[libc++][doc] Updates format related release notes.

[Mordante]

Summary

As suggested by @ldionne.

[avogelsgesang]

Thanks a lot for all the work you have put into implementing std::format and std::print! It's amazing to see this coming together!

libcxx/docs/ReleaseNotes/17.rst

43

Does it make sense to also mention C++23 improvements and std::print?

62

should this be moved down into the format specific section?

65

move down?

66

move down?

69

move into new section?

90–91

I didn't hear the term "main library" before. Is it supposed to be the opposite of "experimental library"? I think that most users didn't use the experimental library before and might even know of its existence. Hopefully the suggested edit is easier to understand?

93

Should the comment on https://libcxx.llvm.org/Status/Cxx20.html#note-p0645 also be updated?

Or maybe just update the versions from 14.0 to 17.0 and remove the note completely?

Same for P1652, P1892, P1868, P2216, P2418

99

The page https://libcxx.llvm.org/Status/Cxx23.html seems to be missing a note for P2286R8 and P2508R1 that they were so far experimental, and claims they were already available in 15.0/16.0

Update both to 17.0?

101

Should we also mention the (partial) implementation of P2585R0?

[avogelsgesang]

libcxx/docs/ReleaseNotes/17.rst

101

Wrong paper number...
I meant P2093R14, i.e. std::print

[Mordante]

Thanks a lot for the feedback! I'll keep this open for Louis to comment. We can always merge documentation updates directly on the release branch.

libcxx/docs/ReleaseNotes/17.rst

43

Yes I noticed that omission after I uploaded the patch and I didn't want to run the CI again.

62

I prefer to keep the things really new in this section. For users of -fexperimental-library this is a new feature.

90–91

Thanks. I was not completely happy with the previous wording too. I like your suggestion.

93

I will update the note. For now I keep the version number as is. Since we now use the experimental library more often we need to figure out a way how we can properly document this. IIRC for ranges we basically didn't update much.

99

Good point. As above we need to discuss how to mark experimental parts in the future.

[Mordante]

libcxx/docs/ReleaseNotes/17.rst

101

I did that above.

[Mordante]

Address review comments and rebased.

[ldionne]

Remember this needs to be cherry-picked to release/17.x or it won't take effect! Thanks!

[avogelsgesang]

libcxx/docs/ReleaseNotes/17.rst

77–79

[Mordante]

Thanks for the reviews, I'll make a backport request later today.

libcxx/docs/ReleaseNotes/17.rst

 What's New in Libc++ 17.0.0?
 ============================
 
 The main focus of the libc++ team has been to implement new C++20 and C++23
 features. Work on the next C++ version, C++26, has started.
 
 The C++20 ``format`` library is marked as stable. The library is not complete since
 the C++20 ``chrono`` library lacks supports for time zones and some clocks.
 
 The C++20 spaceship operator is almost complete. It misses ``long double`` and
 time zone support.
 
 There is an experimental implementation of the C++23 ``std`` module. See
 :ref:`ModulesInLibcxx` for more information.
 
 An experimental implementation of the C++20 ``stop_token`` is available.
 
 Work has started on the C++17 Parallel STL. This feature is experimental, see
 :ref:`pstl-status` for the current status.
 
 
 Implemented Papers
 ------------------
 - P1206R7 - ``ranges::to``: A function to convert any range to a container
 - P2520R0 - ``move_iterator<T*>`` should be a random access iterator
 - P1328R1 - ``constexpr type_info::operator==()``
 - P2693R1 - Formatting ``thread::id`` (the ``stacktrace`` is not done yet)
 - P2675R1 - ``format``'s width estimation is too approximate and not forward compatible
 - P2505R5 - Monadic operations for ``std::expected``
 - P2711R1 - Making Multi-Param Constructors Of views explicit (``join_with_view`` is not done yet)
 - P2572R1 - ``std::format`` fill character allowances
 - P2510R3 - Formatting pointers
 - P2136R3 - ``invoke_r``
 - P2494R2 - Relaxing range adaptors to allow for move only types
 - P2585R0 - Improving default container formatting
 - P0408R7 - Efficient Access to ``basic_stringbuf``'s Buffer
 - P2474R2 - ``views::repeat``
 - P0009R18 - ``mdspan`` (``layout_stride`` is not done yet)
+- P2093R14 - Formatted output (the ``ostream`` overload is not done yet)
+- P2539R4 - Should the output of ``std::print`` to a terminal be synchronized
+  with the underlying stream? (the ``ostream`` overload is not done yet)
+
+With the ``format`` library available in the being marked as stable the
+following papers are now available by default without using
+``-fexperimental-library``:
+
+- P0645 - Text Formatting
+- P1652 - Printf corner cases in std::format
+- P1892 - Extended locale-specific presentation specifiers for std::format
+- P1868 - width: clarifying units of width and precision in std::format
+- P2216 - std::format improvements
+- P2418 - Add support for std::generator-like types to std::format
+- P2286R8 - Formatting Ranges
+- P2508R1 - Exposing std::basic-format-string
 
 Improvements and New Features
 -----------------------------
 - ``std::equal``, ``std::ranges::equal``, ``std::find``, and
   ``std::ranges::find``  are now forwarding to ``std::memcmp`` for trivially
   equality comparable types, 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.
 
 - The performance of ``dynamic_cast`` on its hot paths is greatly improved and is as efficient as the
   ``libsupc++`` implementation. Note that the performance improvements are shipped in ``libcxxabi``.
 
 - `D122780 <https://reviews.llvm.org/D122780>`_ Improved the performance of ``std::sort`` and ``std::ranges::sort``
   by up to 50% for arithmetic types and by approximately 10% for other types.
 
 - The ``<format>`` header is no longer considered experimental. Some
   ``std::formatter`` specializations are not yet available since the class used
   in the specialization has not been implemented in libc++. This prevents the
   feature-test macro to be set.
 

libcxx/docs/Status/Cxx20.rst

.. csv-table::
    :file: Cxx20Papers.csv
    :header-rows: 1
    :widths: auto
 
 .. note::
 
    .. [#note-P0591] P0591: The changes in [mem.poly.allocator.mem] are missing.
    .. [#note-P0645] P0645: The paper is implemented but still marked as an incomplete feature
-      (the feature-test macro is not set and the libary is only available when built with ``-fexperimental-library``).
-      Not yet implemented LWG-issues will cause API and ABI breakage.
+      (the feature-test macro is not set).
    .. [#note-P0966] P0966: It was previously erroneously marked as complete in version 8.0. See `bug 45368 <https://llvm.org/PR45368>`__.
    .. [#note-P0619] P0619: Only sections D.8, D.9, D.10 and D.13 are implemented. Sections D.4, D.7, D.11, D.12, and D.14 remain undone.
    .. [#note-P0883.1] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.
    .. [#note-P0883.2] P0883: ``ATOMIC_FLAG_INIT`` was marked deprecated in version 14.0, but was undeprecated with the implementation of LWG3659 in version 15.0.
    .. [#note-P2231] P2231: Optional is complete. The changes to variant haven't been implemented yet.
    .. [#note-P0660] P0660: Section 32.3 Stop Tokens is complete. ``jthread`` hasn't been implemented yet.
 
 .. _issues-status-cxx20:
 
 Library Working Group Issues Status
 ====================================
 
 .. csv-table::
    :file: Cxx20Issues.csv
    :header-rows: 1
    :widths: auto