November 2018 - ghc-tickets

[GHC] #15681: Take {-# COMPLETE #-} pragma into consideration when using MonadFailDesugaring
by GHC 18 Dec '18

18 Dec '18

#15681: Take {-# COMPLETE #-} pragma into consideration when using MonadFailDesugaring -------------------------------------+------------------------------------- Reporter: chshersh | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.6.1 Keywords: pattern- | Operating System: Unknown/Multiple matching,monadfail,desugaring | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following code: {{{#!hs import Data.List.NonEmpty (NonEmpty (..)) foo :: Monad m => m (NonEmpty a) -> m a foo m = do (x :| _) <- m pure x }}} It works completely fine on GHC 8.6.1 and doesn't require `MonadFail` constraint because `NonEmpty` has only single constructor so there're no other cases in pattern-matching. Howewer, if I rewrite this code using `-XPatternSynonyms` with `{-# COMPLETE #-}` pragma, it doesn't work anymore. {{{#!hs {-# LANGUAGE PatternSynonyms #-} import Data.List.NonEmpty (NonEmpty (..)) newtype Foo a = Foo (NonEmpty a) pattern (:||) :: a -> [a] -> Foo a pattern x :|| xs <- Foo (x :| xs) {-# COMPLETE (:||) #-} foo :: Monad m => m (Foo a) -> m a foo m = do (x :|| _) <- m pure x }}} And I see the following error: {{{ • Could not deduce (Control.Monad.Fail.MonadFail m) arising from a do statement with the failable pattern ‘(x :|| _)’ from the context: MonadFoo m bound by the type signature for: foo :: forall (m :: * -> *) a. MonadFoo m => m (Foo a) -> m a at /Users/fenx/haskell/sandbox/Fail.hs:13:1-37 Possible fix: add (Control.Monad.Fail.MonadFail m) to the context of the type signature for: foo :: forall (m :: * -> *) a. MonadFoo m => m (Foo a) -> m a • In a stmt of a 'do' block: (x :|| _) <- m In the expression: do (x :|| _) <- m pure x In an equation for ‘foo’: foo m = do (x :|| _) <- m pure x | 15 | (x :|| _) <- m | ^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15681> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15808: Master sefaults on windows during aeson build when stage2 libs have dwarf enabled.
by GHC 18 Dec '18

