Supertraits are wrapped at less than `max_width` (sometimes 20+ chars less)

If I format this code with max_width = 50:

// line below is 30 chars
pub(super) unsafe trait A: B {
    fn foo();
}

// line below is 36 chars
pub unsafe trait Trait2: A + B + C {
    fn foo();
}

// line below is 43 chars
pub trait TraitThree: Super1 + Super2 + X {
    fn foo();
}

// line below is 47 chars
trait TraitNumberFour: Super1 + Super2 + Abcd {
    fn foo();
}

// line below is correctly not wrapped
pub const THIS_LINE_IS_50_CHARS: usize = 12345678;

I get this:

// line below is 30 chars
pub(super) unsafe trait A:
    B
{
    fn foo();
}

// line below is 36 chars
pub unsafe trait Trait2:
    A + B + C
{
    fn foo();
}

// line below is 43 chars
pub trait TraitThree:
    Super1 + Super2 + X
{
    fn foo();
}

// line below is 47 chars
trait TraitNumberFour:
    Super1 + Super2 + Abcd
{
    fn foo();
}

// line below is correctly not wrapped
pub const THIS_LINE_IS_50_CHARS: usize = 12345678;

All of the supertraits were moved to a separate line even though none of the original lines exceeded the max width.

The same thing happens with other values of max_width, including the default of 100.

No source file or test is named. Reproduce the examples with max_width values of 50 and 100, then trace the formatter's supertrait wrapping behavior. Done means lines that already fit within max_width remain unwrapped, with regression coverage for the shown trait declarations.