1 files changed, 288 insertions, 0 deletions
diff --git a/libcxx/test/std/utilities/expected/expected.expected/monadic/and_then.pass.cpp b/libcxx/test/std/utilities/expected/expected.expected/monadic/and_then.pass.cpp
new file mode 100644
index 000000000000..1630931d4a85
--- /dev/null
+++ b/libcxx/test/std/utilities/expected/expected.expected/monadic/and_then.pass.cpp
@@ -0,0 +1,288 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <expected>
+
+// template<class F> constexpr auto and_then(F&& f) &;
+// template<class F> constexpr auto and_then(F&& f) const &;
+// template<class F> constexpr auto and_then(F&& f) &&;
+// template<class F> constexpr auto and_then(F&& f) const &&;
+
+#include <cassert>
+#include <concepts>
+#include <expected>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+struct LVal {
+  constexpr std::expected<int, int> operator()(int&) { return 1; }
+  std::expected<int, int> operator()(const int&)  = delete;
+  std::expected<int, int> operator()(int&&)       = delete;
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct CLVal {
+  std::expected<int, int> operator()(int&) = delete;
+  constexpr std::expected<int, int> operator()(const int&) { return 1; }
+  std::expected<int, int> operator()(int&&)       = delete;
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct RVal {
+  std::expected<int, int> operator()(int&)       = delete;
+  std::expected<int, int> operator()(const int&) = delete;
+  constexpr std::expected<int, int> operator()(int&&) { return 1; }
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct CRVal {
+  std::expected<int, int> operator()(int&)       = delete;
+  std::expected<int, int> operator()(const int&) = delete;
+  std::expected<int, int> operator()(int&&)      = delete;
+  constexpr std::expected<int, int> operator()(const int&&) { return 1; }
+};
+
+struct RefQual {
+  constexpr std::expected<int, int> operator()(int) & { return 1; }
+  std::expected<int, int> operator()(int) const&  = delete;
+  std::expected<int, int> operator()(int) &&      = delete;
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct CRefQual {
+  std::expected<int, int> operator()(int) & = delete;
+  constexpr std::expected<int, int> operator()(int) const& { return 1; }
+  std::expected<int, int> operator()(int) &&      = delete;
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct RVRefQual {
+  std::expected<int, int> operator()(int) &      = delete;
+  std::expected<int, int> operator()(int) const& = delete;
+  constexpr std::expected<int, int> operator()(int) && { return 1; }
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct RVCRefQual {
+  std::expected<int, int> operator()(int) &      = delete;
+  std::expected<int, int> operator()(int) const& = delete;
+  std::expected<int, int> operator()(int) &&     = delete;
+  constexpr std::expected<int, int> operator()(int) const&& { return 1; }
+};
+
+struct UnexpectedLVal {
+  constexpr std::expected<int, int> operator()(int&) { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(const int&)  = delete;
+  std::expected<int, int> operator()(int&&)       = delete;
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct UnexpectedCLVal {
+  std::expected<int, int> operator()(int&) = delete;
+  constexpr std::expected<int, int> operator()(const int&) { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(int&&)       = delete;
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct UnexpectedRVal {
+  std::expected<int, int> operator()(int&)       = delete;
+  std::expected<int, int> operator()(const int&) = delete;
+  constexpr std::expected<int, int> operator()(int&&) { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(const int&&) = delete;
+};
+
+struct UnexpectedCRVal {
+  std::expected<int, int> operator()(int&)       = delete;
+  std::expected<int, int> operator()(const int&) = delete;
+  std::expected<int, int> operator()(int&&)      = delete;
+  constexpr std::expected<int, int> operator()(const int&&) { return std::expected<int, int>(std::unexpected<int>(5)); }
+};
+
+struct UnexpectedRefQual {
+  constexpr std::expected<int, int> operator()(int) & { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(int) const&  = delete;
+  std::expected<int, int> operator()(int) &&      = delete;
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct UnexpectedCRefQual {
+  std::expected<int, int> operator()(int) & = delete;
+  constexpr std::expected<int, int> operator()(int) const& { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(int) &&      = delete;
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct UnexpectedRVRefQual {
+  std::expected<int, int> operator()(int) &      = delete;
+  std::expected<int, int> operator()(int) const& = delete;
+  constexpr std::expected<int, int> operator()(int) && { return std::expected<int, int>(std::unexpected<int>(5)); }
+  std::expected<int, int> operator()(int) const&& = delete;
+};
+
+struct UnexpectedRVCRefQual {
+  std::expected<int, int> operator()(int) &      = delete;
