[PATCH v3] libstdc++: Provide formatter for vector<bool>::reference [PR109162]
Jonathan Wakely
jwakely@redhat.com
Fri Apr 4 09:48:48 GMT 2025
On 04/04/25 11:20 +0200, Tomasz Kamiński wrote:
>This patch implement formatter for vector<bool>::reference which
>is part of P2286R8.
>
>To indicate partial support we define __glibcxx_format_ranges macro
>value 1, without defining __cpp_lib_format_ranges.
>
>To avoid including the whole content of the <format> header, we
>introduce new bits/formatfwd.h forward declares classes required
>for newly introduce formatter.
>
>The signatures of the user-facing parse and format method of the provided
>formatters deviate from the standard by constraining types of params:
>* _Bit_reference instead T satisfying is-vector-bool-reference<T>
>* _CharT is constrained __formatter::__char
>* basic_format_parse_context<_CharT> for parse argument
>* basic_format_context<_Out, _CharT> for format second argument
>The standard specifies last three of above as unconstrained types, which leads
>to formattable<vector<bool>::reference, char32_t> (and any other type as char)
>being true.
The code looks good, just some comments on the changelog and comments:
> PR libstdc++/109162
>
>libstdc++-v3/ChangeLog:
>
> * include/Makefile.am: Add bits/formatfwd.h.
> * include/Makefile.in: Add bits/formatfwd.h.
> * include/bits/version.def:
> Define __glibcxx_format_ranges without corresponding std name.
The line above should start after "version.def:" rather than on a new
line.
> * include/bits/version.h: Regenerate.
> * include/std/format (basic_format_context, __format::__char):
> Move declartions to bits/formatfwd.h.
> (formatter<_Tp, _CharT>): Remove default argument for _CharT
> parameter, now specified in forward declaration in bits/formatfwd.h.
> * include/std/vector (formatter<_Bit_reference, _CharT>: Define.
Missing ')'
> * include/bits/formatfwd.h: New file with forward declartions
Spelling: "declarations"
> for bits of std/format.
> * testsuite/23_containers/vector/bool/format.cc: New test.
>---
>Updated to use no_stdname in version.def.
>
> libstdc++-v3/include/Makefile.am | 1 +
> libstdc++-v3/include/Makefile.in | 1 +
> libstdc++-v3/include/bits/formatfwd.h | 68 +++++++++++++++++++
> libstdc++-v3/include/bits/version.def | 18 ++---
> libstdc++-v3/include/bits/version.h | 9 +++
> libstdc++-v3/include/std/format | 14 +---
> libstdc++-v3/include/std/vector | 32 +++++++++
> .../23_containers/vector/bool/format.cc | 67 ++++++++++++++++++
> 8 files changed, 189 insertions(+), 21 deletions(-)
> create mode 100644 libstdc++-v3/include/bits/formatfwd.h
> create mode 100644 libstdc++-v3/testsuite/23_containers/vector/bool/format.cc
>
>diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>index 4dc771a540c..537774c2668 100644
>--- a/libstdc++-v3/include/Makefile.am
>+++ b/libstdc++-v3/include/Makefile.am
>@@ -195,6 +195,7 @@ bits_headers = \
> ${bits_srcdir}/cow_string.h \
> ${bits_srcdir}/deque.tcc \
> ${bits_srcdir}/erase_if.h \
>+ ${bits_srcdir}/formatfwd.h \
> ${bits_srcdir}/forward_list.h \
> ${bits_srcdir}/forward_list.tcc \
> ${bits_srcdir}/fs_dir.h \
>diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
>index 0e3d09b3a75..7b96b2207f8 100644
>--- a/libstdc++-v3/include/Makefile.in
>+++ b/libstdc++-v3/include/Makefile.in
>@@ -548,6 +548,7 @@ bits_freestanding = \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/cow_string.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/deque.tcc \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/erase_if.h \
>+@GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/formatfwd.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/forward_list.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/forward_list.tcc \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/fs_dir.h \
>diff --git a/libstdc++-v3/include/bits/formatfwd.h b/libstdc++-v3/include/bits/formatfwd.h
>new file mode 100644
>index 00000000000..5450ad1297f
>--- /dev/null
>+++ b/libstdc++-v3/include/bits/formatfwd.h
>@@ -0,0 +1,68 @@
>+// <format> Formatting -*- C++ -*-
>+
>+// Copyright The GNU Toolchain Authors.
