{"ast_node_type":"other","tokens":[{"end":79,"kind":"keyword","start":0,"text":"Err(tcx.dcx().emit_err(errors::ConstParamTyImplOnUnsized"}]}
            Err(tcx.dcx().emit_err(errors::ConstParamTyImplOnUnsized { span }))
            let span = tcx.hir_expect_item(impl_did).expect_impl().self_ty.span;
        }