On Wed, 24 Aug 2022, Patrick Palka wrote:
> r13-2159-g72886fcc626953 introduced some testsuite regressions in C++23
> mode:
>
> FAIL: 20_util/pair/requirements/explicit_instantiation/1.cc (test for
> excess errors)
> FAIL: 20_util/tuple/53648.cc (test for excess errors)
> FAIL: 20_util/tuple/cons/noexcept_specs.cc (test for excess errors)
> FAIL: 20_util/tuple/requirements/explicit_instantiation.cc (test for excess
> errors)
>
> The test noexcept_specs.cc just needs to be updated to consider the
> additional converting constructors of tuple in C++23 mode, which happen
> to improve constructing from a const tuple rvalue containing rvalue
> reference elements (for the better, as far as I can tell).
>
> The other three tests fail because they explicitly instantiate a
> specialization
> of tuple whose elements are not all const swappable, which in C++23 mode now
> results in a hard error due to tuple's new const swap member function. Rather
> than XFAILing the tests in C++23 mode, this patch adds non-standard
> constraints
> to this member function so that we continue to accept such explicit
> instantiations.
>
> Tested on x86_64-pc-linux-gnu with and without
> --target_board=unix/-std=gnu++23,
> does this look OK for trunk?
>
> libstdc++-v3/ChangeLog:
>
> * include/std/tuple (tuple::swap const): Add is_swappable_v constraints.
D'oh, pair's const swap needs the same workaround:
-- >8 --
libstdc++-v3/ChangeLog:
* include/bits/stl_pair.h (pair::swap const): Add non-standard
is_swappable_v constraints.
* include/std/tuple (tuple::swap const): Likewise.
* testsuite/20_util/tuple/cons/noexcept_specs.cc: Update some
asserts in C++23 mode.
---
libstdc++-v3/include/bits/stl_pair.h | 8 ++++
libstdc++-v3/include/std/tuple | 9 ++++
.../20_util/tuple/cons/noexcept_specs.cc | 41 +++++++++++++++++++
3 files changed, 58 insertions(+)
diff --git a/libstdc++-v3/include/bits/stl_pair.h
b/libstdc++-v3/include/bits/stl_pair.h
index bffca0daf65..a65a4763c54 100644
--- a/libstdc++-v3/include/bits/stl_pair.h
+++ b/libstdc++-v3/include/bits/stl_pair.h
@@ -213,10 +213,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
#if __cplusplus > 202002L
+ // As an extension, we constrain the const swap member function
+ // in order to continue accepting explicit instantiation of tuple
+ // specializations whose elements are not all const swappable.
+ // Without this constraint, such an explicit instantiation would
+ // also instantiate the ill-formed body of this function and yield
+ // a hard error. This constraint shouldn't affect the behavior of
+ // valid programs.
constexpr void
swap(const pair& __p) const
noexcept(__and_v<__is_nothrow_swappable<const _T1>,
__is_nothrow_swappable<const _T2>>)
+ requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
{
using std::swap;
swap(first, __p.first);
diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 05433d5ae36..9d1abc2f80e 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -1176,9 +1176,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ _Inherited::_M_swap(__in); }
#if __cplusplus > 202002L
+ // As an extension, we constrain this const swap member function
+ // in order to continue accepting explicit instantiation of tuple
+ // specializations whose elements are not all const swappable.
+ // Without this constraint, such an explicit instantiation would
+ // also instantiate the ill-formed body of this function and
+ // yield a hard error. This constraint shouldn't affect the behavior of
+ // valid programs.
constexpr void
swap(const tuple& __in) const
noexcept(__and_v<__is_nothrow_swappable<const _Elements>...>)
+ requires (is_swappable_v<const _Elements> && ...)
{ _Inherited::_M_swap(__in); }
#endif // C++23
};
@@ -1730,6 +1738,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
swap(const tuple& __in) const
noexcept(__and_v<__is_nothrow_swappable<const _T1>,
__is_nothrow_swappable<const _T2>>)
+ requires is_swappable_v<const _T1> && is_swappable_v<const _T2>
{ _Inherited::_M_swap(__in); }
#endif // C++23
};
diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/noexcept_specs.cc
b/libstdc++-v3/testsuite/20_util/tuple/cons/noexcept_specs.cc
index 6044a377348..a326d1bc228 100644
--- a/libstdc++-v3/testsuite/20_util/tuple/cons/noexcept_specs.cc
+++ b/libstdc++-v3/testsuite/20_util/tuple/cons/noexcept_specs.cc
@@ -503,7 +503,17 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(!std::is_nothrow_constructible<BT, IT&>::value, "");
static_assert(!std::is_nothrow_constructible<BT, const IT &>::value, "");
static_assert(!std::is_nothrow_constructible<BT, std::tuple<int&>>::value,
"");
+#if __cplusplus > 202002L
+ // C++23 extended tuple's constructor overload set as part of P2321R2, after
+ // which its converting constructors more accurately forward the elements
+ // from a non-const tuple lvalue and from a const tuple rvalue. In
particular
+ // for the below test we now forward int&& as an rvalue reference instead of
+ // as an lvalue reference, which means we now select the noexcept B(int&&)
+ // ctor instead of the non-noexcept B(const int&) ctor.
