pragma experimental ABIEncoderV2;
contract Test {
    struct S { int a; }
    function f(S calldata s) external { s = S(2); }
    function g(S calldata s) external { S memory m; s = m; }
}
// ----
// TypeError: (114-115): External function arguments of reference type are read-only.
// TypeError: (118-122): Type "struct Test.S memory" is not implicitly convertible to expected type "struct Test.S calldata".
// TypeError: (178-179): External function arguments of reference type are read-only.
// TypeError: (182-183): Type "struct Test.S memory" is not implicitly convertible to expected type "struct Test.S calldata".