18 Dec '18

#15808: Master sefaults on windows during aeson build when stage2 libs have dwarf enabled. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I haven't had any luck with reproducing it outside of building the aeson package with cabal yet. So for now just documenting the fact. build.mk used {{{ GhcLibHcOpts += -g3 GhcRtsHcOpts += -g3 STRIP_CMD = : BUILD_PROF_LIBS = NO SplitObjs = NO SplitSections = NO HADDOCK_DOCS = NO BUILD_SPHINX_HTML = NO BUILD_SPHINX_PDF = NO BUILD_MAN = NO }}} Error log: {{{ "E:/ghc_dwarf/inplace/bin/ghc-stage2.exe" "--make" "-fbuilding-cabal- package" "-O" "-outputdir" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build" "-odir" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build" "-hidir" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build" "-stubdir" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build""-i" "-iC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build" "-i." "-iattoparsec-iso8601/" "-ipure" "-iC:\ghc\msys64\home\Andi\aeson_repro \dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\autogen" "-iC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\global- autogen" "-IC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\autogen" "-IC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\global- autogen" "-IC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build" "-Iinclude" "-IC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\include" "-optP-include" "-optPC:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\autogen\cabal_macros.h" "-this-unit-id" "aeson-1.4.1.0-inplace" "-hide-all-packages" "-Wmissing- home-modules" "-no-user-package-db" "-package-db" "C:\Users\Andi\AppData\Roaming\cabal\store\ghc-8.7.20181025\package.db" "-package-db" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\packagedb\ghc-8.7.20181025" "-package-db" "C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\package.conf.inplace" "-package-id" "attoparsec-0.13.2.2-8913a968506e9e83757f6fe696d6fe61e0d4b4a8" "-package- id" "base-4.12.0.0" "-package-id" "base- compat-0.10.5-34e11ceb2d98e0262d1d958bca2afc3184e70c60" "-package-id" "bytestring-0.10.8.2" "-package-id" "containers-0.6.0.1" "-package-id" "deepseq-1.4.4.0" "-package-id" "dlist-0.8.0.5-681a0f929505417757ba9f9981a50ab1d7c8a0e0" "-package-id" "ghc-prim-0.5.3" "-package-id" "hashable-1.2.7.0-50f89c5dee92df34fc2d6540cfde1983f26d8e31" "-package-id" "primitive-0.6.4.0-c08c185073660c1604acdddfe5c369afae583ba2" "-package-id" "scientific-0.3.6.2-4bea197b4523e02da61c34a1eed01432d9fefff6" "-package- id" "tagged-0.8.6-d3cce1acba663b646f565adb64d80579664d8caa" "-package-id" "template-haskell-2.14.0.0" "-package-id" "text-1.2.3.1" "-package-id" "th-abstraction-0.2.8.0-e197ba78a6de8bf8fc5d00ecb5a358a8b27bcc92" "-package-id" "time-1.8.0.2" "-package-id" "time-locale- c_-0.1.1.5-7549537073e62ce01921c89c30cc6cafeed99b5b" "-package-id" "unordered-con_-0.2.9.0-f5cd33176070f516c88b1aac3ef61959b09fcfa6" "-package-id" "uuid-types-1.0.3-f68643250767dce83d2c227104d15a0aa9c3c77f" "-package-id" "vector-0.12.0.1-3a9a26f81a463f0efefa41528af3e27d3a88cc7d" "-XHaskell2010" "Data.Aeson" "Data.Aeson.Encoding" "Data.Aeson.Parser" "Data.Aeson.Text" "Data.Aeson.Types" "Data.Aeson.TH" "Data.Aeson.QQ.Simple" "Data.Aeson.Encoding.Internal" "Data.Aeson.Internal" "Data.Aeson.Internal.Time" "Data.Aeson.Parser.Internal" "Data.Aeson.Encode" "Data.Aeson.Compat" "Data.Aeson.Encoding.Builder" "Data.Aeson.Internal.Functions" "Data.Aeson.Parser.Unescape" "Data.Aeson.Parser.Time" "Data.Aeson.Types.FromJSON" "Data.Aeson.Types.Generic" "Data.Aeson.Types.ToJSON" "Data.Aeson.Types.Class" "Data.Aeson.Types.Internal" "Data.Attoparsec.Time" "Data.Attoparsec.Time.Internal" "Data.Aeson.Parser.UnescapePure" "-Wall" "-O2" "-hide-all-packages" "-g13" [ 2 of 25] Compiling Data.Aeson.Internal.Functions ( Data\Aeson\Internal\Functions.hs, C:\ghc\msys64\home\Andi\aeson_repro \dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Internal\Functions.o ) [Data.HashMap.Strict changed] [ 5 of 25] Compiling Data.Aeson.Types.Generic ( Data\Aeson\Types\Generic.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Types\Generic.o ) [Prelude.Compat changed] [ 6 of 25] Compiling Data.Aeson.Types.Internal ( Data\Aeson\Types\Internal.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Types\Internal.o ) [Data.Vector changed] [ 7 of 25] Compiling Data.Aeson.Parser.Internal ( Data\Aeson\Parser\Internal.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Parser\Internal.o ) [Data.Scientific changed] [ 8 of 25] Compiling Data.Aeson.Parser ( Data\Aeson\Parser.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Parser.o ) [Data.Aeson.Parser.Internal changed] [ 9 of 25] Compiling Data.Attoparsec.Time.Internal ( attoparsec- iso8601\Data\Attoparsec\Time\Internal.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Attoparsec\Time\Internal.o ) [Prelude.Compat changed] attoparsec-iso8601\Data\Attoparsec\Time\Internal.hs:24:1: warning: [-Wunused-imports] The import of `Unsafe.Coerce' is redundant except perhaps to import instances from `Unsafe.Coerce' To import instances alone, use: import Unsafe.Coerce() | 24 | import Unsafe.Coerce (unsafeCoerce) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [10 of 25] Compiling Data.Attoparsec.Time ( attoparsec- iso8601\Data\Attoparsec\Time.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Attoparsec\Time.o ) [Data.Attoparsec.Text changed] [11 of 25] Compiling Data.Aeson.Parser.Time ( Data\Aeson\Parser\Time.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Parser\Time.o ) [Data.Attoparsec.Text changed] [12 of 25] Compiling Data.Aeson.Types.FromJSON ( Data\Aeson\Types\FromJSON.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Types\FromJSON.o ) [Data.Primitive.PrimArray changed] [13 of 25] Compiling Data.Aeson.Internal ( Data\Aeson\Internal.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Internal.o ) [Data.Aeson.Types.FromJSON changed] [14 of 25] Compiling Data.Aeson.Internal.Time ( Data\Aeson\Internal\Time.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Internal\Time.o ) [Data.Attoparsec.Time.Internal changed] [15 of 25] Compiling Data.Aeson.Encoding.Builder ( Data\Aeson\Encoding\Builder.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Encoding\Builder.o ) [Data.Vector changed] [16 of 25] Compiling Data.Aeson.Encoding.Internal ( Data\Aeson\Encoding\Internal.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Encoding\Internal.o ) [Data.Scientific changed] [17 of 25] Compiling Data.Aeson.Encoding ( Data\Aeson\Encoding.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Encoding.o ) [Data.Aeson.Encoding.Internal changed] [18 of 25] Compiling Data.Aeson.Types.ToJSON ( Data\Aeson\Types\ToJSON.hs, C:\ghc\msys64\home\Andi\aeson_repro\dist- newstyle\build\x86_64-windows\ghc-8.7.20181025\aeson-1.4.1.0\build\Data\Aeson\Types\ToJSON.o ) [Data.Primitive.PrimArray changed] Access violation in generated code when executing data at 0x103fec440 Attempting to reconstruct a stack trace... Frame Code address * 0x845d9c0 0x103fec440 * 0x845da20 0x400c0f8 E:\ghc_dwarf\inplace\bin\ghc- stage2.exe+0x3c0c0f8 * 0x845da80 0x3fec9a1 E:\ghc_dwarf\inplace\bin\ghc- stage2.exe+0x3bec9a1 * 0x845dab0 0x3feca31 E:\ghc_dwarf\inplace\bin\ghc- stage2.exe+0x3beca31 * 0x845dab8 0x34c8934 E:\ghc_dwarf\inplace\bin\ghc- stage2.exe+0x30c8934 * 0x845dac0 0xfa340 * 0x845dac8 0x2a940b78 * 0x845dad0 0x2a98cd69 * 0x845dad8 0x2a98d7d0 CallStack (from HasCallStack): die', called at .\\Distribution\\Client\\ProjectOrchestration.hs:977:55 in main:Distribution.Client.ProjectOrchestration cabal.exe: Failed to build aeson-1.4.1.0-inplace. The build process terminated with exit code 11 }}} I could only reproduce it with master on Windows so far. It always triggers but under very specific circumstances: * GHC built with the flags above, adding dwarf info to the ghc executable or removing dwarf info eliminates the issue. * Only on a complete rebuild of aeson. Restarting the crashed build finishes without an error. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15808> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15003: Data.List documentation should list complexities of more functions
by GHC 18 Dec '18

