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[GHC] #14636: GHC Panic
by GHC 04 Jan '18

04 Jan '18

#14636: GHC Panic -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- {{{ $ ghci -ignore-dot-ghci -XPolyKinds -XDataKinds GHCi, version 8.3.20171208: http://www.haskell.org/ghc/ :? for help Prelude> import Data.Proxy Prelude Data.Proxy> data ID :: a -> a -> * Prelude Data.Proxy> :kind (Proxy :: _ ID) ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.3.20171208 for x86_64-unknown-linux): piResultTy k_a1yY[tau:1] ID Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1144:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:951:35 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Prelude Data.Proxy> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14636> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14633: -fwarn-redundant-constraints false positive
by GHC 04 Jan '18

04 Jan '18

#14633: -fwarn-redundant-constraints false positive -------------------------------------+------------------------------------- Reporter: ghorn | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I had code which compiled cleanly on GHC 8.0.2 with -fwarn-redundant- constraints which now gives a warning on GHC 8.2.2. Here is the code, and my workaround: {{{#!haskell {-# OPTIONS_GHC -Wall -Werror -fwarn-redundant-constraints #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE FlexibleContexts #-} module Bug ( bug , workaround ) where import GHC.Generics ( D1, Datatype, Meta, Rep, datatypeName ) import Data.Proxy ( Proxy ) -- /home/greghorn/hslibs/ghc82_bug_maybe/Bug.hs:17:1: warning: [-Wredundant-constraints] -- • Redundant constraint: Rep a ~ D1 d p -- • In the type signature for: -- bug :: forall a (d :: Meta) (p :: * -> *). -- (Datatype d, Rep a ~ D1 d p) => -- Proxy a -> String -- | -- 25 | bug :: forall a d p . (Datatype d, Rep a ~ D1 d p) => Proxy a -> String -- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bug :: forall a d p . (Datatype d, Rep a ~ D1 d p) => Proxy a -> String bug = const name where name = datatypeName (undefined :: D1 d p b) type family GetD a :: Meta where GetD (D1 d p) = d workaround :: forall a d p . (Datatype (GetD (Rep a)), Rep a ~ D1 d p) => Proxy a -> String workaround = const name where name = datatypeName (undefined :: D1 d p b) }}} I suspect it is a bug because if I remove the "redundant" constraint it no longer typechecks. Here is a minimal setup to reproduce with stack: {{{ name: bug version: 0.0.0.2 license: AllRightsReserved author: Greg Horn maintainer: gregmainland(a)gmail.com build-type: Simple cabal-version: >=1.10 library exposed-modules: Bug build-depends: base >= 4.7 && < 5 default-language: Haskell2010 }}} {{{ resolver: lts-10.2 compiler-check: newer-minor # Local packages, usually specified by relative directory name packages: - . }}} Alternatively: {{{ git clone https://github.com/ghorn/ghc-redundant-constraint-bug cd ghc-redundant-constraint-bug stack build }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14633> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14607: Core Lint error
by GHC 03 Jan '18

03 Jan '18

#14607: Core Lint error -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: TypeInType, | Operating System: Unknown/Multiple DeferredTypeErrors | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #14605 #14584 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This produces long {{{#!hs {-# Language DerivingStrategies #-} {-# Language GADTs #-} {-# Language GeneralizedNewtypeDeriving #-} {-# Language InstanceSigs #-} {-# Language KindSignatures #-} {-# Language TypeFamilies #-} {-# Language TypeInType #-} {-# Language TypeOperators #-} import Data.Kind data DEFUNC :: Type -> Type -> Type where (:~>) :: a -> b -> DEFUNC a b type a ~> b = DEFUNC a b -> Type data LamCons a :: Type ~> Type where LamCons :: a -> LamCons a ([a] :~> [a]) class Mk (app :: Type ~> Type) where type Arg app :: Type mk :: Arg app -> app (a :~> b) instance Mk (LamCons a :: Type ~> Type) where type Arg (LamCons a) = a mk :: a -> LamCons (a :~> b) mk = LamCons }}} erros with `ghci -ignore-dot-ghci -fdefer-type-errors -dcore-lint bug.hs` on GHC 8.2.1 and 8.3.20171208. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14607> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14605: Core Lint error
by GHC 03 Jan '18

