From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [PATCH] libstdc++: Constrain std::vector default constructor [PR113841]
Date: Tue, 19 Mar 2024 15:57:32 +0000 [thread overview]
Message-ID: <20240319155858.3406992-1-jwakely@redhat.com> (raw)
This fixes the problem in the PR, which is revealed by the new
concept-based constraints on std::pair constructors in C++20 mode. That
makes this a C++20 regression, as the PR's example compiles with C++17.
We need something similar for std::basic_string too, which I'll do
later.
Any comments?
Tested aarch64-linux.
-- >8 --
This is needed to avoid errors outside the immediate context when
evaluating is_default_constructible_v<vector<T, A>> when A is not
default constructible.
To avoid diagnostic regressions for 23_containers/vector/48101_neg.cc we
need to make the std::allocator<cv T> partial specializations default
constructible, which they probably should have been anyway.
libstdc++-v3/ChangeLog:
PR libstdc++/113841
* include/bits/allocator.h (allocator<cv T>): Add default
constructor to partial specializations for cv-qualified types.
* include/bits/stl_vector.h (_Vector_impl::_Vector_impl()):
Constrain so that it's only present if the allocator is default
constructible.
* include/bits/stl_bvector.h (_Bvector_impl::_Bvector_impl()):
Likewise.
* testsuite/23_containers/vector/cons/113841.cc: New test.
---
libstdc++-v3/include/bits/allocator.h | 3 ++
libstdc++-v3/include/bits/stl_bvector.h | 3 ++
libstdc++-v3/include/bits/stl_vector.h | 3 ++
.../23_containers/vector/cons/113841.cc | 34 +++++++++++++++++++
4 files changed, 43 insertions(+)
create mode 100644 libstdc++-v3/testsuite/23_containers/vector/cons/113841.cc
diff --git a/libstdc++-v3/include/bits/allocator.h b/libstdc++-v3/include/bits/allocator.h
index ff4f5b9137b..9e75b37fce7 100644
--- a/libstdc++-v3/include/bits/allocator.h
+++ b/libstdc++-v3/include/bits/allocator.h
@@ -254,6 +254,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
typedef _Tp value_type;
+ allocator() { }
template<typename _Up> allocator(const allocator<_Up>&) { }
};
@@ -262,6 +263,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
typedef _Tp value_type;
+ allocator() { }
template<typename _Up> allocator(const allocator<_Up>&) { }
};
@@ -270,6 +272,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
typedef _Tp value_type;
+ allocator() { }
template<typename _Up> allocator(const allocator<_Up>&) { }
};
/// @endcond
diff --git a/libstdc++-v3/include/bits/stl_bvector.h b/libstdc++-v3/include/bits/stl_bvector.h
index a3343d95b36..d567e26f4e4 100644
--- a/libstdc++-v3/include/bits/stl_bvector.h
+++ b/libstdc++-v3/include/bits/stl_bvector.h
@@ -593,6 +593,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_GLIBCXX20_CONSTEXPR
_Bvector_impl() _GLIBCXX_NOEXCEPT_IF(
is_nothrow_default_constructible<_Bit_alloc_type>::value)
+#if __cpp_concepts
+ requires is_default_constructible_v<_Bit_alloc_type>
+#endif
: _Bit_alloc_type()
{ }
diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index a8d387f40a1..31169711a48 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -135,6 +135,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
_GLIBCXX20_CONSTEXPR
_Vector_impl() _GLIBCXX_NOEXCEPT_IF(
is_nothrow_default_constructible<_Tp_alloc_type>::value)
+#if __cpp_lib_concepts
+ requires is_default_constructible_v<_Tp_alloc_type>
+#endif
: _Tp_alloc_type()
{ }
diff --git a/libstdc++-v3/testsuite/23_containers/vector/cons/113841.cc b/libstdc++-v3/testsuite/23_containers/vector/cons/113841.cc
new file mode 100644
index 00000000000..a7721d27f79
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/cons/113841.cc
@@ -0,0 +1,34 @@
+// { dg-do compile { target c++20 } }
+
+#include <vector>
+
+template<typename T>
+struct Alloc
+{
+ using value_type = T;
+
+ Alloc(int) { } // not default constructible
+
+ template<typename U> Alloc(const Alloc<U>&) { }
+
+ T* allocate(std::size_t n) { return std::allocator<T>().allocate(n); }
+ void deallocate(T* p, std::size_t n) { std::allocator<T>().deallocate(p, n); }
+};
+
+template<typename T> struct wrap { T t; };
+
+template<typename T> void do_adl(T&) { }
+
+void test_pr113841()
+{
+ using test_type = std::vector<int, Alloc<int>>;
+ std::pair<const int, wrap<test_type>>* h = nullptr;
+ do_adl(h);
+}
+
+void test_pr113841_bool()
+{
+ using test_type = std::vector<bool, Alloc<bool>>;
+ std::pair<const int, wrap<test_type>>* h = nullptr;
+ do_adl(h);
+}
--
2.44.0
next reply other threads:[~2024-03-19 15:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-19 15:57 Jonathan Wakely [this message]
2024-03-22 22:50 ` Jonathan Wakely
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