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Re: [GHC] #4945: Another SpecConstr infelicity
by GHC 31 Mar '17

31 Mar '17

#4945: Another SpecConstr infelicity -------------------------------------+------------------------------------- Reporter: batterseapower | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.0.1 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | simplCore/should_compile/T4945 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by mpickering): * keywords: => SpecConstr -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4945#comment:19> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13435: Segfaults on levity-polymorphic type class
by GHC 31 Mar '17

31 Mar '17

#13435: Segfaults on levity-polymorphic type class -------------------------------------+------------------------------------- Reporter: Iceland_jack | 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: -------------------------------------+------------------------------------- {{{#!hs {-# Language FlexibleInstances, TypeFamilies, TypeInType, MagicHash #-} import Data.Kind import GHC.Exts class Shw (a :: TYPE rep) where shw :: a -> String instance Int# ~ a => Shw (a :: TYPE IntRep) where shw a = "I#" ++ show (I# a) main = putStrLn (shw 3#) }}} induces a segfault {{{ $ runghc --version runghc 8.0.1 $ runghc test.hs I#Segmentation fault }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13435> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13503: "ghc: panic" when trying to build purescript with profiling
by GHC 31 Mar '17

31 Mar '17

#13503: "ghc: panic" when trying to build purescript with profiling -------------------------------------+------------------------------------- Reporter: rintcius | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: MacOS X Architecture: Other | Type of failure: Compile-time | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- i got the following panic when trying to build purescript with profiling (the plain build works ok) {{{ $ stack build --executable-profiling --library-profiling --ghc-options ="-fprof-auto -rtsopts" purescript-0.11.1: build Preprocessing library purescript-0.11.1... [ 23 of 145] Compiling Language.PureScript.Constants ( src/Language/PureScript/Constants.hs, .stack- work/dist/x86_64-osx/Cabal-1.24.2.0/build/Language/PureScript/Constants.p_o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-apple-darwin): kindPrimRep.go rep_sfuE Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- While building package purescript-0.11.1 using: /Users/rintciusblok/.stack/setup-exe-cache/x86_64-osx/setup-Simple- Cabal-1.24.2.0-ghc-8.0.2 --builddir=.stack- work/dist/x86_64-osx/Cabal-1.24.2.0 build lib:purescript exe:purs --ghc- options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 }}} If this report needs to be reduced, I'd be happy to do that, but I would need some guidance in that case. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13503> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so.
by GHC 31 Mar '17

31 Mar '17

#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving, | newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #10577, #13117 | Differential Rev(s): Phab:D978 Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * cc: dfeuer (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:49> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13328: Foldable, Functor, and Traversable deriving handle phantom types badly
by GHC 31 Mar '17

31 Mar '17

#13328: Foldable, Functor, and Traversable deriving handle phantom types badly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Keywords: deriving-perf | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Suppose we have {{{#!hs data Phantom a = Z | S (Phantom a) }}} We'd like to get something like {{{#!hs foldMap _ _ = mempty fmap = coerce traverse _ m = pure (coerce m) }}} But instead we actually pattern match all the way down! Basically, we want to treat "has a phantom role" and "does not occur" similarly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13328> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13494: ASSERT failed in compiler/typecheck/TcErrors.hs
by GHC 30 Mar '17

30 Mar '17

#13494: ASSERT failed in compiler/typecheck/TcErrors.hs -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 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: -------------------------------------+------------------------------------- One of the commits in the range https://github.com/ghc/ghc/compare/a6675a93efe7...de4723fd6d97 which were commited by SPJ, broke running the test suite with a `-DDEBUG` compiler: {{{ +++ /tmp/ghctest-sw9832/test spaces/./indexed- types/should_fail/T2627b.run/T2627b.comp.stderr.normalised 2017-03-27 16:28:10.448037112 +0000 @@ -1,13 +1,17 @@ +ghc: panic! (the 'impossible' happened) + (GHC version 8.3.20170327 for x86_64-unknown-linux): + ASSERT failed! + b0_a1gy[tau:4] + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + pprPanic, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors -T2627b.hs:20:24: - Couldn't match type â€˜b0â€™ with â€˜Dual (Dual b0)â€™ - arising from a use of â€˜connâ€™ - â€˜b0â€™ is untouchable - inside the constraints: b ~ W e f - bound by a pattern with constructor: - Wr :: forall e f. e -> Comm f -> Comm (W e f), - in an equation for â€˜connâ€™ - at T2627b.hs:20:14-19 - In the expression: conn undefined undefined - In an equation for â€˜connâ€™: - conn (Rd k) (Wr a r) = conn undefined undefined +Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} See https://s3.amazonaws.com/archive.travis-ci.org/jobs/215578687/log.txt for a full log. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13494> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13446: Deferred type error sneaks in with -fno-defer-type-errors enabled
by GHC 30 Mar '17

