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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-9644] libstdc++: Disable std::formatter specializations (LWG 3944) Date: Sat, 23 Mar 2024 11:09:20 +0000 (GMT) [thread overview] Message-ID: <20240323110920.A5C2A3858D37@sourceware.org> (raw) https://gcc.gnu.org/g:543585046d17add37c0108b06d2884d0e03cedde commit r14-9644-g543585046d17add37c0108b06d2884d0e03cedde Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Mar 21 11:15:06 2024 +0000 libstdc++: Disable std::formatter specializations (LWG 3944) This was just approved in Tokyo as a DR for C++23. It doesn't affect us yet, because we don't implement the __cpp_lib_format_ranges features. We can add the disabled specializations and add a testcase now though. libstdc++-v3/ChangeLog: * include/std/format (formatter): Disable specializations that would allow sequences of narrow characters to be formatted as wchar_t without conversion, as per LWG 3944. * testsuite/std/format/formatter/lwg3944.cc: New test. Diff: --- libstdc++-v3/include/std/format | 23 ++++++++++++++++ .../testsuite/std/format/formatter/lwg3944.cc | 31 ++++++++++++++++++++++ 2 files changed, 54 insertions(+) diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format index 613016d1a10..22dcb5f24bd 100644 --- a/libstdc++-v3/include/std/format +++ b/libstdc++-v3/include/std/format @@ -2478,6 +2478,29 @@ namespace __format }; /// @} +#if defined _GLIBCXX_USE_WCHAR_T && __cpp_lib_format_ranges + // _GLIBCXX_RESOLVE_LIB_DEFECTS + // 3944. Formatters converting sequences of char to sequences of wchar_t + + namespace __format { struct __disabled; } + + // std::formatter<__disabled, C> uses the primary template, which is disabled. + template<> + struct formatter<char*, wchar_t> + : private formatter<__format::__disabled, wchar_t> { }; + template<> + struct formatter<const char*, wchar_t> + : private formatter<__format::__disabled, wchar_t> { }; + template<size_t _Nm> + struct formatter<char[_Nm], wchar_t> + : private formatter<__format::__disabled, wchar_t> { }; + template<class _Traits, class _Allocator> + struct formatter<basic_string<char, _Traits, _Allocator>, wchar_t> + : private formatter<__format::__disabled, wchar_t> { }; + template<class _Traits> + struct formatter<basic_string_view<char, _Traits>, wchar_t> + : private formatter<__format::__disabled, wchar_t> { }; +#endif /// @cond undocumented namespace __format diff --git a/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc b/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc new file mode 100644 index 00000000000..ff5f075bcc8 --- /dev/null +++ b/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc @@ -0,0 +1,31 @@ +// { dg-do compile { target c++20 } } +// { dg-options "-Wno-unused-result" } + +// LWG 3944. Formatters converting sequences of char to sequences of wchar_t + +#include <format> + +void test_lwg3944() +{ + // Ill-formed in C++20 and C++23 + const char* cstr = "hello"; + char* str = const_cast<char*>(cstr); + std::format(L"{}", str); // { dg-error "here" } + std::format(L"{}",cstr); // { dg-error "here" } + + // Ill-formed in C++20 + // In C++23 they give L"['h', 'e', 'l', 'l', 'o']" + std::format(L"{}", "hello"); // { dg-error "here" } + std::format(L"{}", std::string_view("hello")); // { dg-error "here" } + std::format(L"{}", std::string("hello")); // { dg-error "here" } +#ifdef __cpp_lib_format_ranges + // LWG 3944 does not change this, it's still valid. + std::format(L"{}", std::vector{'h', 'e', 'l', 'l', 'o'}); +#endif +} + +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } +// { dg-prune-output "use of deleted function" } +// { dg-prune-output "no matching function" } +// { dg-prune-output "has no member named 'parse'" } +// { dg-prune-output "not a constant expression" }
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