September 2017 - ghc-tickets

[GHC] #11767: Add @since annotations for base instances
by GHC 26 May '18

26 May '18

#11767: Add @since annotations for base instances -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Core | Version: 7.10.3 Libraries | 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: -------------------------------------+------------------------------------- Up until now we haven't been adding `@since` annotations for instances that we add to `base` (see Phab:D2051 for the discussion that spurred this ticket). We should try to get better coverage here. Unfortunately, we currently have no way to place Haddock comments on derived instances, which limits our ability consistently add these annotations. We'll need to work out some mechanism for this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11767> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12447: Pretty-printing of equality `~` without parentheses
by GHC 26 May '18

26 May '18

#12447: Pretty-printing of equality `~` without parentheses -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- Based off on [https://github.com/ekmett/constraints/blob/master/src/Data/Constraint/Defer… Data.Constraint.Deferrable] {{{#!hs {-# Language RankNTypes, ConstraintKinds #-} import Data.Typeable class Deferrable p where deferEither :: proxy p -> (p => r) -> Either String r instance (Typeable a, Typeable b) => Deferrable (a ~ b) where deferEither = undefined }}} `PolyKinds` aren't enabled so `deferEither @(_ ~ _)` is not enough to select the `Deferrable (a ~ b)` instance, but it is displayed without parentheses {{{ $ ghci -XTypeApplications -ignore-dot-ghci tyiS.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( tyiS.hs, interpreted ) Ok, modules loaded: Main. *Main> :t deferEither @(_ ~ _) deferEither @(_ ~ _) :: Deferrable t ~ t1 => proxy t ~ t1 -> (t ~ t1 => r) -> Either String r }}} Instead of a preferable {{{#!hs deferEither @(_ ~ _) :: Deferrable (t ~ t1) => proxy (t ~ t1) -> (t ~ t1 => r) -> Either String r }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12447> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11540: ghc accepts non-standard type without language extension
by GHC 26 May '18

26 May '18

#11540: ghc accepts non-standard type without language extension -------------------------------------+------------------------------------- Reporter: augustss | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 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 accepts this {{{ f :: Eq a => Eq b => a -> b -> Bool f a b = a==a && b==b }}} The nested contexts should require some language extension. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11540> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14246: Probably AllowAmbiguousTypes + UndecidableInstances + TypeInType
by GHC 26 May '18

26 May '18

#14246: Probably AllowAmbiguousTypes + UndecidableInstances + TypeInType -------------------------------------+------------------------------------- Reporter: Toricon | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Windows Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- ghc.exe: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-mingw32): isInjectiveTyCon sees a TcTyCon KLN {{{#!hs {-# LANGUAGE RankNTypes, GADTs, TypeOperators, PolyKinds, DataKinds, TypeFamilies, AllowAmbiguousTypes, UndecidableInstances, TypeInType #-} module MCS.Function where import MCS.Core --import MCS.Value import Data.Kind -- necessary for * type family KLN (n :: k) :: Nat where KLN (f :: v -> k) = S (KLN (forall t. f t)) KLN (f :: *) = Z type family Reveal (n :: k) (l :: Vect (KLN n) L) :: * where Reveal (f :: v -> k) (Cons (Label (t :: v)) l) = Reveal (f t) l Reveal (a :: *) Nil = a }}} The problem *has* to be somewhere in the KLN / Reveal interaction, so I removed everything else for this. Every other weird area is commented out or unused, and the bug vanished when KLN / Reveal was commented out. KLN shouldn't even work. If it _could_ be interaction with the rest of the document, I'll put that back in. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14246> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14172: GHC hangs during type-checking
by GHC 26 May '18

26 May '18

#14172: GHC hangs during type-checking -------------------------------------+------------------------------------- Reporter: lightandlight | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC 8.0.2 doesn't terminate when type checking this file: {{{#!hs import Control.Lens import Data.Functor.Compose traverseCompose :: (a -> f b) -> g a -> f (h _) traverseCompose = _Wrapping Compose . traverse }}} This is the smallest type signature I could find that still causes the problem. GHCi infers the type without issue, and when I annotate it with the correct type signature, the file is successfully compiled. Using base-4.9.1.0, lens-4.14.1, and transformers-0.5.2.0 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14172> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13746: Typeable changes in base-4.10 break ChasingBottoms's test suite
by GHC 26 May '18

