[libc++] [docs] Add C++2b (to be C++23) status page.

[curdeius]

Summary

Also:

• Fix header line in all status tables.
• Use C++20 instead of C++2a.

[miscco]

Awesome, thanks a lot!

[Mordante]

Thanks for the patch.
One minor nit, other than that LGTM.

libcxx/docs/Cxx2aStatus.rst

18

Can you add a line mentioning the standard was approved in September 2020?
(https://herbsutter.com/2020/09/06/c20-approved-c23-meetings-and-schedule-update/)

[ldionne]

LGTM with @Mordante 's suggestion. Thanks!

libcxx/docs/Cxx1yStatus.rst

 
 .. _paper-status-cxx1y:
 
 Paper Status
 ====================================
 
 .. csv-table::
    :file: Cxx1yStatusPaperStatus.csv
+   :header-rows: 1
    :widths: auto
 
 
 .. _issues-status-cxx1y:
 
 Library Working Group Issues Status
 ====================================
 
 .. csv-table::
    :file: Cxx1yStatusIssuesStatus.csv
+   :header-rows: 1
    :widths: auto
 
 Last Updated: 25-Mar-2014

libcxx/docs/Cxx1zStatus.rst

 
 .. _paper-status-cxx1z:
 
 Paper Status
 ====================================
 
 .. csv-table::
    :file: Cxx1zStatusPaperStatus.csv
+   :header-rows: 1
    :widths: auto
 
 .. note::
 
    .. [#note-P0433] P0433: So far, only the ``<string>``, sequence containers, container adaptors and ``<regex>`` portions of P0433 have been implemented.
    .. [#note-P0607] P0607: The parts of P0607 that are not done are the ``<regex>`` bits.
 
 
 .. _issues-status-cxx1z:
 
 Library Working Group Issues Status
 ====================================
 
 .. csv-table::
    :file: Cxx1zStatusIssuesStatus.csv
+   :header-rows: 1
    :widths: auto
 
 Last Updated: 17-Nov-2020

libcxx/docs/Cxx2aStatus.rst

 .. _cxx2a-status:
 
 ================================
-libc++ C++2a Status
+libc++ C++20 Status
 ================================
 
 .. include:: Helpers/Styles.rst
 
 .. contents::
    :local:
 
 
 Overview
 ================================
 
-In July 2017, the C++ standard committee created a draft for the next version of the C++ standard, known here as "C++2a" (probably to be C++20).
+In July 2017, the C++ standard committee created a draft for the next version of the C++ standard, initially known as "C++2a".
+In September 2020, the C++ standard committee approved this draft, and sent it to ISO for approval as C++20.
 
 This page shows the status of libc++; the status of clang's support of the language features is `here <https://clang.llvm.org/cxx_status.html#cxx2a>`__.
 
 .. attention:: Features in unreleased drafts of the standard are subject to change.
 
 The groups that have contributed papers:
 
 -  CWG - Core Language Working group
 -  LWG - Library working group
 -  SG1 - Study group #1 (Concurrency working group)
 
 .. note:: "Nothing to do" means that no library changes were needed to implement this change.
 
 .. _paper-status-cxx2a:
 
 Paper Status
 ====================================
 
 .. csv-table::
    :file: Cxx2aStatusPaperStatus.csv
+   :header-rows: 1
    :widths: auto
 
 .. note::
 
    .. [#note-P0202] P0202: The missing bits in P0202 are in ``copy`` and ``copy_backwards`` (and the ones that call them: ``copy_n``, ``set_union``, ``set_difference``, and ``set_symmetric_difference``). This is because the first two algorithms have specializations that call ``memmove`` which is not constexpr. See `Bug 25165 <https://bugs.llvm.org/show_bug.cgi?id=25165>`__
    .. [#note-P0600] P0600: The missing bits in P0600 are in |sect|\ [mem.res.class], |sect|\ [mem.poly.allocator.class], and |sect|\ [container.node.overview].
    .. [#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 ``std::allocator`` part is implemented.
 
 
 .. _issues-status-cxx2a:
 
 Library Working Group Issues Status
 ====================================
 
 .. csv-table::
    :file: Cxx2aStatusIssuesStatus.csv
+   :header-rows: 1
    :widths: auto
 
 Last Updated: 24-Nov-2020

libcxx/docs/Cxx2bStatus.rst

+.. _cxx2b-status:
+
+================================
+libc++ C++2b Status
+================================
+
+.. include:: Helpers/Styles.rst
+
+.. contents::
+   :local:
+
+
+Overview
+================================
+
+In November 2020, the C++ standard committee adopted the first changes to the next version of the C++ standard, known here as "C++2b" (probably to be C++23).
+
+.. This page shows the status of libc++; the status of clang's support of the language features is `here <https://clang.llvm.org/cxx_status.html#cxx2b>`__.
+
+.. attention:: Features in unreleased drafts of the standard are subject to change.
+
+The groups that have contributed papers:
+
+-  CWG - Core Language Working group
+-  LWG - Library working group
+-  SG1 - Study group #1 (Concurrency working group)
+
+.. note:: "Nothing to do" means that no library changes were needed to implement this change.
+
+.. _paper-status-cxx2b:
+
+Paper Status
+====================================
+
+.. csv-table::
+   :file: Cxx2bStatusPaperStatus.csv
+   :header-rows: 1
+   :widths: auto
+
+.. _issues-status-cxx2b:
+
+.. Library Working Group Issues Status
+.. ====================================
+
+.. .. csv-table::
+..    :file: Cxx2bStatusIssuesStatus.csv
+..    :header-rows: 1
+..    :widths: auto
+
+Last Updated: 30-Nov-2020

libcxx/docs/Cxx2bStatusPaperStatus.csv

+"Paper #","Group","Paper Name","Meeting","Status","First released version"
+"`P0881R7 <https://wg21.link/P0881R7>`__","LWG","A Proposal to add stacktrace library","Autumn 2020","",""
+"`P0943R6 <https://wg21.link/P0943R6>`__","LWG","Support C atomics in C++","Autumn 2020","",""
+"`P1048R1 <https://wg21.link/P1048R1>`__","LWG","A proposal for a type trait to detect scoped enumerations","Autumn 2020","",""
+"`P1679R3 <https://wg21.link/P1679R3>`__","LWG","string contains function","Autumn 2020","",""
+"","","","","",""

libcxx/docs/index.rst

.. toctree::
    ReleaseNotes
    UsingLibcxx
    BuildingLibcxx
    TestingLibcxx
    Contributing
    Cxx1yStatus
    Cxx1zStatus
    Cxx2aStatus
+   Cxx2bStatus
 
 
 .. toctree::
     :hidden:
 
     AddingNewCIJobs
     FeatureTestMacroTable
 

 
 C++ Dialect Support
 ---------------------
 
 * C++11 - Complete
 * :ref:`C++14 - Complete <cxx1y-status>`
 * :ref:`C++17 - In Progress <cxx1z-status>`
 * :ref:`C++20 - In Progress <cxx2a-status>`
+* :ref:`C++2b - Not Started <cxx2b-status>`
 * `Post C++14 Technical Specifications - In Progress <http://libcxx.llvm.org/ts1z_status.html>`__
 * :ref:`C++ Feature Test Macro Status <feature-status>`
 
 Notes and Known Issues
 ----------------------
 
 This list contains known issues with libc++