[libc++][format] Implements formatter thread::id.

[Mordante]

Summary

Since stacktrace header is WIP and it's not sure that will be done
before LLVM17 update the documentation. When the header is implemented
implementing the formatter is trivial, so that can be done quickly
afterwards.

Implements parts of:

• P2693R1 Formatting thread::id and stacktrace

[Mordante]

Retrigger CI.

[Mordante]

CI fixes.

[Mordante]

CI Fixes.

[Mordante]

CI fixes.

[Mordante]

CI fixes and try to fix an Apple system.

[Mordante]

Retry CI.

[Mordante]

CI Test.

[Mordante]

Implements pointer based formatting for Apple platforms.

[Mordante]

Rebased and get a full CI run again.

[Mordante]

Removes debug code.

[Mordante]

Attempts to fix the CI.

[Mordante]

CI fixes.

[Mordante]

Use a different approach to try to fix the CI.

[Mordante]

libcxx/include/thread

261

Note before I used a larger if constexpr. but that failed. In the not taken branches the reinterpret_cast caused compilation errors.

264

TODO remove.

[Mordante]

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.format.pass.cpp

18

Review all test to match the availablity as changed in D134598.

[ldionne]

libcxx/include/thread

239

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.tests.h

18

std::stringstream s; s << id;
assert(s.str() == std::format("{}", id);

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/parse.pass.cpp

50

This seems a bit clever to me. Can we pass the expected end position as a parameter to the function explicitly? So this would look like it == fmt.begin() + offset. If you have this pattern in other places, I'm OK to land the patch as-is but we could have a simple patch to change all of them.

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/stream.pass.cpp

31–32

While we're at it, can we also test the output stream version on an empty std::thread::id?

40–42

[Mordante]

Thanks for the review!

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.tests.h

18

As discussed this change is already done in stream.pass.cpp.

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/stream.pass.cpp

31–32

Based on [thread.thread.id]/1

An object of type thread​::​id provides a unique identifier for each thread of execution and a single distinct value for all thread objects that do not represent a thread of execution ([thread.thread.class]).
Each thread of execution has an associated thread​::​id object that is not equal to the thread​::​id object of any other thread of execution and that is not equal to the thread​::​id object of any thread object that does not represent threads of execution.

That value is unspecified and may differ between implementations; I expect it will be different.

[Mordante]

Rebased, addresses review comment, and get a CI run.

NOTE: Clang-Format Team Automated Review Comment

It looks like your clang-format review does not contain any unit tests, please try to ensure all code changes have a unit test (unless this is an NFC or refactoring, adding documentation etc..)

Add your unit tests in clang/unittests/Format and you can build with ninja FormatTests. We recommend using the verifyFormat(xxx) format of unit tests rather than EXPECT_EQ as this will ensure you change is tolerant to random whitespace changes (see FormatTest.cpp as an example)

For situations where your change is altering the TokenAnnotator.cpp which can happen if you are trying to improve the annotation phase to ensure we are correctly identifying the type of a token, please add a token annotator test in TokenAnnotatorTest.cpp

[Mordante]

CI fixes.

[Mordante]

CI fixes

[Mordante]

CI fixes.

[Mordante]

CI fixes

[Mordante]

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/parse.pass.cpp

50

See D147885

[manojgupta]

Just a heads up, with this change, we are hitting issues in building gdb. Appreciate any ideas on what is wrong.

aarch64-cros-linux-gnu-clang++ -x c++    -I. -I. -I./config -DLOCALEDIR="\"/usr/share/locale\"" -DHAVE_CONFIG_H -I./../include/opcode   -I../bfd -I./../bfd -I./../include -I../libdecnumber -I./../libdecnumber  -I./../gnulib/import -I../gnulib/import -I./.. -I..  -DTUI=1    -I./.. -pthread  -Wall -Wpointer-arith -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wempty-body -Wunused-but-set-parameter -Wunused-but-set-variable -Wno-sign-compare -Wno-error=maybe-uninitialized -Wno-mismatched-tags -Wno-error=deprecated-register -Wsuggest-override -Wimplicit-fallthrough=3 -Wduplicated-cond -Wshadow=local -Wdeprecated-copy -Wdeprecated-copy-dtor -Wredundant-move -Wmissing-declarations -Wmissing-prototypes -Wstrict-null-sentinel -Wformat -Wformat-nonliteral  -Os -pipe -march=armv8-a+crc+crypto -ftree-vectorize -g -ffunction-sections -fdata-sections     -c -o minsyms.o -MT minsyms.o -MMD -MP -MF ./.deps/minsyms.Tpo minsyms.c
 In file included from minsyms.c:56:
 In file included from ./../gdbsupport/parallel-for.h:25:
 In file included from /usr/bin/../include/c++/v1/thread:100:
 In file included from /usr/bin/../include/c++/v1/__format/formatter_integral.h:32:
 In file included from /usr/bin/../include/c++/v1/locale:203:
 /usr/bin/../include/c++/v1/__locale:600:5: error: '__abi_tag__' attribute only applies to structs, variables, functions, and namespaces
     _LIBCPP_INLINE_VISIBILITY
     ^
 /usr/bin/../include/c++/v1/__config:668:37: note: expanded from macro '_LIBCPP_INLINE_VISIBILITY'
 #  define _LIBCPP_INLINE_VISIBILITY _LIBCPP_HIDE_FROM_ABI
                                     ^
 /usr/bin/../include/c++/v1/__config:647:26: note: expanded from macro '_LIBCPP_HIDE_FROM_ABI'
           __attribute__((__abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_VERSIONED_IDENTIFIER))))
                          ^
 In file included from minsyms.c:56:
 In file included from ./../gdbsupport/parallel-for.h:25:
 In file included from /usr/bin/../include/c++/v1/thread:100:
 In file included from /usr/bin/../include/c++/v1/__format/formatter_integral.h:32:
 In file included from /usr/bin/../include/c++/v1/locale:203:
 /usr/bin/../include/c++/v1/__locale:601:37: error: expected ';' at end of declaration list
     char_type toupper(char_type __c) const
                                     ^
 /usr/bin/../include/c++/v1/__locale:607:48: error: too many arguments provided to function-like macro invocation
     const char_type* toupper(char_type* __low, const char_type* __high) const
                                                ^
 ./../include/safe-ctype.h:146:9: note: macro 'toupper' defined here
 #define toupper(c) do_not_use_toupper_with_safe_ctype
         ^
 In file included from minsyms.c:56:
 In file included from ./../gdbsupport/parallel-for.h:25:
 In file included from /usr/bin/../include/c++/v1/thread:100:
 In file included from /usr/bin/../include/c++/v1/__format/formatter_integral.h:32:
 In file included from /usr/bin/../include/c++/v1/locale:203:
 /usr/bin/../include/c++/v1/__locale:619:48: error: too many arguments provided to function-like macro invocation
     const char_type* tolower(char_type* __low, const char_type* __high) const
                                                ^
 ./../include/safe-ctype.h:148:9: note: macro 'tolower' defined here
 #define tolower(c) do_not_use_tolower_with_safe_ctype
         ^

