March 2018 - ghc-tickets

[GHC] #10056: Inconsistent precedence of ~
by GHC 30 Jul '18

30 Jul '18

#10056: Inconsistent precedence of ~ -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 (Parser) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following compiles as expected: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family Foo a b f :: (Foo a b ~ Int) => a -> b -> b f = error "" }}} but this fails: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family a \\ b f :: (a \\ b ~ Int) => a -> b -> b f = error "" }}} with the error > "The second argument of `(\\)` should have kind `*`, but `b ~ Int` has kind `Constraint`." Thus the first example is being parsed as `(Foo a b) ~ Int`, while the second is parsed as `a \\ (b ~ Int)`. I believe the second example should compile, i.e. `(\\)` and `Foo` should have the same precedence, both of which are higher than `(~)`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10056> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14873: GHC HEAD regression (piResultTy)
by GHC 30 Jul '18

30 Jul '18

#14873: GHC HEAD regression (piResultTy) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.5 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (Originally noticed [https://travis- ci.org/goldfirere/singletons/jobs/347945148#L1179 here].) The following program typechecks on GHC 8.2.2 on GHC 8.4.1, but panics on GHC HEAD: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Kind (Type) data family Sing (a :: k) newtype instance Sing (f :: k1 ~> k2) = SLambda { applySing :: forall t. Sing t -> Sing (Apply f t) } data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type infixr 0 ~> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2 class SingI (a :: k) where sing :: Sing a data ColSym1 :: f a -> a ~> Bool type instance Apply (ColSym1 x) y = Col x y class PColumn (f :: Type -> Type) where type Col (x :: f a) (y :: a) :: Bool class SColumn (f :: Type -> Type) where sCol :: forall (x :: f a) (y :: a). Sing x -> Sing y -> Sing (Col x y :: Bool) instance (SColumn f, SingI x) => SingI (ColSym1 (x :: f a) :: a ~> Bool) where sing = SLambda (sCol (sing @_ @x)) }}} {{{ $ /opt/ghc/head/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.5.20180201 for x86_64-unknown-linux): piResultTy k_aZU[tau:1] (a_aW8[sk:1] |> <*>_N) Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:947:35 in ghc:Type }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14873> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13451: Bind implicit parameter in patterns
by GHC 30 Jul '18

30 Jul '18

#13451: Bind implicit parameter in patterns -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple ImplicitParams | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Is there any reason why variables for `ImplicitParams` can't be bound in patterns, so you can write {{{#!hs data Exp = Val Int | Op Op Exp Exp data Op = Add | Mul data Protect where Protect :: (?op :: Op) => Protect protectOp :: Exp -> Maybe Protect protectOp (Op ?op _ _) = Just Protect protectOp _ = Nothing }}} instead of {{{#!hs protectOp :: Exp -> Maybe Protect protectOp (Op op _ _) = Just Protect where ?op = op protectOp _ = Nothing }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13451> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11549: Add -fshow-runtime-rep
by GHC 29 Jul '18

29 Jul '18

#11549: Add -fshow-runtime-rep -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- As discussed in several interwoven threads ([https://mail.haskell.org/pipermail/ghc-devs/2016-February/011268.html original], [https://mail.haskell.org/pipermail/haskell- cafe/2016-February/122914.html café]), it has been suggested to add a flag `-fshow-runtime-rep`. Without this flag enabled, the pretty printer will instantiate any `RuntimeRep` type parameters to `PtrRep Lifted`. This has the effect of changing {{{ ($) :: forall (r :: RuntimeRep) (a :: *) (b :: TYPE r). (a -> b) -> a -> b }}} to {{{ ($) :: (a -> b) -> a -> b }}} under the default GHCi settings. Note that `Levity` becomes `RuntimeRep` after #11471 is complete. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11549> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10184: Coercible solver incomplete with recursive newtypes
by GHC 29 Jul '18

29 Jul '18

#10184: Coercible solver incomplete with recursive newtypes -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: low | Milestone: ⊥ Component: Compiler | Version: 7.10.1-rc3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following module fails to compile due to infinite recursion: {{{ import Data.Coerce newtype Bar a = Bar (Either a (Bar a)) newtype Age = MkAge Int x :: Bar Age x = coerce (Bar (Left (5 :: Int))) }}} It tries to coerce `Bar Int` to `Bar Age`. This is clearly doable, via tyconapp decomposition. But we don't find it. Before worrying too much about it, though, we'll wait for a real example. Do speak up if this problem is ruining your day! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10184> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14247: Fails to coerce between newtypes directly
by GHC 29 Jul '18

29 Jul '18

#14247: Fails to coerce between newtypes directly -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new 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: -------------------------------------+------------------------------------- {{{#!hs import Data.Coerce import Data.Type.Coercion newtype W a = W a newtype A = MkA (W A) a :: Coercion A A a = Coercion b :: Coercion a a' -> Coercion a (W a') b Coercion = Coercion c :: Coercion A (W A) c = b a }}} works just fine but the following fail: {{{#!hs -- • Couldn't match representation of type ‘A’ with that of ‘W A’ -- arising from a use of ‘Coercion’ -- • In the expression: Coercion -- In an equation for ‘d’: d = Coercion d :: Coercion A (W A) d = Coercion -- • Couldn't match representation of type ‘A’ with that of ‘W A’ -- arising from a use of ‘coerce’ -- • In the expression: coerce -- In an equation for ‘e’: e = coerce e :: A -> W A e = coerce }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14247> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9936: Data.Fixed truncates 5.17 to 5.16
by GHC 28 Jul '18

