January 2016 - ghc-tickets

[GHC] #11456: Type application and :set +c command cause panic
by GHC 23 Mar '16

23 Mar '16

#11456: Type application and :set +c command cause panic -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple TypeApplications GHCi | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Type applications and the [https://downloads.haskell.org/~ghc/master /users-guide/ghci.html#ghci-cmd-:set%20+c :set +c] command don't play nice {{{#!hs {-# LANGUAGE TypeApplications #-} a = show @Int }}} {{{ % ghci -ignore-dot-ghci GHCi, version 8.1.20160117: http://www.haskell.org/ghc/ :? for help Prelude> :set +c Prelude> :load Panic.hs [1 of 1] Compiling Main ( Panic.hs, interpreted ) Ok, modules loaded: Main. Collecting type info for 1 module(s) ... Error while getting type info from Main: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20160117 for x86_64-unknown-linux): dsExpr:HsTypeOut Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *Main> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11456> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11512: An unwritten kind variable is "specified", when it shouldn't be.
by GHC 23 Mar '16

23 Mar '16

#11512: An unwritten kind variable is "specified", when it shouldn't be. -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This fails: {{{#!hs {-# LANGUAGE PolyKinds, TypeApplications, ScopedTypeVariables #-} module Bug where import Data.Proxy class C a where foo :: Proxy a bar :: forall a. C a => Proxy a bar = foo @a }}} But it really should work, because the invisible kind variable to class `C` should not be available for type application. On the last line, `foo @_ @a` works, when you explicitly instantiate the kind variable. Also, saying `:t foo` in GHCi shows the specified kind variable. Will fix. At some point. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11512> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11334: GHC panic when calling typeOf on a promoted data constructor
by GHC 21 Mar '16

21 Mar '16

#11334: GHC panic when calling typeOf on a promoted data constructor -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Here's what I did in GHCi to trigger the panic: {{{ $ inplace/bin/ghc-stage2 --interactive GHCi, version 8.1.20160101: http://www.haskell.org/ghc/ :? for help λ> :set -XDataKinds λ> :m Data.Typeable Data.Functor.Compose λ> typeOf (Proxy :: Proxy 'Compose) ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160101 for x86_64-unknown-linux): piResultTy * TYPE 'Lifted * Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Enabling `-XPolyKinds` doesn't trigger the error, though; #10343 will be triggered instead: {{{ λ> :set -XPolyKinds λ> typeOf (Proxy :: Proxy 'Compose) <interactive>:5:1: error: • No instance for (Typeable a0) arising from a use of ‘typeOf’ • In the expression: typeOf (Proxy :: Proxy Compose) In an equation for ‘it’: it = typeOf (Proxy :: Proxy Compose) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11334> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11329: Visible type applications: failing tests with WAY=hpc
by GHC 20 Mar '16

20 Mar '16

#11329: Visible type applications: failing tests with WAY=hpc -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.11 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-head --info | grep Project [("Project name","The Glorious Glasgow Haskell Compilation System") ,("Project version","8.1.20151231") ,("Project Git commit id","8afeaad919dc67643b4eff14efafb48b59039b2b") }}} {{{ $ make slowtest TEST='VtaParse Vta1 Vta2' VERBOSE=2 TEST_HC=ghc-head ... =====> VtaParse(normal) 1 of 3 [0, 0, 0] =====> VtaParse(hpc) 1 of 3 [0, 0, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): dsExpr:HsTypeOut Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for VtaParse(hpc) =====> VtaParse(optasm) 1 of 3 [0, 1, 0] =====> Vta1(normal) 2 of 3 [0, 1, 0] =====> Vta1(hpc) 2 of 3 [0, 1, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): dsExpr:HsTypeOut Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for Vta1(hpc) =====> Vta1(optasm) 2 of 3 [0, 2, 0] =====> Vta2(normal) 3 of 3 [0, 2, 0] =====> Vta2(hpc) 3 of 3 [0, 2, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): dsExpr:HsTypeOut Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for Vta2(hpc) =====> Vta2(optasm) 3 of 3 [0, 3, 0] Unexpected results from: TEST="Vta1 Vta2 VtaParse" }}} Tests added in commit 2db18b8135335da2da9918b722699df684097be9. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11329> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10075: Muddling Constraint and * means that Core is inconsistent
by GHC 17 Mar '16

