xref: /freebsd/contrib/llvm-project/libcxx/include/__format/unicode.h (revision 7fdf597e96a02165cfe22ff357b857d5fa15ed8a)
1 // -*- C++ -*-
2 //===----------------------------------------------------------------------===//
3 //
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef _LIBCPP___FORMAT_UNICODE_H
11 #define _LIBCPP___FORMAT_UNICODE_H
12 
13 #include <__assert>
14 #include <__bit/countl.h>
15 #include <__concepts/same_as.h>
16 #include <__config>
17 #include <__format/extended_grapheme_cluster_table.h>
18 #include <__format/indic_conjunct_break_table.h>
19 #include <__iterator/concepts.h>
20 #include <__iterator/readable_traits.h> // iter_value_t
21 #include <__utility/unreachable.h>
22 #include <string_view>
23 
24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
25 #  pragma GCC system_header
26 #endif
27 
28 _LIBCPP_BEGIN_NAMESPACE_STD
29 
30 #if _LIBCPP_STD_VER >= 20
31 
32 namespace __unicode {
33 
34 // Helper struct for the result of a consume operation.
35 //
36 // The status value for a correct code point is 0. This allows a valid value to
37 // be used without masking.
38 // When the decoding fails it know the number of code units affected. For the
39 // current use-cases that value is not needed, therefore it is not stored.
40 // The escape routine needs the number of code units for both a valid and
41 // invalid character and keeps track of it itself. Doing it in this result
42 // unconditionally would give some overhead when the value is unneeded.
43 struct __consume_result {
44   // When __status == __ok it contains the decoded code point.
45   // Else it contains the replacement character U+FFFD
46   char32_t __code_point : 31;
47 
48   enum : char32_t {
49     // Consumed a well-formed code point.
50     __ok = 0,
51     // Encountered invalid UTF-8
52     __error = 1
53   } __status : 1 {__ok};
54 };
55 static_assert(sizeof(__consume_result) == sizeof(char32_t));
56 
57 #  ifndef _LIBCPP_HAS_NO_UNICODE
58 
59 /// Implements the grapheme cluster boundary rules
60 ///
61 /// These rules are used to implement format's width estimation as stated in
62 /// [format.string.std]/11
63 ///
64 /// The Standard refers to UAX \#29 for Unicode 12.0.0
65 /// https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundary_Rules
66 ///
67 /// The data tables used are
68 /// https://www.unicode.org/Public/UCD/latest/ucd/auxiliary/GraphemeBreakProperty.txt
69 /// https://www.unicode.org/Public/UCD/latest/ucd/emoji/emoji-data.txt
70 /// https://www.unicode.org/Public/UCD/latest/ucd/auxiliary/GraphemeBreakTest.txt (for testing only)
71 
72 inline constexpr char32_t __replacement_character = U'\ufffd';
73 
74 // The error of a consume operation.
75 //
76 // This sets the code point to the replacement character. This code point does
77 // not participate in the grapheme clustering, so grapheme clustering code can
78 // ignore the error status and always use the code point.
79 inline constexpr __consume_result __consume_result_error{__replacement_character, __consume_result::__error};
80 
81 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool __is_high_surrogate(char32_t __value) {
82   return __value >= 0xd800 && __value <= 0xdbff;
83 }
84 
85 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool __is_low_surrogate(char32_t __value) {
86   return __value >= 0xdc00 && __value <= 0xdfff;
87 }
88 
89 // https://www.unicode.org/glossary/#surrogate_code_point
90 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_surrogate(char32_t __value) {
91   return __value >= 0xd800 && __value <= 0xdfff;
92 }
93 
94 // https://www.unicode.org/glossary/#code_point
95 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_code_point(char32_t __value) {
96   return __value <= 0x10ffff;
97 }
98 
99 // https://www.unicode.org/glossary/#unicode_scalar_value
100 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr bool __is_scalar_value(char32_t __value) {
101   return __unicode::__is_code_point(__value) && !__unicode::__is_surrogate(__value);
102 }
103 
104 template <contiguous_iterator _Iterator>
105   requires same_as<iter_value_t<_Iterator>, char>
106 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_continuation(_Iterator __char, int __count) {
107   do {
108     if ((*__char & 0b1100'0000) != 0b1000'0000)
109       return false;
110     --__count;
111     ++__char;
112   } while (__count);
113   return true;
114 }
115 
116 /// Helper class to extract a code unit from a Unicode character range.
