time vertically.

I don't think this is pretty or a optimal fix (as we've to format twice) but I wanted to open a PR to generate a conversation about it. Maybe we can discuss a better solution to the problem now it has been identified a little more.

[IVIURRAY]

What I would really like to achive is getting definitive_tactic() to handle this correctly but that relys on the argument_shape which is correct.

rustfmt/src/attr.rs

Lines 133 to 138 in 6356fca

	let tactic = definitive_tactic(
	&all_items,
	ListTactic::HorizontalVertical,
	Separator::Comma,
	argument_shape.width,
	);

So which ever way I look at this, I always come back to these lines of code which are ignoring that final ,.

rustfmt/src/lists.rs

Lines 245 to 247 in 6356fca

	let (sep_count, total_width) = calculate_width(items.clone());
	let total_sep_len = sep.len() * sep_count.saturating_sub(1);
	let real_total = total_width + total_sep_len;