17 Mar '16

#10075: Muddling Constraint and * means that Core is inconsistent -------------------------------------+------------------------------------- Reporter: goldfire | 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 | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I can say this: {{{ type family F (a :: k) type instance F (a :: Constraint) = Int type instance F (a :: *) = Bool }}} This compiles to the following Core: {{{ F :: forall (k :: BOX). k -> * axF1 :: [a :: Constraint].F Constraint a ~ Int axF2 :: [a :: *]. F * a ~ Bool }}} I can then build the following: {{{ sym axF1[Any Constraint] ; axF2[Any *] :: Int ~ Bool }}} The transitivity is sound because, in Core, `Constraint` and `*` are indistinguishable. I don't think there's a way to actually cause a bug in a running program due to this problem, but we should probably patch it up. Possible resolution: Have `coreView` change `Constraint` to `*`. Possible resolution once we have `* :: *`: Make `Constraint` and `*` representationally equal. In other words, it would be as if `Constraint` were a newtype around `*`. I haven't thought out the ramifications of this decision, but there's something nice about it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10075> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10303: Make it easier to print stack traces when debugging GHC itself
by GHC 17 Mar '16

17 Mar '16

#10303: Make it easier to print stack traces when debugging GHC itself -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- As suggested in [http://mail.haskell.org/pipermail/ghc- devs/2015-February/008271.html the mailing list], GHC should have better support for printing its own stack trace when profiling is enabled. This ticket is to track progress toward this goal. There are a few moving parts: * Just having `pprTrace` use `traceStack` is a bad idea, because a profiled compiler will spew lots and lots and lots of output. Instead, I propose a new `pprTraceStack :: String -> SDoc -> a -> a`. * Currently, `ASSERT` will print a stack trace, but it's sometimes the wrong one. `ASSERT` throws an error; if this error is caught and re- thrown, the stack trace is at the re-throw. Instead, it should be at the origin. * Is it worth adding a new mode in `build.mk` that enables profiling, `DEBUG`, and `-fprof-auto`, just to get good stack traces? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10303> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9803: Poor error message for unbound variable in pattern synonym
by GHC 17 Mar '16

17 Mar '16

#9803: Poor error message for unbound variable in pattern synonym -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 | Type of failure: hour) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- When I say {{{ pattern OneElt = [x] }}} I get {{{ Right-hand side of bidirectional pattern synonym cannot be used as an expression [x] }}} I have two complaints with this error message: 1. It's very unclear what's actually wrong with the pattern -- `[x]` looks like a perfectly fine expression, until I realize that `x` is unbound. 2. The herald of the error is more than 80 characters (if you count the indentation) and wraps on my 80-character terminal. GHC tends to avoid this elsewhere, and so the wrapping is suboptimal. I would easily say that issue (1) is more important than issue (2). Perhaps this would be better: {{{ Variable `x' is unbound in the bidirectional pattern synonym `OneElt': [x] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9803> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8132: Warning for Typeable instances misplaced
by GHC 16 Mar '16