30 Mar '17

#13446: Deferred type error sneaks in with -fno-defer-type-errors enabled -------------------------------------+------------------------------------- Reporter: RyanGlScott | 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: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a very perplexing bug that MitchellSalad discovered and advertised in [https://www.reddit.com/r/haskell/comments/604mze/deferred_type_errors_witho… this Reddit post]. Consider this code: {{{#!hs {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# OPTIONS_GHC -fno-defer-type-errors #-} module Main where import Data.Coerce (Coercible) import GHC.Exts (Constraint) import GHC.TypeLits (Symbol) data Dict :: Constraint -> * where Dict :: a => Dict a infixr 9 :- newtype a :- b = Sub (a => Dict b) instance a => Show (a :- b) where showsPrec d (Sub Dict) = showParen (d > 10) $ showString "Sub Dict" class Lifting p f where lifting :: p a :- p (f a) data Blah a = Blah newtype J (a :: JType) = J (Blah (J a)) newtype JComparable a = JComparable (J (T (JTy a))) instance Lifting JReference JComparable where lifting = Sub 'a' class (Coercible a (J (JTy a))) => JReference a where type JTy a :: JType type T a = 'Generic ('Iface "java.lang.Comparable") '[a] data JType = Class Symbol | Generic JType [JType] | Iface Symbol type JObject = J (Class "java.lang.Object") instance JReference JObject where type JTy JObject = 'Class "java.lang.Object" main :: IO () main = print (lifting :: JReference JObject :- JReference (JComparable JObject)) }}} There are three concerning things about this: 1. Look at the line `lifting = Sub 'a'`. That's obviously bogus, as `Char`s are not `Dict`s! Yet GHC 8.0.2 and HEAD readily typecheck this code without warnings. 2. So now that we seem to have circumvented type safety, what happens if we actually try to //run// code which uses this bogus `Lifting` instance? Something truly bizarre, that's what: {{{ $ /opt/ghc/8.0.2/bin/ghci Bug.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Ok, modules loaded: Main. λ> main *** Exception: Bug.hs:34:17: error: • Couldn't match expected type ‘Dict (JReference (JComparable a))’ with actual type ‘Char’ • In the first argument of ‘Sub’, namely ‘'a'’ In the expression: Sub 'a' In an equation for ‘lifting’: lifting = Sub 'a' • Relevant bindings include lifting :: JReference a :- JReference (JComparable a) (bound at Bug.hs:34:3) (deferred type error) }}} Somehow, we managed to defer a type mismatch between `Char` and `Dict`. All while `-fno-defer-type-errors` is enabled! 3. Worst of all, this is a regression from GHC 8.0.1, as it will actually detect the type mismatch at compile-time: {{{ $ /opt/ghc/8.0.1/bin/ghci Bug.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:34:17: error: • Couldn't match expected type ‘Dict (JReference (JComparable a))’ with actual type ‘Char’ • In the first argument of ‘Sub’, namely ‘'a'’ In the expression: Sub 'a' In an equation for ‘lifting’: lifting = Sub 'a' • Relevant bindings include lifting :: JReference a :- JReference (JComparable a) (bound at Bug.hs:34:3) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13446> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13410: GHC HEAD regression: Template variable unbound in rewrite rule
by GHC 30 Mar '17

