[libcxx-commits] [libcxx] 239189c - [libc++] Disable mistakenly enabled `optional<T&>` constructors for `optional<T>` (#194446)
via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Apr 29 03:15:50 PDT 2026
Author: William Tran-Viet
Date: 2026-04-29T18:15:45+08:00
New Revision: 239189ca28847aa4797368827107c22c32080509
URL: https://github.com/llvm/llvm-project/commit/239189ca28847aa4797368827107c22c32080509
DIFF: https://github.com/llvm/llvm-project/commit/239189ca28847aa4797368827107c22c32080509.diff
LOG: [libc++] Disable mistakenly enabled `optional<T&>` constructors for `optional<T>` (#194446)
Resolves #194415
- A constructor specifically meant for `optional<T&>` was left enabled
for `optional<T>`
- Fix it, and add a test to check for regression.
- This patch also corrects the constraints for `optional(optional<U>&)`
and `optional(const optional<U>&)` , as they were incorrectly
disallowing [valid conversions](https://godbolt.org/z/1r5Ea7z5M)
- Also, correct the `noexcept` specification.
- Add tests for both corrections.
Added:
Modified:
libcxx/include/optional
libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/const_optional_U.pass.cpp
libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/optional_U.pass.cpp
libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/ref_constructs_from_temporary.verify.cpp
libcxx/test/std/utilities/optional/optional.object/optional_helper_types.h
Removed:
################################################################################
diff --git a/libcxx/include/optional b/libcxx/include/optional
index 9eed886aa4636..f7e12f84beba0 100644
--- a/libcxx/include/optional
+++ b/libcxx/include/optional
@@ -893,6 +893,10 @@ private:
template <class _Up>
constexpr static bool __libcpp_opt_ref_ctor_deleted =
is_lvalue_reference_v<_Tp> && reference_constructs_from_temporary_v<_Tp, _Up>;
+
+ template <class _Up>
+ constexpr static bool __ref_ctor_enabled =
+ is_lvalue_reference_v<_Tp> && !reference_constructs_from_temporary_v<_Tp, _Up>;
# endif
// LWG2756: conditionally explicit conversion from _Up
@@ -1000,7 +1004,7 @@ public:
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_implicit<_Up>(), int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional(const optional<_Up>& __v)
# if _LIBCPP_STD_VER >= 26
- noexcept(is_lvalue_reference_v<_Tp> && is_nothrow_constructible_v<_Tp&, _Up&>)
+ noexcept(is_lvalue_reference_v<_Tp> && is_nothrow_constructible_v<_Tp&, const _Up&>)
# endif
{
this->__construct_from(__v);
@@ -1008,7 +1012,7 @@ public:
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_explicit<_Up>(), int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit optional(const optional<_Up>& __v)
# if _LIBCPP_STD_VER >= 26
- noexcept(is_lvalue_reference_v<_Tp> && is_nothrow_constructible_v<_Tp&, _Up&>)
+ noexcept(is_lvalue_reference_v<_Tp> && is_nothrow_constructible_v<_Tp&, const _Up&>)
# endif
{
this->__construct_from(__v);
@@ -1046,25 +1050,25 @@ public:
// optional(optional<U>& rhs)
template <class _Up>
- requires(!__libcpp_opt_ref_ctor_deleted<_Up>) && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
- (!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, _Up&>
+ requires __ref_ctor_enabled<_Up&> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) && (!is_same_v<_Tp&, _Up>) &&
+ is_constructible_v<_Tp&, _Up&>
_LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_Up&, _Tp&>)
optional(optional<_Up>& __rhs) noexcept(is_nothrow_constructible_v<_Tp&, _Up&>) {
this->__construct_from(__rhs);
}
template <class _Up>
- requires __libcpp_opt_ref_ctor_deleted<_Up> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
+ requires __libcpp_opt_ref_ctor_deleted<_Up&> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
(!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, _Up&>
