Function unwrap_array_expr 

pub(crate) fn unwrap_array_expr<'tcx>(
    tcx: TyCtxt<'tcx>,
    def_id: DefId,
    expr: &Expr,
) -> Option<Ty<'tcx>>

Extract the inner type from [T] (the SplitTransmute([T], [U]) notation), then resolve it via parse_type. The [T] argument arrives as either Expr::Array (JSON path, parsed via syn::parse_str::<Expr>) or Expr::Verbatim (source annotation path, where parse_property_arg’s type-first parse turns Type::Slice into Verbatim); both are unwrapped to the element type T.