>+//
>+// This file is part of the GNU ISO C++ Library. This library is free
>+// software; you can redistribute it and/or modify it under the
>+// terms of the GNU General Public License as published by the
>+// Free Software Foundation; either version 3, or (at your option)
>+// any later version.
>+
>+// This library is distributed in the hope that it will be useful,
>+// but WITHOUT ANY WARRANTY; without even the implied warranty of
>+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>+// GNU General Public License for more details.
>+
>+// Under Section 7 of GPL version 3, you are granted additional
>+// permissions described in the GCC Runtime Library Exception, version
>+// 3.1, as published by the Free Software Foundation.
>+
>+// You should have received a copy of the GNU General Public License and
>+// a copy of the GCC Runtime Library Exception along with this program;
>+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
>+// <http://www.gnu.org/licenses/>.
>+
>+/** @file include/format
This should be bits/formatfwd.h
>+ * This is a Standard C++ Library header.
This should be the internal header comment instead:
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{format}
The @headername{xxx} doxygen macro expands to "Instead, include <xxx>."
>+ */
>+
>+#ifndef _GLIBCXX_FORMAT_FWD_H
>+#define _GLIBCXX_FORMAT_FWD_H 1
>+
>+#ifdef _GLIBCXX_SYSHDR
>+#pragma GCC system_header
>+#endif
We should normally include <bits/version.h> before checking any
__glibcxx_xxx feature test macro:
>+#ifdef __glibcxx_format // C++ >= 20 && HOSTED
If you want to avoid re-including bits/version.h here because it's
guaranteed that formatfwd.h is only included after it, please add a
comment before the #ifdef. Something like:
// <bits/version.h> must have been included before this header:
>+namespace std _GLIBCXX_VISIBILITY(default)
>+{
>+_GLIBCXX_BEGIN_NAMESPACE_VERSION
>+
>+ // [format.context], class template basic_format_context
>+ template<typename _Out, typename _CharT> class basic_format_context;
>+
>+ // [format.parse.ctx], class template basic_format_parse_context
>+ template<typename _CharT> class basic_format_parse_context;
>+
>+ // [format.formatter], formatter
>+ template<typename _Tp, typename _CharT = char> struct formatter;
>+
>+namespace __format
>+{
>+#ifdef _GLIBCXX_USE_WCHAR_T
>+ template<typename _CharT>
>+ concept __char = same_as<_CharT, char> || same_as<_CharT, wchar_t>;
>+#else
>+ template<typename _CharT>
>+ concept __char = same_as<_CharT, char>;
>+#endif
>+
>+ template<__char _CharT>
>+ struct __formatter_int;
>+}
>+
>+_GLIBCXX_END_NAMESPACE_VERSION
>+} // namespace std
>+#endif // __glibcxx_format
>+#pragma GCC diagnostic pop
>+#endif // _GLIBCXX_FORMAT_FWD_H
>diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>index 8569d9fa0ad..8f609b469cc 100644
>--- a/libstdc++-v3/include/bits/version.def
>+++ b/libstdc++-v3/include/bits/version.def
>@@ -1406,18 +1406,18 @@ ftms = {
> };
> };
>
>-// ftms = {
>- // name = format_ranges;
>+ftms = {
>+ name = format_ranges;
> // 202207 P2286R8 Formatting Ranges
> // 202207 P2585R1 Improving default container formatting
> // LWG3750 Too many papers bump __cpp_lib_format
>- // TODO: #define __cpp_lib_format_ranges 202207L
