May 2017 - ghc-tickets

[GHC] #13710: panic with boot and -jX
by GHC 29 Jul '17

29 Jul '17

#13710: panic with boot and -jX -------------------------------------+------------------------------------- Reporter: pacak | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 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: -------------------------------------+------------------------------------- {{{ % cat A.hs module A where }}} {{{ % cat A.hs-boot module A ( A ) where type A = Maybe () yay :: A -> IO () }}} {{{ % cat B.hs module B where import {-# SOURCE #-} A }}} This panics: {{{ % rm -rf o ; ghc -j2 -outputdir o B [1 of 3] Compiling A[boot] ( A.hs-boot, o/A.o-boot ) [2 of 3] Compiling A ( A.hs, o/A.o ) <no location info>: error: ghc: panic! (the 'impossible' happened) (GHC version 8.2.0.20170503 for x86_64-unknown-linux): tcIfaceGlobal (local): not found You are in a maze of twisty little passages, all alike. While forcing the thunk for TyThing A which was lazily initialized by initIfaceCheck typecheckLoop, I tried to tie the knot, but I couldn't find A in the current type environment. If you are developing GHC, please read Note [Tying the knot] and Note [Type-checking inside the knot]. Consider rebuilding GHC with profiling for a better stack trace. Contents of current type environment: [r15J :-> Identifier ‘$trModule’] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1134:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in ghc:Outputable pprPanic, called at compiler/iface/TcIface.hs:1689:23 in ghc:TcIface Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This works: {{{ % rm -rf o ; ghc -j1 -outputdir o B [1 of 3] Compiling A[boot] ( A.hs-boot, o/A.o-boot ) [2 of 3] Compiling A ( A.hs, o/A.o ) A.hs-boot:3:1: error: ‘A.A’ is exported by the hs-boot file, but not exported by the module | 3 | type A = Maybe () | ^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13710> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12989: ($) can have a more general type
by GHC 28 Jul '17

28 Jul '17

#12989: ($) can have a more general type -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The documentation (in section 9.12.1 for GHC 8; I don't know what section it is in 8.2) suggests a hypothetical type for `($)`: {{{#!hs bad :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (a :: TYPE r1) (b :: TYPE r2). (a -> b) -> a -> b bad f x = f x }}} It explains, correctly, that this definition will not work because `x` has a representation-polymorphic type. However, this doesn't actually explain why `($)` doesn't have that type! Indeed, both GHC 8 and 8.2 accept the following: {{{#!hs good :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (a :: TYPE r1) (b :: TYPE r2). (a -> b) -> a -> b good f = f }}} This has very slightly different semantics, but anyone relying on the difference is already doing something they shouldn't. It may or may not be possible to retain the current semantics with some care and magic, if we so desire. I didn't really know how to characterize this ticket properly. It could be considered a documentation bug or a compiler feature request. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12989> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13541: Make it easier to use the gold linker
by GHC 28 Jul '17

28 Jul '17

#13541: Make it easier to use the gold linker -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- As pointed out in #4862, the `gold` linker is significantly faster than BFD `ld`. Currently we use whatever linker `gcc` uses by default. This is an unfortunate situation for users as few packagers take the effort to configure their builds to use `gold`. I think we should consider the following, > Introduce a configure flag (to both the source distribution, and the distributed binary distributions), `--enable-gold`. When enabled, `configure` will check for the functioning of `gcc -fuse-ld=gold`. If found to work `-fuse-ld=gold` would be added to GHC's `optl`. The flag would throw an error on non-ELF platforms (which are not supported by `gold`). While there is admittedly not a whole lot of precedent for this, the status quo means we are leaving a significant bit of compiler performance on the table in a majority of cases. Given that `stack` uses GHC's official bindists, we should try to improve this situation. * -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13541> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13601: GHC errors but hangs
by GHC 28 Jul '17