18 Dec '18

#15003: Data.List documentation should list complexities of more functions -------------------------------------+------------------------------------- Reporter: gbaz | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.4.3 Component: | Version: 8.2.2 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Lots of functions in `Data.List` have overtly obvious complexity, like `delete`. It would still be nice to list all the complexities explicitly, especially for beginners. Also, just to set a good example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15003> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15968: configure doesn't error out when --enable-dwarf-unwind is given but libdw cannot be found
by GHC 18 Dec '18

18 Dec '18

#15968: configure doesn't error out when --enable-dwarf-unwind is given but libdw cannot be found -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Build System | Version: 8.6.2 (make) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Against expectations, the GHC bindist supposedly having DWARF support provided at https://downloads.haskell.org/~ghc/8.4.4/ghc-8.4.4-x86_64-deb9-linux- dwarf.tar.xz doesn't actually have DWARF support. According to bgamari, this is because `./configure --enable-dwarf-unwind` doesn't actually complain when the required dependency `libdw` isn't found; instead, it continues silently. Most programs I know will barf out when something isn't found but also *explicitly* requested via the command line; for the cases where this wasn't, the project maintainers did consider this a bug. GHC's `./configure` suite should fail hard when `--enable-dwarf-unwind` is given but `libdw` cannot be found. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15968> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15923: Skip performance tests if not in a git repo
by GHC 17 Dec '18

