Function rustc_hir_pretty::print_crate

pub fn print_crate<'a>(
    sm: &'a SourceMap,
    krate: &Mod<'_>,
    filename: FileName,
    input: String,
    attrs: &'a dyn Fn(HirId) -> &'a [Attribute],
    ann: &'a dyn PpAnn,
) -> String

Requires you to pass an input filename and reader so that it can scan the input text for comments to copy forward.