Contents of __locale at line 600:

_LIBCPP_INLINE_VISIBILITY
char_type toupper(char_type __c) const
{
    return do_toupper(__c);
}

[manojgupta]

I have opened a bug at issuetracker.google.com/issues/277967395

[tahonermann]

Adding Corentin for awareness.

[manojgupta]

Hmm, looking deeper, gdb (actually binutils), is doing something weird.

https://github.com/bminor/binutils-gdb/blob/master/include/safe-ctype.h

/* Prevent the users of safe-ctype.h from accidently using the routines
   from ctype.h.  Initially, the approach was to produce an error when
   detecting that ctype.h has been included.  But this was causing
   trouble as ctype.h might get indirectly included as a result of
   including another system header (for instance gnulib's stdint.h).
   So we include ctype.h here and then immediately redefine its macros.  */

#include <ctype.h>
#undef isalpha
#define isalpha(c) do_not_use_isalpha_with_safe_ctype
#undef isalnum
#define isalnum(c) do_not_use_isalnum_with_safe_ctype
<snip>

So any use of isupper/islower etc will cause an error.
Why this patch is triggering it:
It adds an include of #include <__format/formatter_integral.h> which ends up including <locale> which has internal definitions of isupper/islower causing clang to complain.
Any suggestions on what would be the right fix here?

[tahonermann]

It adds an include of #include <__format/formatter_integral.h> which ends up including <locale> which has internal definitions of isupper/islower causing clang to complain.

Any suggestions on what would be the right fix here?

It sounds like safe-ctype.h should also add a #include of <locale> (when compiling as C++) to avoid interfering with the std::locale variants of those functions.

[manojgupta]

Thanks, sent a patch to gdb at https://sourceware.org/pipermail/gdb-patches/2023-April/198870.html

libcxx/docs/FeatureTestMacroTable.rst

.. table:: Current Status
     ``__cpp_lib_constexpr_cmath``                     *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_memory``                    ``202202L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_typeinfo``                  ``202106L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_expected``                            ``202202L``
     ------------------------------------------------- -----------------
+    ``__cpp_lib_formatters``                          *unimplemented*
+    ------------------------------------------------- -----------------
     ``__cpp_lib_forward_like``                        ``202207L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_invoke_r``                            ``202106L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_is_scoped_enum``                      ``202011L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_move_only_function``                  *unimplemented*
     ------------------------------------------------- -----------------

libcxx/docs/ReleaseNotes.rst

 
 What's New in Libc++ 17.0.0?
 ============================
 
 Implemented Papers
 ------------------
 - P2520R0 - ``move_iterator<T*>`` should be a random access iterator
 - P1328R1 - ``constexpr type_info::operator==()``
+- P1413R3 - Formatting ``thread::id`` (the ``stacktrace`` is not done yet)
 
 Improvements and New Features
 -----------------------------
 - ``std::equal`` and ``std::ranges::equal`` are now forwarding to ``std::memcmp`` for integral types and pointers,
   which can lead up to 40x performance improvements.
 
 - ``std::string_view`` now provides iterators that check for out-of-bounds accesses when the safe
   libc++ mode is enabled.

libcxx/docs/Status/Cxx2b.rst

 
 .. note::
 
    .. [#note-P0533R9] P0533R9: ``isfinite``, ``isinf``, ``isnan`` and ``isnormal`` are implemented.
    .. [#note-P1413R3] P1413R3: ``std::aligned_storage_t`` and ``std::aligned_union_t`` are marked deprecated, but
       clang doesn't issue a diagnostic for deprecated using template declarations.
    .. [#note-P2520R0] P2520R0: Libc++ implemented this paper as a DR in C++20 as well.
    .. [#note-P2711R1] P2711R1: ``join_with_view`` hasn't been done yet since this type isn't implemented yet.
+   .. [#note-P2693R1] P1413R3: The formatter for ``std::thread::id`` is implemented.
+      The formatter for ``stacktrace`` is not implemented, since ``stacktrace`` is
+      not implemented yet.
 
 .. _issues-status-cxx2b:
 
 Library Working Group Issues Status
 ====================================
 
 .. csv-table::
    :file: Cxx2bIssues.csv
    :header-rows: 1
    :widths: auto
 
 .. note::
 
    .. [#note-LWG3798] LWG3798: ``join_with_view``, ``zip_transform_view``, and ``adjacent_transform_view`` haven't been done yet since these types aren't implemented yet.

