December 2025 - ghc-devs

GitLab read only/licensing.
by Andreas Klebinger 08 Dec '25

08 Dec '25

As many of you might have noticed GitLab forced our GitLab instance into read only mode today. We are currently working to resolve this. Without going into too much detail Ben has reach out to GitLab for a renewal of the current license over a month ago and multiple times since. Sadly GitLab hasn't been very responsive so far. I hope we can find a workaround in short order. Cheers Andreas

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Strange package error -- HELP!
by Simon Peyton Jones 03 Dec '25

03 Dec '25

Friends I'm getting this from my newly-built in-tree compiler ~/code/HEAD-11/_build/ghc-stage1 -c T24984.hs -O T24984.hs:1:1: error: [ ]8;;https://errors.haskell.org/messages/GHC-45102 \GHC-45102 ]8;; \] Ambiguous module name ‘Prelude’. * it was found in multiple packages: base-4.22.0.0 base-4.22.0.0* What a bonkers message. What is going wrong? I do see this: ls -d /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base* /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base-4.22.0.0-c7d2 /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base-4.22.0.0-inplace simonpj@LHR-WD-22561:~/code/HEAD-11/testsuite/tests/perf/compiler$ So there are two base packages around somehow. I don't know if that's the reason. I'd love a bit of help.. it's super annoying Maybe it's some leftover not-clean stuff -- but how would I diagnose? How can I see what package directories it is looking in, which package files it is reading? THanks Simon

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Strange behaviors regarding plugin-related compiler options
by Wolfgang Jeltsch 03 Dec '25

03 Dec '25

Hi! While working with a GHC plugin, I accidentally found out the following behaviors: * The use of a plugin, at least one that is declared as pure, doesn’t make the compiled module considered unsafe even when `-fplugin-trustworthy` is missing. * Any option of the form `-fplugin-opt⟨some-garbage⟩` is accepted. Is any of these two behaviors intended? I’m using GHC 9.12.2 through Cabal. All the best, Wolfgang

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GHC 9.14.1-rc3 is now available
by Zubin Duggal 02 Dec '25

02 Dec '25

The previous email had an incorrect subject line, GHC 9.14.1-rc3 is what it was intended to say. The contents following this are the same. The GHC developers are very pleased to announce the availability of the third release candidate of GHC 9.14.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. The changes from the second release candidate are: - Fix RTS segfaults in certain situations (#26495) - Fix use after free on windows due to a linker optimisation introduced in an earlier RC (#26613) GHC 9.14 will bring a number of new features and improvements, including: * Significant improvements in specialisation: * The `SPECIALISE` pragma now allows use of type application syntax * The `SPECIALISE` pragma can be used to specialise for expression arguments as well as type arguments. * Specialisation is now considerably more reliable in the presence of `newtype`s * Significant GHCi improvements including: * Correctness and performance improvements in the bytecode interpreter * Features in the GHCi debugger * Support for multiple home units in GHCi * Implementation of the [Explicit Level Imports proposal][levels] * `RequiredTypeArguments` can now be used in more contexts * SSE/AVX2 support in the x86 native code generator backend * A major update of the Windows toolchain and improved compatibility with macOS Tahoe * ... and many more A full accounting of changes can be found in the [release notes][]. Given the many specialisation improvements and their potential for regression, we would very much appreciate testing and performance characterisation on downstream workloads. Note that while this release makes many improvements in the specialisation optimisation, polymorphic specialisation will remain disabled by default in the final release due to concern over regressions of the sort identified in [#26329][T26329]. Users needing more aggressive specialisation can explicitly enable this feature with the `-fpolymorphic-specialisation` flag. Depending upon our experience with 9.14.1, we may enable this feature by default in a later minor release. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to that these sponsors and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket][] if you see anything amiss. [downloads.haskell.org] https://downloads.haskell.org/ghc/9.14.1-rc3 [release notes]: https://downloads.haskell.org/ghc/9.14.1-rc3/docs/users_guide/9.14.1-notes.… [ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new [macos]: https://gitlab.haskell.org/ghc/ghc/-/issues/26166 [T26329]: https://gitlab.haskell.org/ghc/ghc/-/issues/26329 [levels]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0682-e…

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GHC 9.12.3-rc3 is now available
by Zubin Duggal 02 Dec '25

02 Dec '25

The GHC developers are very pleased to announce the availability of the third release candidate of GHC 9.14.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. The changes from the second release candidate are: - Fix RTS segfaults in certain situations (#26495) - Fix use after free on windows due to a linker optimisation introduced in an earlier RC (#26613) GHC 9.14 will bring a number of new features and improvements, including: * Significant improvements in specialisation: * The `SPECIALISE` pragma now allows use of type application syntax * The `SPECIALISE` pragma can be used to specialise for expression arguments as well as type arguments. * Specialisation is now considerably more reliable in the presence of `newtype`s * Significant GHCi improvements including: * Correctness and performance improvements in the bytecode interpreter * Features in the GHCi debugger * Support for multiple home units in GHCi * Implementation of the [Explicit Level Imports proposal][levels] * `RequiredTypeArguments` can now be used in more contexts * SSE/AVX2 support in the x86 native code generator backend * A major update of the Windows toolchain and improved compatibility with macOS Tahoe * ... and many more A full accounting of changes can be found in the [release notes][]. Given the many specialisation improvements and their potential for regression, we would very much appreciate testing and performance characterisation on downstream workloads. Note that while this release makes many improvements in the specialisation optimisation, polymorphic specialisation will remain disabled by default in the final release due to concern over regressions of the sort identified in [#26329][T26329]. Users needing more aggressive specialisation can explicitly enable this feature with the `-fpolymorphic-specialisation` flag. Depending upon our experience with 9.14.1, we may enable this feature by default in a later minor release. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to that these sponsors and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket][] if you see anything amiss. [downloads.haskell.org] https://downloads.haskell.org/ghc/9.14.1-rc3 [release notes]: https://downloads.haskell.org/ghc/9.14.1-rc3/docs/users_guide/9.14.1-notes.… [ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new [macos]: https://gitlab.haskell.org/ghc/ghc/-/issues/26166 [T26329]: https://gitlab.haskell.org/ghc/ghc/-/issues/26329 [levels]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0682-e…

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