January 2019 - ghc-tickets

[GHC] #16160: TH_NestedSplices fails on Windows
by GHC 27 Jan '19

27 Jan '19

#16160: TH_NestedSplices fails on Windows ----------------------------------------+--------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- {{{ Compile failed (exit code 11) errors were: Access violation in generated code when executing data at 0x0 Attempting to reconstruct a stack trace... Frame Code address Null address *** unexpected failure for TH_NestedSplices(normal) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16160> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16231: GHCi under powershell fails to find libgmp-10.dll when built with hadrian.
by GHC 27 Jan '19

27 Jan '19

#16231: GHCi under powershell fails to find libgmp-10.dll when built with hadrian. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Build System | Version: 8.6.3 (Hadrian) | Keywords: | Operating System: Windows Architecture: | Type of failure: GHCi crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The reason seems to be that it's placed in bin, but windows looks for it under lib. Or at least it works if I copy the file over manually. GHCi works fine under msys however so only the windows shells seem to be affected. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16231> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3205: Generalized isomorphic deriving
by GHC 27 Jan '19

27 Jan '19

#3205: Generalized isomorphic deriving -------------------------------------+------------------------------------- Reporter: ajd | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.10.2 Resolution: | Keywords: language, | deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by harpocrates): Isn't this feature request now implemented as `DerivingVia`? Perhaps we could close this ticket? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3205#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16244: Couldn't match kind ‘k1’ with ‘k1’
by GHC 27 Jan '19

27 Jan '19

#16244: Couldn't match kind ‘k1’ with ‘k1’ -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler | Version: 8.6.3 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following program gives a hopelessly confusing error message on GHC 8.6.3 and HEAD: {{{#!hs {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE PolyKinds #-} module Bug where import Data.Kind type Const a b = a type SameKind (a :: k) (b :: k) = (() :: Constraint) class SameKind a b => C (k :: Const Type a) (b :: k) }}} {{{ $ /opt/ghc/8.6.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:11:18: error: • Couldn't match kind ‘k1’ with ‘k1’ • In the second argument of ‘SameKind’, namely ‘b’ In the class declaration for ‘C’ | 11 | class SameKind a b => C (k :: Const Type a) (b :: k) | ^ }}} I imagine that the real issue is that `SameKind a b` would force `a :: k`, which would be ill-scoped. But figuring that out from this strange error message requires a lot of thought. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16244> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13512: GHC incorrectly warns that a variable used in a type application is unused
by GHC 27 Jan '19

27 Jan '19

#13512: GHC incorrectly warns that a variable used in a type application is unused -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This bug is reproducible on GHC 8.0.1, 8.0.2, 8.2, and HEAD. {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeInType #-} {-# OPTIONS_GHC -Wunused-foralls #-} module Bug where import Data.Proxy proxy :: forall k (a :: k). Proxy a proxy = Proxy data SomeProxy where SomeProxy :: forall k (a :: k). Proxy a -> SomeProxy someProxy :: forall k (a :: k). SomeProxy someProxy = SomeProxy (proxy @k @a) }}} {{{ $ /opt/ghc/head/bin/ghci Bug.hs GHCi, version 8.3.20170327: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:17:23: warning: [-Wunused-foralls] Unused quantified type variable ‘(a :: k)’ In the type ‘forall k (a :: k). SomeProxy’ | 17 | someProxy :: forall k (a :: k). SomeProxy | ^^^^^^^^ Ok, modules loaded: Bug. }}} But that `a` is used in `proxy @k @a`! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13512> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9173: Better type error messages
by GHC 27 Jan '19

27 Jan '19

#9173: Better type error messages ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Generating better type-error messages is a hoary chestnut, but Herbert brought my attention to [https://pay.reddit.com/r/haskell/comments/26tcrk/curious_with_a_bit_of_begi… this thread on reddit], which has the following idea. At the moment, from {{{ module Foo where addThree = \x -> x + 3 :: Int y = addThree $ Just 5 }}} we get this error: {{{ Foo.hs:2:20 Couldn't match expected type `Int' with actual type `Maybe a0' In the return type of a call of `Just' In the second argument of `($)', namely `Just 5' In the expression: addThree $ Just 5 }}} Maybe we could generate this instead {{{ Foo.hs:2:20 inferred: "Just 5" has type "Maybe a0" expected: second argument of "($)" must have type "Int" in the expression: addThree $ Just 5 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9173> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15621: Error message involving type families points to wrong location
by GHC 27 Jan '19