libcxx/docs/Status/Cxx2bPapers.csv

 "`P0290R4 <https://wg21.link/P0290R4>`__","LWG", "``apply()`` for ``synchronized_value<T>``","February 2023","","","|concurrency TS|"
 "`P2770R0 <https://wg21.link/P2770R0>`__","LWG", "Stashing stashing ``iterators`` for proper flattening","February 2023","","","|ranges|"
 "`P2164R9 <https://wg21.link/P2164R9>`__","LWG", "``views::enumerate``","February 2023","","","|ranges|"
 "`P2711R1 <https://wg21.link/P2711R1>`__","LWG", "Making multi-param constructors of ``views`` ``explicit``","February 2023","|Partial| [#note-P2711R1]_","","|ranges|"
 "`P2609R3 <https://wg21.link/P2609R3>`__","LWG", "Relaxing Ranges Just A Smidge","February 2023","","","|ranges|"
 "`P2713R1 <https://wg21.link/P2713R1>`__","LWG", "Escaping improvements in ``std::format``","February 2023","","","|format|"
 "`P2675R1 <https://wg21.link/P2675R1>`__","LWG", "``format``'s width estimation is too approximate and not forward compatible","February 2023","","","|format|"
 "`P2572R1 <https://wg21.link/P2572R1>`__","LWG", "``std::format`` fill character allowances","February 2023","","","|format|"
-"`P2693R1 <https://wg21.link/P2693R1>`__","LWG", "Formatting ``thread::id`` and ``stacktrace``","February 2023","","","|format|"
+"`P2693R1 <https://wg21.link/P2693R1>`__","LWG", "Formatting ``thread::id`` and ``stacktrace``","February 2023","|Partial| [#note-P2693R1]_","","|format|"
 "`P2679R2 <https://wg21.link/P2679R2>`__","LWG", "Fixing ``std::start_lifetime_as`` for arrays","February 2023","","",""
 "`P2674R1 <https://wg21.link/P2674R1>`__","LWG", "A trait for implicit lifetime types","February 2023","","",""
 "`P2655R3 <https://wg21.link/P2655R3>`__","LWG", "``common_reference_t`` of ``reference_wrapper`` Should Be a Reference Type","February 2023","","",""
 "`P2652R2 <https://wg21.link/P2652R2>`__","LWG", "Disallow User Specialization of ``allocator_traits``","February 2023","","",""
 "`P2787R1 <https://wg21.link/P2787R1>`__","LWG", "``pmr::generator`` - Promise Types are not Values","February 2023","","",""
 "`P2614R2 <https://wg21.link/P2614R2>`__","LWG", "Deprecate ``numeric_limits::has_denorm``","February 2023","","",""
 "`P2588R3 <https://wg21.link/P2588R3>`__","LWG", "``barrier``’s phase completion guarantees","February 2023","","",""
 "`P2763R1 <https://wg21.link/P2763R1>`__","LWG", "``layout_stride`` static extents default constructor fix","February 2023","","",""
 "`P2736R2 <https://wg21.link/P2736R2>`__","CWG","Referencing The Unicode Standard","February 2023","","","|format|"

libcxx/docs/Status/FormatPaper.csv

 `[format.range.fmtset] <https://wg21.link/format.range.fmtset>`_,"Formatting for ranges: set",,Mark de Wever,|Complete|,Clang 16
 `[format.range] <https://wg21.link/format.range>`_,"Formatting for ranges: container adaptors",,Mark de Wever,|Complete|,Clang 16
 `[format.range] <https://wg21.link/format.range>`_,"Formatting for ranges: ``pair`` and ``tuple``",,Mark de Wever,|Complete|,Clang 16
 `[format.range] <https://wg21.link/format.range>`_,"Formatting for ranges: ``vector<bool>``",,Mark de Wever,|Complete|,Clang 16
 "`P2585R0 <https://wg21.link/P2585R0>`__","Improving default container formatting"
 `[format.range.fmtstr] <https://wg21.link/format.range.fmtstr>`_,"Formatting for ranges: strings",,Mark de Wever,|In Progress|,
 `[format.range.fmtstr] <https://wg21.link/format.range.fmtstr>`_,"Formatting for ranges: strings",,Mark de Wever,|In Progress|,
 "`P2693R1 <https://wg21.link/P2693R1>`__","Formatting ``thread::id`` and ``stacktrace``"
-`[thread.thread.id] <https://wg21.link/thread.thread.id>`_,"Formatting ``thread::id``",,Mark de Wever,|In Progress|,
+`[thread.thread.id] <https://wg21.link/thread.thread.id>`_,"Formatting ``thread::id``",,Mark de Wever,|Complete|,Clang 17
 `[stacktrace.format] <https://wg21.link/stacktrace.format>`_,"Formatting ``stacktrace``",A ``<stacktrace>`` implementation,Mark de Wever,,

libcxx/include/__format/parser_std_format_spec.h

inline constexpr __fields __fields_floating_point{
     .__locale_specific_form_ = true,
     .__type_                 = true};
 inline constexpr __fields __fields_string{.__precision_ = true, .__type_ = true};
 inline constexpr __fields __fields_pointer{.__type_ = true};
 
 #  if _LIBCPP_STD_VER >= 23
 inline constexpr __fields __fields_tuple{.__use_range_fill_ = true};
 inline constexpr __fields __fields_range{.__use_range_fill_ = true};
+inline constexpr __fields __fields_fill_align_width{};
 #  endif
 
 enum class _LIBCPP_ENUM_VIS __alignment : uint8_t {
   /// No alignment is set in the format string.
   __default,
   __left,
   __center,
   __right,

libcxx/include/__threading_support

#endif // _LIBCPP_STD_VER <= 17
     _LIBCPP_INLINE_VISIBILITY
     basic_ostream<_CharT, _Traits>&
     operator<<(basic_ostream<_CharT, _Traits>& __os, __thread_id __id);
 
 private:
     _LIBCPP_INLINE_VISIBILITY
     __thread_id(__libcpp_thread_id __id) : __id_(__id) {}
 
