On Tue, Oct 14, 2025 at 2:53 PM Jonathan Wakely <[email protected]> wrote:
> On Wed, 10 Sep 2025 at 15:53 +0200, Tomasz Kamiński wrote:
> >This patch implements _Escaping_sink that stores characters in a local
> (stack)
> >buffer. When the buffer is full, the range of characters is escaped and
> written
> >to the underlying sink.
> >
> >To support above, the __write_escaped_unicode_part function are defined.
> >It takes __str and __prev_esc by reference. The __prev_esc value is
> updated based
> >on the last character written. If the buffer ends with an incomplete code
> point
> >sequence, __str is left non-empty and the characters are not written.
> >_Escaping_sink then copies these characters to the front of the buffer to
> >reconstruct the full code point.
> >
> >__formatter__str::_M_format_range now uses _Escaping_sink to escape any
> >non-continuous character sequences.
> >
> >This addresses PR119820 by removing the code constructing string
> >completely.
> >
> > PR libstdc++/PR119820
> >
> >libstdc++-v3/ChangeLog:
> >
> > * include/std/format (__format::__write_escape_seqs)
> > (__format::_Escaping_sink): Define.
> > (__format::__write_escaped_unicode_part): Extract from
> > __format::__write_escaped_unicode.
> > (__format::__write_escaped_unicode): Forward to
> > __write_escaped_unicode_part.
> > (__formatter_str::_M_format_range): Use _Escaping sink.
> > * testsuite/std/format/ranges/string.cc: New tests for
> > character which codepoints will be split in buffer and
> > escaping. Invoked test_padding.
> >---
> >v2 just updates the patch description.
> >
> > libstdc++-v3/include/std/format | 197 +++++++++++++-----
> > .../testsuite/std/format/ranges/string.cc | 89 ++++++++
> > 2 files changed, 231 insertions(+), 55 deletions(-)
> >
> >diff --git a/libstdc++-v3/include/std/format
> b/libstdc++-v3/include/std/format
> >index d6a2170e45d..347f9f0a479 100644
> >--- a/libstdc++-v3/include/std/format
> >+++ b/libstdc++-v3/include/std/format
> >@@ -105,6 +105,7 @@ namespace __format
> > template<typename _CharT> class _Sink;
> > template<typename _CharT> class _Fixedbuf_sink;
> > template<typename _Out, typename _CharT> class _Padding_sink;
> >+ template<typename _Out, typename _CharT> class _Escaping_sink;
> >
> > // Output iterator that writes to a type-erase character sink.
> > template<typename _CharT>
> >@@ -1066,6 +1067,17 @@ namespace __format
> > return ++__out;
> > }
> >
> >+ template<typename _Out, typename _CharT>
> >+ _Out
> >+ __write_escape_seqs(_Out __out, basic_string_view<_CharT> __units)
> >+ {
> >+ using _UChar = make_unsigned_t<_CharT>;
> >+ for (_CharT __c : __units)
> >+ __out = __format::__write_escape_seq(
> >+ __out, static_cast<_UChar>(__c),
> _Escapes<_CharT>::_S_x());
>
> This is always a _Sink_iter, so we don't need to pass
> std::move(__out), right?
>
Yes, but that the case everywhere, so I will just add std::move here for
consistency.
>
> OK for trunk.