>- // values = {
>- // v = 202207;
>- // cxxmin = 23;
>- // hosted = yes;
>- // };
>-// };
>+ no_stdname = true; // TODO remove
>+ values = {
>+ v = 1; // TODO 202207
>+ cxxmin = 23;
>+ hosted = yes;
>+ };
>+};
>
> ftms = {
> name = freestanding_algorithm;
>diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>index f7c9849893d..f05c3fd13c0 100644
>--- a/libstdc++-v3/include/bits/version.h
>+++ b/libstdc++-v3/include/bits/version.h
>@@ -1555,6 +1555,15 @@
> #endif /* !defined(__cpp_lib_expected) && defined(__glibcxx_want_expected) */
> #undef __glibcxx_want_expected
>
>+#if !defined(__cpp_lib_format_ranges)
>+# if (__cplusplus >= 202100L) && _GLIBCXX_HOSTED
>+# define __glibcxx_format_ranges 1L
>+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_format_ranges)
>+# endif
>+# endif
>+#endif /* !defined(__cpp_lib_format_ranges) && defined(__glibcxx_want_format_ranges) */
>+#undef __glibcxx_want_format_ranges
>+
> #if !defined(__cpp_lib_freestanding_algorithm)
> # if (__cplusplus >= 202100L)
> # define __glibcxx_freestanding_algorithm 202311L
>diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
>index 9ef719edcf0..01a53143d1c 100644
>--- a/libstdc++-v3/include/std/format
>+++ b/libstdc++-v3/include/std/format
>@@ -52,6 +52,7 @@
> #include <string_view>
> #include <string>
> #include <bits/monostate.h>
>+#include <bits/formatfwd.h>
> #include <bits/ranges_base.h> // input_range, range_reference_t
> #include <bits/ranges_util.h> // subrange
> #include <bits/ranges_algobase.h> // ranges::copy
>@@ -73,9 +74,6 @@ namespace std _GLIBCXX_VISIBILITY(default)
> {
> _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;
>
>@@ -178,7 +176,7 @@ namespace __format
> // [format.formatter], formatter
>
> /// The primary template of std::formatter is disabled.
>- template<typename _Tp, typename _CharT = char>
>+ template<typename _Tp, typename _CharT>
> struct formatter
> {
> formatter() = delete; // No std::formatter specialization for this type.
>@@ -923,14 +921,6 @@ namespace __format
> bool _M_hasval = false;
> };
>
>-#ifdef _GLIBCXX_USE_WCHAR_T
>- template<typename _CharT>
>- concept __char = same_as<_CharT, char> || same_as<_CharT, wchar_t>;
>-#else
>- template<typename _CharT>
>- concept __char = same_as<_CharT, char>;
>-#endif
>-
> template<__char _CharT>
> struct __formatter_str
> {
>diff --git a/libstdc++-v3/include/std/vector b/libstdc++-v3/include/std/vector
>index 0f043340fe5..9cf292e444b 100644
>--- a/libstdc++-v3/include/std/vector
>+++ b/libstdc++-v3/include/std/vector
>@@ -157,4 +157,36 @@ _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace std
> #endif // __cpp_lib_erase_if
>
>+#ifdef __glibcxx_format_ranges // C++ >= 20 && HOSTED
>+#include <bits/formatfwd.h>
>+
>+namespace std _GLIBCXX_VISIBILITY(default)
>+{
>+_GLIBCXX_BEGIN_NAMESPACE_VERSION
>+ // Standard does not constrain accepted _CharT and declares it as formatter
>+ // of Tp that statisfies is-vector-bool-reference<T>,
>+ template<__format::__char _CharT>
>+ struct formatter<_GLIBCXX_STD_C::_Bit_reference, _CharT> {
New line before the '{' please, and the "public:" access-specifier is
redundant here:
>+ public:
>+ // Standard declares this as template accepting unconstrained
>+ // ParseContext type.