+    _LIBCPP_HIDE_FROM_ABI friend __libcpp_thread_id __get_underlying_id(const __thread_id __id) { return __id.__id_; }
+
     friend __thread_id this_thread::get_id() _NOEXCEPT;
     friend class _LIBCPP_TYPE_VIS thread;
     friend struct _LIBCPP_TEMPLATE_VIS hash<__thread_id>;
 };
 
 inline _LIBCPP_HIDE_FROM_ABI
 bool operator==(__thread_id __x, __thread_id __y) _NOEXCEPT {
   // Don't pass id==0 to underlying routines

libcxx/include/thread

 bool operator> (thread::id x, thread::id y) noexcept;             // removed in C++20
 bool operator>=(thread::id x, thread::id y) noexcept;             // removed in C++20
 strong_ordering operator<=>(thread::id x, thread::id y) noexcept; // C++20
 
 template<class charT, class traits>
 basic_ostream<charT, traits>&
 operator<<(basic_ostream<charT, traits>& out, thread::id id);
 
+template<class charT>
+struct formatter<thread::id, charT>;
+
 namespace this_thread
 {
 
 thread::id get_id() noexcept;
 
 void yield() noexcept;
 
 template <class Clock, class Duration>
 void sleep_until(const chrono::time_point<Clock, Duration>& abs_time);
 
 template <class Rep, class Period>
 void sleep_for(const chrono::duration<Rep, Period>& rel_time);
 
 }  // this_thread
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__availability>
 #include <__chrono/steady_clock.h>
 #include <__chrono/time_point.h>
+#include <__concepts/arithmetic.h>
 #include <__condition_variable/condition_variable.h>
 #include <__config>
 #include <__exception/terminate.h>
+#include <__format/concepts.h>
+#include <__format/format_parse_context.h>
+#include <__format/formatter.h>
+#include <__format/formatter_integral.h>
+#include <__format/parser_std_format_spec.h>
 #include <__functional/hash.h>
 #include <__memory/addressof.h>
 #include <__memory/unique_ptr.h>
 #include <__mutex/mutex.h>
 #include <__mutex/unique_lock.h>
 #include <__thread/poll_with_backoff.h>
 #include <__thread/timed_backoff_policy.h>
 #include <__threading_support>

 };
 
 template<class _CharT, class _Traits>
 _LIBCPP_INLINE_VISIBILITY
 basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, __thread_id __id)
 {return __os << __id.__id_;}
 
+#if _LIBCPP_STD_VER >= 23
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS formatter<__thread_id, _CharT> {
+  public:
+    _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
+        -> decltype(__parse_ctx.begin()) {
+        return __parser_.__parse(__parse_ctx, __format_spec::__fields_fill_align_width);
+    }
+
+    _LIBCPP_HIDE_FROM_ABI auto format(__thread_id __id, auto& __ctx) const -> decltype(__ctx.out()) {
+        // In __threading_support __libcpp_thread_id is either a
+        // unsigned long long or a pthread_t.
+        //
+        // The type of pthread_t is left unspecified in POSIX so it can be any
+        // type. The most logical types are an integral or pointer.
+        // On Linux systems pthread_t is an unsigned long long.
+        // On Apple systems pthread_t is a pointer type.
+        //
+        // Note the output should match what the stream operator does. Since
+        // the ostream operator has been shipped years before this formatter
+        // was added to the Standard, this formatter does what the stream
+        // operator does. This may require platform specific changes.
+
+        using _Tp = decltype(__get_underlying_id(__id));
+        using _Cp = conditional_t<integral<_Tp>, _Tp, conditional_t<is_pointer_v<_Tp>, uintptr_t, void>>;
+        static_assert(!is_same_v<_Cp, void>, "unsupported thread::id type, please file a bug report");
+
+        __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
+        if constexpr (is_pointer_v<_Tp>) {
+          __specs.__std_.__alternate_form_ = true;
+          __specs.__std_.__type_           = __format_spec::__type::__hexadecimal_lower_case;
+        }
+        return __formatter::__format_integer(reinterpret_cast<_Cp>(__get_underlying_id(__id)), __ctx, __specs);
+    }
+
+    __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__right};
+};
+#endif // _LIBCPP_STD_VER >= 23
+
 class _LIBCPP_TYPE_VIS thread
 {
     __libcpp_thread_t __t_;
 
     thread(const thread&);
     thread& operator=(const thread&);
 public:
     typedef __thread_id id;

libcxx/include/version

__cpp_lib_erase_if                                      202002L <deque> <forward_list> <list>
                                                                 <map> <set> <string>
                                                                 <unordered_map> <unordered_set> <vector>
 __cpp_lib_exchange_function                             201304L <utility>
 __cpp_lib_execution                                     201902L <execution>
                                                         201603L // C++17
 __cpp_lib_expected                                      202202L <expected>
 __cpp_lib_filesystem                                    201703L <filesystem>
 __cpp_lib_format                                        202106L <format>
+__cpp_lib_formatters                                    202302L <stacktrace> <thread>
 __cpp_lib_forward_like                                  202207L <utility>
 __cpp_lib_gcd_lcm                                       201606L <numeric>
 __cpp_lib_generic_associative_lookup                    201304L <map> <set>
 __cpp_lib_generic_unordered_lookup                      201811L <unordered_map> <unordered_set>
 __cpp_lib_hardware_interference_size                    201703L <new>
 __cpp_lib_has_unique_object_representations             201606L <type_traits>
 __cpp_lib_hypot                                         201603L <cmath>
 __cpp_lib_incomplete_container_elements                 201505L <forward_list> <list> <vector>