117 ///
118 /// The stored range is a view. There are multiple specialization for different
119 /// character types.
120 template <class _CharT>
121 class __code_point_view;
122 
123 /// UTF-8 specialization.
124 template <>
125 class __code_point_view<char> {
126   using _Iterator = basic_string_view<char>::const_iterator;
127 
128 public:
129   _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
130       : __first_(__first), __last_(__last) {}
131 
132   _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
133   _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
134 
135   // https://www.unicode.org/versions/latest/ch03.pdf#G7404
136   // Based on Table 3-7, Well-Formed UTF-8 Byte Sequences
137   //
138   // Code Points        First Byte Second Byte Third Byte Fourth Byte  Remarks
139   // U+0000..U+007F     00..7F                                         U+0000..U+007F 1 code unit range
140   //                    C0..C1     80..BF                              invalid overlong encoding
141   // U+0080..U+07FF     C2..DF     80..BF                              U+0080..U+07FF 2 code unit range
142   //                    E0         80..9F      80..BF                  invalid overlong encoding
143   // U+0800..U+0FFF     E0         A0..BF      80..BF                  U+0800..U+FFFF 3 code unit range
144   // U+1000..U+CFFF     E1..EC     80..BF      80..BF
145   // U+D000..U+D7FF     ED         80..9F      80..BF
146   // U+D800..U+DFFF     ED         A0..BF      80..BF                  invalid encoding of surrogate code point
147   // U+E000..U+FFFF     EE..EF     80..BF      80..BF
148   //                    F0         80..8F      80..BF     80..BF       invalid overlong encoding
149   // U+10000..U+3FFFF   F0         90..BF      80..BF     80..BF       U+10000..U+10FFFF 4 code unit range
150   // U+40000..U+FFFFF   F1..F3     80..BF      80..BF     80..BF
151   // U+100000..U+10FFFF F4         80..8F      80..BF     80..BF
152   //                    F4         90..BF      80..BF     80..BF       U+110000.. invalid code point range
153   //
154   // Unlike other parsers, these invalid entries are tested after decoding.
155   // - The parser always needs to consume these code units
156   // - The code is optimized for well-formed UTF-8
157   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
158     _LIBCPP_ASSERT_INTERNAL(__first_ != __last_, "can't move beyond the end of input");
159 
160     // Based on the number of leading 1 bits the number of code units in the
161     // code point can be determined. See
162     // https://en.wikipedia.org/wiki/UTF-8#Encoding
163     switch (std::countl_one(static_cast<unsigned char>(*__first_))) {
164     case 0:
165       return {static_cast<unsigned char>(*__first_++)};
166 
167     case 2: {
168       if (__last_ - __first_ < 2 || !__unicode::__is_continuation(__first_ + 1, 1)) [[unlikely]]
169         break;
170 
171       char32_t __value = static_cast<unsigned char>(*__first_++) & 0x1f;
172       __value <<= 6;
173       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
174 
175       // These values should be encoded in 1 UTF-8 code unit.
176       if (__value < 0x0080) [[unlikely]]
177         return __consume_result_error;
178 
179       return {__value};
180     }
181 
182     case 3: {
183       if (__last_ - __first_ < 3 || !__unicode::__is_continuation(__first_ + 1, 2)) [[unlikely]]
184         break;
185 
186       char32_t __value = static_cast<unsigned char>(*__first_++) & 0x0f;
187       __value <<= 6;
188       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
189       __value <<= 6;
190       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
191 
192       // These values should be encoded in 1 or 2 UTF-8 code units.
193       if (__value < 0x0800) [[unlikely]]
194         return __consume_result_error;
195 
196       // A surrogate value is always encoded in 3 UTF-8 code units.