03 Jan '18

#14605: Core Lint error -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: TypeInType, | Operating System: Unknown/Multiple DeferredTypeErrors | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This piece of code fails when run with `ghci -ignore-dot-ghci -fdefer- type-errors -dcore-lint bug.hs`, maybe same as my previous #14584. {{{#!hs {-# Language DerivingStrategies #-} {-# Language GeneralizedNewtypeDeriving #-} {-# Language InstanceSigs #-} {-# Language KindSignatures #-} {-# Language PolyKinds #-} {-# Language ScopedTypeVariables #-} {-# Language TypeApplications #-} {-# Language TypeFamilies #-} {-# Language TypeInType #-} {-# Language TypeOperators #-} {-# Language UndecidableInstances #-} import Data.Kind import Data.Functor.Identity import Data.Functor.Product type a <-> b = a -> b -> Type class Iso (iso :: a <-> b) where iso :: a -> b osi :: b -> a data Iso_Bool :: Either () () <-> Bool instance Iso Iso_Bool where class Representable f where type Rep f :: Type index :: f a -> (Rep f -> a) tabulate :: (Rep f -> a) -> f a class Comonad w where extract :: w a -> a duplicate :: w a -> w (w a) newtype Co f a = Co (f a) deriving newtype (Functor, Representable) instance (Representable f, Monoid (Rep f)) => Comonad (Co f) where extract = (`index` mempty) newtype WRAP (iso::old <-> new) f a = WRAP (f a) instance (Representable f, Rep f ~ old, Iso iso) => Representable (WRAP (iso :: old <-> new) f) where type Rep (WRAP (iso :: old <-> new) f) = new index :: WRAP iso f a -> (new -> a) index (WRAP fa) = index fa . osi @old @new @iso tabulate :: (new -> a) -> WRAP iso f a tabulate gen = WRAP $ tabulate (gen . iso @old @new @iso) newtype PAIR a = PAIR (Co (WRAP Iso_Bool (Product Identity Identity)) a) deriving newtype Comonad }}} I unfortunately don't have time to find a more minimal example. Core linter vomits a lot of errors on 8.2.1 & 8.3.20171208. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14605> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14629: Seemingly unused qualified import affects method visibility
by GHC 03 Jan '18

03 Jan '18

#14629: Seemingly unused qualified import affects method visibility -------------------------------------+------------------------------------- Reporter: gelisam | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: ticket:3992, | ticket:10890 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Here is a simple test case: {{{#!hs module MyLib where class MyClass a where myMethod :: a -> a }}} {{{#!hs module MyModule where import MyLib (MyClass) --import qualified MyLib as L data Foo = Foo instance MyClass Foo where -- error: ‘myMethod’ is not a (visible) method of class ‘MyClass’ myMethod Foo = Foo }}} Since I have only imported `MyClass` and not its methods (that would be `import MyLib (MyClass(..))`), the error is correct, `myMethod` is not visible. But if I uncomment the `import qualified MyLib as L` line, the error disappears even though I do not use `L` anywhere. Writing `L.myMethod Foo = Foo` is not even legal! ----- I filed this under "confusing error message", so let me show you the conditions under which the above behaviour was confusing. We were using [https://hackage.haskell.org/package/classy- prelude-1.3.1/docs/ClassyPrelude.html classy-prelude] instead of `Prelude`, but we were not familiar with all the differences between the two preludes. We started with code like this, which did not compile: {{{#!hs {-# LANGUAGE NoImplicitPrelude #-} module MyModule import ClassyPrelude data Foo a = Foo instance Foldable Foo where -- 'foldMap' is not a (visible) method of class 'Foldable' foldMap = undefined }}} So we clarified that we meant `Prelude.Foldable`, in case `ClassyFoldable.Foldable` meant something different. {{{#!hs {-# LANGUAGE NoImplicitPrelude #-} module MyModule import ClassyPrelude import qualified Prelude data Foo a = Foo instance Prelude.Foldable Foo where foldMap = undefined }}} This compiled, so we first thought that `Prelude.Foldable` and `ClassyPrelude.Foldable` were two different type classes, but we later discovered that `ClassyPrelude.Foldable` is a re-export of `Prelude.Foldable`. So the following means the same thing and also compiles: {{{#!hs {-# LANGUAGE NoImplicitPrelude #-} module MyModule import ClassyPrelude import qualified Prelude data Foo a = Foo instance ClassyPrelude.Foldable Foo where foldMap = undefined }}} At this point, the qualified `Prelude` import doesn't seem used anywhere, so we thought it was safe to remove it: {{{#!hs {-# LANGUAGE NoImplicitPrelude #-} import ClassyPrelude data Foo a = Foo instance ClassyPrelude.Foldable Foo where -- 'foldMap' is not a (visible) method of class 'Foldable' foldMap = undefined }}} But `ClassyPrelude.foldMap` is ''not'' the same as `Prelude.foldMap`, so this did not compile and it wasn't clear why. One way to make this less confusing would be to allow qualified method names; this way, we would have tried both `Prelude.foldMap = undefined` and `ClassyPrelude.foldMap = undefined`, and we would have discovered the source of the problem. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14629> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12022: unsafeShiftL and unsafeShiftR are not marked as INLINE
by GHC 03 Jan '18