>
>
> >+ return __out;
> >+ }
> >+
> > template<typename _Out, typename _CharT>
> > _Out
> > __write_escaped_char(_Out __out, _CharT __c)
> >@@ -1124,12 +1136,10 @@ namespace __format
> >
> > template<typename _CharT, typename _Out>
> > _Out
> >- __write_escaped_unicode(_Out __out,
> >- basic_string_view<_CharT> __str,
> >- _Term_char __term)
> >+ __write_escaped_unicode_part(_Out __out, basic_string_view<_CharT>&
> __str,
> >+ bool& __prev_esc, _Term_char __term)
> > {
> > using _Str_view = basic_string_view<_CharT>;
> >- using _UChar = make_unsigned_t<_CharT>;
> > using _Esc = _Escapes<_CharT>;
> >
> > static constexpr char32_t __replace = U'\uFFFD';
> >@@ -1143,10 +1153,10 @@ namespace __format
> > }();
> >
> > __unicode::_Utf_view<char32_t, _Str_view> __v(std::move(__str));
> >+ __str = {};
> >+
> > auto __first = __v.begin();
> > auto const __last = __v.end();
> >-
> >- bool __prev_esc = true;
> > while (__first != __last)
> > {
> > bool __esc_ascii = false;
> >@@ -1185,15 +1195,32 @@ namespace __format
> > __out = __format::__write_escaped_char(__out, *__first.base());
> > else if (__esc_unicode)
> > __out = __format::__write_escape_seq(__out, *__first,
> _Esc::_S_u());
> >- else // __esc_replace
> >- for (_CharT __c : _Str_view(__first.base(),
> __first._M_units()))
> >- __out = __format::__write_escape_seq(__out,
> >-
> static_cast<_UChar>(__c),
> >- _Esc::_S_x());
> >+ // __esc_replace
> >+ else if (_Str_view __units(__first.base(), __first._M_units());
> >+ __units.end() != __last.base())
> >+ __out = __format::__write_escape_seqs(__out, __units);
> >+ else
> >+ {
> >+ __str = __units;
> >+ return __out;
> >+ }
> >+
> > __prev_esc = true;
> > ++__first;
> >-
> > }
> >+
> >+ return __out;
> >+ }
> >+
> >+ template<typename _CharT, typename _Out>
> >+ _Out
> >+ __write_escaped_unicode(_Out __out, basic_string_view<_CharT> __str,
> >+ _Term_char __term)
> >+ {
> >+ bool __prev_escape = true;
> >+ __out = __format::__write_escaped_unicode_part(__out, __str,
> >+ __prev_escape,
> __term);
> >+ __out = __format::__write_escape_seqs(__out, __str);
> > return __out;
> > }
> >
> >@@ -1412,55 +1439,28 @@ namespace __format
> > size_t(ranges::distance(__rg)));
> > return format(__str, __fc);
> > }
> >- else if (!_M_spec._M_debug)
> >+ else
> > {
> >+ auto __handle_debug = [this, &__rg]<typename _NOut>(_NOut
> __nout)
> >+ {
> >+ if (!_M_spec._M_debug)
> >+ return ranges::copy(__rg, std::move(__nout)).out;
> >+
> >+ _Escaping_sink<_NOut, _CharT>
> >+ __sink(std::move(__nout), _Term_quote);
> >+ ranges::copy(__rg, __sink.out());
> >+ return __sink._M_finish();
> >+ };
> >+
> > const size_t __padwidth = _M_spec._M_get_width(__fc);
> > if (__padwidth == 0 && _M_spec._M_prec_kind == _WP_none)
> >- return ranges::copy(__rg, __fc.out()).out;
> >+ return __handle_debug(__fc.out());
> >
> >- _Padding_sink<_Out, _CharT> __sink(__fc.out(), __padwidth,
> >-
> _M_spec._M_get_precision(__fc));
> >- ranges::copy(__rg, __sink.out());
> >+ _Padding_sink<_Out, _CharT>
> >+ __sink(__fc.out(), __padwidth,
> _M_spec._M_get_precision(__fc));
> >+ __handle_debug(__sink.out());
> > return __sink._M_finish(_M_spec._M_align, _M_spec._M_fill);
> > }
> >- else if constexpr (ranges::forward_range<_Rg> ||
> ranges::sized_range<_Rg>)
> >- {
> >- const size_t __n(ranges::distance(__rg));
> >- size_t __w = __n;
> >- if constexpr
> (!__unicode::__literal_encoding_is_unicode<_CharT>())
> >- if (size_t __max = _M_spec._M_get_precision(__fc); __n >
> __max)
> >- __w == __max;