 # define __cpp_lib_byteswap                             202110L
 # define __cpp_lib_constexpr_bitset                     202207L
 # define __cpp_lib_constexpr_charconv                   202207L
 // # define __cpp_lib_constexpr_cmath                      202202L
 # undef  __cpp_lib_constexpr_memory
 # define __cpp_lib_constexpr_memory                     202202L
 # define __cpp_lib_constexpr_typeinfo                   202106L
 # define __cpp_lib_expected                             202202L
+# if !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_format) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+// #   define __cpp_lib_formatters                         202302L
+# endif
 # define __cpp_lib_forward_like                         202207L
 # define __cpp_lib_invoke_r                             202106L
 # define __cpp_lib_is_scoped_enum                       202011L
 // # define __cpp_lib_move_only_function                   202110L
 # undef  __cpp_lib_optional
 # define __cpp_lib_optional                             202110L
 // # define __cpp_lib_out_ptr                              202106L
 # define __cpp_lib_ranges_as_rvalue                     202207L

libcxx/test/libcxx/transitive_includes/cxx03.csv

 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error type_traits
 system_error version
+thread array
 thread chrono
 thread compare
 thread cstddef
 thread cstdint
 thread cstring
 thread ctime
 thread functional
 thread iosfwd
 thread limits
+thread locale
 thread new
 thread ratio
+thread string
+thread string_view
 thread system_error
 thread tuple
 thread type_traits
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple exception
 tuple iosfwd
 tuple new
 tuple type_traits
 tuple typeinfo

libcxx/test/libcxx/transitive_includes/cxx11.csv

 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error type_traits
 system_error version
+thread array
 thread chrono
 thread compare
 thread cstddef
 thread cstdint
 thread cstring
 thread ctime
 thread functional
 thread iosfwd
 thread limits
+thread locale
 thread new
 thread ratio
+thread string
+thread string_view
 thread system_error
 thread tuple
 thread type_traits
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple exception
 tuple iosfwd
 tuple new
 tuple type_traits
 tuple typeinfo

libcxx/test/libcxx/transitive_includes/cxx14.csv

 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error type_traits
 system_error version
+thread array
 thread chrono
 thread compare
 thread cstddef
 thread cstdint
 thread cstring
 thread ctime
 thread functional
 thread iosfwd
 thread limits
+thread locale
 thread new
 thread ratio
+thread string
+thread string_view
 thread system_error
 thread tuple
 thread type_traits
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple exception
 tuple iosfwd
 tuple new
 tuple type_traits
 tuple typeinfo

libcxx/test/libcxx/transitive_includes/cxx17.csv

 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error type_traits
 system_error version
+thread array
 thread chrono
 thread compare
 thread cstddef
 thread cstdint
 thread cstring
 thread ctime
 thread functional
 thread iosfwd
 thread limits
+thread locale
 thread new
 thread ratio
+thread string
+thread string_view
 thread system_error
 thread tuple
 thread type_traits
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple exception
 tuple iosfwd
 tuple new
 tuple type_traits
 tuple typeinfo

libcxx/test/libcxx/transitive_includes/cxx20.csv

 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error type_traits
 system_error version
+thread array
 thread compare
 thread cstddef
 thread cstdint
+thread cstdlib
 thread cstring
 thread ctime
 thread functional
 thread iosfwd
 thread limits
+thread locale
 thread new
 thread ratio
+thread stdexcept
+thread string
+thread string_view
 thread system_error
 thread tuple
 thread type_traits
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple exception
 tuple iosfwd
 tuple new
 tuple type_traits
 tuple typeinfo

libcxx/test/libcxx/transitive_includes/cxx2b.csv

 system_error compare
 system_error cstddef
 system_error cstdint
 system_error cstring
 system_error limits
 system_error stdexcept
 system_error string
 system_error version
+thread array
 thread compare
 thread cstddef
+thread cstdint
+thread cstdlib
 thread ctime
 thread iosfwd
 thread limits
+thread locale
 thread ratio
+thread stdexcept
+thread string
+thread string_view
 thread system_error
 thread tuple
+thread vector
 thread version
 tuple compare
 tuple cstddef
 tuple version
 type_traits cstddef
 type_traits cstdint
 type_traits version
 typeindex compare

libcxx/test/std/language.support/support.limits/support.limits.general/thread.version.compile.pass.cpp

 // clang-format off
 
 // UNSUPPORTED: no-threads
 
 // <thread>
 
 // Test the feature test macros defined by <thread>
 
-/*  Constant             Value
-    __cpp_lib_jthread    201911L [C++20]
+/*  Constant                Value
+    __cpp_lib_formatters    202302L [C++2b]
+    __cpp_lib_jthread       201911L [C++20]
 */
 
 #include <thread>
 #include "test_macros.h"
 
 #if TEST_STD_VER < 14
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_jthread
 #   error "__cpp_lib_jthread should not be defined before c++20"
 # endif
 
 #elif TEST_STD_VER == 14
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_jthread
 #   error "__cpp_lib_jthread should not be defined before c++20"
 # endif
 
 #elif TEST_STD_VER == 17
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_jthread
 #   error "__cpp_lib_jthread should not be defined before c++20"
 # endif
 
 #elif TEST_STD_VER == 20
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_jthread
 #     error "__cpp_lib_jthread should be defined in c++20"
 #   endif
 #   if __cpp_lib_jthread != 201911L
 #     error "__cpp_lib_jthread should have the value 201911L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_jthread
 #     error "__cpp_lib_jthread should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
 #elif TEST_STD_VER > 20
 
 # if !defined(_LIBCPP_VERSION)
+#   ifndef __cpp_lib_formatters
+#     error "__cpp_lib_formatters should be defined in c++2b"
+#   endif
+#   if __cpp_lib_formatters != 202302L
+#     error "__cpp_lib_formatters should have the value 202302L in c++2b"
+#   endif
+# else // _LIBCPP_VERSION
+#   ifdef __cpp_lib_formatters
+#     error "__cpp_lib_formatters should not be defined because it is unimplemented in libc++!"
+#   endif
+# endif
+
+# if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_jthread
 #     error "__cpp_lib_jthread should be defined in c++2b"
 #   endif
 #   if __cpp_lib_jthread != 201911L
 #     error "__cpp_lib_jthread should have the value 201911L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_jthread
 #     error "__cpp_lib_jthread should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
 #endif // TEST_STD_VER > 20
 

libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp

/*  Constant                                       Value
     __cpp_lib_endian                               201907L [C++20]
     __cpp_lib_erase_if                             202002L [C++20]
     __cpp_lib_exchange_function                    201304L [C++14]
     __cpp_lib_execution                            201603L [C++17]
                                                    201902L [C++20]
     __cpp_lib_expected                             202202L [C++2b]
     __cpp_lib_filesystem                           201703L [C++17]
     __cpp_lib_format                               202106L [C++20]
+    __cpp_lib_formatters                           202302L [C++2b]
     __cpp_lib_forward_like                         202207L [C++2b]
     __cpp_lib_gcd_lcm                              201606L [C++17]
     __cpp_lib_generic_associative_lookup           201304L [C++14]
     __cpp_lib_generic_unordered_lookup             201811L [C++20]
     __cpp_lib_hardware_interference_size           201703L [C++17]
     __cpp_lib_has_unique_object_representations    201606L [C++17]
     __cpp_lib_hypot                                201603L [C++17]
     __cpp_lib_incomplete_container_elements        201505L [C++17]