197       if (__unicode::__is_surrogate(__value)) [[unlikely]]
198         return __consume_result_error;
199 
200       return {__value};
201     }
202 
203     case 4: {
204       if (__last_ - __first_ < 4 || !__unicode::__is_continuation(__first_ + 1, 3)) [[unlikely]]
205         break;
206 
207       char32_t __value = static_cast<unsigned char>(*__first_++) & 0x07;
208       __value <<= 6;
209       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
210       __value <<= 6;
211       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
212       __value <<= 6;
213       __value |= static_cast<unsigned char>(*__first_++) & 0x3f;
214 
215       // These values should be encoded in 1, 2, or 3 UTF-8 code units.
216       if (__value < 0x10000) [[unlikely]]
217         return __consume_result_error;
218 
219       // A value too large is always encoded in 4 UTF-8 code units.
220       if (!__unicode::__is_code_point(__value)) [[unlikely]]
221         return __consume_result_error;
222 
223       return {__value};
224     }
225     }
226     // An invalid number of leading ones can be garbage or a code unit in the
227     // middle of a code point. By consuming one code unit the parser may get
228     // "in sync" after a few code units.
229     ++__first_;
230     return __consume_result_error;
231   }
232 
233 private:
234   _Iterator __first_;
235   _Iterator __last_;
236 };
237 
238 #    ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
239 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_surrogate_pair_high(wchar_t __value) {
240   return __value >= 0xd800 && __value <= 0xdbff;
241 }
242 
243 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_surrogate_pair_low(wchar_t __value) {
244   return __value >= 0xdc00 && __value <= 0xdfff;
245 }
246 
247 /// This specialization depends on the size of wchar_t
248 /// - 2 UTF-16 (for example Windows and AIX)
249 /// - 4 UTF-32 (for example Linux)
250 template <>
251 class __code_point_view<wchar_t> {
252   using _Iterator = typename basic_string_view<wchar_t>::const_iterator;
253 
254 public:
255   static_assert(sizeof(wchar_t) == 2 || sizeof(wchar_t) == 4, "sizeof(wchar_t) has a not implemented value");
256 
257   _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
258       : __first_(__first), __last_(__last) {}
259 
260   _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
261   _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
262 
263   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
264     _LIBCPP_ASSERT_INTERNAL(__first_ != __last_, "can't move beyond the end of input");
265 
266     char32_t __value = static_cast<char32_t>(*__first_++);
267     if constexpr (sizeof(wchar_t) == 2) {
268       if (__unicode::__is_low_surrogate(__value)) [[unlikely]]
269         return __consume_result_error;
270 
271       if (__unicode::__is_high_surrogate(__value)) {
272         if (__first_ == __last_ || !__unicode::__is_low_surrogate(static_cast<char32_t>(*__first_))) [[unlikely]]
273           return __consume_result_error;
274 
275         __value -= 0xd800;
276         __value <<= 10;
277         __value += static_cast<char32_t>(*__first_++) - 0xdc00;
278         __value += 0x10000;
279 
280         if (!__unicode::__is_code_point(__value)) [[unlikely]]
281           return __consume_result_error;
282       }
283     } else {
284       if (!__unicode::__is_scalar_value(__value)) [[unlikely]]
285         return __consume_result_error;
286     }
287 
288     return {__value};
289   }
290 
291 private:
292   _Iterator __first_;
293   _Iterator __last_;
294 };
295 #    endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
296 
297 // State machine to implement the Extended Grapheme Cluster Boundary
298 //
299 // The exact rules may change between Unicode versions.
300 // This implements the extended rules see
301 // https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries
302 class __extended_grapheme_cluster_break {
303   using __EGC_property  = __extended_grapheme_custer_property_boundary::__property;
304   using __inCB_property = __indic_conjunct_break::__property;
305 
306 public:
307   _LIBCPP_HIDE_FROM_ABI constexpr explicit __extended_grapheme_cluster_break(char32_t __first_code_point)
308       : __prev_code_point_(__first_code_point),
309         __prev_property_(__extended_grapheme_custer_property_boundary::__get_property(__first_code_point)) {
310     // Initializes the active rule.