constexpr explicit optional(optional<_Up>& __rhs) noexcept = delete;
// optional(const optional<U>&)
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_implicit<_Up>(), int> = 0>
- requires __libcpp_opt_ref_ctor_deleted<_Up>
+ requires __libcpp_opt_ref_ctor_deleted<const _Up&>
optional(const optional<_Up>&) = delete;
template <class _Up, enable_if_t<_CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_explicit<_Up>(), int> = 0>
- requires __libcpp_opt_ref_ctor_deleted<_Up>
+ requires __libcpp_opt_ref_ctor_deleted<const _Up&>
explicit optional(const optional<_Up>&) = delete;
// optional(optional<U>&&)
@@ -1078,16 +1082,16 @@ public:
// optional(const optional<U>&&)
template <class _Up>
- requires(!__libcpp_opt_ref_ctor_deleted<_Up>) && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
- (!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, _Up>
+ requires __ref_ctor_enabled<const _Up> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
+ (!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, const _Up>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit(!is_convertible_v<const _Up, _Tp&>)
optional(const optional<_Up>&& __v) noexcept(is_nothrow_constructible_v<_Tp&, const _Up>) {
this->__construct_from(std::move(__v));
}
template <class _Up>
- requires __libcpp_opt_ref_ctor_deleted<_Up> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
- (!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, _Up>
+ requires __libcpp_opt_ref_ctor_deleted<const _Up> && (!is_same_v<remove_cvref_t<_Tp>, optional<_Up>>) &&
+ (!is_same_v<_Tp&, _Up>) && is_constructible_v<_Tp&, const _Up>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 optional(const optional<_Up>&& __v) noexcept = delete;
# endif
diff --git a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/const_optional_U.pass.cpp b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/const_optional_U.pass.cpp
index 597110bcb54fe..844317c8570d9 100644
--- a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/const_optional_U.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/const_optional_U.pass.cpp
@@ -151,6 +151,37 @@ constexpr bool test_ref() {
assert(*o2 == 1);
}
+ {
+ const std::optional<int> o1{2};
+ std::optional<const int&> o2(o1);
+ assert(*o2 == 2);
+ assert(&(*o2) == &(*o1));
+ }
+
+ {
+ const std::optional<ReferenceConversion<int>> o1({1, 2});
+ std::optional<const int&> o2(o1);
+ assert(o2.has_value());
+ assert(&(*o2) == &o1->lvalue);
+ assert(*o2 == 1);
+ }
+
+ {
+ const std::optional<ReferenceConversion<int>> o1({1, 2});
+ std::optional<const int&> o2(std::move(o1));
+ assert(o2.has_value());
+ assert(&(*o2) == &o1->rvalue);
+ assert(*o2 == 2);
+ }
+
+ {
+ const std::optional<ReferenceConversionThrows<int>> o1({1, 2});
+ ASSERT_NOT_NOEXCEPT(std::optional<const int&>(o1));
+ ASSERT_NOT_NOEXCEPT(std::optional<const int&>(std::move(o1)));
+ }
+
+ static_assert(!std::is_constructible_v<std::optional<int>, const std::optional<ConstRValueOnly<int>>&&>);
+
return true;
}
#endif
diff --git a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/optional_U.pass.cpp b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/optional_U.pass.cpp
index 39a80efa475f7..03082033cd4dc 100644
--- a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/optional_U.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/optional_U.pass.cpp
@@ -144,6 +144,36 @@ constexpr bool test_ref() {
assert(*o2 == 1);
}
+ {
+ std::optional<int> o1(1);
+ std::optional<const int&> o2(o1);
+ assert(o2.has_value());
+ assert(*o2 == 1);
+ assert(&(*o2) == &(*o1));
+ }
+
+ {
+ std::optional<ReferenceConversion<int>> o1({1, 2});
+ std::optional<const int&> o2(o1);
+ assert(o2.has_value());
+ assert(*o2 == 1);
+ assert(&(*o2) == &o1->lvalue);