+  std::expected<int, int> operator()(int) const& = delete;
+  std::expected<int, int> operator()(int) &&     = delete;
+  constexpr std::expected<int, int> operator()(int) const&& { return std::expected<int, int>(std::unexpected<int>(5)); }
+};
+
+struct NonCopyable {
+  constexpr NonCopyable(int) {}
+  NonCopyable(const NonCopyable&) = delete;
+};
+
+struct NonMovable {
+  constexpr NonMovable(int) {}
+  NonMovable(NonMovable&&) = delete;
+};
+
+struct NonConst {
+  std::expected<int, int> non_const() { return 1; }
+};
+
+template <class E, class F>
+concept has_and_then = requires(E&& e, F&& f) {
+  {std::forward<E>(e).and_then(std::forward<F>(f))};
+};
+
+static_assert( has_and_then<std::expected<int, int>&, std::expected<int, int>(int&)>);
+static_assert(!has_and_then<std::expected<int, NonCopyable>&, std::expected<int, NonCopyable>(int&)>);
+static_assert( has_and_then<const std::expected<int, int>&, std::expected<int, int>(const int&)>);
+static_assert(!has_and_then<const std::expected<int, NonCopyable>&, std::expected<int, NonCopyable>(const int&)>);
+static_assert( has_and_then<std::expected<int, int>&&, std::expected<int, int>(int)>);
+static_assert(!has_and_then<std::expected<int, NonMovable>&&, std::expected<int, NonMovable>(int)>);
+static_assert( has_and_then<const std::expected<int, int>&&, std::expected<int, int>(const int)>);
+static_assert(!has_and_then<const std::expected<int, NonMovable>&&, std::expected<int, NonMovable>(const int)>);
+
+// [LWG 3877] https://cplusplus.github.io/LWG/issue3877, check constraint failing but not compile error inside the function body.
+static_assert(!has_and_then<const std::expected<int, std::unique_ptr<int>>&, int()>);
+static_assert(!has_and_then<const std::expected<int, std::unique_ptr<int>>&&, int()>);
+
+// clang-format off
+constexpr void test_val_types() {
+  // Test & overload
+  {
+    // Without &qualifier on F'soperator()
+    {
+      std::expected<int, int> e{0};
+      std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(LVal{});
+      assert(val == 1);
+      assert(e.and_then(UnexpectedLVal{}).error() == 5);
+    }
+
+    // With & qualifier on F's operator()
+    {
+      std::expected<int, int> e{0};
+      RefQual l{};
+      std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(l);
+      assert(val == 1);
+      UnexpectedRefQual nl{};
+      assert(e.and_then(nl).error() == 5);
+    }
+  }
+
+  // Test const& overload
+  {
+    // Without & qualifier on F's operator()
+    {
+      const std::expected<int, int> e{0};
+      std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(CLVal{});
+      assert(val == 1);
+      assert(e.and_then(UnexpectedCLVal{}).error() == 5);
+    }
+
+    // With & qualifier on F's operator()
+    {
+      const std::expected<int, int> e{0};
+      const CRefQual l{};
+      std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(l);
+      assert(val == 1);
+      const UnexpectedCRefQual nl{};
+      assert(e.and_then(nl).error() == 5);
+    }
+  }
+
+  // Test && overload
+  {
+    // Without & qualifier on F's operator()
+    {
+      std::expected<int, int> e{0};
+      std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(RVal{});
+      assert(val == 1);
+      assert(std::move(e).and_then(UnexpectedRVal{}).error() == 5);
+    }
+
+    // With & qualifier on F's operator()
+    {
+      std::expected<int, int> e{0};
+      std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(RVRefQual{});
+      assert(val == 1);
+      assert(e.and_then(UnexpectedRVRefQual{}).error() == 5);
+    }
+  }
+
+  // Test const&& overload
+  {
+    // Without & qualifier on F's operator()
+    {
+      const std::expected<int, int> e{0};
+      std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(CRVal{});
+      assert(val == 1);
+      assert(std::move(e).and_then(UnexpectedCRVal{}).error() == 5);
+    }
+
+    // With & qualifier on F's operator()
+    {
+      const std::expected<int, int> e{0};
+      const RVCRefQual l{};
+      std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(std::move(l));
+      assert(val == 1);
+      const UnexpectedRVCRefQual nl{};
+      assert(std::move(e).and_then(std::move(nl)).error() == 5);
+    }
+  }
+}
+// clang-format on
+
+// check that the lambda body is not instantiated during overload resolution
+constexpr void test_sfinae() {
+  std::expected<NonConst, int> e(std::unexpected<int>(2));
+  auto l = [](auto&& x) { return x.non_const(); };
+  e.and_then(l);
+  std::move(e).and_then(l);
+}
+
+constexpr bool test() {
+  test_sfinae();
+  test_val_types();
+
+  std::expected<int, int> e(std::unexpected<int>(1));
+  const auto& ce = e;
+
+  const auto never_called = [](int) {
+    assert(false);
+    return std::expected<int, int>();
+  };
+
+  e.and_then(never_called);
+  std::move(e).and_then(never_called);
+  ce.and_then(never_called);
+  std::move(ce).and_then(never_called);
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}