311     if (__prev_property_ == __EGC_property::__Extended_Pictographic)
312       __active_rule_ = __rule::__GB11_emoji;
313     else if (__prev_property_ == __EGC_property::__Regional_Indicator)
314       __active_rule_ = __rule::__GB12_GB13_regional_indicator;
315     else if (__indic_conjunct_break::__get_property(__first_code_point) == __inCB_property::__Consonant)
316       __active_rule_ = __rule::__GB9c_indic_conjunct_break;
317   }
318 
319   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(char32_t __next_code_point) {
320     __EGC_property __next_property = __extended_grapheme_custer_property_boundary::__get_property(__next_code_point);
321     bool __result                  = __evaluate(__next_code_point, __next_property);
322     __prev_code_point_             = __next_code_point;
323     __prev_property_               = __next_property;
324     return __result;
325   }
326 
327   // The code point whose break propery are considered during the next
328   // evaluation cyle.
329   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr char32_t __current_code_point() const { return __prev_code_point_; }
330 
331 private:
332   // The naming of the identifiers matches the Unicode standard.
333   // NOLINTBEGIN(readability-identifier-naming)
334 
335   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool
336   __evaluate(char32_t __next_code_point, __EGC_property __next_property) {
337     switch (__active_rule_) {
338     case __rule::__none:
339       return __evaluate_none(__next_code_point, __next_property);
340     case __rule::__GB9c_indic_conjunct_break:
341       return __evaluate_GB9c_indic_conjunct_break(__next_code_point, __next_property);
342     case __rule::__GB11_emoji:
343       return __evaluate_GB11_emoji(__next_code_point, __next_property);
344     case __rule::__GB12_GB13_regional_indicator:
345       return __evaluate_GB12_GB13_regional_indicator(__next_code_point, __next_property);
346     }
347     __libcpp_unreachable();
348   }
349 
350   _LIBCPP_HIDE_FROM_ABI constexpr bool __evaluate_none(char32_t __next_code_point, __EGC_property __next_property) {
351     // *** Break at the start and end of text, unless the text is empty. ***
352 
353     _LIBCPP_ASSERT_INTERNAL(__prev_property_ != __EGC_property::__sot, "should be handled in the constructor"); // GB1
354     _LIBCPP_ASSERT_INTERNAL(__prev_property_ != __EGC_property::__eot, "should be handled by our caller");      // GB2
355 
356     // *** Do not break between a CR and LF. Otherwise, break before and after controls. ***
357     if (__prev_property_ == __EGC_property::__CR && __next_property == __EGC_property::__LF) // GB3
358       return false;
359 
360     if (__prev_property_ == __EGC_property::__Control || __prev_property_ == __EGC_property::__CR ||
361         __prev_property_ == __EGC_property::__LF) // GB4
362       return true;
363 
364     if (__next_property == __EGC_property::__Control || __next_property == __EGC_property::__CR ||
365         __next_property == __EGC_property::__LF) // GB5
366       return true;
367 
368     // *** Do not break Hangul syllable sequences. ***
369     if (__prev_property_ == __EGC_property::__L &&
370         (__next_property == __EGC_property::__L || __next_property == __EGC_property::__V ||
371          __next_property == __EGC_property::__LV || __next_property == __EGC_property::__LVT)) // GB6
372       return false;
373 
374     if ((__prev_property_ == __EGC_property::__LV || __prev_property_ == __EGC_property::__V) &&
375         (__next_property == __EGC_property::__V || __next_property == __EGC_property::__T)) // GB7
376       return false;
377 
378     if ((__prev_property_ == __EGC_property::__LVT || __prev_property_ == __EGC_property::__T) &&
379         __next_property == __EGC_property::__T) // GB8
380       return false;
381 
382     // *** Do not break before extending characters or ZWJ. ***
383     if (__next_property == __EGC_property::__Extend || __next_property == __EGC_property::__ZWJ)
384       return false; // GB9
385 
386     // *** Do not break before SpacingMarks, or after Prepend characters. ***
387     if (__next_property == __EGC_property::__SpacingMark) // GB9a
388       return false;
389 
390     if (__prev_property_ == __EGC_property::__Prepend) // GB9b
391       return false;
392 
393     // *** Do not break within certain combinations with Indic_Conjunct_Break (InCB)=Linker. ***
394     if (__indic_conjunct_break::__get_property(__next_code_point) == __inCB_property::__Consonant) {
395       __active_rule_                     = __rule::__GB9c_indic_conjunct_break;
396       __GB9c_indic_conjunct_break_state_ = __GB9c_indic_conjunct_break_state::__Consonant;
397       return true;
398     }
399 
400     // *** Do not break within emoji modifier sequences or emoji zwj sequences. ***
401     if (__next_property == __EGC_property::__Extended_Pictographic) {
402       __active_rule_      = __rule::__GB11_emoji;
403       __GB11_emoji_state_ = __GB11_emoji_state::__Extended_Pictographic;
404       return true;
405     }
406 
407     // *** Do not break within emoji flag sequences ***
408 
409     // That is, do not break between regional indicator (RI) symbols if there
410     // is an odd number of RI characters before the break point.
