Rustfmt inserts newlines before `where` blocks regardless of length

I'm sure I'm not the only one to have been caught by this, but I've not been able to locate either existing or historical options to deal with this, nor any existing issues.

Anyway, the following snippet, despite not exceeding any of the line length limits in any fashion (that I'm aware of) is still chopped up into multiple lines.

Before:

pub struct S<T> where T: Copy {
    pub value: T,
}

After:

pub struct S<T>
where
    T: Copy,
{
    pub value: T,
}

I would really appreciate an option to keep where blocks on the same line as their attached item until they exceed a maximum length - my vertical space is quite precious and it's fairly irritating to have already-concise lines which fall well short of the column limit suddenly take up double the number of lines.

I'm not sure whether this is a bug (because it does seem excessive) or whether rustfmt is just lacking an option to do this.

Start by reproducing the supplied Rust snippet with rustfmt and comparing the current output with the requested compact where-clause layout. Trace the formatter's handling of where blocks and determine whether the change should be an option or a default behavior; done means concise blocks remain on one line when within the configured limit, with coverage for the example.