Function rustfmt_format_diff::scan_diff

pub(crate) fn scan_diff<R>(
    from: R,
    skip_prefix: u32,
    file_filter: &str
) -> Result<(HashSet<String>, Vec<Range>), FormatDiffError>where
    R: Read,

Scans a diff from from, and returns the set of files found, and the ranges in those files.