411     if (__next_property == __EGC_property::__Regional_Indicator) { // GB12 + GB13
412       __active_rule_ = __rule::__GB12_GB13_regional_indicator;
413       return true;
414     }
415 
416     // *** Otherwise, break everywhere. ***
417     return true; // GB999
418   }
419 
420   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool
421   __evaluate_GB9c_indic_conjunct_break(char32_t __next_code_point, __EGC_property __next_property) {
422     __inCB_property __break = __indic_conjunct_break::__get_property(__next_code_point);
423     if (__break == __inCB_property::__none) {
424       __active_rule_ = __rule::__none;
425       return __evaluate_none(__next_code_point, __next_property);
426     }
427 
428     switch (__GB9c_indic_conjunct_break_state_) {
429     case __GB9c_indic_conjunct_break_state::__Consonant:
430       if (__break == __inCB_property::__Extend) {
431         return false;
432       }
433       if (__break == __inCB_property::__Linker) {
434         __GB9c_indic_conjunct_break_state_ = __GB9c_indic_conjunct_break_state::__Linker;
435         return false;
436       }
437       __active_rule_ = __rule::__none;
438       return __evaluate_none(__next_code_point, __next_property);
439 
440     case __GB9c_indic_conjunct_break_state::__Linker:
441       if (__break == __inCB_property::__Extend) {
442         return false;
443       }
444       if (__break == __inCB_property::__Linker) {
445         return false;
446       }
447       if (__break == __inCB_property::__Consonant) {
448         __GB9c_indic_conjunct_break_state_ = __GB9c_indic_conjunct_break_state::__Consonant;
449         return false;
450       }
451       __active_rule_ = __rule::__none;
452       return __evaluate_none(__next_code_point, __next_property);
453     }
454     __libcpp_unreachable();
455   }
456 
457   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool
458   __evaluate_GB11_emoji(char32_t __next_code_point, __EGC_property __next_property) {
459     switch (__GB11_emoji_state_) {
460     case __GB11_emoji_state::__Extended_Pictographic:
461       if (__next_property == __EGC_property::__Extend) {
462         __GB11_emoji_state_ = __GB11_emoji_state::__Extend;
463         return false;
464       }
465       [[fallthrough]];
466     case __GB11_emoji_state::__Extend:
467       if (__next_property == __EGC_property::__ZWJ) {
468         __GB11_emoji_state_ = __GB11_emoji_state::__ZWJ;
469         return false;
470       }
471       if (__next_property == __EGC_property::__Extend)
472         return false;
473       __active_rule_ = __rule::__none;
474       return __evaluate_none(__next_code_point, __next_property);
475 
476     case __GB11_emoji_state::__ZWJ:
477       if (__next_property == __EGC_property::__Extended_Pictographic) {
478         __GB11_emoji_state_ = __GB11_emoji_state::__Extended_Pictographic;
479         return false;
480       }
481       __active_rule_ = __rule::__none;
482       return __evaluate_none(__next_code_point, __next_property);
483     }
484     __libcpp_unreachable();
485   }
486 
487   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool
488   __evaluate_GB12_GB13_regional_indicator(char32_t __next_code_point, __EGC_property __next_property) {
489     __active_rule_ = __rule::__none;
490     if (__next_property == __EGC_property::__Regional_Indicator)
491       return false;
492     return __evaluate_none(__next_code_point, __next_property);
493   }
494 
495   char32_t __prev_code_point_;
496   __EGC_property __prev_property_;
497 
498   enum class __rule {
499     __none,
500     __GB9c_indic_conjunct_break,
501     __GB11_emoji,
502     __GB12_GB13_regional_indicator,
503   };
504   __rule __active_rule_ = __rule::__none;
505 
506   enum class __GB11_emoji_state {
507     __Extended_Pictographic,
508     __Extend,
509     __ZWJ,
510   };
511   __GB11_emoji_state __GB11_emoji_state_ = __GB11_emoji_state::__Extended_Pictographic;
512 
513   enum class __GB9c_indic_conjunct_break_state {
514     __Consonant,
515     __Linker,
516   };
517 
518   __GB9c_indic_conjunct_break_state __GB9c_indic_conjunct_break_state_ = __GB9c_indic_conjunct_break_state::__Consonant;
519 
520   // NOLINTEND(readability-identifier-naming)
521 };
522 
523 /// Helper class to extract an extended grapheme cluster from a Unicode character range.