27 Jan '19

#15621: Error message involving type families points to wrong location -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 (Type checker) | Keywords: TypeFamilies | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following program: {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Type.Equality type family F a f :: () f = let a :: F Int :~: F Int a = Refl b :: F Int :~: F Bool b = Refl in () }}} This doesn't typecheck, which isn't surprising, since `F Int` doesn't equal `F Bool` in the definition of `b`. What //is// surprising is where the error message points to: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:12:11: error: • Couldn't match type ‘F Int’ with ‘F Bool’ Expected type: F Int :~: F Int Actual type: F Bool :~: F Bool NB: ‘F’ is a non-injective type family • In the expression: Refl In an equation for ‘a’: a = Refl In the expression: let a :: F Int :~: F Int a = Refl b :: F Int :~: F Bool .... in () | 12 | a = Refl | ^^^^ }}} This claims that the error message arises from the definition of `a`, which is completely wrong! As evidence, if you comment out `b`, then the program typechecks again. Another interesting facet of this bug is that if you comment out `a`: {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Type.Equality type family F a f :: () f = let {- a :: F Int :~: F Int a = Refl -} b :: F Int :~: F Bool b = Refl in () }}} Then the error message will actually point to `b` this time: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:15:11: error: • Couldn't match type ‘F Int’ with ‘F Bool’ Expected type: F Int :~: F Bool Actual type: F Bool :~: F Bool NB: ‘F’ is a non-injective type family • In the expression: Refl In an equation for ‘b’: b = Refl In the expression: let b :: F Int :~: F Bool b = Refl in () | 15 | b = Refl | ^^^^ }}} The use of type families appears to be important to triggering this bug, since I can't observe this behavior without the use of `F`. This is a regression that was introduced at some point between GHC 8.0.2 and 8.2.2, since 8.2.2 gives the incorrect error message shown above, while 8.0.2 points to the right location: {{{ $ /opt/ghc/8.0.2/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:15:11: error: • Couldn't match type ‘F Int’ with ‘F Bool’ Expected type: F Int :~: F Bool Actual type: F Int :~: F Int NB: ‘F’ is a type function, and may not be injective • In the expression: Refl In an equation for ‘b’: b = Refl In the expression: let a :: F Int :~: F Int a = Refl b :: F Int :~: F Bool .... in () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15621> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15753: Inconsistent pattern-match warnings when using guards versus case expressions
by GHC 26 Jan '19

