April 2019 - ghc-devs

Getting Rewrite Rules from ModGuts
by Bill Hallahan 12 Apr '19

12 Apr '19

Hi, I'm trying to use the GHC API (8.2.2) to extract the rewrite rules from a module, but have run into some difficulties. I've written the following code (all code is also attached as files): module Main where import GHC import GHC.Paths import HscTypes main :: IO () main = do loadProj "Test.hs" loadProj :: FilePath -> IO () loadProj src = do modgutss <- runGhc (Just libdir) $ do flags <- getSessionDynFlags _ <- setSessionDynFlags flags target <- guessTarget src Nothing _ <- setTargets [target] _ <- load LoadAllTargets mod_graph <- getModuleGraph parsed_mods <- mapM parseModule mod_graph typed_mods <- mapM typecheckModule parsed_mods desug_mods <- mapM desugarModule typed_mods return $ map coreModule desug_mods let rules = map (\mg -> ( moduleNameString . moduleName $ mg_module mg , length $ mg_rules mg) ) modgutss print $ rules return () It loads Test.hs (see below my signature) which contains a single rewrite rule. Then, it obtains the ModGuts, and prints a tuple of the name of the module, and the length of the rule list. I would expect this to be ("Test", 1), but, in fact, what gets printed is ("Test", 0). For some reason, the ModGuts does not have the rewrite rule from the file. I'm guessing I'm misunderstanding something about how the GHC API works. If anyone has any advice about how to fix this code to load rewrite rules (or even where to begin looking) I would appreciate it! Thanks, Bill Hallahan Test.hs: module Test where import Prelude hiding (map) map :: (a -> b) -> [a] -> [b] map f (x:xs) = f x:map f xs map _ [] = [] {-# NOINLINE [0] map #-} {-# RULES "map/map" forall f g xs . map f (map g xs) = map (f . g) xs #-}

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[ANNOUNCE] GHC 8.6.5-rc1 is now available
by Ben Gamari 12 Apr '19

12 Apr '19

Hello everyone, The GHC team is proud to announce the first release candidate of 8.6.5. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.6.5-rc1 This release fixes a handful of issues with 8.6.4: - Binary distributions once again ship with Haddock documentation including syntax highlighted source of core libraries (#16445) - A build system issue where use of GCC with `-flto` broke `configure` was fixed (#16440) - An bug affecting Windows platforms wherein XMM register values could be mangled when entering STG has been fixed (#16514) - Several Windows packaging issues resulting from the recent CI rework. (#16408, #16398, #16516) Since this is a relatively small bugfix release we are bypassing the alpha releases and moving right to the release candidate stage. If all goes well the final release will be cut next week. As always, if anything looks amiss do let us know. Happy testing! Cheers, - Ben

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Unable to build a profiled version of GHC Head
by Roland Senn 09 Apr '19

09 Apr '19

Hi, I'm unable to build a profiled version of GHC Head. I did: git clone --recursive https://gitlab.haskell.org/ghc/ghc ghcprof cd ghcprof git remote set-url --add origin https://gitlab.haskell.org/RolandSenn/ghc git remote set-url --delete origin https://gitlab.haskell.org/ghc/ghc git remote add upstream https://gitlab.haskell.org/ghc/ghc git fetch upstream git push origin master hadrian/build.sh -c --flavour=prof -j2 I get the follwoing failure: ... | Run Ghc CompileCWithGhc Stage1: utils/hp2ps/Utilities.c => _build/stage1/utils/hp2ps/build/c/Utilities.dyn_o | Run Cc FindCDependencies Stage1: libraries/ghc-prim/cbits/atomic.c => _build/stage1/libraries/ghc-prim/build/c/cbits/atomic.p_o.d | Run Ghc CompileCWithGhc Stage1: libraries/ghc-prim/cbits/atomic.c => _build/stage1/libraries/ghc-prim/build/c/cbits/atomic.p_o | Run HsCpp: compiler/prelude/primops.txt.pp => _build/stage1/compiler/build/primops.txt | Run GenPrimopCode: _build/stage1/compiler/build/primops.txt => _build/stage1/libraries/ghc-prim/build/GHC/Prim.hs libraries/ghc-prim/cbits/atomic.c: In function ‘hs_atomic_nand8’: libraries/ghc-prim/cbits/atomic.c:181:10: error: note: ‘__sync_fetch_and_nand’ changed semantics in GCC 4.4 return __sync_fetch_and_nand((volatile StgWord8 *) x, (StgWord8) val); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | 181 | return __sync_fetch_and_nand((volatile StgWord8 *) x, (StgWord8) val); | ^ | Run Cc FindCDependencies Stage1: libraries/ghc-prim/cbits/pext.c => _build/stage1/libraries/ghc-prim/build/c/cbits/pext.dyn_o.d | Run Cc FindCDependencies Stage1: utils/hp2ps/Main.c => _build/stage1/utils/hp2ps/build/c/Main.dyn_o.d | Run Ghc CompileCWithGhc Stage1: libraries/ghc-prim/cbits/pext.c => _build/stage1/libraries/ghc-prim/build/c/cbits/pext.dyn_o | Run GenPrimopCode: _build/stage1/compiler/build/primops.txt => _build/stage1/libraries/ghc-prim/build/GHC/PrimopWrappers.hs | Run Ghc FindHsDependencies Stage1: libraries/ghc-prim/GHC/CString.hs (and 7 more) => _build/stage1/libraries/ghc-prim/.dependencies.mk | Run Ghc CompileCWithGhc Stage1: libraries/ghc-prim/cbits/pext.c => _build/stage1/libraries/ghc-prim/build/c/cbits/pext.p_o | Remove file _build/stage1/libraries/ghc-prim/.dependencies.mk.bak Error when running Shake build system: at action, called at src/Rules.hs:68:19 in main:Rules at need, called at src/Rules.hs:85:5 in main:Rules * Depends on: _build/stage1/bin/ghc at need, called at src/Utilities.hs:71:18 in main:Utilities * Depends on: _build/stage1/libraries/ghc-prim/build/libHSghc-prim-0.6.1_p-ghc8.9.20190408.so at need, called at src/Rules/Library.hs:121:5 in main:Rules.Library * Depends on: _build/stage1/libraries/ghc-prim/build/GHC/IntWord64.p_dyn_o at error, called at src/Hadrian/Oracles/TextFile.hs:65:20 in main:Hadrian.Oracles.TextFile * Raised the exception: No dependencies found for file '_build/stage1/libraries/ghc-prim/build/GHC/IntWord64.p_dyn_o' I'm using Debian 9; x64_86; GHC 8.6.3; gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516 Any ideas what's wrong? Many thanks and kind regards Roland