 # ifdef __cpp_lib_filesystem
 #   error "__cpp_lib_filesystem should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_format
 #   error "__cpp_lib_format should not be defined before c++20"
 # endif
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_forward_like
 #   error "__cpp_lib_forward_like should not be defined before c++2b"
 # endif
 
 # ifdef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should not be defined before c++17"
 # endif
 

 # ifdef __cpp_lib_filesystem
 #   error "__cpp_lib_filesystem should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_format
 #   error "__cpp_lib_format should not be defined before c++20"
 # endif
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_forward_like
 #   error "__cpp_lib_forward_like should not be defined before c++2b"
 # endif
 
 # ifdef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should not be defined before c++17"
 # endif
 

 #     error "__cpp_lib_filesystem should not be defined when the requirement '!defined(_LIBCPP_AVAILABILITY_HAS_NO_FILESYSTEM)' is not met!"
 #   endif
 # endif
 
 # ifdef __cpp_lib_format
 #   error "__cpp_lib_format should not be defined before c++20"
 # endif
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_forward_like
 #   error "__cpp_lib_forward_like should not be defined before c++2b"
 # endif
 
 # ifndef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should be defined in c++17"
 # endif
 # if __cpp_lib_gcd_lcm != 201606L

 #     error "__cpp_lib_format should have the value 202106L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_format
 #     error "__cpp_lib_format should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
+# ifdef __cpp_lib_formatters
+#   error "__cpp_lib_formatters should not be defined before c++2b"
+# endif
+
 # ifdef __cpp_lib_forward_like
 #   error "__cpp_lib_forward_like should not be defined before c++2b"
 # endif
 
 # ifndef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should be defined in c++20"
 # endif
 # if __cpp_lib_gcd_lcm != 201606L

 #     error "__cpp_lib_format should have the value 202106L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_format
 #     error "__cpp_lib_format should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
+# if !defined(_LIBCPP_VERSION)
+#   ifndef __cpp_lib_formatters
+#     error "__cpp_lib_formatters should be defined in c++2b"
+#   endif
+#   if __cpp_lib_formatters != 202302L
+#     error "__cpp_lib_formatters should have the value 202302L in c++2b"
+#   endif
+# else // _LIBCPP_VERSION
+#   ifdef __cpp_lib_formatters
+#     error "__cpp_lib_formatters should not be defined because it is unimplemented in libc++!"
+#   endif
+# endif
+
 # ifndef __cpp_lib_forward_like
 #   error "__cpp_lib_forward_like should be defined in c++2b"
 # endif
 # if __cpp_lib_forward_like != 202207L
 #   error "__cpp_lib_forward_like should have the value 202207L in c++2b"
 # endif
 
 # ifndef __cpp_lib_gcd_lcm

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.format.pass.cpp

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Fix this test using GCC, it currently times out.
+// UNSUPPORTED: gcc-12
+
+// TODO FMT This test should not require std::to_chars(floating-point)
+// This test requires std::to_chars(floating-point), which is in the dylib
+// XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0}}
+
+// <thread>
+
+// template<class charT>
+// struct formatter<thread::id, charT>;
+
+// template<class... Args>
+//   string format(format_string<Args...> fmt, Args&&... args);
+// template<class... Args>
+//   wstring format(wformat_string<Args...> fmt, Args&&... args);
+
+#include <format>
+#include <cassert>
+
+#include "assert_macros.h"
+#include "concat_macros.h"
+#include "format.functions.tests.h"
+#include "test_format_string.h"
+#include "test_macros.h"
+
+auto test = []<class CharT, class... Args>(
+                std::basic_string_view<CharT> expected, test_format_string<CharT, Args...> fmt, Args&&... args) {
+  std::basic_string<CharT> out = std::format(fmt, std::forward<Args>(args)...);
+  TEST_REQUIRE(out == expected,
+               TEST_WRITE_CONCATENATED(
+                   "\nFormat string   ", fmt, "\nExpected output ", expected, "\nActual output   ", out, '\n'));
+};
+
+auto test_exception = []<class CharT, class... Args>(std::string_view, std::basic_string_view<CharT>, Args&&...) {
+  // After P2216 most exceptions thrown by std::format become ill-formed.
+  // Therefore this tests does nothing.
+};
+
+int main(int, char**) {
+  format_tests<char>(test, test_exception);
+
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  format_tests<wchar_t>(test, test_exception);
+#endif
+
+  return 0;
+}

