March 2025 - ghc-devs

GHC memory usage when typechecking from source vs. loading ModIfaces
by Gergő Érdi 03 Apr '25

03 Apr '25

Hi, I’m using the GHC API to typecheck 35,000 modules that form a complicated dependency graph (with multiple top-level modules, i.e. there’s no single “god module” that would transitively depend on everything else), and I noticed that peak memory usage is wildly different when everything is done from scratch vs. when everything is loaded from files containing ModIfaces: 17G vs. 8G. This ratio replicates for smaller samples as well, e.g. 80M vs 33M for 407 modules. I’m aware of https://gitlab.haskell.org/ghc/ghc/-/issues/13586 and so when I finish typechecking a module, I take the resulting ModIface and create the ModDetails that ends up in the HomeUnitGraph from that. My understanding of Matt’s original GHC fix in https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5478 is that it does the same, i.e. it only makes a fresh ModDetails only once per module, after the ModIface is ready. But of course that still means that ModDetails can only keep growing as more and more parts of it are used for typechecking more and more dependants. Could that be the cause? I tried a crude experiment of “putting the toothpaste back in the tube” by replacing all ModDetails with a fresh one in the HUG after each finished typechecking , but that’s a complete disaster for memory usage: even for the small 407 module example, the memory usage shoots up to 1.5G. I can imagine it’s because imported Ids are probably not shared anymore between different importer modules. Any ideas on how I could improve memory usage in the from-scratch case, so that it's more similar to the from-ModIface case? Thanks, Gergo

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gitlab.haskell.org reboot this evening
by Ben Gamari 31 Mar '25

31 Mar '25

Hi all, As part of finalizing the migration I will be rebooting gitlab.haskell.org at 17:00 EDT today. I expect the outage will last around 5 minutes. Cheers, - Ben

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gitlab.haskell.org outage this weekend
by Ben Gamari 29 Mar '25

29 Mar '25

Hi all, As you may know, Haskell.org is currently in the process of moving its infrastructure to new hosting facilities. As part of this effort, GHC's GitLab instance will be taken down for migration on Saturday 29 March 2025 from 09:00 to 17:00. This includes our issue tracker, CI infrastructure, Docker registry, serving of artifacts. Apologies for the inconvenience but we hope that this will be the last time we need to have such a prolonged outage in quite a while. Cheers, - Ben

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CFP - Haskell Implementors' Workshop 2025
by Andreas Herrmann 27 Mar '25

27 Mar '25

Call for proposals for the Haskell Implementors' Workshop https://haskell.foundation/events/2025-haskell-implementors-workshop.html June 6, 2025 Organized by the Haskell Community Co-located with ZuriHac 2025 and Haskell Ecosystem Workshop 2025 Hosted by the Haskell Foundation at Eastern Switzerland University of Applied Sciences (OST) https://www.ost.ch/en/university-of-applied-sciences/campus/rapperswil-jona… ## Overview * Deadline: April 4, 2025 * Notification: May 5, 2025 * Workshop: June 6, 2025 The 17th Haskell Implementors' Workshop is to be held alongside ZuriHac 2025 this year near Zurich. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure to share their work and to discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos, and lightning talks. In the past the Haskell Implementors’ Workshop was co-located with ICFP (International Conference on Functional Programming). However, in recent years it has become more and more challenging to attract a large enough audience and sufficiently many speakers for an appealing program. ZuriHac and the Haskell Ecosystem Workshop have become an important annual gathering of a large part of the Haskell community. This year the Haskell Implementors’ Workshop will be co-located with these events to be accessible to a broader audience. ## Scope and Target Audience The Haskell Implementors' Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community are encouraged to attend the workshop - we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are especially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimization and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment ## Talks We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Submissions can be made via the form linked below until April 4, 2025 (anywhere on earth). https://docs.google.com/forms/d/e/1FAIpQLSdczGbxJYGc4eusvPrxwBbZl561PnKeYno… We will also have a lightning talks session. Lightning talks should be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. ## Program Committee * Luite Stegeman * Jaro Reinders * Emily Pillmore * Rodrigo Mesquita * Ian-Woo Kim * Andreas Herrmann (chair) ## Contact * Andreas Herrmann

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GHC 9.6.7 is now available
by Luite Stegeman 24 Mar '25

24 Mar '25

The GHC developers are very pleased to announce the availability of GHC 9.6.7. Binary distributions, source distributions, and documentation are available at https://downloads.haskell.org/ghc/9.6.7 We hope to have this release available via ghcup shortly. GHC 9.6.7 brings number of fixes, including: - GHC’s internal Unique type has been widened to 64-bits on 32-bit architectures, avoiding potential miscompilations on large projects. - Fix a runtime crash when using the compacting GC, caused by black holes in large objects. - Added new flags -fspec-eval and -fspec-eval-dictfun to allow switching off speculative evaluation. The following libraries have been updated since GHC 9.6.6: - base-4.18.3.0 - filepath-1.4.301.0 - unix-2.8.6.0 - bytestring-0.11.5.4 - array-0.5.8.0 A more detailed description can be found in the [release notes] and a full list of changes in [GHC!13841] and [GHC!13891] Note about Haskell Language Server and building GHC 9.8+: The change of Unique to 64 bit [GHC#22010] adds the exported symbol ghc_unique_counter64 to the RTS. Unfortunately it's impossible to avoid this without breaking other things. If you encounter a linker error related to ghc_unique_counter64 when building GHC (or building a GHC-derived package like ghc-lib-parser) with GHC 9.6.7, you probably have to add this [fix] to the program you're building. We would like to thank GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, 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. Please give this release a try and open a [ticket] if you see anything amiss. ~ Luite [release notes]: https://downloads.haskell.org/ghc/9.6.7/docs/users_guide/9.6.7-notes.html [GHC!13841]: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13841 [GHC!13891]: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13891 [GHC#22010]: https://gitlab.haskell.org/ghc/ghc/-/issues/22010 [fix] https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13743 [ticket] https://gitlab.haskell.org/ghc/ghc/-/issues/new

