- ghc-devs - Haskell.org

Error message degradation for (<= :: Nat -> Nat -> Constraint) in GHC 9.2+
by Christiaan Baaij 17 Jun '21

17 Jun '21

Hi Ghc-Devs, When upgrading one of our tc plugins https://hackage.haskell.org/package/ghc-typelits-natnormalise to GHC 9.2, one of our tests, repeated here: ``` {-# LANGUAGE DataKinds, TypeFamilies, TypeOperators #-} module TestInEq where import Data.Proxy import GHC.TypeLits proxyInEq :: (a <= b) => Proxy a -> Proxy b -> () proxyInEq _ _ = () proxyInEq1 :: Proxy a -> Proxy (a+1) -> () proxyInEq1 = proxyInEq ``` degraded quite badly in terms of the error message. Where in GHC 9.0.1 we get: ``` TestInEq.hs:11:14: error: • Couldn't match type ‘a <=? (a + 1)’ with ‘'True’ arising from a use of ‘proxyInEq’ • In the expression: proxyInEq In an equation for ‘proxyInEq1’: proxyInEq1 = proxyInEq • Relevant bindings include proxyInEq1 :: Proxy a -> Proxy (a + 1) -> () (bound at TestInEq.hs:11:1) | 11 | proxyInEq1 = proxyInEq | ``` with GHC 9.2.0.20210422 we get: ``` TestInEq.hs:11:14: error: • Couldn't match type ‘Data.Type.Ord.OrdCond (CmpNat a (a + 1)) 'True 'True 'False’ with ‘'True’ arising from a use of ‘proxyInEq’ • In the expression: proxyInEq In an equation for ‘proxyInEq1’: proxyInEq1 = proxyInEq • Relevant bindings include proxyInEq1 :: Proxy a -> Proxy (a + 1) -> () (bound at TestInEq.hs:11:1) | 11 | proxyInEq1 = proxyInEq | ``` Errors messages involving type-level naturals and their operations already weren't the poster-child of comprehensable GHC error messages, but this change has made the situation worse in my opinion. This change in error message is due to: https://gitlab.haskell.org/ghc/ghc/-/commit/eea96042f1e8682605ae68db10f2bcd… Is there a way we can get the nicer pre-9.2.0.2021 error message again before the proper 9.2.1 release? e.g. by doing one of the following: 1. Reinstate `(<=? :: Nat -> Nat -> Bool)` as a builtin type family 2. Somehow add a custom type-error to `Data.Type.Ord.OrdCond` 3. Don't expand type aliases in type errors What do you think? should this be fixed? should this be fixed before the 9.2.1 release? -- Christiaan

5 6

Re[2]: GHC and the future of Freenode
by Sebastian Graf 16 Jun '21

16 Jun '21

Re: memory usage: I get that people don't like bloated Electron clients when they already run a browser instance, but fortunately, Element doesn't need to be run as a standalone app (*). Well, except when you want to search encrypted history. But then you're out of luck with irccloud, too... I run Element in a pinned Firefox tab, and according to its task manager it reports 27.4MB, which is about the same for my WhatsApp tab. It's a bit more than irccloud (about 20MB), but I also have quite a few chats in that one tab. It's also quite a lot less than every individual MR page of our GitLab instance (27-110MB), of which I have pinned about 5-10 at any time, so it really doesn't matter much. Since the Matrix<->Libera.chat bridge works now, I have next to no incentive to push for Matrix at the moment, although I still would prefer it. All arguments have been said, so I won't repeat them. It seems like this discussion will go stale in time without anyone stepping up to force a migration. Fine with me. Sebastian ------ Originalnachricht ------ Von: "Jakub Zalewski" <jakzale(a)gmail.com> An: "Janek Stolarek" <jwstolarek(a)gmail.com>; ghc-devs(a)haskell.org Gesendet: 16.06.2021 17:02:28 Betreff: Re: GHC and the future of Freenode >On Tue Jun 15, 2021 at 3:18 PM CEST, Janek Stolarek wrote: >> Apparently, Freenode deleted all registered users and channels several >> hours ago. > >I guess that should solve the problem of communities being split between >Freenode and Libera. > >If I may add towards using IRC, even though it may seem archaic towards >newcomers: > >- it allows them to join without registration (via web.libera.chat), and >- it allows them to use a client of their choosing (I am not aware of > any stable Matrix clients beside Element). > >From my own experience, Electron-based clients (Element included) >consume unreasonable amounts of RAM: Element is consuming ~700MiB of >RAM just to stay idle on my machine. To give a fair comparison, the tab >for irccloud tends to consume ~300MiB. > >-- >Jakub >_______________________________________________ >ghc-devs mailing list >ghc-devs(a)haskell.org >http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

