Function module_usage_analysis 

pub fn module_usage_analysis(
    module: &Module,
    already_used: &mut UsedItems,
    to_analyze: &mut UsedItems,
    ignore_visibility: bool,
) -> Result<(), UsageError>

Find declarations used in external modules which this module depends on, no matter what.

Currently, only items referenced by module-scope const_asserts are always included.

See usage_analysis.