524 ///
525 /// This function is used to determine the column width of an extended grapheme
526 /// cluster. In order to do that only the first code point is evaluated.
527 /// Therefore only this code point is extracted.
528 template <class _CharT>
529 class __extended_grapheme_cluster_view {
530   using _Iterator = typename basic_string_view<_CharT>::const_iterator;
531 
532 public:
533   _LIBCPP_HIDE_FROM_ABI constexpr explicit __extended_grapheme_cluster_view(_Iterator __first, _Iterator __last)
534       : __code_point_view_(__first, __last), __at_break_(__code_point_view_.__consume().__code_point) {}
535 
536   struct __cluster {
537     /// The first code point of the extended grapheme cluster.
538     ///
539     /// The first code point is used to estimate the width of the extended
540     /// grapheme cluster.
541     char32_t __code_point_;
542 
543     /// Points one beyond the last code unit in the extended grapheme cluster.
544     ///
545     /// It's expected the caller has the start position and thus can determine
546     /// the code unit range of the extended grapheme cluster.
547     _Iterator __last_;
548   };
549 
550   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __cluster __consume() {
551     char32_t __code_point = __at_break_.__current_code_point();
552     _Iterator __position  = __code_point_view_.__position();
553     while (!__code_point_view_.__at_end()) {
554       if (__at_break_(__code_point_view_.__consume().__code_point))
555         break;
556       __position = __code_point_view_.__position();
557     }
558     return {__code_point, __position};
559   }
560 
561 private:
562   __code_point_view<_CharT> __code_point_view_;
563   __extended_grapheme_cluster_break __at_break_;
564 };
565 
566 template <contiguous_iterator _Iterator>
567 __extended_grapheme_cluster_view(_Iterator, _Iterator) -> __extended_grapheme_cluster_view<iter_value_t<_Iterator>>;
568 
569 #  else //  _LIBCPP_HAS_NO_UNICODE
570 
571 // For ASCII every character is a "code point".
572 // This makes it easier to write code agnostic of the _LIBCPP_HAS_NO_UNICODE define.
573 template <class _CharT>
574 class __code_point_view {
575   using _Iterator = typename basic_string_view<_CharT>::const_iterator;
576 
577 public:
578   _LIBCPP_HIDE_FROM_ABI constexpr explicit __code_point_view(_Iterator __first, _Iterator __last)
579       : __first_(__first), __last_(__last) {}
580 
581   _LIBCPP_HIDE_FROM_ABI constexpr bool __at_end() const noexcept { return __first_ == __last_; }
582   _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __position() const noexcept { return __first_; }
583 
584   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __consume_result __consume() noexcept {
585     _LIBCPP_ASSERT_INTERNAL(__first_ != __last_, "can't move beyond the end of input");
586     return {static_cast<char32_t>(*__first_++)};
587   }
588 
589 private:
590   _Iterator __first_;
591   _Iterator __last_;
592 };
593 
594 #  endif //  _LIBCPP_HAS_NO_UNICODE
595 
596 } // namespace __unicode
597 
598 #endif //_LIBCPP_STD_VER >= 20
599 
600 _LIBCPP_END_NAMESPACE_STD
601 
602 #endif // _LIBCPP___FORMAT_UNICODE_H
603