Function write_diff 

pub fn write_diff<W: Write>(
    w: &mut W,
    diff: &CtprofDiff,
    baseline_path: &Path,
    candidate_path: &Path,
    group_by: GroupBy,
    display: &DisplayOptions,
) -> Result

Render CtprofDiff into w. The formatter layer lives here so tests can inspect exactly what print_diff would emit without shelling through stdout capture. Write errors propagate as std::fmt::Error — callers that write into an infallible sink (String) can unwrap or ignore.

display controls per-row column layout, terminal-width wrapping, and per-section filtering: see DisplayFormat / Column / Section / DisplayOptions for the resolution rules. Each sub-emitter is gated on DisplayOptions::is_section_enabled before its data-availability check, so --sections always wins over the per-section zero-suppression heuristic.