1 0

GHC and the future of Freenode
by Ben Gamari 16 Jun '21

16 Jun '21

Hi all, As you may have heard the Freenode IRC network, long the home of #ghc and several other prominent Haskell channels, appears to be in the middle of a rather nasty hostile takeover [1,2,3,4]. As a consequence, it seems it will be necessary to migrate the #ghc community elsewhere. The next question is, of course, where will this be. One option is Liberachat, the spiritual successor of Freenode. However, in recent years I have also heard an increasingly loud choir of users, contributors, and potential-contributors note how archane IRC feels when compared to other modern chat platforms. Using IRC effectively in a collaborative environment essentially requires that all parties use a bouncer; however, this is (understandably) isn't something that most users are willing to do. Consequently, I think it would be wise to expand our search space to include other FOSS platforms. At the moment, I can see the following options: 1. Remain on IRC and move to Liberachat, the spiritual successor of Freenode 2. Remain on IRC and move to OFTC, another widely used network 3. Move to [Matrix] 4. Move to [Zulip] My sense is that of the non-IRC options Matrix is the truest successor to IRC, being a federated protocol with a wide array of (if somewhat immature) clients. I know some of our contributors already use it and in principle one could configure an IRC-to-Matrix bridge for those existing contributors who would rather continue using IRC. Zulip, while also being FOSS, is far more centralized than Matrix and appears to be more of a chat web application than an open protocol. Do you know of any other options? Thoughts? Cheers, - Ben [1]: https://gist.github.com/joepie91/df80d8d36cd9d1bde46ba018af497409 [2]: https://fuchsnet.ch/freenode-resign-letter.txt [3]: https://gist.github.com/aaronmdjones/1a9a93ded5b7d162c3f58bdd66b8f491 [4]: https://mniip.com/freenode.txt [Matrix]: https://www.matrix.org/ [Zulip]:

20 27

abstract interpreter for GHC Core or STG
by Csaba Hruska 14 Jun '21

14 Jun '21

Hello, I wonder if there was an attempt in the past to create an abstract interpreter for GHC Core or STG to approximate the program runtime behaviour? I'm curious because I'd like to turn my external STG interterpreter to an abstract interpreter using the AAM (Abstracting Abstract Machines) method. This approach seems promising to me because a single Haskell code base (ext STG interpreter) could be the specification of the Haskell operational semantics and also be a detailed static analyzer that could help optimization transformations. I'm interested in any attempt that happened during GHC/Haskell evolution. Regards, Csaba Hruska

3 9

Anyone ever wondered what our favourite merge bot is up to?
by Matthew Pickering 10 Jun '21

10 Jun '21

Hi all, I added a new dashboard on grafana which exposes some of the systemd logs from marge-bot. https://grafana.gitlab.haskell.org/d/iiCppweMz/marge-bot?orgId=2&refresh=5m You can use the logs to see why marge doesn't want to merge your MR or whether she is dead. Cheers, Matt

3 3

[Haskell] [ANNOUNCE] GHC 8.10.5 released
by Zubin Duggal 05 Jun '21

05 Jun '21

The GHC team is very pleased to announce the availability of GHC 8.10.5. Source and binary distributions are available at the [usual place](https://downloads.haskell.org/ghc/8.10.5/). This release adds native ARM/Darwin support, as well as bringing performance improvements and fixing numerous bugs of varying severity present in the 8.10 series: - First-class support for Apple M1 hardware using GHC's LLVM ARM backend - Fix a bug resulting in segmentation faults where code may be unloaded prematurely when using the parallel garbage collector (#19417) along with other bugs in the GC and linker (#19147, #19287) - Improve code layout fixing certain performance regressions (#18053) and other code generation bug fixes (#19645) - Bug fixes for signal handling when using the pthread itimer implementation. - Improvements to the specializer and simplifier reducing code size and and memory usage (#17151, #18923,#18140, #10421, #18282, #13253). - Fix a bug where typechecker plugins could be run with an inconsistent typechecker environment (#19191). - Fix a simplifier bug which lead to an exponential blow up and excessive memory usage in certain cases A complete list of bug fixes and improvements can be found in the release notes: [release notes](https://downloads.haskell.org/~ghc/8.10.5/docs/html/users_guide/8.10… As always, feel free to report any issues you encounter via [gitlab.haskell.org](https://gitlab.haskell.org/ghc/ghc/-/issues/new).

