Function local_must_write_args 

pub(super) fn local_must_write_args(
    tcx: TyCtxt<'_>,
    callee: DefId,
    context: &CallContext,
) -> Option<Vec<usize>>

Return callee argument indices that are definitely written on every reachable return path, pruning paths infeasible under context. Works for any callee with available MIR, and follows wrapper calls (Vec::push → push_mut) with bounded depth.