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* [gcc r14-7174] libstdc++: Fix std::runtime_format deviations from the spec [PR113320]
@ 2024-01-12 9:49 Jonathan Wakely
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From: Jonathan Wakely @ 2024-01-12 9:49 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:5fbc1b2e7c1bdf11f64765b278f477310c0f3436
commit r14-7174-g5fbc1b2e7c1bdf11f64765b278f477310c0f3436
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Jan 10 20:54:11 2024 +0000
libstdc++: Fix std::runtime_format deviations from the spec [PR113320]
I seem to have implemented this feature based on the P2918R0 revision,
not the final P2918R2 one that was approved for C++26. This commit fixes
it.
The runtime-format-string type should not have a publicly accessible
data member, so add a constructor and make it a friend of
basic_format_string. It should also be non-copyable, so that it can only
be constructed from a prvalue via temporary materialization. Change the
basic_format_string constructor parameter to pass by value. Also add
noexcept to the constructors and runtime_format generator functions.
libstdc++-v3/ChangeLog:
PR libstdc++/113320
* include/std/format (__format::_Runtime_format_string): Add
constructor and disable copy operations.
(basic_format_string(_Runtime_format_string)): Add noexcept and
take parameter by value not rvalue reference.
(runtime_format): Add noexcept.
* testsuite/std/format/runtime_format.cc: Check noexcept. Check
that construction is only possible from prvalues, not xvalues.
Reviewed-by: Daniel Krügler <daniel.kruegler@gmail.com>
Diff:
---
libstdc++-v3/include/std/format | 30 ++++++++++++++++------
.../testsuite/std/format/runtime_format.cc | 11 ++++++++
2 files changed, 33 insertions(+), 8 deletions(-)
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 7440a25ea97..540f8b805f8 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -70,6 +70,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// [format.context], class template basic_format_context
template<typename _Out, typename _CharT> class basic_format_context;
+ // [format.fmt.string], class template basic_format_string
+ template<typename _CharT, typename... _Args> struct basic_format_string;
+
/// @cond undocumented
namespace __format
{
@@ -83,7 +86,20 @@ namespace __format
using __format_context = basic_format_context<_Sink_iter<_CharT>, _CharT>;
template<typename _CharT>
- struct _Runtime_format_string { basic_string_view<_CharT> _M_str; };
+ struct _Runtime_format_string
+ {
+ [[__gnu__::__always_inline__]]
+ _Runtime_format_string(basic_string_view<_CharT> __s) noexcept
+ : _M_str(__s) { }
+
+ _Runtime_format_string(const _Runtime_format_string&) = delete;
+ void operator=(const _Runtime_format_string&) = delete;
+
+ private:
+ basic_string_view<_CharT> _M_str;
+
+ template<typename, typename...> friend struct std::basic_format_string;
+ };
} // namespace __format
/// @endcond
@@ -104,8 +120,6 @@ namespace __format
template<typename _Context>
class basic_format_arg;
- // [format.fmt.string], class template basic_format_string
-
/** A compile-time checked format string for the specified argument types.
*
* @since C++23 but available as an extension in C++20.
@@ -119,7 +133,7 @@ namespace __format
basic_format_string(const _Tp& __s);
[[__gnu__::__always_inline__]]
- basic_format_string(__format::_Runtime_format_string<_CharT>&& __s)
+ basic_format_string(__format::_Runtime_format_string<_CharT> __s) noexcept
: _M_str(__s._M_str)
{ }
@@ -144,14 +158,14 @@ namespace __format
#if __cplusplus > 202302L
[[__gnu__::__always_inline__]]
inline __format::_Runtime_format_string<char>
- runtime_format(string_view __fmt)
- { return {__fmt}; }
+ runtime_format(string_view __fmt) noexcept
+ { return __fmt; }
#ifdef _GLIBCXX_USE_WCHAR_T
[[__gnu__::__always_inline__]]
inline __format::_Runtime_format_string<wchar_t>
- runtime_format(wstring_view __fmt)
- { return {__fmt}; }
+ runtime_format(wstring_view __fmt) noexcept
+ { return __fmt; }
#endif
#endif // C++26
diff --git a/libstdc++-v3/testsuite/std/format/runtime_format.cc b/libstdc++-v3/testsuite/std/format/runtime_format.cc
index 174334c7676..f2bfa5b434d 100644
--- a/libstdc++-v3/testsuite/std/format/runtime_format.cc
+++ b/libstdc++-v3/testsuite/std/format/runtime_format.cc
@@ -29,6 +29,17 @@ test_internal_api()
VERIFY( s == "0x315" );
}
+static_assert( noexcept(std::format_string<>(std::runtime_format(""))) );
+static_assert( noexcept(std::wformat_string<>(std::runtime_format(L""))) );
+static_assert( noexcept(std::format_string<int>(std::runtime_format(""))) );
+static_assert( noexcept(std::wformat_string<char>(std::runtime_format(L""))) );
+// A format string can be constructed from the result of std::runtime_format
+// using copy elision, but cannot be constructed from an xvalue.
+static_assert( !std::is_constructible_v<std::format_string<>,
+ decltype(std::runtime_format(""))&&> );
+static_assert( !std::is_constructible_v<std::wformat_string<>,
+ decltype(std::runtime_format(L""))&&> );
+
int main()
{
test_char();
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