- ghc-devs - Haskell.org

margebot.
by Phyx 13 Aug '19

13 Aug '19

Hello, margebot seems down, or did I miss a memo on how to commit now? Cheers, Tamar

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Gitlab's disk full again
by Ömer Sinan Ağacan 11 Aug '19

11 Aug '19

Hi, Just yesterday Gitlab was giving 500 because the disk was full. Ben deleted some files, but in less than 24h it's full again. This started happening regularly, I wonder if we could do something about this. The reason this time seems to be that Gitlab started generating 22G-large backups daily since the 7th. I'm not sure how important those backups are so I'm not deleting them. There's also a large docker-registry directory (101G). I think it might be good to set up some kind of downtime monitoring or maybe something on the Gitlab server to send an email when the disk is nearly full. It could send an email to people who has access to the server. It'd also be good to come up with an action plan when this happens. I have access to the server, but I have no idea which files are important. Documenting Gitlab setup (and the server details) in more details might be helpful. Does anyone have any other ideas to keep the server running? Ömer

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PseudoOps in primops.txt.pp
by Sebastian Graf 11 Aug '19

11 Aug '19

Hey fellow devs, While implementing new PseudoOps, a couple of questions popped up: 1. What are PseudoOps? When do we want to declare one? There doesn't seem to be any documentation around them. I only figured out that I probably want a PseudoOp by comparing to PrimOps I thought would be lowered at a similar stage (i.e. somewhere in Core or STG). 2. Why aren't GHC.Magic.{lazy,noinline,oneShot} PseudoOps? 3. Since we have to set all the IdInfo for `seq` and `noinline` manually, why is this incomplete? I.e., I'd expect a useful strictness signature and arity for both of these. Thanks! Sebastian

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LoadAllTargets not loading dependencies
by Sam Halliday 07 Aug '19

07 Aug '19

Hello all, I've been following along with Stephen Diehl's blog series on the ghc api and I am using `load LoadAllTargets` on a .hs file (let's call it Wibble.hs) and then typechecking. All seems well until I add a second module (let's call it Wobble.hs) in the same package and import it from Wibble. I can see that the load has correctly calculated the dependency graph and includes Wobble in the dependencies of Wibble. But if I try to typecheck Wibble, then I get an error: Could not find module ‘Wobble’ Use -v to see a list of the files searched for. | 4 | import Wobble | ^^^^^^^^^^^^^^^^^^^^^^^ I have separately compiled the package, and can see its packagedb is listed in the .ghc.env file. What else do I need to do so that Wibble can see Wobble? -- Best regards, Sam

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ModuleInfo.minf_rdr_env not exposed
by Sam Halliday 07 Aug '19

07 Aug '19

Hi all, Is there a reason why minf_rdr_env (a field in ModuleInfo) is not exposed? It's possible to reconstruct it in 8.4.4 (the only version I'm looking at) with a TypecheckedModule via let (tc_gbl_env, _) = GHC.tm_internals_ tmod minf_rdr_env = tcg_rdr_env tc_gbl_env It's a useful thing to have for editor tooling (e.g. to get the correct qualified imported symbols that may be autocompleted). -- Best regards, Sam

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Conveniently searching GitLab
by Ben Gamari 06 Aug '19

06 Aug '19

Hello everyone, I've long found GitLab's search interface to be rather clunky. Several of the issues I've noted have been reported upstream but progress in resolving them seems to be slow. Consequently, I have implemented a workaround [1] which addresses most of my typical use-cases. This is essentially a thin wrapper around GitLab's various search facilities which intelligently routes requests according to a simple (and hopefully intuitive) query syntax. For instance, to * navigate to GHC issue #123: search for `#123` * search for GHC issues related to unboxed tuples: search for `# unboxed tuples` * navigate to the `ghc/head.hackage` project: search for `ghc/head.hackage>` * navigate to merge request !3 of the `ghc/head.hackage` project: search for `ghc/head.hackage!3` * navigate to commit e130fb57f7991575d848612abafe9ad10129131c of the `ghc/ghc` project: search for `ghc/ghc@e130fb57f7991575d848612abafe9ad10129131c` * search for merge requests of `haskell/ghcup` pertaining to Darwin: search for `haskell/ghcup! Darwin` Note that, as seen in the first two examples, the project name defaults to `ghc/ghc` if omitted. This interface is best used via your browser's search keywords feature [2]. To add a search keyword in Firefox you can right click on the search query input field and select "Add search keyword". To my surprise I didn't find a similarly convenient shortcut in Chromium. If you can think of any way in which the service can be improved, feel free to open a pull request against the upstream repository [3]. Cheers, - Ben [1] https://search.gitlab.haskell.org/ [2] http://kb.mozillazine.org/Using_keyword_searches [3] https://gitlab.haskell.org/bgamari/gitlab-search-service