16 Mar '16

#8132: Warning for Typeable instances misplaced -------------------------+------------------------------------------------- Reporter: | Owner: scottgw | Status: new Type: bug | Milestone: Priority: | Version: 7.7 normal | Operating System: Unknown/Multiple Component: | Type of failure: Incorrect warning at Compiler | compile-time Keywords: | Test Case: Architecture: | Blocking: Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | -------------------------+------------------------------------------------- There is currently a warning for hand-rolled instances of Typeable. However, this leads to some pretty surprising error messages: because the instance is ignored any code that relies on that instance in the same module just fails, which appears pretty weird to the user. {{{ #!haskell import Data.Typeable data K = K instance Typeable K where typeRep _ = undefined ex :: TypeRep ex = typeRep (undefined :: Proxy K) }}} Gives as an error: {{{ No instance for (Typeable * K) arising from a use of ‛typeRep’ In the expression: typeRep (undefined :: Proxy K) In an equation for ‛ex’: ex = typeRep (undefined :: Proxy K) }}} Which is of course surprising because the user just defined the instance. After commenting out the code that uses the instance, one gets: {{{ TypEx.hs:1:1: Warning: Typeable instances can only be derived; ignoring the following instance: instance Typeable * K -- Defined at TypEx.hs:5:10 }}} This information should clearly be somehow presented before or with the previous error if the user is to have any way to figure out what is going on. I suppose this could be fixed by: 1. Turning the Typeable instance warning into an error 2. Checking the missing instance in the existing error for Typeable and suggest that the user should look for hand written instances as a source of the problem. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8132> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11401: No match in record selector ctev_dest
by GHC 16 Mar '16

16 Mar '16

#11401: No match in record selector ctev_dest -------------------------------------+------------------------------------- Reporter: Lemming | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc1 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: -------------------------------------+------------------------------------- With the llvm-tf package I got the following problem: {{{ $ cat RecordSelectorCtevDest.hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FlexibleInstances #-} module RecordSelectorCtevDest where import Data.Word (Word32, ) import Foreign.Ptr (Ptr, ) newtype Value a = Value a newtype Function a = Function a newtype CodeGenFunction r a = CodeGenFunction a bind :: CodeGenFunction r a -> (a -> CodeGenFunction r b) -> CodeGenFunction r b bind (CodeGenFunction a) k = k a class (f ~ CalledFunction g, r ~ CallerResult g, g ~ CallerFunction f r) => CallArgs f g r where type CalledFunction g :: * type CallerResult g :: * type CallerFunction f r :: * call :: Function f -> g instance CallArgs (IO a) (CodeGenFunction r (Value a)) r where type CalledFunction (CodeGenFunction r (Value a)) = IO a type CallerResult (CodeGenFunction r (Value a)) = r type CallerFunction (IO a) r = CodeGenFunction r (Value a) call = undefined instance CallArgs b b' r => CallArgs (a -> b) (Value a -> b') r where type CalledFunction (Value a -> b') = a -> CalledFunction b' type CallerResult (Value a -> b') = CallerResult b' type CallerFunction (a -> b) r = Value a -> CallerFunction b r call = undefined test :: Function (IO (Ptr a)) -> Function (Ptr a -> IO Word32) -> CodeGenFunction Word32 (Value Word32) test start fill = bind (call start) (call fill) $ ghci-8.0.0.20160109 RecordSelectorCtevDest.hs GHCi, version 8.0.0.20160109: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling RecordSelectorCtevDest ( RecordSelectorCtevDest.hs, interpreted ) *** Exception: No match in record selector ctev_dest }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11401> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11407: -XTypeInType uses up all memory when used in data family instance
by GHC 16 Mar '16

16 Mar '16

#11407: -XTypeInType uses up all memory when used in data family instance -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compiling this code with GHC 8.1 causes all my memory to be used very quickly: {{{#!hs {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} module TypeInTypeEatsAllMemory where import Data.Kind type Const a b = a data family UhOh (f :: k1) (a :: k2) (b :: k3) data instance UhOh (f :: * -> * -> *) (a :: forall a) (b :: Const * a) = UhOh }}} On the other hand, this code compiles without issue: {{{#!hs {-# LANGUAGE TypeInType #-} module TypeInTypeEatsAllMemory where import Data.Kind type Const a b = a data UhOh (f :: * -> * -> *) (a :: forall a) (b :: Const * a) = UhOh }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11407> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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