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Losing (parallel) sleep over module dependencies
by Matthew Pickering 09 Apr '19

09 Apr '19

Hi all, I get worried quite often about the interaction of two facts 1. Adding a new dependency to a module is easy. 2. Adding a new dependency changes the build graph and potentially reduces the amount of parallelism which the build is capable of. Has anyone thought of any strategies to analyse the dependency graph of GHC so that a linter can be created to warn against any changes which create dependencies which affect the parallelism? hs-boot files make this issue even worse I think but I'm not sure of the precise recompilation semantics. It would be quite straight forward to index ghc as it is being built to create a dependency graph (at the identifier) level but it's unclear to me whether it is possible to do anything productive with this information. Cheers, Matt

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Validation Failures on aarch64
by Travis Whitaker 09 Apr '19

09 Apr '19

Hello GHC devs, When attempting to validate a patch on aarch64, it seems there are a large number of validation failures: SUMMARY for test run started at Mon Apr 8 07:19:05 2019 UTC 0:15:35 spent to go through 6890 total tests, which gave rise to 17169 test cases, of which 10018 were skipped 41 had missing libraries 3151 expected passes 150 expected failures 11 caused framework failures 0 caused framework warnings 0 unexpected passes 3798 unexpected failures 0 unexpected stat failures The failures seem consistent on recent-ish master, specifically the neighborhood of 6113d0d4540af7853c71e9f42a41c3b0bab386fd. Is this to be expected? Thanks, Travis Whitaker

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Merge Request Submission Confusion
by Ara Adkins 08 Apr '19

08 Apr '19

Hey all, I'm trying to submit a minor MR as described on the wiki [0]. I can't seem to find the mentioned 'New Merge Request' button, however. Do I need a specific set of permissions to open MRs? Any pointers would be appreciated. Best, _ara [0] https://gitlab.haskell.org/ghc/ghc/wikis/home#opening-a-merge-request

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CI execution
by Sylvain Henry 08 Apr '19

08 Apr '19

Hi devs, It seems that the CI doesn't check branches in GHC forks on Gitlab anymore. Is is intentional? Is there a way to trigger a CI execution manually on a specific branch? Thanks, Sylvain

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Proposal: Don't read environment files by default
by Matthew Pickering 08 Apr '19

08 Apr '19

Hi all, Environment files have caused a large amount of pain for users because they are read by default by GHC. For example: https://github.com/haskell/cabal/issues/4542 Cabal developers have indicated that they are not going to stop generating them by default despite the overwhelming user pressure. Therefore I propose that users should opt-in to using environment files by having to explicitly pass a flag to enable the search behavior. This will provide a much better user experience overall and will stop tooling having to isolate itself from their existence. Cheers, Matt

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Re: Recover role of a type variable in source Haskell
by Ryan Scott 07 Apr '19

07 Apr '19

It depends on what you mean by "source Haskell". If you're willing to consider including Template Haskell in your definition of "source", then the answer is yes, since there is a reifyRoles function [1] which gives you this information. I'm not aware of another way to accomplish this (without resorting to something like the GHC API). Ryan S. ----- [1] https://hackage.haskell.org/package/template-haskell-2.14.0.0/docs/Language…

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Recover role of a type variable in source Haskell
by chessai . 07 Apr '19

07 Apr '19

Hi devs, Is it possible to programmatically recover the role of a type variable? Or, possibly, a list of the roles of the type variables from left to right? For example, if i have: data Foo a = Foo (1) newtype Bar a b = Bar (a -> b) (1) Getting the role list of (1) would give me [Phantom], and (2) would give me [Representational, Representational]. I know in compiler/types/TyCon.hs that TyCon has a list of Roles in it, but there doesn't seem to be any machinery available to do this in source haskell. Thanks

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