[libcxx-commits] [libcxx] [libc++][doc] Update the release notes for LLVM 18 (PR #78324)

[Louis Dionne via libcxx-commits]

================
@@ -191,18 +229,26 @@ ABI Affecting Changes
   to throw a different exception when attempting allocations that are too large
   (``std::bad_alloc`` vs ``std::length_error``).
 
-- The layout of some views inside ``std::ranges`` that use the ``movable-box`` exposition-only type as an implementation 
-  detail has changed in order to fix a bug which could result in overwriting user data following the ``movable-box``
-  <https://github.com/llvm/llvm-project/issues/70506>. 
-  This was caused by incorrect usage of the ``[[no_unique_address]]`` attribute inside the implementation of ``movable-box``. 
-  This only affects the layout of the following views: ``take_while_view``, ``filter_view``, ``single_view``, ``drop_while_view``, 
-  ``repeat_view``, ``transform_view``, ``chunk_by_view``. In order to avoid silent breakage, an ABI tag has been added to 
-  these views such that their mangled name will be different starting in this version of libc++. 
-  As a result, attempting to call a function that expects one of these views will fail to link until the code has been rebuilt 
-  against a matching version of libc++. In practice, we believe it is unusual for these views to appear at ABI boundaries so this 
-  should not be a major problem for most users. However it is probably worth auditing ranges-heavy code for ABI boundaries that 
+- The layout of some views inside ``std::ranges`` that use the ``movable-box`` exposition-only type as an implementation
+  detail has changed in order to fix a `bug <https://github.com/llvm/llvm-project/issues/70506>`_ which could result in
+  overwriting user data following the ``movable-box``.
+  This was caused by incorrect usage of the ``[[no_unique_address]]`` attribute inside the implementation of ``movable-box``.
+  This affects the layout of the following views: ``take_while_view``, ``filter_view``, ``single_view``, ``drop_while_view``,
+  ``repeat_view``, ``transform_view``, ``chunk_by_view``. In order to avoid silent breakage, an ABI tag has been added to
+  these views such that their mangled name will be different starting in this version of libc++.
+  As a result, attempting to call a function that expects one of these views will fail to link until the code has been rebuilt
+  against a matching version of libc++. In practice, we believe it is unusual for these views to appear at ABI boundaries so this
+  should not be a major problem for most users. However it is probably worth auditing ranges-heavy code for ABI boundaries that
   would contain these views, or for types that contain these views as members and which are passed across ABI boundaries.
 
+- Some properties of libc++ may cause ODR-violations when mixing multiple libc++
+  instances. To avoid these, often benign, ODR-violations the ODR-affecting
+  properties are now part of the ABI tag. The ODR-affecting properties are:
+
+    - library version
+    - exceptions vs no-exceptions
+    - hardening mode
----------------
ldionne wrote:

Let's add:

```
This should not be ABI-affecting except that libc++ will be more robust against different configurations of it being used in different translation units.
```

Also, the library version was already part of the ABI tag, so that property wasn't added in LLVM 18.

https://github.com/llvm/llvm-project/pull/78324