1//===----------------------------------------------------------------------===//
2// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
3// See https://llvm.org/LICENSE.txt for license information.
4// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
5//
6//===----------------------------------------------------------------------===//
7
8// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
9
10// constexpr bool has_value() const noexcept;
11
12#include <cassert>
13#include <concepts>
14#include <expected>
15#include <optional>
16#include <type_traits>
17#include <utility>
18
19#include "test_macros.h"
20#include "../../types.h"
21
22// Test noexcept
23template <class T>
24concept HasValueNoexcept =
25 requires(T t) {
26 { t.has_value() } noexcept;
27 };
28
29struct Foo {};
30static_assert(!HasValueNoexcept<Foo>);
31
32static_assert(HasValueNoexcept<std::expected<int, int>>);
33static_assert(HasValueNoexcept<const std::expected<int, int>>);
34
35constexpr bool test() {
36 // has_value
37 {
38 const std::expected<int, int> e(5);
39 assert(e.has_value());
40 }
41
42 // !has_value
43 {
44 const std::expected<int, int> e(std::unexpect, 5);
45 assert(!e.has_value());
46 }
47
48 // The following tests check that the "has_value" flag is not overwritten
49 // by the constructor of the value. This could happen because the flag is
50 // stored in the tail padding of the value.
51 //
52 // The first test is a simplified version of the real code where this was
53 // first observed.
54 //
55 // The other tests use a synthetic struct that clobbers its tail padding
56 // on construction, making the issue easier to reproduce.
57 //
58 // See https://github.com/llvm/llvm-project/issues/68552 and the linked PR.
59 {
60 auto f1 = []() -> std::expected<std::optional<int>, long> { return 0; };
61
62 auto f2 = [&f1]() -> std::expected<std::optional<int>, int> {
63 return f1().transform_error([](auto) { return 0; });
64 };
65
66 auto e = f2();
67 assert(e.has_value());
68 }
69 {
70 const std::expected<TailClobberer<0>, bool> e = {};
71 // clang-cl does not support [[no_unique_address]] yet.
72#if !(defined(TEST_COMPILER_CLANG) && defined(_MSC_VER))
73 LIBCPP_STATIC_ASSERT(sizeof(TailClobberer<0>) == sizeof(e));
74#endif
75 assert(e.has_value());
76 }
77
78 return true;
79}
80
81int main(int, char**) {
82 test();
83 static_assert(test());
84 return 0;
85}
86

source code of libcxx/test/std/utilities/expected/expected.expected/observers/has_value.pass.cpp