Function rustfmt_nightly::types::format_function_type

fn format_function_type<'a, I>(
    inputs: I, 
    output: &FnRetTy, 
    variadic: bool, 
    span: Span, 
    context: &RewriteContext<'_>, 
    shape: Shape
) -> Option<String> where
    I: ExactSizeIterator,
    <I as Iterator>::Item: Deref,
    <I::Item as Deref>::Target: Rewrite + Spanned + 'a,