[Clang] [NFC] Add release note about libstdc++ bug

[Sirraide]

Adding a release note about this as discussed in #92439.

(This is an NFC change, but I’m adding you as reviewers in case there is anything you want to add to this since you were involved in the discussion.)

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (Sirraide)

Changes

Adding a release note about this as discussed in #92439.

(This is an NFC change, but I’m adding you as reviewers in case there is anything you want to add to this since you were involved in the discussion.)

This closes #92439.

---

Full diff: https://github.com/llvm/llvm-project/pull/93059.diff

1 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+12)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5a123b0b86dda..58c73fb6947ce 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -59,6 +59,18 @@ C++ Specific Potentially Breaking Changes
 - Clang now performs semantic analysis for unary operators with dependent operands
   that are known to be of non-class non-enumeration type prior to instantiation.
 
+  This change uncovered a bug in libstdc++ 14.1.0 which may cause compile failures
+  on systems using that version of libstdc++ and Clang 19, with an error that looks
+  something like this:
+
+  .. code-block:: text
+
+    <source>:4:5: error: expression is not assignable
+    4 |     ++this;
+      |     ^ ~~~~
+
+  To fix this, update libstdc++ to a newer version, such as 14.1.1 or 14.2.
+
 ABI Changes in This Version
 ---------------------------
 - Fixed Microsoft name mangling of implicitly defined variables used for thread

[cor3ntin]

This closes #92439.

It does not (s++++ is still not diagnosed)

[Sirraide]

This closes #92439.

It does not (s++++ is still not diagnosed)

Oh, right; this was mainly in reference to the libstdc++ bug since that’s what’s most of the discussion on that issue has been about. I’d maybe suggest moving the s++++ case to a different issue?

[cor3ntin]

I would keep that issue and just remove the fixes (We can still link the issue to this PR by posting a link in a comment)

[Sirraide]

I would keep that issue and just remove the fixes

Done

[cor3ntin]

(I also think that the libstdc++ bug demonstrated some usefulness for a ++this -> ++*this fixit... maybe?)

[cor3ntin]

Thanks for doing this!

[Sirraide]

(I also think that the libstdc++ bug demonstrated some usefulness for a ++this -> ++*this fixit... maybe?)

That does sound like it might be useful; I’m going to open another issue about that so we don’t forget about it.

[Sirraide]

I’ve opened an issue to add a fix-it hint and tagged it as a good first issue because for once this is something that seems like it would be fairly straight-forward to do: #93066