28 Jul '17

#13601: GHC errors but hangs -------------------------------------+------------------------------------- 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 TypeFamilies, DataKinds, TypeInType #-} import GHC.Exts import Prelude (Bool(True,False),Integer,Ordering,undefined) import qualified Prelude import Data.Kind -------------------- -- class hierarchy type family Rep (rep :: RuntimeRep) :: RuntimeRep where -- Rep IntRep = IntRep -- Rep DoubleRep = IntRep -- Rep PtrRepUnlifted = IntRep -- Rep PtrRepLifted = PtrRepLifted class Boolean (Logic a) => Eq (a :: TYPE rep) where type Logic (a :: TYPE rep) :: TYPE (Rep rep) (==) :: a -> a -> Logic a class Eq a => POrd (a :: TYPE rep) where inf :: a -> a -> a class POrd a => MinBound (a :: TYPE rep) where minBound :: () -> a class POrd a => Lattice (a :: TYPE rep) where sup :: a -> a -> a class (Lattice a, MinBound a) => Bounded (a :: TYPE rep) where maxBound :: () -> a class Bounded a => Complemented (a :: TYPE rep) where not :: a -> a class Bounded a => Heyting (a :: TYPE rep) where infixr 3 ==> (==>) :: a -> a -> a class (Complemented a, Heyting a) => Boolean a (||) :: Boolean a => a -> a -> a (||) = sup (&&) :: Boolean a => a -> a -> a (&&) = inf }}} hangs with {{{ $ ghci a.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( a.hs, interpreted ) a.hs:18:16: error: C-c C-cInterrupted. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13768: Incorrect warnings generated by exhaustiveness checker with pattern synonyms / GADT combination
by GHC 28 Jul '17

28 Jul '17

#13768: Incorrect warnings generated by exhaustiveness checker with pattern synonyms / GADT combination -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 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 module {{{ {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE ViewPatterns #-} module PatSynEx where data NS (f :: k -> *) (xs :: [k]) = NS Int data IsNS (f :: k -> *) (xs :: [k]) where IsZ :: f x -> IsNS f (x ': xs) IsS :: NS f xs -> IsNS f (x ': xs) isNS :: NS f xs -> IsNS f xs isNS = undefined pattern Z :: () => (xs' ~ (x ': xs)) => f x -> NS f xs' pattern Z x <- (isNS -> IsZ x) pattern S :: () => (xs' ~ (x ': xs)) => NS f xs -> NS f xs' pattern S p <- (isNS -> IsS p) {-# COMPLETE Z, S #-} data SList :: [k] -> * where SNil :: SList '[] SCons :: SList (x ': xs) go :: SList ys -> NS f ys -> Int go SCons (Z _) = 0 go SCons (S _) = 1 go SNil _ = error "inaccessible" }}} produces the following warnings with both GHC 8.2 and 8.3: {{{ PatSynEx.hs:31:1: warning: [-Woverlapping-patterns] Pattern match has inaccessible right hand side In an equation for ‘go’: go SCons (Z _) = ... | 31 | go SCons (Z _) = 0 | ^^^^^^^^^^^^^^^^^^ PatSynEx.hs:32:1: warning: [-Woverlapping-patterns] Pattern match is redundant In an equation for ‘go’: go SCons (S _) = ... | 32 | go SCons (S _) = 1 | ^^^^^^^^^^^^^^^^^^ }}} Neither warning seems correct. The first case is not inaccessible, the second case is not redundant. The catch-all case has always been required with GHC even though it is not really reachable, but that's not the subject of this issue. I tried to simplify the issue further by getting rid of the `f` argument in `NS` and `IsNS`, but that made the issue disappear. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13768> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables)
by GHC 28 Jul '17

28 Jul '17

#12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 7.10.3 (Type checker) | Keywords: GADTs, | Operating System: Unknown/Multiple ScopedTypeVariables | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs data Exp a where Tru :: Ty Bool eval :: Exp a -> a eval Tru = True }}} Works fine, as does {{{#!hs eval :: Exp a -> a eval (Tru :: Exp _) = True }}} But {{{#!hs eval :: Exp a -> a eval (Tru :: Exp Bool) = True }}} doesn't, is this an intended design of GADTs/ScopedTypeVariables that the type equality constraint isn't in scope in the type signature of the pattern match, I would like to match on an existential type in my own code: {{{#!hs compile (ArrIx arr index :: Exp (Sca elt)) = do ... }}} It can be worked around by writing: {{{#!hs eval a@Tru = case a :: Exp Bool of }}} but for my own code it seems I must write {{{#!hs compile uuu@(ArrIx arr index :: Exp a) = do case uuu :: (a ~ Sca elt) => Exp (Sca elt) of }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12018> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13430: Can't scope type variables when pattern matching on GADTs
by GHC 27 Jul '17

