In which I learn about expected-error@.*

Author: cor3ntin

libcxx/include/__expected/expected.h

@@ -845,7 +845,7 @@ class expected : private __expected_base<_Tp, _Err> {
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& value() const&& {
-    static_assert(bool(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>),
+    static_assert(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>,
                   "error_type has to be both copy constructible and constructible from decltype(std::move(error()))");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::move(error()));
@@ -854,7 +854,7 @@ class expected : private __expected_base<_Tp, _Err> {
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& value() && {
-    static_assert(bool(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>),
+    static_assert(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>,
                   "error_type has to be both copy constructible and constructible from decltype(std::move(error()))");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::move(error()));

libcxx/test/libcxx/utilities/expected/expected.expected/value.observers.verify.cpp

@@ -95,6 +95,8 @@ void test() {
       std::expected<int, CopyConstructibleButNotMoveConstructible> e;
       [[maybe_unused]] auto val = std::move(e).value();
       // expected-error-re@*:* {{static assertion failed {{.*}}error_type has to be both copy constructible and constructible from decltype(std::move(error()))}}
+      // The following diagnostic is emmitted in expected.h:
+      // expected-error@*:* {{call to deleted constructor of 'CopyConstructibleButNotMoveConstructible'}}
     }
   }
 
@@ -118,6 +120,8 @@ void test() {
       const std::expected<int, CopyConstructibleButNotMoveConstructible> e;
       [[maybe_unused]] auto val = std::move(e).value();
       // expected-error-re@*:* {{static assertion failed {{.*}}error_type has to be both copy constructible and constructible from decltype(std::move(error()))}}
+      // The following diagnostic is emmitted in expected.h:
+      // expected-error@*:* {{call to deleted constructor of 'CopyConstructibleButNotMoveConstructible'}}
     }
   }
 // These diagnostics happen when we try to construct bad_expected_access from the non copy-constructible error type.