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What should it mean for a record selector to be "covered"?
by Florian Ragwitz 23 Mar '25

23 Mar '25

Let's say you have data Foo = Foo { fooX, fooY :: Int } For coverage reporting, HPC creates a coverage box for each top-level definition. These boxes will be ticked appropriately at runtime when the fooX and fooY bindings are used directly. However, they won't be ticked if you pattern match on the constructor, such as f (Foo x y) = ... f Foo{ fooX = fooX } = ... f Foo{ fooX = x } = ... f Foo{ fooX } = ... f Foo{..} = ... and variations thereof. This is understandable, but can lead to some undesirable or unexpected behaviour for users of RecordWildCards or RecordPuns especially. E.g. https://gitlab.haskell.org/ghc/ghc/-/issues/17834 and https://github.com/PostgREST/postgrest/issues/2627#issuecomment-1435642297. GHC already seems to acknowledge this, at least to some extent, via its treatment of unused top-level binding warnings when using RecordWildCards, RecordPuns, or record patterns, where f Foo{ fooX } = ... or f Foo{ fooX = x } = ... will not emit a -Wunused-top-binds warning for fooX while still emitting one for fooY, and where f Foo{..} = ... will not emit any -Wunused-top-bind warnings at all. Given these observations, and assuming that the current HPC behaviour is undesirable, I’d like some guidance on what the exact desired behavior for HPC coverage should be for record selectors. In particular: * Should a record selector be considered "covered" simply by being bound in a pattern match? * Or should it only be marked as covered if the bound symbol is actually used? If the latter is preferable, would a change that initially marks them as covered upon binding (thereby aligning HPC with the treatment of unused binding warnings) be acceptable as an interim step toward the larger goal? Thanks for your time and insights!

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fail to build ghc in github action
by chaowen guo 23 Mar '25

23 Mar '25

i fork the ghc repo from github and use the following workflow on: push jobs: build: runs-on: ubuntu-24.04 steps: - uses: actions/checkout@main - run: | git submodule update --init --recursive sudo apt install -y --no-install-recommends alex happy python3 boot ./configure hadrian/build Warning: Specifying an absolute path to the project file is deprecated. Use 1178 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>--project-dir to set the project's directory. 1179 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Config file path source is default config file. 1180 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Config file not found: /home/runner/.config/cabal/config 1181 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Writing default configuration to /home/runner/.config/cabal/config 1182 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Configuration is affected by the following files: 1183 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>- cabal.project 1184 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Warning: The package list for 'hackage.haskell.org' does not exist. Run 'cabal 1185 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>update' to download it. 1186 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Warning: There is no index-state for 'hackage.haskell.org' exactly at the 1187 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>requested timestamp (2025-01-27T17:45:32Z). Also, there are no index-states 1188 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>before the one requested, so the repository 'hackage.haskell.org' will be 1189 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>empty. 1190 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Resolving dependencies... 1191 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Error: [Cabal-7107] 1192 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>Could not resolve dependencies: 1193 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>[__0] trying: hadrian-0.1.0.0 (user goal) 1194 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>[__1] trying: hadrian:+selftest 1195 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>[__2] unknown package: QuickCheck (dependency of hadrian +selftest) 1196 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>[__2] fail (backjumping, conflict set: QuickCheck, hadrian, hadrian:selftest) 1197 <https://github.com/chaowenguo1/ghc/actions/runs/14017990071/job/39246149896…>After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: hadrian, hadrian:selftest, QuickCheck i have no idea what happen. please help.

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Haskell.org mailing list status
by Ben Gamari 20 Mar '25

20 Mar '25

Hi all, As you may have noticed, yesterday brought an unexpected influx of traffic from haskell.org's mailing lists. This was the result of fixing an interruption in mailing list message delivery which began in late February as a result of on-going infrastructure migration efforts. We are monitoring the situation to ensure that this issue does not recur but if you see anything amiss don't hesitate to contact admin(a)haskell.org. Thank you for your understanding and help! Cheers, - Ben

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Gitlab access
by Jar Jar 19 Mar '25

19 Mar '25

Hi ghc-devs, Please accept gitlab access request for : spamdefence+haskell(a)torinthiel.pl Kind Regards, JJ

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GHC 9.12.2 is now available
by Ben Gamari 14 Mar '25

14 Mar '25

The GHC developers are happy to announce the release of GHC 9.12.2. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org] We hope to have this release available via `ghcup` shortly. This is a small release fixing a critical code generation bug, #25653, affecting some subword division operations. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status]. We would like to thank IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, 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 who contribute their code, tickets, and energy to the GHC project. As always, do give this release a try and open a [ticket] if you see anything amiss. [release notes]: https://downloads.haskell.org/ghc/9.12.2/docs/users_guide/9.12.2-notes.html [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.2 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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