17 Dec '18

#15923: Skip performance tests if not in a git repo -------------------------------------+------------------------------------- Reporter: davide | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.6.3 Component: Test Suite | Version: 8.6.2 Keywords: performance | Operating System: Unknown/Multiple tests git notes | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: 12758 Differential Rev(s): | Wiki Page: | Performance/Tests -------------------------------------+------------------------------------- As of #12758 performance tests now compare to the results of the previous commit. Results are stored in git notes. If for some reason the rood directory is not a git repo, we have no results to compare to, nor can we save the new results to git notes. Hence we should skip all performance tests. Such a use case was encountered in simonpj's workflow where he copies/syslinks the work tree without the .git directory before validating. An open question is can we allow performance testing while not in a git repo or by adjusting the workflow? Tasks: * When the ghc root directory is not a git repository, skip all performance tests. * Update the [https://ghc.haskell.org/trac/ghc/wiki/Performance/Tests wiki page]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15923> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15950: Hadrian build fails on Windows
by GHC 17 Dec '18

17 Dec '18

#15950: Hadrian build fails on Windows -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.8.1 Component: Build System | Version: 8.6.2 (Hadrian) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As of {{{ $ hadrian/build.cabal.sh -j5 --flavour=Quick ... $ hadrian/build.cabal.sh -j5 --flavour=Quick | ContextData oracle: resolving data for 'iserv' (Stage1, v)... | Configure package 'iserv' Configuring iserv-8.7.1... creating C:\msys64\home\ben\ghc\builds\0\project-0\_build\stage1\utils\iserv\build "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--numeric-version" ]0;1s (99%)C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe is version 8.7.20181126 "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe" "--version" C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe is version 8.7.20181126 "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--supported-languages" "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "-- info" Reading installed packages... "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe" "dump" "--global" "-v0" "--global-package- db=C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage1/lib/package.conf.d" "C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--print-libdir" "-ghcversion- file=C:/msys64/home/ben/ghc/builds/0/project-0/_build/generated/ghcversion.h" CallStack (from HasCallStack): die', called at .\Distribution\Simple\Configure.hs:969:20 in Cabal-2.5.0.0-inplace:Distribution.Simple.Configure configureFinalizedPackage, called at .\Distribution\Simple\Configure.hs:467:12 in Cabal-2.5.0.0-inplace:Distribution.Simple.Configure configure, called at .\Distribution\Simple.hs:596:20 in Cabal-2.5.0.0-inplace:Distribution.Simple confHook, called at .\Distribution\Simple\UserHooks.hs:67:5 in Cabal-2.5.0.0-inplace:Distribution.Simple.UserHooks configureAction, called at .\Distribution\Simple.hs:178:19 in Cabal-2.5.0.0-inplace:Distribution.Simple defaultMainHelper, called at .\Distribution\Simple.hs:148:3 in Cabal-2.5.0.0-inplace:Distribution.Simple defaultMainWithHooksNoReadArgs, called at src\Hadrian\Haskell\Cabal\Parse.hs:145:14 in main:Hadrian.Haskell.Cabal.Parse hadrian.exe: Encountered missing dependencies: libiserv ==8.7.* }}} (Ignore garbage characters due to Window's broken ANSI console support) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15950> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14146: Can GHC propose kind restrictions?
by GHC 17 Dec '18

17 Dec '18

#14146: Can GHC propose kind restrictions? -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is UX. As my code gets more polykinded I find myself in situations such as these all the more often {{{#!hs instance (Comonad f, Representable f, Comonad g, Representable g) => Comonad (Compose f g) where extract = undefined duplicate = undefined instance ComonadApply (Compose f g) where (<@>) = undefined }}} {{{ /tmp/a.hs:20:10-35: error: • No instance for (Comonad (Compose f g)) arising from the superclasses of an instance declaration • In the instance declaration for ‘ComonadApply (Compose f g)’ | 20 | instance ComonadApply (Compose f g) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^ Failed, modules loaded: none. }}} It would help me if GHC looked up a `Comonad (Compose _ _)` instance, compared the kinds {{{#!hs Comonad (Compose (f :: Type -> Type) (g :: Type -> Type) :: Type -> Type) ComonadApply (Compose (f :: k -> Type) (g :: Type -> k) :: Type -> Type) }}} a simple suggestion like this would be helpful {{{ • No instance for (Comonad (Compose f g)) arising from the superclasses of an instance declaration Try adding a kind signature (ComonadApply (Compose (f :: Type -> Type) g)). }}} Even more amazing would be {{{ • No instance for (Comonad (Compose f g)) arising from the superclasses of an instance declaration Try adding a context (Comonad f, Representable f, Comonad g, Representable g) => ComonadApply (Compose f g) }}} Which the compiler could in theory guess, since following GHC's suggestion iteratively you end up with {{{#!hs ComonadApply (Compose (f :: Type -> Type) g) -- ==> add (Comonad f) to the context of the instance declaration Comonad f => ComonadApply (Compose f g) -- ==> add (Comonad g) to the context of the instance declaration (Comonad f, Comonad g) => ComonadApply (Compose f g) -- ==> add (Representable f) to the context of the instance declaration (Comonad f, Comonad g, Representable g) => ComonadApply (Compose f g) -- ==> add (Representable f) to the context of the instance declaration (Comonad f, Comonad g, Representable g, Representable f) => ComonadApply (Compose f g) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14146> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13992: Error message, room for improvement (polykinds)
by GHC 17 Dec '18