03 Jan '18

#12022: unsafeShiftL and unsafeShiftR are not marked as INLINE -------------------------------------+------------------------------------- Reporter: Rufflewind | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 7.10.3 libraries/base | Keywords: performance, | Operating System: Unknown/Multiple inline, bits | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given that they are fairly essential operations in core libraries such as containers, I think it would be useful to have them marked as INLINE (or INLINABLE at the very least). See also: https://github.com/haskell/containers/pull/216 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12022> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14628: Panic (No skolem Info) in GHCi
by GHC 03 Jan '18

03 Jan '18

#14628: Panic (No skolem Info) in GHCi -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: #13393 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Loading the following code in GHCi causes a panic. Versions affected at least 8.2.2 and 8.0.2 {{{ module Main where import System.IO import Control.Monad.IO.Class import Control.Monad.Trans.State import Text.Printf putArrayBytes :: Handle -- ^ output file handle -> [String] -- ^ byte-strings -> IO Int -- ^ total number of bytes written putArrayBytes outfile xs = do let writeCount x = modify' (+ length x) >> liftIO (putLine x) :: MonadIO m => StateT Int m () execStateT (mapM_ writeCount xs) 0 where putLine = hPutStrLn outfile . (" "++) . concatMap (printf "0x%02X,") {- ghci: :break 12 46 :trace putArrayBytes stdout [['1'..'9'],['2'..'8'],['3'..'7']] snd $ runStateT _result 0 -} main = undefined }}} {{{ Configuring GHCi with the following packages: GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( C:\test\test.hs, interpreted ) Ok, one module loaded. Loaded GHCi configuration from C:\Users\Andi\AppData\Local\Temp\ghci34988 \ghci-script *Main> :break 12 46 Breakpoint 0 activated at C:\test\test.hs:12:46-63 *Main> :trace putArrayBytes stdout [['1'..'9'],['2'..'8'],['3'..'7']] Stopped in Main.putArrayBytes.writeCount, C:\test\test.hs:12:46-63 _result :: StateT Int m () = _ putLine :: [Char] -> IO () = _ x :: [Char] = "123456789" [C:\test\test.hs:12:46-63] [C:\test\test.hs:12:46-63] *Main> snd $ runStateT _result 0 <interactive>:3:7: error:<interactive>: panic! (the 'impossible' happened) (GHC version 8.2.2 for x86_64-unknown-mingw32): No skolem info: m_I5Cm[rt] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler\utils\Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler\utils\Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler\typecheck\TcErrors.hs:2653:5 in ghc:TcErrors Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [C:\test\test.hs:12:46-63] [C:\test\test.hs:12:46-63] *Main> :r [1 of 1] Compiling Main ( C:\test\test.hs, interpreted ) Ok, one module loaded. *Main> :break 12 46 Breakpoint 1 activated at C:\test\test.hs:12:46-63 *Main> :trace putArrayBytes stdout [['1'..'9'],['2'..'8'],['3'..'7']] Stopped in Main.putArrayBytes.writeCount, C:\test\test.hs:12:46-63 _result :: StateT Int m () = _ putLine :: [Char] -> IO () = _ x :: [Char] = "123456789" [C:\test\test.hs:12:46-63] [C:\test\test.hs:12:46-63] *Main> snd $ runStateT _result 0 <interactive>:7:7: error:<interactive>: panic! (the 'impossible' happened) (GHC version 8.2.2 for x86_64-unknown-mingw32): No skolem info: m_I5Nz[rt] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler\utils\Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler\utils\Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler\typecheck\TcErrors.hs:2653:5 in ghc:TcErrors Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [C:\test\test.hs:12:46-63] [C:\test\test.hs:12:46-63] *Main> }}} Maybe related to #13393. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14628> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1620: ModBreaks.modBreaks_array not initialised
by GHC 02 Jan '18

02 Jan '18

#1620: ModBreaks.modBreaks_array not initialised -------------------------------------+------------------------------------- Reporter: guest | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.8.2 Resolution: | Keywords: debugger Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => debugger -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1620#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1379: Allow breakpoints and single-stepping for functions defined interactively
by GHC 02 Jan '18

02 Jan '18

#1379: Allow breakpoints and single-stepping for functions defined interactively -------------------------------------+-------------------------------- Reporter: Michael D. Adams | Owner: (none) Type: feature request | Status: new Priority: lowest | Milestone: Component: GHCi | Version: 6.7 Resolution: | Keywords: debugger Operating System: Linux | Architecture: x86 Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+-------------------------------- Changes (by RyanGlScott): * keywords: => debugger -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1379#comment:21> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1377: GHCi debugger tasks
by GHC 02 Jan '18

02 Jan '18

#1377: GHCi debugger tasks -------------------------------------+------------------------------------- Reporter: simonmar | Owner: mnislaih Type: task | Status: new Priority: lowest | Milestone: Component: GHCi | Version: 6.7 Resolution: | Keywords: debugger Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => debugger -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1377#comment:25> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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