[libc++] Add empty release notes file for LLVM 20

[ldionne]

While we haven't branched yet, this will make it easier for folks to add release notes for PRs that won't be merged before the LLVM 19 branch point.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

Changes

While we haven't branched yet, this will make it easier for folks to add release notes for PRs that won't be merged before the LLVM 19 branch point.

---

Full diff: https://github.com/llvm/llvm-project/pull/98355.diff

2 Files Affected:

• (modified) libcxx/docs/ReleaseNotes.rst (+2-1)
• (added) libcxx/docs/ReleaseNotes/20.rst (+75)

diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
index d25f2d06a56f3..5d98ade8d9918 100644
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -1,10 +1,11 @@
 .. include:: ReleaseNotes/19.rst
 
-.. Make sure to reference the previous release notes in a toctree to avoid Sphinx errors.
+.. Make sure to reference the non-live release notes in a toctree to avoid Sphinx errors.
 .. toctree::
     :hidden:
 
     ReleaseNotes/18
+    ReleaseNotes/20
 
 .. The release notes are in versioned files, but we make sure to keep publishing
 .. them in an unversioned ReleaseNotes.html page for external sites to reference.
diff --git a/libcxx/docs/ReleaseNotes/20.rst b/libcxx/docs/ReleaseNotes/20.rst
new file mode 100644
index 0000000000000..be4e1c2f9a4dd
--- /dev/null
+++ b/libcxx/docs/ReleaseNotes/20.rst
@@ -0,0 +1,75 @@
+===========================================
+Libc++ 20.0.0 (In-Progress) Release Notes
+===========================================
+
+.. contents::
+   :local:
+   :depth: 2
+
+Written by the `Libc++ Team <https://libcxx.llvm.org>`_
+
+.. warning::
+
+   These are in-progress notes for the upcoming libc++ 20.0.0 release.
+   Release notes for previous releases can be found on
+   `the Download Page <https://releases.llvm.org/download.html>`_.
+
+Introduction
+============
+
+This document contains the release notes for the libc++ C++ Standard Library,
+part of the LLVM Compiler Infrastructure, release 20.0.0. Here we describe the
+status of libc++ in some detail, including major improvements from the previous
+release and new feature work. For the general LLVM release notes, see `the LLVM
+documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
+be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
+
+For more information about libc++, please see the `Libc++ Web Site
+<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.
+
+Note that if you are reading this file from a Git checkout or the
+main Libc++ web page, this document applies to the *next* release, not
+the current one. To see the release notes for a specific release, please
+see the `releases page <https://llvm.org/releases/>`_.
+
+What's New in Libc++ 20.0.0?
+==============================
+
+Implemented Papers
+------------------
+
+- TODO
+
+
+Improvements and New Features
+-----------------------------
+
+- TODO
+
+
+Deprecations and Removals
+-------------------------
+
+- TODO: The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable and the ``_LIBCPP_ENABLE_ASSERTIONS`` macro that were used to enable
+  the safe mode will be removed in LLVM 20.
+
+
+Upcoming Deprecations and Removals
+----------------------------------
+
+LLVM 21
+~~~~~~~
+
+- TODO
+
+
+ABI Affecting Changes
+---------------------
+
+- TODO
+
+
+Build System Changes
+--------------------
+
+- TODO

[mordante]

Thanks I was considering to create a similar patch :-) LGTM!