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Solving stuck type families with a TC plugin
by Sandy Maguire 05 Aug '19

05 Aug '19

Hi all, I'm attempting to use a plugin to solve a generic type family CmpType (a :: k) (b :: k) :: Ordering by doing some sort of arbitrary hashing on `a` and `b` and ensuring they're the same. In the past, I've been successful at getting GHC to unify things by emitting new wanted CNonCanonical cts. This sort of works: mkWanted :: TyCon -> CompareType -> TcPluginM Ct mkWanted cmpType cmp = do (ev, _) <- unsafeTcPluginTcM . runTcSDeriveds $ newWantedEq (cmpTypeLoc cmp) Nominal (cmpTypeType cmp) (doCompare cmp) pure $ CNonCanonical ev Which is to say that this will compile: foo :: Proxy 'EQ foo = Proxy @(CmpType 2 2) So far so good! However, this acts strangely. For example, if I ask for bar with the incorrect type: bar :: Proxy 'GT bar = Proxy @(CmpType 2 2) I get the error: • Couldn't match type ‘CmpType 2 2’ with ‘'GT’ Expected type: Proxy 'GT Actual type: Proxy (CmpType 2 2) when I would expect • Couldn't match type ‘'EQ’ with ‘'GT’ This is more than just an issue with the error messages. A type family that is stuck on the result of CmpType, even after I've solved CmpType via the above! type family IsEQ (a :: Ordering) :: Bool where IsEQ 'EQ = 'True IsEQ _ = 'False zop :: Proxy 'True zop = Proxy @(IsEQ (CmpType 2 2)) • Couldn't match type ‘IsEQ (CmpType 2 2)’ with ‘'True’ Expected type: Proxy 'True Actual type: Proxy (IsEQ (CmpType 2 2)) Any suggestions for what I might be doing wrong, and how to convince GHC to make `zop` work properly? Thanks!

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a better workflow?
by Richard Eisenberg 04 Aug '19

04 Aug '19

Hi devs, Having gotten back to spending more time on GHC, I've found myself frequently hitting capacity limits on my machine. At one point, I could use a server at work that was a workhorse, but that's not possible any more (for boring reasons). It was great, and I miss it. So I started wondering about renting an AWS instance to help, but I quickly got overwhelmed by choice in setting that up. It's now pretty clear that their free services won't serve me, even as a trial prototype. So before diving deeper, I thought I'd ask: has anyone tried this? Or does anyone have a workflow that they like? Problems I have in want of a solution: - Someone submits an MR and I'm reviewing it. I want to interact with it. This invariably means building from scratch and waiting 45 minutes. - I work on a patch for a few weeks, on and off. It's ready, but I want to rebase. So I build from scratch and wait 45 minutes. - I make a controversial change and want to smoke out any programs that fail. So I run the testsuite and wait over an hour. This gets tiresome quickly. Most days of GHC hacking require at least one forced task-switch due to these wait times. If I had a snappy server, perhaps these times would be lessened. By the way, I'm aware of ghc-artefact-nix, but I don't know how to use it. I tried it twice. The first time, I think it worked. But by the second time, it had been revamped (ghc-head-from), and I think I needed to go into two subshells to get it working... and then the ghc I had didn't include the MR code. I think. It's hard to be sure when you're not sure whether or not the patch itself is working. Part of the problem is that I don't use Nix and mostly don't know what I'm doing when I follow the ghc-artefact-nix instructions, which seem to target Nix users. Thanks! Richard

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Invalid link in the wiki page "Building GHC on Windows"
by Joan Karadimov 04 Aug '19

04 Aug '19

Inside this wiki page: https://gitlab.haskell.org/ghc/ghc/wikis/building/preparation/windows ... there is a link to the latest cabal release. The link is: https://www.haskell.org/cabal/release/cabal-install-2.4.1.0/cabal-install-2… That link is not valid. It should be something like: https://downloads.haskell.org/cabal/cabal-install-2.4.1.0/cabal-install-2.4… The latter link is taken from https://www.haskell.org/cabal/download.html.

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api to access .hi files
by Sam Halliday 02 Aug '19

02 Aug '19

Hello all, I'd like to learn how to use the ghc api programmatically, but I am finding the haddocks (on hackage) to be a bit overwhelming. Could somebody please help me out by pointing me in the direction of the parts of the haddocks that are relevant to access information from .hi files that are available in the current build environment? In particular, I'm mostly interested in gathering information about symbols and their type signatures. As a first exercise: given a module+import section for a haskell source file, I want to find out which symbols (and their types) are available. Like :browse in ghci, but programmatically. PS: I'm aware that the .hie format is up and coming. I'm very excited by this! But I'm going to be using ghc-8.4.x and ghc-8.6.x for the foreseeable future, so I am mostly interested in what they have to offer. -- Best regards, Sam

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