30 Mar '17

#13410: GHC HEAD regression: Template variable unbound in rewrite rule -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- `hybrid-vectors-0.2.1` currently fails to build with GHC HEAD. I've attached a minimized repro file with no dependencies (it's 410 lines long, since I had to copy-paste a lot of code from `vector` in order to reproduce this). The attached file builds on GHC 7.10.3 and 8.0.2, but fails on GHC HEAD with this panic: {{{ $ ~/Software/ghc2/inplace/bin/ghc-stage2 -O2 -fforce-recomp Bug.hs [1 of 1] Compiling Data.Vector.Hybrid.Internal ( Bug.hs, Bug.o ) Bug.hs:389:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gmbasicOverlaps’, ‘gmbasicInitialize’, and ‘gmbasicUnsafeRead’ • In the instance declaration for ‘GMVector (MVector u v) (a, b)’ | 389 | instance (GMVector u a, GMVector v b) => GMVector (MVector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Bug.hs:407:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gbasicUnsafeFreeze’, ‘gbasicUnsafeThaw’, ‘gbasicLength’, ‘gbasicUnsafeSlice’, and ‘gbasicUnsafeIndexM’ • In the instance declaration for ‘GVector (Vector u v) (a, b)’ | 407 | instance (GVector u a, GVector v b) => GVector (Vector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.3.20170310 for x86_64-unknown-linux): Template variable unbound in rewrite rule Variable: sc_s8FV Rule "SC:$j0" Rule bndrs: [sc_s8FV, sc_s8FW, sc_s8FX, sg_s8FY, sc_s8FU] LHS args: [sc_s8FU, (MV @ (GMutable u_a4oM) @ (GMutable v_a4oO) @ (PrimState (ST RealWorld)) @ (a_a4oN, b_a4oP) @ a_a4oN @ b_a4oP @~ (<(a_a4oN, b_a4oP)>_N :: ((a_a4oN, b_a4oP) :: *) ~# ((a_a4oN, b_a4oP) :: *)) sc_s8FW sc_s8FX) `cast` (sg_s8FY :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Actual args: [sc_s8FS, wild_X3x `cast` (Sub (Sym (D:R:GMutableVector[0] <u_a4oM>_N <v_a4oO>_N)) <PrimState (ST RealWorld)>_N (Sym cobox_a4Gz) :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable pprPanic, called at compiler/specialise/Rules.hs:579:19 in ghc:Rules }}} Some important things to note: * `-O2` is required to trigger this bug; using `-O1` or below works fine. * The problematic code is the `Read (Vector u v c)` instance at the very bottom. In particular, commenting out the last line `readPrec = greadPrec` makes the panic go away. * Moreover, there's a particular `INLINE` pragma in the `GMVector (MVector u v) (a, b)` instance that is critical to triggering the panic (it's on line 394; I've added a comment `Removing this INLINE pragma makes it compile` above it). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13410> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13441: Type inference failure in bidirectional pattern synonym and GADT pattern match
by GHC 30 Mar '17

30 Mar '17

#13441: Type inference failure in bidirectional pattern synonym and GADT pattern match -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In my musings in preparation toward teaching my undergrads about GADTs, I tried defining the usual old `Vec` in terms of `FList`s (definition below) and pattern synonyms. Here is the code: {{{ {-# LANGUAGE ScopedTypeVariables, PatternSynonyms, DataKinds, PolyKinds, GADTs, TypeOperators, TypeFamilies #-} module VecFList where import Data.Functor.Identity data FList f xs where FNil :: FList f '[] (:@) :: f x -> FList f xs -> FList f (x ': xs) data Nat = Zero | Succ Nat type family Length (xs :: [k]) :: Nat where Length '[] = Zero Length (_ ': xs) = Succ (Length xs) type family Replicate (n :: Nat) (x :: a) = (r :: [a]) where Replicate Zero _ = '[] Replicate (Succ n) x = x ': Replicate n x type Vec n a = FList Identity (Replicate n a) pattern Nil :: forall n a. n ~ Length (Replicate n a) => n ~ Zero => Vec n a pattern Nil = FNil pattern (:>) :: forall n a. n ~ Length (Replicate n a) => forall m. n ~ Succ m => a -> Vec m a -> Vec n a pattern x :> xs <- Identity x :@ xs where x :> xs = Identity x :@ xs }}} This fails with {{{ /Users/rae/temp/Bug.hs:30:34: error: • Could not deduce: m0 ~ Length xs arising from the "provided" constraints claimed by the signature of ‘:>’ from the context: n ~ Length (Replicate n a) bound by the type signature of pattern synonym ‘:>’ at /Users/rae/temp/Bug.hs:30:11-12 • In the declaration for pattern synonym ‘:>’ • Relevant bindings include xs :: FList Identity xs (bound at /Users/rae/temp/Bug.hs:30:34) }}} If I comment out the last two lines (the "explicitly bidirectional" part), compilation succeeds, even though the reported error is on the first line of the `:>` pattern synonym definition (the pattern part). Also, the following separate declaration compiles without incident: {{{ (>>>) :: forall n a. n ~ Length (Replicate n a) => forall m. n ~ Succ m => a -> Vec m a -> Vec n a x >>> xs = Identity x :@ xs }}} I believe the original program should compile, and should continue to compile if I replace the `<-` in the patsyn definition with `=`. For the curious: I tried putting an injectivity annotation on `Replicate` to avoid those `n ~ Length (Replicate n a)` constraints, but type family injectivity just isn't strong enough. Also, I'm not at all sure this definition is any use. But the behavior I report above shouldn't happen, regardless. Reproducible in HEAD. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13441> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13489: openTempFile fails when the template parameter contain a path separator
by GHC 30 Mar '17

30 Mar '17

#13489: openTempFile fails when the template parameter contain a path separator -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | 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: -------------------------------------+------------------------------------- If the template string contains a path separator, for example "a/b" then openTempFile just fails with a message which does not even indicate what the problem might be. It displays the following message: {{{ mod: /tmp/: openTempFile: does not exist (No such file or directory) }}} It can either provide a better error message, saying that path separator is not allowed or if it is legal to allow a path separator then it should create that path in the temp dir. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13489> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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