Dear GHC release stakeholders,
We are approaching a release candidate for GHC 9.12.5. Currently there's
only one blocking patch
(https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15640) that still
needs to be backported and the test-suite seems to be doing well.
Here are some important notes for this release of GHC 9.12.
1. Our Darwin CI is now running on MacOS version 26 for the aarch64
runners and on MacOS version 15 for the x86_64 runner. The SDK version
on the MacOS 15 runner is 26.2, the SDK version on the aarch64 runners
is 26.4. Note that this may affect bindists.
2. See https://gitlab.haskell.org/ghc/ghc/-/issues/27286 for an
exhaustive list of MRs that have been backported.
3. If you are a distributor of haskell packages like stackage or
nixpkgs, I would appreciate testing an RC with you, as soon as it's
there. Please reach out if that's the case.
4. In ncoordinatio with the cabal developers, the GHC team has decided
to stop maintaining the V1 ghc semaphore protocol that had some
fundamental architectural flaws. While this is technically a
(performance) regression (cabal versions that only support v1 will fall
back to -j1 even when passed -jsem with 9.12.5) and adds a significant
feature, it is the most pragmatic approach to fixing the glaring issues
with the previous semaphore implementation without having to maintain a
fundamentally broken design. Please check out
https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15729 for further
information. We expect that `-jsem` will work out of the box with the
next released cabal version and 9.12.5.
I expect a release candidate to appear this week, depending on progress
of the blocking patch.
Please don't hesitate to reach out if you have any questions or remarks.
Best
Magnus
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