release/20.x: [libc++] Add missing release note for LLVM 20 about zip_view (#134144) #134313
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@frederick-vs-ja What do you think about merging this PR to the release branch? |
llvmbot
added
the
libc++
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@llvm/pr-subscribers-libcxx Author: None (llvmbot) ChangesBackport 2cd8edd Requested by: @ldionne Full diff: https://github.com/llvm/llvm-project/pull/134313.diff 1 Files Affected:
diff --git a/libcxx/docs/ReleaseNotes/20.rst b/libcxx/docs/ReleaseNotes/20.rst
index 57ab0c167544b..06e6e673b5508 100644
--- a/libcxx/docs/ReleaseNotes/20.rst
+++ b/libcxx/docs/ReleaseNotes/20.rst
@@ -162,6 +162,12 @@ Deprecations and Removals
- Non-conforming extension ``packaged_task::result_type`` is deprecated. It will be removed in LLVM 21.
+- The changes for ``ranges::zip_view`` from `P2165R4 <https://wg21.link/P2165R4>`_ have been implemented. This can
+ lead to code assuming that ``zip_view`` produces ``std::pair`` to stop compiling now that it produces ``std::tuple``.
+ The cases are rare since ``tuple`` and ``pair`` are compatible for the most part, but this can lead to code that
+ was previously accepted now being rejected. This is necessary for libc++ to be conforming, so we don't provide any
+ way to opt-out of that behavior.
+
Upcoming Deprecations and Removals
----------------------------------
@@ -205,3 +211,8 @@ ABI Affecting Changes
- The localization support base API has been reimplemented, leading to different functions being exported from the
libc++ built library on Windows and Windows-like platforms.
+
+- The changes for ``ranges::zip_view`` from `P2165R4 <https://wg21.link/P2165R4>`_ have been implemented. This changes
+ the element type of ``zip_view`` from a ``std::pair`` to a ``std::tuple`` in some cases. This is technically an ABI
+ break, however since ``zip_view`` is generally not an ABI sensitive type, we don't expect users to encounter any
+ issues and we don't provide a way to change this behavior, which would make libc++ non-conforming.
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frederick-vs-ja
approved these changes
Apr 4, 2025
github-project-automation
bot
moved this from Needs Triage
to Needs Merge
in LLVM Release Status
…4144) We should have had a release note in LLVM 20 about implementing P2165R4 since that is technically an ABI and API break for zip_view. We don't expect anyone to actually hit the ABI issue, but we've come across some (fairly small) breakage due to the API change, so this should at least be mentioned in the release notes. (cherry picked from commit 2cd8edd)
github-project-automation
bot
moved this from Needs Merge
to Done
in LLVM Release Status
|
@ldionne (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
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Backport 2cd8edd
Requested by: @ldionne