28 Jul '18

#9936: Data.Fixed truncates 5.17 to 5.16 -------------------------------------+------------------------------------- Reporter: singpolyma | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.6.3 libraries/base | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- `(realToFrac (5.17 :: Double) :: Centi) == 5.16` is true -- it should be false. The offender seems to be the assumption in `fromRational`: `fromRational r = withResolution (\res -> MkFixed (floor (r * (toRational res))))` Uses `floor` assuming that the underlying floating point value is stored purely and not as 0.999999 or similar -- switching it to `round` fixes this issue. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9936> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10919: ghc: panic! (the 'impossible' happened) ... Dynamic linker not initialised
by GHC 28 Jul '18

28 Jul '18

#10919: ghc: panic! (the 'impossible' happened) ... Dynamic linker not initialised -------------------------------------+------------------------------------- Reporter: recursion- | Owner: ninja | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: panic | Operating System: Linux impossible linker initialized | Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | -------------------------------------+------------------------------------- When trying to build the CUDA accelerate backend I get the following "complier panic": {{{ me@box:~/accelerate-cuda-0.15.0.0$ cabal build Building accelerate-cuda-0.15.0.0... Preprocessing library accelerate-cuda-0.15.0.0... Data/Array/Accelerate/CUDA/CodeGen/Base.hs:5:14: Warning: -XOverlappingInstances is deprecated: instead use per-instance pragmas OVERLAPPING/OVERLAPPABLE/OVERLAPS [ 7 of 33] Compiling Data.Array.Accelerate.CUDA.CodeGen.Type ( Data/Array/Accelerate/CUDA/CodeGen/Type.hs, dist/build/Data/Array/Accelerate/CUDA/CodeGen/Type.o ) <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.10.2 for x86_64-unknown-linux): Dynamic linker not initialised Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [ 9 of 33] Compiling Data.Array.Accelerate.CUDA.Debug ( Data/Array/Accelerate/CUDA/Debug.hs, dist/build/Data/Array/Accelerate/CUDA/Debug.o ) <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.10.2 for x86_64-unknown-linux): Dynamic linker not initialised Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [10 of 33] Compiling Data.Array.Accelerate.CUDA.Analysis.Launch ( Data/Array/Accelerate/CUDA/Analysis/Launch.hs, dist/build/Data/Array/Accelerate/CUDA/Analysis/Launch.o ) <no location info>: <command line>: can't load .so/.DLL for: /home/me/.cabal/lib/x86_64 -linux-ghc-7.10.2/cuda-0.6.7.0-EMlxEWvymgZGXnLSaVKypt/libHScuda-0.6.7.0 -EMlxEWvymgZGXnLSaVKypt-ghc7.10.2.so (libcudart.so.7.5: cannot open shared object file: No such file or directory) }}} This is the accelerate cuda package version 0.15.0.0: https://hackage.haskell.org/package/accelerate-cuda I changed the constraints from base==4.7.* to base==4.8.* to allow for compilation with GHC 7.10.2. After installing the dependencies through cabal and attempting to manually build the package manuall with cabal build I get the above mentioned compiler panics. GHC instructed me to report the issue as a bug (defect) so I did. I'd like to get this library to build with the newest version of GHC so please let me know how to proceed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10919> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12694: GHC HEAD no longer reports inaccessible code
by GHC 27 Jul '18

27 Jul '18

#12694: GHC HEAD no longer reports inaccessible code -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | 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: -------------------------------------+------------------------------------- Given this A.hs: {{{ {-# LANGUAGE GADTs #-} module A where f :: Bool ~ Int => a -> b f x = x }}} I get: {{{ ezyang@sabre:~$ ghc-head --version The Glorious Glasgow Haskell Compilation System, version 8.1.20161010 ezyang@sabre:~$ ghc-head --make A.hs [1 of 1] Compiling A ( A.hs, A.o ) A.hs:4:1: warning: [-Woverlapping-patterns] Pattern match is redundant In an equation for ‘f’: f x = ... }}} In contrast: {{{ ezyang@sabre:~$ ghc-8.0 --make A.hs [1 of 1] Compiling A ( A.hs, A.o ) A.hs:3:6: error: • Couldn't match type ‘Bool’ with ‘Int’ Inaccessible code in the type signature for: f :: Bool ~ Int => a -> b • In the ambiguity check for ‘f’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: f :: Bool ~ Int => a -> b }}} Is this expected? I'd expect at least a warning! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12694> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13766: Confusing "reudundant pattern match" in 8.0, no warning at all in 8.2
by GHC 27 Jul '18

27 Jul '18

#13766: Confusing "reudundant pattern match" in 8.0, no warning at all in 8.2 -------------------------------------+------------------------------------- Reporter: edsko | 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: -------------------------------------+------------------------------------- I couldn't find an existing ticket about this, so I figured I'd file this even though it's probably an instance of a more general problem. Consider {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# OPTIONS_GHC -Wall -Woverlapping-patterns #-} module T where class C a where c :: a -> a instance Int ~ Bool => C Int where c = id }}} yields {{{ T.hs:10:3: warning: [-Woverlapping-patterns] Pattern match is redundant In an equation for ‘c’: c = ... }}} which I suppose makes _some_ amount of sense but is highly confusing nonetheless :) Now in 8.2 I don't get this warning, but in fact I don't get any warning at all, which I'm not entirely sure is better. In the real code obviously the superclass constraint was far more complicated and it was nice of ghc to warn me (albeit in a roundabout way) that it was unsatisfiable. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13766> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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