1 1

[CI] macOS builds
by Moritz Angermann 05 Jun '21

05 Jun '21

Hi there! You might have seen failed or stuck or pending darwin builds. Our CI builders we got generously donated have ~250GB of disk space (which should be absolutely adequat for what we do), and macOS BigSur does some odd reservation of 200GB in /System/Volumes/Data, this is despite automatic updates being disabled and time machine being disabled. It used to happen only when the system was expecting an update to be performed and the 200GB were freed after the update was done. After the latest update to 11.4, however, it seems to have not freed that space. This leaves the CI machine with ~50GB for for the system + build tools + gitlab checkouts and builds, and they frequently run out of space :-/ If someone knows how to prevent the system from doing stupid stuff like this (my hunch is it's keeping a backup of the system pre-udpate, for disaster recovery). Please come forward, my google searches haven't revealed anything useful yet. I have filed a TSI with Apple (still had a few on my developer account), but I don't expect them to come back to me before the end of June. Next week is WWDC, and there will be a massive backlog of issues that queued up leading up to, and during the WWDC. I've also only had very marginal success with them resolving issues that were not "you wrote this program wrong". If everything fails, maybe the solution is to attach some usbc ssd's to the macs and have gitlab builds be run dedicatedly on those disks. I'm a bit concerned about performance but we would have to see. Any ideas are welcome, please also feel free to hit me up on libera.chat#ghc, or the haskell foundations slack. Cheers, Moritz

1 0

value of documenting error messages?
by Richard Eisenberg 03 Jun '21

03 Jun '21

Hi devs, Take a quick look at https://gitlab.haskell.org/ghc/ghc/-/blob/6db8a0f76ec45d47060e28bb303e9eef6… <https://gitlab.haskell.org/ghc/ghc/-/blob/6db8a0f76ec45d47060e28bb303e9eef6…> You will see a datatype there with constructors describing error messages that GHC might produce. These constructors have comments describing the error, sometimes giving an example, and sometimes listing test cases. More datatypes like this one and more constructors in these datatypes are on the way. Question: Is there sufficient value in carefully documenting each constructor? In my ideal world, each constructor would have a high-level description, a detailed description of each field, an example of a program that generates the error, and one or more test cases that test the output. Along the way, we might discover that no such test case exists, and then we would add. However, generating this documentation is hard. I was thinking of whipping up an army of volunteers (Hécate has advised me how to do this) to do the work, but that army will need to be fed (with instructions, supervision, and reviews) and will want to know that their work is important. Is this effort worthwhile? Do we see ourselves maintaining this documentation? Or is the effort better spent elsewhere, perhaps tagging each constructor with an ID and then making wiki pages? Not sure what's best -- would love ideas! Credit to Alfredo di Napoli, who's done the heavy lifting of getting us this far. Relevant tickets: Original: https://gitlab.haskell.org/ghc/ghc/-/issues/18516 Tasks left: https://gitlab.haskell.org/ghc/ghc/-/issues/19905 Thanks, Richard

10 16

ghcup failed
by Simon Peyton Jones 02 Jun '21

02 Jun '21

Dear devs I wanted to install GHC 8.10 on my WSL2 (Windows Subsystem for Linux) computer. So I went here https://www.haskell.org/ghcup/ and followed the instructions (the curl … command). There was a long pause then [ Info ] verifying digest of: ghc-8.10.4-x86_64-deb9-linux.tar.xz [ Info ] Unpacking: ghc-8.10.4-x86_64-deb9-linux.tar.xz to /tmp/ghcup-khiegA [ Info ] Installing GHC (this may take a while) [ Error ] BuildFailed failed in dir "/tmp/ghcup-khiegA": NonZeroExit 2 "make" ["install"] Check the logs at "/home/simonpj/.ghcup/logs" and the build directory "/tmp/ghcup-khiegA" for more clues. Make sure to clean up "/tmp/ghcup-khiegA" afterwards. "_eghcup --cache install ghc recommended" failed! I looked in the logs as suggested, and found this in the tail of ghc-make.log Installing library in /home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/libiserv-8.10.4 "utils/ghc-cabal/dist-install/build/tmp/ghc-cabal-bindist" copy compiler stage2 "strip" '' '/home/simonpj/.ghcup/ghc/8.10.4' '/home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4' '/home/simonpj/.ghcup/ghc/8.10.4/share/doc/ghc-8.10.4/html/libraries' 'v p dyn' Installing library in /home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/ghc-8.10.4 "/home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/bin/ghc-pkg" --force --global-package-db "/home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/package.conf.d" update rts/dist/package.conf.install ghc-pkg: Couldn't open database /home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/package.conf.d for modification: {handle: /home/simonpj/.ghcup/ghc/8.10.4/lib/ghc-8.10.4/package.conf.d/package.cache.lock}: hLock: invalid argument (Invalid argument) ghc.mk:967: recipe for target 'install_packages' failed make[1]: *** [install_packages] Error 1 Makefile:51: recipe for target 'install' failed make: *** [install] Error 2 So I seem to be stuck. Any ideas? I feel embarrassed not to be able to install GHC 😊. Simon

4 4

GitLab downtime
by Ben Gamari 02 Jun '21

02 Jun '21

Hi all, Today I'm going to be working on migrating our GitLab instance to a new machine. Starting in likely an hour there will be a few hours of downtime while the migration proceeds. I will send an email when the downtime begins and concludes. Apologies for the late notice! Cheers, - Ben

6 10