> >-
> >- if (__w <= __format::__stackbuf_size<_CharT>)
> >- {
> >- _CharT __buf[__format::__stackbuf_size<_CharT>];
> >- ranges::copy_n(ranges::begin(__rg), __w, __buf);
> >- return _M_format_escaped(_String_view(__buf, __n), __fc);
> >- }
> >- else if constexpr (ranges::random_access_range<_Rg>)
> >- {
> >- ranges::iterator_t<_Rg> __first = ranges::begin(__rg);
> >- ranges::subrange __sub(__first, __first + __w);
> >- return _M_format_escaped(_String(from_range, __sub),
> __fc);
> >- }
> >- else if (__w <= __n)
> >- {
> >- ranges::subrange __sub(
> >- counted_iterator(ranges::begin(__rg), __w),
> >- default_sentinel);
> >- return _M_format_escaped(_String(from_range, __sub),
> __fc);
> >- }
> >- else if constexpr (ranges::sized_range<_Rg>)
> >- return _M_format_escaped(_String(from_range, __rg), __fc);
> >- else
> >- {
> >- // N.B. preserve the computed size
> >- ranges::subrange __sub(__rg, __n);
> >- return _M_format_escaped(_String(from_range, __sub),
> __fc);
> >- }
> >- }
> >- else
> >- return _M_format_escaped(_String(from_range, __rg), __fc);
> > }
> >
> > constexpr void
> >@@ -3915,6 +3915,93 @@ namespace __format
> > }
> > };
> >
> >+ template<typename _Out, typename _CharT>
> >+ class _Escaping_sink : public _Buf_sink<_CharT>
> >+ {
> >+ using _Esc = _Escapes<_CharT>;
> >+
> >+ _Out _M_out;
> >+ _Term_char _M_term : 2;
> >+ unsigned _M_prev_escape : 1;
> >+ unsigned _M_out_discards : 1;
> >+
> >+ void
> >+ _M_sync_discarding()
> >+ {
> >+ if constexpr (is_same_v<_Out, _Sink_iter<_CharT>>)
> >+ _M_out_discards = _M_out._M_discarding();
> >+ }
> >+
> >+ void
> >+ _M_write()
> >+ {
> >+ span<_CharT> __bytes = this->_M_used();
> >+ basic_string_view<_CharT> __str(__bytes.data(), __bytes.size());
> >+
> >+ size_t __rem = 0;
> >+ if constexpr (__unicode::__literal_encoding_is_unicode<_CharT>())
> >+ {
> >+ bool __prev_escape = _M_prev_escape;
> >+ _M_out = __format::__write_escaped_unicode_part(
> >+ std::move(_M_out), __str, __prev_escape, _M_term);
> >+ _M_prev_escape = __prev_escape;
> >+
> >+ __rem = __str.size();
> >+ if (__rem > 0 && __str.data() != this->_M_buf) [[unlikely]]
> >+ ranges::move(__str, this->_M_buf);
> >+ }
> >+ else
> >+ _M_out = __format::__write_escaped_ascii(
> >+ std::move(_M_out), __str, _M_term);
> >+
> >+ this->_M_reset(this->_M_buf, __rem);
> >+ _M_sync_discarding();
> >+ }
> >+
> >+ void
> >+ _M_overflow() override
> >+ {
> >+ if (_M_out_discards)
> >+ this->_M_rewind();
> >+ else
> >+ _M_write();
> >+ }
> >+
> >+ bool
> >+ _M_discarding() const override
> >+ { return _M_out_discards; }
> >+
> >+ public:
> >+ [[__gnu__::__always_inline__]]
> >+ explicit
> >+ _Escaping_sink(_Out __out, _Term_char __term)
> >+ : _M_out(std::move(__out)), _M_term(__term),
> >+ _M_prev_escape(true), _M_out_discards(false)
> >+ {
> >+ _M_out = __format::__write(std::move(_M_out),
> _Esc::_S_term(_M_term));
> >+ _M_sync_discarding();
> >+ }
> >+
> >+ _Out
> >+ _M_finish()
> >+ {
> >+ if (_M_out_discards)
> >+ return std::move(_M_out);
> >+
> >+ if (!this->_M_used().empty())
> >+ {
> >+ _M_write();
> >+ if constexpr (__unicode::__literal_encoding_is_unicode<_CharT>())
> >+ if (auto __rem = this->_M_used(); !__rem.empty())
> >+ {
> >+ basic_string_view<_CharT> __str(__rem.data(),
> __rem.size());
> >+ _M_out = __format::__write_escape_seqs(std::move(_M_out),
> __str);
> >+ }
> >+ }
> >+ return __format::__write(std::move(_M_out),
> _Esc::_S_term(_M_term));
> >+ }
> >+ };
> >+
> > enum class _Arg_t : unsigned char {