+ static_assert(std::is_nothrow_constructible<BT, const
std::tuple<int&&>>::value, "");
+#else
static_assert(!std::is_nothrow_constructible<BT, const
std::tuple<int&&>>::value, "");
+#endif
static_assert(test_trait::is_nothrow_convertible<int,BT>::value,"");
static_assert(!test_trait::is_nothrow_convertible<const int,BT>::value,"");
@@ -515,7 +525,13 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(!test_trait::is_nothrow_convertible<IT&,BT>::value,"");
static_assert(!test_trait::is_nothrow_convertible<const IT &,BT>::value,"");
static_assert(!test_trait::is_nothrow_convertible<std::tuple<int&>,BT>::value,"");
+#if __cplusplus > 202002L
+ // See the note about P2321R2 above.
+ static_assert(test_trait::is_nothrow_convertible<const
std::tuple<int&&>,BT>::value,"");
+#else
static_assert(!test_trait::is_nothrow_convertible<const
std::tuple<int&&>,BT>::value,"");
+#endif
+
static_assert(!std::is_nothrow_constructible<BT, B>::value, "");
@@ -528,7 +544,12 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(std::is_nothrow_constructible<BT, BT&>::value, "");
static_assert(std::is_nothrow_constructible<BT, const BT &>::value, "");
static_assert(std::is_nothrow_constructible<BT, std::tuple<B&>>::value, "");
+#if __cplusplus > 202002L
+ // See the note about P2321R2 above.
+ static_assert(!std::is_nothrow_constructible<BT, const
std::tuple<B&&>>::value, "");
+#else
static_assert(std::is_nothrow_constructible<BT, const
std::tuple<B&&>>::value, "");
+#endif
static_assert(!test_trait::is_nothrow_convertible<B,BT>::value,"");
static_assert(test_trait::is_nothrow_convertible<const B,BT>::value,"");
@@ -540,7 +561,12 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(test_trait::is_nothrow_convertible<BT&,BT>::value,"");
static_assert(test_trait::is_nothrow_convertible<const BT &,BT>::value,"");
static_assert(test_trait::is_nothrow_convertible<std::tuple<B&>,BT>::value,"");
+#if __cplusplus > 202002L
+ // See the note about P2321R2 above.
+ static_assert(!test_trait::is_nothrow_convertible<const
std::tuple<B&&>,BT>::value,"");
+#else
static_assert(test_trait::is_nothrow_convertible<const
std::tuple<B&&>,BT>::value,"");
+#endif
/* explicit */
static_assert(std::is_nothrow_constructible<DT, int>::value, "");
@@ -553,7 +579,12 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(!std::is_nothrow_constructible<DT, IT&>::value, "");
static_assert(!std::is_nothrow_constructible<DT, const IT &>::value, "");
static_assert(!std::is_nothrow_constructible<DT, std::tuple<int&>>::value,
"");
+#if __cplusplus > 202002L
+ // See the note about P2321R2 above.
+ static_assert(std::is_nothrow_constructible<DT, const
std::tuple<int&&>>::value, "");
+#else
static_assert(!std::is_nothrow_constructible<DT, const
std::tuple<int&&>>::value, "");
+#endif
static_assert(!std::is_nothrow_constructible<DT, D>::value, "");
static_assert(std::is_nothrow_constructible<DT,const D>::value, "");
@@ -565,7 +596,12 @@ namespace
NothrowCopyThrowMoveThrowCopyConversionNothrowMoveConversion
static_assert(std::is_nothrow_constructible<DT, DT&>::value, "");
static_assert(std::is_nothrow_constructible<DT, const DT &>::value, "");
static_assert(std::is_nothrow_constructible<DT, std::tuple<D&>>::value, "");
+#if __cplusplus > 202002L
+ // See note about P2321R2 above.
+ static_assert(!std::is_nothrow_constructible<DT, const
std::tuple<D&&>>::value, "");
+#else
static_assert(std::is_nothrow_constructible<DT, const
std::tuple<D&&>>::value, "");
+#endif
static_assert(!test_trait::is_nothrow_convertible<DT,DT>::value,"");
static_assert(test_trait::is_nothrow_convertible<const DT,DT>::value,"");
@@ -884,7 +920,12 @@ namespace ThrowMoveNothrowConversion
static_assert(std::is_nothrow_constructible<DT, IT&>::value, "");
static_assert(std::is_nothrow_constructible<DT, const IT &>::value, "");
static_assert(std::is_nothrow_constructible<DT, std::tuple<int&>>::value,
"");
+#if __cplusplus > 202002L
+ // See the note about P2321R2 above.
+ static_assert(!std::is_nothrow_constructible<DT, const
std::tuple<int&&>>::value, "");
+#else
static_assert(std::is_nothrow_constructible<DT, const
std::tuple<int&&>>::value, "");
+#endif
static_assert(test_trait::is_nothrow_convertible<DT,DT>::value,"");
static_assert(test_trait::is_nothrow_convertible<D,DT>::value,"");
--
2.37.2.382.g795ea8776b
