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From: Jonathan Wakely <redi@gcc.gnu.org>
To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org
Subject: [gcc r12-6698] libstdc++: Limit new basic_string(nullptr_t) constructor to C++23 [PR104099]
Date: Tue, 18 Jan 2022 20:43:53 +0000 (GMT) [thread overview]
Message-ID: <20220118204353.8A14C385802C@sourceware.org> (raw)
https://gcc.gnu.org/g:fe3ed885cda5ab920d361b694ee539242052022f
commit r12-6698-gfe3ed885cda5ab920d361b694ee539242052022f
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Jan 18 16:26:45 2022 +0000
libstdc++: Limit new basic_string(nullptr_t) constructor to C++23 [PR104099]
The new deleted constructors added by P2166R1 are a breaking change,
making previously valid code ill-formed in C++23. As a result, they
should only be defined for C++23 and not for C++11 and up.
libstdc++-v3/ChangeLog:
PR libstdc++/104099
* include/bits/basic_string.h (basic_string(nullptr_t)): Only
define for C++23.
(operator=(nullptr_t)): Likewise.
* include/bits/cow_string.h: Likewise.
* include/std/string_view (basic_string_view(nullptr_t)):
Likewise.
* testsuite/21_strings/basic_string/cons/char/nullptr.cc: Adjust
expected error. Add examples that become ill-formed in C++23.
* testsuite/21_strings/basic_string_view/cons/char/nonnull.cc:
Adjust expected errors.
* testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc:
Likewise.
Diff:
---
libstdc++-v3/include/bits/basic_string.h | 4 +++-
libstdc++-v3/include/bits/cow_string.h | 4 +++-
libstdc++-v3/include/std/string_view | 3 ++-
.../21_strings/basic_string/cons/char/nullptr.cc | 26 +++++++++++++++++++++-
.../basic_string_view/cons/char/nonnull.cc | 3 ++-
.../basic_string_view/cons/wchar_t/nonnull.cc | 3 ++-
6 files changed, 37 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index a91ba5114b1..fc6a303a957 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -728,10 +728,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
else
_M_construct(__str.begin(), __str.end(), std::forward_iterator_tag());
}
+#endif // C++11
+#if __cplusplus >= 202100L
basic_string(nullptr_t) = delete;
basic_string& operator=(nullptr_t) = delete;
-#endif // C++11
+#endif // C++23
/**
* @brief Construct string as copy of a range.
diff --git a/libstdc++-v3/include/bits/cow_string.h b/libstdc++-v3/include/bits/cow_string.h
index 84aab2f33c6..a49a5b04f2f 100644
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -665,10 +665,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
else
_M_dataplus._M_p = _S_construct(__str.begin(), __str.end(), __a);
}
+#endif // C++11
+#if __cplusplus >= 202100L
basic_string(nullptr_t) = delete;
basic_string& operator=(nullptr_t) = delete;
-#endif // C++11
+#endif // C++23
/**
* @brief Construct string as copy of a range.
diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index 99080e9eccd..bccf4d1847f 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -167,10 +167,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
noexcept(noexcept(ranges::size(__r)) && noexcept(ranges::data(__r)))
: _M_len(ranges::size(__r)), _M_str(ranges::data(__r))
{ }
+
+ basic_string_view(nullptr_t) = delete;
#endif // C++23
#endif // C++20
- basic_string_view(nullptr_t) = delete;
constexpr basic_string_view&
operator=(const basic_string_view&) noexcept = default;
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc
index fdb24aeeb89..a69fa614ba3 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/nullptr.cc
@@ -1,4 +1,28 @@
// { dg-do compile { target c++11 } }
#include <string>
-std::string s = nullptr; // { dg-error "deleted" "P2166R1" }
+std::string s = nullptr; // { dg-error "deleted" "P2166R1" { target c++23 } }
+
+struct S
+{
+ operator const char*() const { return ""; }
+ operator std::nullptr_t() const { return {}; }
+};
+
+std::string s2{ S{} }; // { dg-error "deleted" "PR 104099" { target c++23 } }
+
+#if __cpp_concepts
+struct J
+{
+ // In C++20 this selects basic_string(const char*),
+ // in C++23 it's ambiguous due to basic_string(nullptr_t).
+ template<typename T>
+ requires (!std::is_same_v<std::allocator<char>, T>)
+ && (!std::is_same_v<std::string, T>)
+ && (!std::is_same_v<char, T>)
+ && (!std::is_same_v<std::string_view, T>)
+ operator T() const { return {}; }
+};
+
+std::string s3{ J{} }; // { dg-error "ambiguous" "PR 104099" { target c++23 } }
+#endif
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
index 00bb8e414b8..2e43788e4f5 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/char/nonnull.cc
@@ -25,5 +25,6 @@ test01()
{
std::string_view s((const char*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::string_view t((char*)nullptr); // { dg-warning "\\\[-Wnonnull" }
- std::string_view u(nullptr); // { dg-error "deleted" }
+ std::string_view u(nullptr); // { dg-warning "\\\[-Wnonnull" "" { target c++20_down } }
+// { dg-error "deleted" "P2166R1" { target c++23 } 0 }
}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
index 685d48c3fd7..a146d383324 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/cons/wchar_t/nonnull.cc
@@ -25,5 +25,6 @@ test01()
{
std::wstring_view s((const wchar_t*)nullptr); // { dg-warning "\\\[-Wnonnull" }
std::wstring_view t((wchar_t*)nullptr); // { dg-warning "\\\[-Wnonnull" }
- std::wstring_view u(nullptr); // { dg-error "deleted" }
+ std::wstring_view u(nullptr); // { dg-warning "\\\[-Wnonnull" "" { target c++20_down } }
+// { dg-error "deleted" "P2166R1" { target c++23 } 0 }
}
reply other threads:[~2022-01-18 20:43 UTC|newest]
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