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.tests.h

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_STD_THREAD_THREAD_THREADS_THREAD_THREAD_CLASS_THREAD_THREAD_ID_FORMAT_FUNCTIONS_TESTS_H
+#define TEST_STD_THREAD_THREAD_THREADS_THREAD_THREAD_CLASS_THREAD_THREAD_ID_FORMAT_FUNCTIONS_TESTS_H
+
+#include <thread>
+
+#include "format.functions.common.h"
+#include "test_macros.h"
+
+template <class CharT, class TestFunction, class ExceptionTest>
+void format_tests(TestFunction check, ExceptionTest check_exception) {
+  // Note the output of std::thread::id is unspecified. The output text is the
+  // same as the stream operator. Since that format is already released this
+  // test follows the practice on existing systems.
+  std::thread::id input{};
+
+  /***** Test the type specific part *****/
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
+  check(SV("0"), SV("{}"), input);
+
+  // *** align-fill & width ***
+  check(SV("    0"), SV("{:5}"), input);
+  check(SV("0****"), SV("{:*<5}"), input);
+  check(SV("__0__"), SV("{:_^5}"), input);
+  check(SV("::::0"), SV("{::>5}"), input); // This is not a range, so : is allowed as fill character.
+
+  check(SV("    0"), SV("{:{}}"), input, 5);
+  check(SV("0****"), SV("{:*<{}}"), input, 5);
+  check(SV("__0__"), SV("{:_^{}}"), input, 5);
+  check(SV("####0"), SV("{:#>{}}"), input, 5);
+#else  // !defined(__APPLE__) && !defined(__FreeBSD__)
+  check(SV("0x0"), SV("{}"), input);
+
+  // *** align-fill & width ***
+  check(SV("    0x0"), SV("{:7}"), input);
+  check(SV("0x0****"), SV("{:*<7}"), input);
+  check(SV("__0x0__"), SV("{:_^7}"), input);
+  check(SV("::::0x0"), SV("{::>7}"), input); // This is not a range, so : is allowed as fill character.
+
+  check(SV("    0x0"), SV("{:{}}"), input, 7);
+  check(SV("0x0****"), SV("{:*<{}}"), input, 7);
+  check(SV("__0x0__"), SV("{:_^{}}"), input, 7);
+  check(SV("####0x0"), SV("{:#>{}}"), input, 7);
+#endif // !defined(__APPLE__) && !defined(__FreeBSD__)
+
+  /***** Test the type generic part *****/
+  check_exception("The format-spec fill field contains an invalid character", SV("{:}<}"), input);
+  check_exception("The format-spec fill field contains an invalid character", SV("{:{<}"), input);
+
+  // *** sign ***
+  check_exception("The replacement field misses a terminating '}'", SV("{:-}"), input);
+  check_exception("The replacement field misses a terminating '}'", SV("{:+}"), input);
+  check_exception("The replacement field misses a terminating '}'", SV("{: }"), input);
+
+  // *** alternate form ***
+  check_exception("The replacement field misses a terminating '}'", SV("{:#}"), input);
+
+  // *** zero-padding ***
+  check_exception("A format-spec width field shouldn't have a leading zero", SV("{:0}"), input);
+
+  // *** precision ***
+  check_exception("The replacement field misses a terminating '}'", SV("{:.}"), input);
+
+  // *** locale-specific form ***
+  check_exception("The replacement field misses a terminating '}'", SV("{:L}"), input);
+
+  // *** type ***
+  for (std::basic_string_view<CharT> fmt : fmt_invalid_types<CharT>(""))
+    check_exception("The replacement field misses a terminating '}'", fmt, input);
+}
+
+#endif // TEST_STD_THREAD_THREAD_THREADS_THREAD_THREAD_CLASS_THREAD_THREAD_ID_FORMAT_FUNCTIONS_TESTS_H

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.functions.vformat.pass.cpp

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Fix this test using GCC, it currently times out.
+// UNSUPPORTED: gcc-12
+
+// TODO FMT This test should not require std::to_chars(floating-point)
+// This test requires std::to_chars(floating-point), which is in the dylib
+// XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0}}
+
+// <thread>
+
+// template<class charT>
+// struct formatter<thread::id, charT>;
+
+// string vformat(string_view fmt, format_args args);
+// wstring vformat(wstring_view fmt, wformat_args args);
+
+#include <format>
+#include <cassert>
+
+#include "assert_macros.h"
+#include "concat_macros.h"
+#include "format.functions.tests.h"
+#include "test_macros.h"
+
+auto test = []<class CharT, class... Args>(
+                std::basic_string_view<CharT> expected, std::basic_string_view<CharT> fmt, Args&&... args) {
+  std::basic_string<CharT> out = std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...));
+  TEST_REQUIRE(out == expected,
+               TEST_WRITE_CONCATENATED(
+                   "\nFormat string   ", fmt, "\nExpected output ", expected, "\nActual output   ", out, '\n'));
+};
+
+auto test_exception =
+    []<class CharT, class... Args>(
+        [[maybe_unused]] std::string_view what,
+        [[maybe_unused]] std::basic_string_view<CharT> fmt,
+        [[maybe_unused]] Args&&... args) {
+      TEST_VALIDATE_EXCEPTION(
+          std::format_error,
+          [&]([[maybe_unused]] const std::format_error& e) {
+            TEST_LIBCPP_REQUIRE(
+                e.what() == what,
+                TEST_WRITE_CONCATENATED(
+                    "\nFormat string   ", fmt, "\nExpected exception ", what, "\nActual exception   ", e.what(), '\n'));
+          },
+          TEST_IGNORE_NODISCARD std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...)));
+    };
+
+int main(int, char**) {
+  format_tests<char>(test, test_exception);
+
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  format_tests<wchar_t>(test, test_exception);
+#endif
+
+  return 0;
+}

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/format.pass.cpp

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Fix this test using GCC, it currently times out.
+// UNSUPPORTED: gcc-12
+
+// <thread>
+
+// template<class charT>
+// struct formatter<thread::id, charT>;
+
+// template<class FormatContext>
+//   typename FormatContext::iterator
+//     format(const T& r, FormatContext& ctx) const;
+
+// Note this tests the basics of this function. It's tested in more detail in
+// the format functions test.
+
+#include <cassert>
+#include <concepts>
+#include <thread>
+
+#include "test_format_context.h"
+#include "test_macros.h"
+#include "make_string.h"
+
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class StringViewT>
+void test_format(StringViewT expected, std::thread::id arg) {
+  using CharT      = typename StringViewT::value_type;
+  using String     = std::basic_string<CharT>;
+  using OutIt      = std::back_insert_iterator<String>;
+  using FormatCtxT = std::basic_format_context<OutIt, CharT>;
+
+  const std::formatter<std::thread::id, CharT> formatter;
+
+  String result;
+  OutIt out             = std::back_inserter(result);
+  FormatCtxT format_ctx = test_format_context_create<OutIt, CharT>(out, std::make_format_args<FormatCtxT>(arg));
+  formatter.format(arg, format_ctx);
+  assert(result == expected);
+}
+
+template <class CharT>
+void test_fmt() {
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
+  test_format(SV("0"), std::thread::id());
+#else
+  test_format(SV("0x0"), std::thread::id());
+#endif
+}
+
+void test() {
+  test_fmt<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test_fmt<wchar_t>();
+#endif
+}
+
+int main(int, char**) {
+  test();
+
+  return 0;
+}

