[libc++] Add a release note about C++03 being frozen after LLVM 21

[philnik777]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/95894.diff

1 Files Affected:

• (modified) libcxx/docs/ReleaseNotes/19.rst (+3-1)

diff --git a/libcxx/docs/ReleaseNotes/19.rst b/libcxx/docs/ReleaseNotes/19.rst
index 71de10abb6eaa..cffe40cec2618 100644
--- a/libcxx/docs/ReleaseNotes/19.rst
+++ b/libcxx/docs/ReleaseNotes/19.rst
@@ -77,6 +77,8 @@ Improvements and New Features
 Deprecations and Removals
 -------------------------
 
+- The status of the C++03 implementation will be frozen. From now on only bug fixes will be back-ported to C++03.
+
 - The C++20 synchronization library (``<barrier>``, ``<latch>``, ``atomic::wait``, etc.) has been deprecated
   in language modes prior to C++20. If you are using these features prior to C++20, please update to ``-std=c++20``.
   In LLVM 20, the C++20 synchronization library will be removed entirely in language modes prior to C++20.
@@ -133,8 +135,8 @@ LLVM 20
 
 LLVM 21
 ~~~~~~~
-TODO
 
+- Libc++ will no longer back-port non-critical bug fixes to C++03.
 
 ABI Affecting Changes
 ---------------------

[ldionne]

Thanks for doing this! I'd like a bit more verbosity though, I think this change is important enough that we need to do a good job at communicating it.

[tschuett]

Could you add a 21.rst with the related news?

[ldionne]

LGTM with the reformulation!

In particular, I think it's important not to commit to a particular implementation of this proposal. The steps laid out in https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc/77319/55 are nice, but we don't know if it's actually going to work exactly that way.

Also, I think we must avoid promising that we're going to freeze the headers completely, since that may not be achievable.