27 Jul '17

#13430: Can't scope type variables when pattern matching on GADTs -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I was very surprised that the following doesn't compile: {{{ {-# LANGUAGE GADTs, ScopedTypeVariables #-} data Foo x where A :: Foo Bool B :: Foo Int foo :: Foo x -> () foo (A :: Foo Bool) = () }}} GHC says that it couldn't match the type `y` with `Bool`. See [this question](http://stackoverflow.com/questions/42824949/type-inference-with- gadts) for a simple motivating example. As someone there pointed out, the situation would be improved with type application (#11350), but this ticket is about bringing the output type in scope with `ScopedTypeVariables`. This most closely reminds me of #1823 (!), but that was resolved many moons ago. This behavior also exists in 7.10.3. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13430> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12369: data families shouldn't be required to have return kind *, data instances should
by GHC 27 Jul '17

27 Jul '17

#12369: data families shouldn't be required to have return kind *, data instances should -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature | Status: new request | Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 (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: -------------------------------------+------------------------------------- I'd like to be able to define {{{#!hs {-# language PolyKinds, KindSignatures, GADTs, TypeFamilies #-} data family Fix :: (k -> *) -> k newtype instance Fix f = In { out :: f (Fix f) } }}} But currently this is disallowed: {{{ Fix.hs:2:1: error: • Kind signature on data type declaration has non-* return kind (k -> *) -> k • In the data family declaration for ‘Fix’ }}} Ultimately I think the issue here is that data __instances__ should be required to end in kind *, not the families, but this generalization didn't mean anything until we had `PolyKinds`. As an example of a usecase, with the above, I could define a bifunctor fixed point such as {{{#!hs newtype instance Fix f a = In2 { out2 :: f (Fix f a) a } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12369> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13610: Unhelpful error messages about lifted and unlifted types
by GHC 27 Jul '17

27 Jul '17

#13610: Unhelpful error messages about lifted and unlifted types -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) 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: -------------------------------------+------------------------------------- I wrote this code: {{{ {-# LANGUAGE MagicHash #-} import GHC.Prim import GHC.Types main = do let primDouble = 0.42## :: Double# let double = 0.42 :: Double IO (\s -> mkWeakNoFinalizer# double () s) }}} and I get this error message: {{{ WeakDouble.hs:8:15: error: • Couldn't match a lifted type with an unlifted type Expected type: (# State# RealWorld, Weak# () #) Actual type: (# State# RealWorld, Weak# () #) • In the expression: mkWeakNoFinalizer# double () s In the first argument of ‘IO’, namely ‘(\ s -> mkWeakNoFinalizer# double () s)’ In a stmt of a 'do' block: IO (\ s -> mkWeakNoFinalizer# double () s) }}} with `-fprint-explicit-kinds`. (Without the flag, it looks the same, but tells me to use this flag…). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13610> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11560: panic: isInjectiveTyCon sees a TcTyCon
by GHC 27 Jul '17

27 Jul '17

#11560: panic: isInjectiveTyCon sees a TcTyCon -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | 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: -------------------------------------+------------------------------------- I typed this into ghci and it panicked. Not sure whether the declaration is really valid anyways, but ghci shouldn't panic on it. {{{ rwbarton@morphism:~/ghc-newest$ ./inplace/bin/ghc-stage2 --interactive GHCi, version 8.1.20160201: http://www.haskell.org/ghc/ :? for help Prelude> :set -XTypeFamilies -XTypeInType Prelude> :m +Data.Kind Prelude Data.Kind> type family T (l :: *) (k :: l) :: * where { T * Int = * } ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160201 for x86_64-unknown-linux): isInjectiveTyCon sees a TcTyCon T Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11560> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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