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/parse.pass.cpp

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Fix this test using GCC, it currently times out.
+// UNSUPPORTED: gcc-12
+
+// <thread>
+
+// template<class charT>
+// struct formatter<thread::id, charT>;
+
+// template<class ParseContext>
+//   constexpr typename ParseContext::iterator
+//     parse(ParseContext& ctx);
+
+// Note this tests the basics of this function. It's tested in more detail in
+// the format functions test.
+
+#include <cassert>
+#include <concepts>
+#include <thread>
+
+#include "test_format_context.h"
+#include "test_macros.h"
+#include "make_string.h"
+
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class StringViewT>
+constexpr void test_parse(StringViewT fmt) {
+  using CharT    = typename StringViewT::value_type;
+  auto parse_ctx = std::basic_format_parse_context<CharT>(fmt);
+  std::formatter<std::thread::id, CharT> formatter;
+  static_assert(std::semiregular<decltype(formatter)>);
+
+  std::same_as<typename StringViewT::iterator> auto it = formatter.parse(parse_ctx);
+  assert(it == fmt.end() - (!fmt.empty() && fmt.back() == '}'));
+}
+
+template <class CharT>
+constexpr void test_fmt() {
+  test_parse(SV(""));
+  test_parse(SV("1"));
+
+  test_parse(SV("}"));
+  test_parse(SV("1}"));
+}
+
+constexpr bool test() {
+  test_fmt<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test_fmt<wchar_t>();
+#endif
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.id/stream.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: no-localization
 
+// TODO FMT This test should not require std::to_chars(floating-point)
+// This test requires std::to_chars(floating-point), which is in the dylib
+// XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0}}
+
 // <thread>
 
 // class thread::id
 
 // template<class charT, class traits>
 // basic_ostream<charT, traits>&
 // operator<<(basic_ostream<charT, traits>& out, thread::id id);
 
 #include <thread>
+#include <format>
 #include <sstream>
 #include <cassert>
 
+#include "make_string.h"
 #include "test_macros.h"
 
-int main(int, char**)
-{
-    std::thread::id id0 = std::this_thread::get_id();
-    std::ostringstream os;
-    os << id0;
+template <class CharT>
+static void test() {
+  std::basic_ostringstream<CharT> os;
 
+#if TEST_STD_VER > 20 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+  // C++23 added a formatter specialization for thread::id.
+  // This changed the requirement of ostream to have a
+  // [thread.thread.id]/2
+  //   The text representation for the character type charT of an object of
+  //   type thread::id is an unspecified sequence of charT ...
+  // This definition is used for both streaming and formatting.
+  //
+  // Test whether the output is identical.
+  std::basic_string<CharT> s = std::format(MAKE_STRING_VIEW(CharT, "{}"), id0);
+  assert(s == os.str());
+#endif
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
   return 0;
 }

libcxx/test/std/utilities/format/format.formattable/concept.formattable.compile.pass.cpp

#ifndef TEST_HAS_NO_LOCALIZATION
   //assert_is_formattable<std::chrono::zoned_time, CharT>();
 
 #endif // TEST_HAS_NO_LOCALIZATION
 }
 
 // Tests for P1636 Formatters for library types
 //
 // The paper hasn't been voted in so currently all formatters are disabled.
-// TODO validate whether the test is correct after the paper has been accepted.
+// Note the paper has been abandoned, the types are kept since other papers may
+// introduce these formatters.
 template <class CharT>
 void test_P1636() {
   assert_is_not_formattable<std::basic_streambuf<CharT>, CharT>();
   assert_is_not_formattable<std::bitset<42>, CharT>();
   assert_is_not_formattable<std::complex<double>, CharT>();
   assert_is_not_formattable<std::error_code, CharT>();
 #ifndef TEST_HAS_NO_FILESYSTEM_LIBRARY
   assert_is_not_formattable<std::filesystem::path, CharT>();
 #endif
   assert_is_not_formattable<std::shared_ptr<int>, CharT>();
 #ifndef TEST_HAS_NO_LOCALIZATION
   if constexpr (!std::same_as<CharT, int>) // sub_match only works with proper character types
     assert_is_not_formattable<std::sub_match<CharT*>, CharT>();
 #endif
 #ifndef TEST_HAS_NO_THREADS
-  assert_is_not_formattable<std::thread::id, CharT>();
+  assert_is_formattable<std::thread::id, CharT>();
 #endif
   assert_is_not_formattable<std::unique_ptr<int>, CharT>();
 }
 
 template <class CharT, class Vector>
 void test_P2286_vector_bool() {
   assert_is_formattable<Vector, CharT>();
   assert_is_formattable<typename Vector::reference, CharT>();

libcxx/utils/generate_feature_test_macro_components.py

"values": {
         "c++20": 202106,
         # "c++23": 202207, Not implemented P2419R2 Clarify handling of encodings in localized formatting of chrono types
         },
     "headers": ["format"],
     "test_suite_guard": "!defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)",
     "libcxx_guard": "!defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)",
     "unimplemented": True,
   }, {
+    "name": "__cpp_lib_formatters",
+    "values": { "c++2b": 202302 },
+    "headers": ["stacktrace", "thread"],
+    "test_suite_guard": "!defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_format) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)",
+    "libcxx_guard": "!defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_format) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)",
+    "unimplemented": True,
+  }, {
     "name": "__cpp_lib_forward_like",
     "values": { "c++2b": 202207 },
     "headers": ["utility"],
   }, {
     "name": "__cpp_lib_gcd_lcm",
     "values": { "c++17": 201606 },
     "headers": ["numeric"],
   }, {