+ }
+
+ {
+ std::optional<ReferenceConversion<int>> o1({1, 2});
+ std::optional<const int&> o2(std::move(o1));
+ assert(o2.has_value());
+ assert(*o2 == 2);
+ assert(&(*o2) == &o1->rvalue);
+ }
+
+ {
+ std::optional<ReferenceConversionThrows<int>> o1({1, 2});
+ ASSERT_NOT_NOEXCEPT(std::optional<const int&>(o1));
+ ASSERT_NOT_NOEXCEPT(std::optional<const int&>(std::move(o1)));
+ }
+
return true;
}
#endif
@@ -164,6 +194,11 @@ int main(int, char**) {
test<Z>(std::move(rhs), true);
}
+#if TEST_STD_VER >= 26
+ // GH: #194415
+ static_assert(!std::is_constructible_v<std::optional<int>, std::optional<LValueOnly<int>>&>);
+#endif
+
static_assert(!(std::is_constructible<optional<X>, optional<Z>>::value), "");
#if TEST_STD_VER >= 26
diff --git a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/ref_constructs_from_temporary.verify.cpp b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/ref_constructs_from_temporary.verify.cpp
index 53ac77a2e5620..d4c95c302d817 100644
--- a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/ref_constructs_from_temporary.verify.cpp
+++ b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/ref_constructs_from_temporary.verify.cpp
@@ -29,12 +29,10 @@ void test() {
const std::optional<int> co(1);
std::optional<int> o0(1);
- // expected-error-re@*:* 10 {{call to deleted constructor of 'std::optional<{{.*}}>'}}
+ // expected-error-re@*:* 8 {{call to deleted constructor of 'std::optional<{{.*}}>'}}
std::optional<const int&> o1{1}; // optional(U&&)
- std::optional<const int&> o2{o0}; // optional(optional<U>&)
- std::optional<const int&> o3{co}; // optional(const optional<U>&)
- std::optional<const int&> o4{std::move(o0)}; // optional(optional<U>&&&)
- std::optional<const int&> o5{std::move(co)}; // optional(optional<U>&&&)
+ std::optional<const int&> o4{std::move(o0)}; // optional(optional<U>&&)
+ std::optional<const int&> o5{std::move(co)}; // optional(optional<U>&&)
std::optional<const X&> o6{1}; // optional(U&&)
std::optional<const X&> o7{o0}; // optional(optional<U>&)
diff --git a/libcxx/test/std/utilities/optional/optional.object/optional_helper_types.h b/libcxx/test/std/utilities/optional/optional.object/optional_helper_types.h
index 704d99acb15e9..d9b17a0b91f3b 100644
--- a/libcxx/test/std/utilities/optional/optional.object/optional_helper_types.h
+++ b/libcxx/test/std/utilities/optional/optional.object/optional_helper_types.h
@@ -21,8 +21,9 @@ struct ReferenceConversion {
constexpr ReferenceConversion(T lval, T rval) : lvalue(lval), rvalue(rval) {}
constexpr operator T&() & noexcept { return lvalue; }
-
+ constexpr operator const T&() const& noexcept { return lvalue; }
constexpr operator T&() && noexcept { return rvalue; }
+ constexpr operator const T&() const&& noexcept { return rvalue; }
};
template <typename T>
@@ -42,6 +43,14 @@ struct ReferenceConversionThrows {
return lvalue;
}
+ constexpr operator const T&() const& {
+ if (throws) {
+ TEST_THROW(1);
+ }
+
+ return lvalue;
+ }
+
constexpr operator T&() && {
if (throws) {
TEST_THROW(2);
@@ -49,6 +58,34 @@ struct ReferenceConversionThrows {
return rvalue;
}
+
+ constexpr operator const T&() const&& {
+ if (throws) {
+ TEST_THROW(2);
+ }
+
+ return rvalue;
+ }
+};
+
+template <typename T>
+struct LValueOnly {
+ T val{};
+
+ constexpr operator T&() & noexcept { return val; }
+ constexpr operator T&() const& = delete;
+ constexpr operator T&() && = delete;
+ constexpr operator T&() const&& = delete;
+};
+
+template <typename T>
+struct ConstRValueOnly {
+ mutable T val{};
+
+ constexpr operator T&() & = delete;
+ constexpr operator T&() const& = delete;
+ constexpr operator T&() && = delete;
+ constexpr operator T&() const&& { return val; };
};
#endif
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