pragma experimental SMTChecker; library L { struct S { uint256[] data; } function f(S memory _s) internal pure returns (uint256) { require(_s.data.length > 0); return 42; } } contract C { using L for L.S; function f() public pure returns (uint256 y) { L.S memory x; y = (x.f)(); assert(y == 42); // should hold } } // ---- // Warning 6031: (289-292): Internal error: Expression undefined for SMT solver. // Warning 6031: (289-292): Internal error: Expression undefined for SMT solver.