Function phase_uses_name_conflicts 

pub fn phase_uses_name_conflicts(
    unit_uses: &HashMap<String, Vec<String>>,
    unit_tables: &HashMap<String, UnitTable>,
    parsed: &[ParsedFile],
    groups: &BTreeMap<String, Vec<usize>>,
    errors: &mut ErrorSink,
)

Phase 6: for each unit, detect when two uses-imported commons declare the same (non-shadowed) type or function name — an unrenamable conflict at the use site. Diagnostics go into errors.