26 Jan '19

#15753: Inconsistent pattern-match warnings when using guards versus case expressions -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple PatternMatchWarnings | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following code (apologies for the rather non-minimal example): {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE EmptyCase #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} {-# OPTIONS_GHC -Wall -Wno-unticked-promoted-constructors #-} module Bug where import Data.Kind import Data.Type.Bool import Data.Type.Equality ((:~:)(..)) import Data.Void data family Sing :: forall k. k -> Type data instance Sing :: Bool -> Type where SFalse :: Sing False STrue :: Sing True data instance Sing :: forall a. [a] -> Type where SNil :: Sing '[] SCons :: Sing x -> Sing xs -> Sing (x:xs) data instance Sing :: forall a b. (a, b) -> Type where STuple2 :: Sing x -> Sing y -> Sing '(x, y) newtype instance Sing (f :: k1 ~> k2) = SLambda { (@@) :: forall t. Sing t -> Sing (f @@ t) } data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type infixr 0 ~> type family (f :: k1 ~> k2) @@ (x :: k1) :: k2 infixl 9 @@ newtype Map k v = MkMap [(k, v)] data instance Sing :: forall k v. Map k v -> Type where SMkMap :: Sing x -> Sing (MkMap x) type family MapEmpty :: Map k v where MapEmpty = MkMap '[] type family MapInsertWith (f :: v ~> v ~> v) (new_k :: k) (new_v :: v) (m :: Map k v) :: Map k v where MapInsertWith _ new_k new_v (MkMap '[]) = MkMap '[ '(new_k, new_v)] MapInsertWith f new_k new_v (MkMap ('(old_k,old_v):old_kvs)) = If (old_k == new_k) (MkMap ('(new_k,f @@ new_v @@ old_v):old_kvs)) (Case (MapInsertWith f new_k new_v (MkMap old_kvs)) old_k old_v) type family Case (m :: Map k v) (old_k :: k) (old_v :: v) :: Map k v where Case (MkMap kvs) old_k old_v = MkMap ('(old_k,old_v) : kvs) sMapInsertWith :: forall k v (f :: v ~> v ~> v) (new_k :: k) (new_v :: v) (m :: Map k v). SEq k => Sing f -> Sing new_k -> Sing new_v -> Sing m -> Sing (MapInsertWith f new_k new_v m) sMapInsertWith _ snew_k snew_v (SMkMap SNil) = SMkMap (STuple2 snew_k snew_v `SCons` SNil) sMapInsertWith sf snew_k snew_v (SMkMap (STuple2 sold_k sold_v `SCons` sold_kvs)) = case sold_k %== snew_k of STrue -> SMkMap (STuple2 snew_k (sf @@ snew_v @@ sold_v) `SCons` sold_kvs) SFalse -> case sMapInsertWith sf snew_k snew_v (SMkMap sold_kvs) of SMkMap skvs -> SMkMap (STuple2 sold_k sold_v `SCons` skvs) class PEq a where type (x :: a) == (y :: a) :: Bool class SEq a where (%==) :: forall (x :: a) (y :: a). Sing x -> Sing y -> Sing (x == y) mapInsertWithNonEmpty1 :: forall k v (f :: v ~> v ~> v) (old_k :: k) (old_v :: v) (old_kvs :: [(k,v)]) (new_k :: k) (new_v :: v) (m :: Map k v). SEq k => Sing f -> Sing new_k -> Sing new_v -> Sing m -> m :~: MkMap ('(old_k,old_v) : old_kvs) -> MapInsertWith f new_k new_v m :~: MapEmpty -> Void mapInsertWithNonEmpty1 sf snew_k snew_v (SMkMap sm) Refl Refl | STuple2 sold_k _ `SCons` sold_kvs <- sm , SFalse <- sold_k %== snew_k = case sMapInsertWith sf snew_k snew_v (SMkMap sold_kvs) of {} mapInsertWithNonEmpty2 :: forall k v (f :: v ~> v ~> v) (old_k :: k) (old_v :: v) (old_kvs :: [(k,v)]) (new_k :: k) (new_v :: v) (m :: Map k v). SEq k => Sing f -> Sing new_k -> Sing new_v -> Sing m -> m :~: MkMap ('(old_k,old_v) : old_kvs) -> MapInsertWith f new_k new_v m :~: MapEmpty -> Void mapInsertWithNonEmpty2 sf snew_k snew_v (SMkMap sm) Refl Refl | STuple2 sold_k _ `SCons` sold_kvs <- sm = case sold_k %== snew_k of SFalse -> case sMapInsertWith sf snew_k snew_v (SMkMap sold_kvs) of {} }}} If you compile this with GHC 8.6.1 or later, you'll notice something interesting happening with the pattern-match coverage checker warnings: {{{ $ /opt/ghc/8.6.1/bin/ghci Bug.hs GHCi, version 8.6.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:78:1: warning: [-Wincomplete-patterns] Pattern match(es) are non-exhaustive In an equation for ‘mapInsertWithNonEmpty1’: Patterns not matched: _ _ _ (SMkMap _) Refl Refl | 78 | mapInsertWithNonEmpty1 sf snew_k snew_v (SMkMap sm) Refl Refl | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... Ok, one module loaded. }}} `mapInsertWithNonEmpty1` is deemed non-exhaustive, but `mapInsertWithNonEmpty2` is deemed exhaustive. However, the code for the two functions are functionally identical—the only difference is that `mapInsertWithNonEmpty1` uses one more pattern guard than `mapInsertWithNonEmpty2` does. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15753> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14259: Worker/Wrapper for sum return
by GHC 26 Jan '19

26 Jan '19

#14259: Worker/Wrapper for sum return -------------------------------------+------------------------------------- Reporter: jheek | 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: -------------------------------------+------------------------------------- GHC version 8.2 introduces Unboxed Sum types. It would be great if the worker/wrapper transformation could make use of this new functionality. For clarification I would expect a function like this: {{{#!haskell maybeEven :: Int -> Maybe Int maybeEven n = case even n of True -> Just n False -> Nothing }}} to be transformed into (the core equivalent) of {{{#!haskell maybeEven :: Int -> Maybe Int MaybeEven (I# n#) = case workerMaybeEven n# of (# | x #) -> Just x (# (# #) | #) -> Nothing workerMaybeEven :: Int# -> (# (# #) | Int #) {-# NOINLINE workerMaybeEven #-} workerMaybeEven n# = case even (I# n#) of True -> (# | I# n# #) False -> (# (# #) | #) }}} Currently the core output for the maybeEven worker is: {{{#!haskell Main.$wmaybeEven :: Int# -> Maybe Int Main.$wmaybeEven = \ (ww_s4WH :: Int#) -> case remInt# ww_s4WH 2# of { __DEFAULT -> GHC.Base.Nothing @ Int; 0# -> GHC.Base.Just @ Int (GHC.Types.I# ww_s4WH) } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14259> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5361: regSpill: out of spill slots!
by GHC 25 Jan '19

25 Jan '19

#5361: regSpill: out of spill slots! -------------------------------------+------------------------------------- Reporter: markwright | Owner: (none) Type: bug | Status: closed Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.1 Resolution: fixed | Keywords: regSpill | panic impossible Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: Compile-time | Test Case: crash | http://hackage.haskell.org/package/SHA Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by AndreasK): This will be properly fixed when https://gitlab.haskell.org/ghc/ghc/merge_requests/219 lands. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5361#comment:17> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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