> > _Arg_none, _Arg_bool, _Arg_c, _Arg_i, _Arg_u, _Arg_ll, _Arg_ull,
> > _Arg_flt, _Arg_dbl, _Arg_ldbl, _Arg_str, _Arg_sv, _Arg_ptr,
> _Arg_handle,
> >diff --git a/libstdc++-v3/testsuite/std/format/ranges/string.cc
> b/libstdc++-v3/testsuite/std/format/ranges/string.cc
> >index 99e5eaf411f..a7d584f8e42 100644
> >--- a/libstdc++-v3/testsuite/std/format/ranges/string.cc
> >+++ b/libstdc++-v3/testsuite/std/format/ranges/string.cc
> >@@ -279,6 +279,93 @@ void test_padding()
> > VERIFY( strip_prefix(resv, 46, '*') );
> > VERIFY( strip_quotes(resv) );
> > VERIFY( resv == in );
> >+
> >+ // width is 5, size is 15
> >+ in = "\u2160\u2161\u2162\u2163\u2164";
> >+ in += in; // width is 10, size is 30
> >+ in += in; // width is 20, size is 60
> >+ in += in; // width is 40, size is 120
> >+ in += in; // width is 80, size is 240
> >+ in += in; // width is 160, size is 480
> >+
> >+ lc.assign_range(in);
> >+
> >+ resv = res = std::format("{:s}", lc);
> >+ VERIFY( resv == in );
> >+
> >+ resv = res = std::format("{:*>10s}", lc);
> >+ VERIFY( resv == in );
> >+
> >+ resv = res = std::format("{:*>200s}", lc);
> >+ VERIFY( strip_prefix(resv, 40, '*') );
> >+ VERIFY( resv == in );
> >+
> >+ resv = res = std::format("{:?s}", lc);
> >+ VERIFY( strip_quotes(resv) );
> >+ VERIFY( resv == in );
> >+
> >+ resv = res = std::format("{:*>10?s}", lc);
> >+ VERIFY( strip_quotes(resv) );
> >+ VERIFY( resv == in );
> >+
> >+ resv = res = std::format("{:*>200?s}", lc);
> >+ VERIFY( strip_prefix(resv, 38, '*') );
> >+ VERIFY( strip_quotes(resv) );
> >+ VERIFY( resv == in );
> >+}
> >+
> >+void test_escaping()
> >+{
> >+ std::string res;
> >+ std::string_view resv;
> >+
> >+ const std::string_view input =
> >+ "\t\n\r\\\""
> >+ "\u008a" // Cc, Control, Line Tabulation Set,
> >+ "\u00ad" // Cf, Format, Soft Hyphen
> >+ "\u1d3d" // Lm, Modifier letter, Modifier Letter Capital Ou
> >+ "\u00a0" // Zs, Space Separator, No-Break Space (NBSP)
> >+ "\u2029" // Zp, Paragraph Separator, Paragraph Separator
> >+ "\U0001f984" // So, Other Symbol, Unicorn Face
> >+ ;
> >+ const std::string_view output =
> >+ R"(\t\n\r\\\")"
> >+ R"(\u{8a})"
> >+ R"(\u{ad})"
> >+ "\u1d3d"
> >+ R"(\u{a0})"
> >+ R"(\u{2029})"
> >+ "\U0001f984";
> >+
> >+ std::forward_list<char> lc(std::from_range, input);
> >+ resv = res = std::format("{:s}", lc);
> >+ VERIFY( resv == input );
> >+ resv = res = std::format("{:?s}", lc);
> >+ VERIFY( strip_quotes(resv) );
> >+ VERIFY( resv == output );
> >+
> >+ // width is 5, size is 15
> >+ std::string in = "\u2160\u2161\u2162\u2163\u2164";
> >+ in += in; // width is 10, size is 30
> >+ in += in; // width is 20, size is 60
> >+ in += in; // width is 40, size is 120
> >+ in += in; // width is 80, size is 240
> >+ in += in; // width is 160, size is 480
> >+ std::string_view inv = in;
> >+
> >+ // last charcter is incomplete
> >+ lc.assign_range(inv.substr(0, 479));
> >+
> >+ // non-debug format, chars copied as is
> >+ resv = res = std::format("{:s}", lc);
> >+ VERIFY( resv == inv.substr(0, 479) );
> >+
> >+ // debug-format, incomplete code-point sequence is copied
> >+ resv = res = std::format("{:?s}", lc);
> >+ VERIFY( strip_quotes(resv) );
> >+ VERIFY( resv.substr(0, 477) == inv.substr(0, 477) );
> >+ resv.remove_prefix(477);
> >+ VERIFY( resv == R"(\x{e2}\x{85})" );
> > }
> >
> > int main()
> >@@ -287,4 +374,6 @@ int main()
> > test_outputs<char>();
> > test_outputs<wchar_t>();
> > test_nested();
> >+ test_padding();
> >+ test_escaping();
> > }
> >--
> >2.51.0
> >
> >
>
>