17 Dec '18

#13992: Error message, room for improvement (polykinds) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: PolyKinds | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Something like {{{#!hs -- • No instance for (Show (Compose Proxy Proxy a)) -- arising from the 'deriving' clause of a data type declaration -- Possible fix: -- use a standalone 'deriving instance' declaration, -- so you can specify the instance context yourself -- • When deriving the instance for (Show (FlipProxy a)) {-# Language DerivingStrategies, GeneralizedNewtypeDeriving, PolyKinds, KindSignatures #-} import Data.Functor.Compose import Data.Proxy import Data.Kind newtype FlipProxy a = FlipProxy_ (Compose Proxy Proxy a) deriving newtype Show }}} where the solution is to constraint the kind of `a :: Type`, it would be nice if GHC could reference kind variables. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13992> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15890: Provide a way for hadrian users to always pass some options to hadrian itself
by GHC 17 Dec '18

17 Dec '18

#15890: Provide a way for hadrian users to always pass some options to hadrian itself -------------------------------------+------------------------------------- Reporter: alpmestan | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.8.1 Component: Build System | Version: 8.7 (Hadrian) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- And more generally, is there any chance that we could make something like our builder `Args`/predicate logic work for specifying arguments to hadrian itself? Regardless of the answer to that last question, it seems only natural to have a simple/trivial solution for the case where we are always passing the same options to hadrian, over and over again, while working on GHC. "Yes, hadrian, I still want to build with the `perf` flavour, still with `integer-simple`, and you should still put all the build artifacts under `./ghc-prof-build/` while using all of my 4 cores", is something that I often told hadrian myself, while investigating a particular problem a few weeks ago, for example. Ryan in particular has expressed interested in having a slightly cleaner solution than writing a tiny wrapper script that just does `hadrian/build.sh --flavour=perf -oghc-prof-build $@` or something along those lines. Especially given that our `Args` infrastructure seems perfect to specify that kind of thing. It does seem a little bit circular though, of course. An alternative would be look at a build.mk-ish file, without support for any Make construct, just the good old key=value syntax + comments, and reconstruct a `Flavour` and everything else out of it. This way, instead of "implicitly" passing the same arguments on the CLI, we would "implicitly" look them up from some file, without having to create a wrapper script. (This build.mk-ish file is something I discussed with hvr some time ago, which he would like so as to programmatically specify how he wants his GHCs. He can't reasonably programmatically edit the settings file.) Thoughts? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15890> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15562: `-XStrict -XNoStrict` is not neutral
by GHC 14 Dec '18

14 Dec '18

#15562: `-XStrict -XNoStrict` is not neutral -------------------------------------+------------------------------------- Reporter: hvr | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I assumed we already had a ticket about this, but it appears we have not. I'm not saying this is a necessarily a bug in the implementation; but we should make sure this is properly documented in the user's guide, and ideally justify why it's done this way rather than the alternatives: As described in StrictPragma, > `Strict` implies `StrictData` Currently however the inverse case does not hold, i.e. `NoStrict` does *not* imply `NoStrictData` This has the surprising property (assuming these were left-most flags on the CLI) that - `-XStrict -XNoStrict` == `-XStrictData` - `-XStrictData -XNoStrict` == `-XStrictData` However, if `-XNoStrict` was to naively imply `-XNoStrictData`, we'd have the properties - `-XStrict -XNoStrict` == *id* - `-XStrictData -XNoStrict` == *id* This might be a bit less confusing; another variant would be - `-XStrict -XNoStrict` == *id* - `-XStrictData -XNoStrict` == `-XStrictData` Btw, I'm not sure what the following means: - `-XStrict -XNoStrictData` == ? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15562> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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