>+ constexpr typename basic_format_parse_context<_CharT>::iterator
>+ parse(basic_format_parse_context<_CharT>& __pc)
>+ { return _M_f.template _M_parse<bool>(__pc); }
>+
>+ // Standard declares this as template accepting unconstrained
>+ // FormatContext type.
>+ template<typename _Out>
>+ typename basic_format_context<_Out, _CharT>::iterator
>+ format(const _GLIBCXX_STD_C::_Bit_reference& __u,
>+ basic_format_context<_Out, _CharT>& __fc) const
>+ { return _M_f.format(static_cast<bool>(__u), __fc); }
>+
>+ private:
>+ __format::__formatter_int<_CharT> _M_f;
>+ };
>+_GLIBCXX_END_NAMESPACE_VERSION
>+} // namespace std
>+#endif // __glibcxx_format_ranges
>+
> #endif /* _GLIBCXX_VECTOR */
>diff --git a/libstdc++-v3/testsuite/23_containers/vector/bool/format.cc b/libstdc++-v3/testsuite/23_containers/vector/bool/format.cc
>new file mode 100644
>index 00000000000..1935d06ff88
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/23_containers/vector/bool/format.cc
>@@ -0,0 +1,67 @@
>+// { dg-do run { target c++23 } }
>+// { dg-timeout-factor 2 }
>+
>+#include <format>
>+#include <vector>
>+#include <chrono> // For _Widen
>+#include <testsuite_hooks.h>
>+
>+static_assert(!std::formattable<std::vector<bool>::reference, int>);
>+static_assert(!std::formattable<std::vector<bool>::reference, char32_t>);
>+
>+template<typename... Args>
>+bool
>+is_format_string_for(const char* str, Args&&... args)
>+{
>+ try {
>+ (void) std::vformat(str, std::make_format_args(args...));
>+ return true;
>+ } catch (const std::format_error&) {
>+ return false;
>+ }
>+}
>+
>+#define WIDEN_(C, S) ::std::chrono::__detail::_Widen<C>(S, L##S)
>+#define WIDEN(S) WIDEN_(_CharT, S)
>+
>+void
>+test_format_string()
>+{
>+ std::vector<bool> v(1, true);
>+ VERIFY( !is_format_string_for("{:?}", v[0]) );
>+ VERIFY( !is_format_string_for("{:P}", v[0]) );
>+
>+ // width needs to integer type
Grammar: "needs to be"
>+ VERIFY( !is_format_string_for("{:{}}", v[0], 1.0f) );
>+}
>+
>+template<typename _CharT>
>+void
>+test_output()
>+{
>+ std::basic_string<_CharT> res;
>+ size_t size = 0;
>+ std::vector<bool> v{true, false};
>+
>+ res = std::format(WIDEN("{}"), v[0]);
>+ VERIFY( res == WIDEN("true") );
>+
>+ res = std::format(WIDEN("{:s}"), v[1]);
>+ VERIFY( res == WIDEN("false") );
>+
>+ res = std::format(WIDEN("{:d} {:#B} {:#o} {:#x}"), v[0], v[1], v[0], v[1]);
>+ VERIFY( res == WIDEN("1 0B0 01 0x0") );
>+
>+ res = std::format(WIDEN("{:{}}"), v[0], 6);
>+ VERIFY( res == WIDEN("true ") );
>+
>+ res = std::format(WIDEN("{:=^#7X}"), v[1]);
>+ VERIFY( res == WIDEN("==0X0==") );
>+}
>+
>+int main()
>+{
>+ test_format_string();
>+ test_output<char>();
>+ test_output<wchar_t>();
>+}
>--
>2.48.1
>
>
More information about the Libstdc++
mailing list