26 May '18

#13746: Typeable changes in base-4.10 break ChasingBottoms's test suite -------------------------------------+------------------------------------- Reporter: refold | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 8.2.1-rc2 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When compiled against base-4.10, `ChasingBottoms`'s test suite fails with: {{{ Approx: ChasingBottomsTestSuite: typeRepTyCon: FunTy CallStack (from HasCallStack): error, called at libraries/base/Data/Typeable/Internal.hs:308:33 in base:Data.Typeable.Internal }}} This is due to the use of `error` in the following function in [https://github.com/ghc/ghc/blob/master/libraries/base/Data/Typeable/Interna… `Data.Typeable.Internal`]: {{{#!hs -- | Observe the type constructor of a type representation typeRepTyCon :: TypeRep a -> TyCon typeRepTyCon (TrTyCon _ tc _) = tc typeRepTyCon (TrApp _ a _) = typeRepTyCon a typeRepTyCon (TrFun _ _ _) = error "typeRepTyCon: FunTy" -- TODO }}} `ChasingBottoms`'s test suite works fine when compiled with GHC 8.0.2. It seems to me that the change in behaviour constitutes a bug or a breaking change (for which there is no mention in the changelog). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13746> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13726: Declaring GADT constructor and associated data family with the same name gives weird error
by GHC 26 May '18

26 May '18

#13726: Declaring GADT constructor and associated data family with the same name gives weird error -------------------------------------+------------------------------------- Reporter: mrkgnao | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- The code this is from is really messy. I'll submit a minimal example in a short while if this isn't a known bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13726> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13192: Ambiguity Caused By PolyKind and Not Helpful Error Messages
by GHC 26 May '18

26 May '18

#13192: Ambiguity Caused By PolyKind and Not Helpful Error Messages -------------------------------------+------------------------------------- Reporter: Shayan-Najd | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | 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 code results in a confusing/wrong error message, blaming a type variable (`a`) being a fixed Skolem variable: {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE PolyKinds #-} data I a type family F x type instance F (I a) = a identity :: F (I a) -> F (I a) identity x = x }}} with the error message {{{ • Couldn't match type ‘F (I a0)’ with ‘F (I a)’ Expected type: F (I a) -> F (I a) Actual type: F (I a0) -> F (I a0) NB: ‘F’ is a type function, and may not be injective The type variable ‘a0’ is ambiguous • In the ambiguity check for ‘identity’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: identity :: F (I a) -> F (I a) | 9 | identity :: F (I a) -> F (I a) | ^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13192> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13118: let binding tuple of lenses error not an expression
by GHC 26 May '18

26 May '18

#13118: let binding tuple of lenses error not an expression -------------------------------------+------------------------------------- Reporter: codygman | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.1 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 error seems to be fixed in GHC Head +/- 10 commits, but exists in GHC 8.0.1. I was told it might be a useful test case. {{{ λ> :t userId userId :: (RElem UserId rs (RIndex UserId rs), Functor f) => (Int -> f Int) -> Record rs -> f (Record rs) λ> let recLenses = userId &: Nil λ> :t recLenses recLenses :: (Functor f, RElem UserId rs (RIndex UserId rs)) => Record '[s :-> ((Int -> f Int) -> Record rs -> f (Record rs))] λ> :t recUncons recUncons :: Record (s :-> a : rs) -> (a, Record rs) λ> :t recUncons recLenses recUncons recLenses :: (Functor f, RElem UserId rs (RIndex UserId rs)) => ((Int -> f Int) -> Record rs -> f (Record rs), Record '[]) λ> let (l, ls) = recUncons recLenses <no location info>: error: not an expression: ‘let (l, ls) = recUncons recLenses’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13118> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13755: GHC-8.0.2+ spits out $dm names in error messages
by GHC 26 May '18

26 May '18

#13755: GHC-8.0.2+ spits out $dm names in error messages -------------------------------------+------------------------------------- Reporter: zilinc | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Example (copied from #12881) {{{ {-# LANGUAGE FlexibleInstances #-} module Bug where class Arbitrary a where shrink :: a -> [a] shrink _ = [] instance Arbitrary a instance Arbitrary Int }}} Error message is: {{{ GHCInstance.hs:10:10: error: • Overlapping instances for Foo Int arising from a use of ‘Main.$dmfoo’ Matching instances: instance Foo a -- Defined at GHCInstance.hs:9:10 instance Foo Int -- Defined at GHCInstance.hs:10:10 • In the expression: Main.$dmfoo @Int In an equation for ‘foo’: foo = Main.$dmfoo @Int In the instance declaration for ‘Foo Int’ }}} Another example: code in #13754 description. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13755> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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