{"ast_node_type":"variable","tokens":[{"end":79,"kind":"keyword","start":0,"text":"let"}]}
        let fn_decl = self.infcx.tcx.hir_fn_decl_by_hir_id(self.mir_hir_id())?;
    ) -> Option<&hir::Ty<'tcx>> {
        let argument_hir_ty: &hir::Ty<'_> = fn_decl.inputs.get(argument_index)?;