April 2017 - ghc-tickets

[GHC] #13626: Ambiguity when exporting a data constructor despite qualification
by GHC 30 Apr '17

30 Apr '17

#13626: Ambiguity when exporting a data constructor despite qualification -------------------------------------+------------------------------------- Reporter: Lemming | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 (Parser) | 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: -------------------------------------+------------------------------------- {{{ $ cat A.hs module A where data T = Cons $ cat B.hs module B (T(T)) where import qualified A data T = T $ ghc-8.2.0.20170422 -Wall B.hs [2 of 2] Compiling B ( B.hs, B.o ) [A changed] B.hs:1:11: error: • Ambiguous occurrence ‘T’ It could refer to either ‘A.T’, imported qualified from ‘A’ at B.hs:3:1-18 or ‘T’, defined at B.hs:5:1 • In the export: T(T) | 1 | module B (T(T)) where | ^^^^ }}} There should be no ambiguity, because there is only one data constructor named `T`. Even if `A.T`'s data constructor would also be called `T` there would be no ambiguity because `A` is imported with qualification. The problem does not appear, if `B.T`'s data constructor is named `Cons`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13626> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3397: :step hangs when -fbreak-on-exception is set
by GHC 30 Apr '17

30 Apr '17

#3397: :step hangs when -fbreak-on-exception is set -------------------------------------+---------------------------------- Reporter: hamish | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 7.2.1 Component: GHCi | Version: 7.10.1-rc2 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: x86 Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+---------------------------------- Changes (by George): * status: new => closed * resolution: => fixed -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3397#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3397: :step hangs when -fbreak-on-exception is set
by GHC 30 Apr '17

30 Apr '17

#3397: :step hangs when -fbreak-on-exception is set -------------------------------------+---------------------------------- Reporter: hamish | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 7.2.1 Component: GHCi | Version: 7.10.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86 Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+---------------------------------- Comment (by George): this seems to be fixed in 8.2.1-rc1: {{{ ghci -ignore-dot-ghci bug3397.hs GHCi, version 8.2.0.20170404: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( bug3397.hs, interpreted ) [flags changed] Ok, modules loaded: Main. *Main> :set -fbreak-on-exception *Main> :steplocal main Stopped in Main.main, bug3397.hs:12:8-34 _result :: IO () = _ [bug3397.hs:12:8-34] [bug3397.hs:12:8-34] *Main> :steplocal Stopped in Main.main, bug3397.hs:12:25-33 _result :: IO () = _ -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3397#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13468: GHC stubbornly produces dead code for empty case with type family
by GHC 29 Apr '17

29 Apr '17

#13468: GHC stubbornly produces dead code for empty case with type family -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following instance: {{{#!hs data Void instance Generic Void where type Rep Void = V1 from x = case x of to x = case x of }}} The pattern checker, when enabled, correctly determines that both `from` and `to` cover all cases. Yay! In order to do this, it has to reduce the `Rep Void` type family application. The optimizer, on the other hand, does not perform this reduction, presumably because it is not known to terminate. Unfortunate in this case, but fine, I suppose. Here's where it gets really unfortunate. If I write {{{#!hs to (x :: V1 r) = case x of }}} then the type checker already has to do the work of unifying `Rep Void` with `V1 r`, but the optimizer doesn't take advantage of it! With `-O2 -ddump-simpl ...`, I get {{{ -- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0} lvl_r2IT :: Addr# lvl_r2IT = "Phantom.hs:18:20-23|case"# -- RHS size: {terms: 2, types: 2, coercions: 0, joins: 0/0} $fGenericVoid1 :: Void $fGenericVoid1 = patError lvl_r2IT -- RHS size: {terms: 6, types: 7, coercions: 0, joins: 0/0} $fGenericVoid_$cto :: forall x. Rep Void x -> Void $fGenericVoid_$cto = \ (@ x_a2HT) (ds_d2J8 :: Rep Void x_a2HT) -> case ds_d2J8 of { __DEFAULT -> $fGenericVoid1 } }}} That seems rather unfortunate. The only workaround I've found so far is to actually write a function just to constrain the type: {{{#!hs absV :: V1 r -> a absV x = case x of instance Generic Void where ... to = absV }}} Finally, this is clean: {{{ -- RHS size: {terms: 5, types: 12, coercions: 0, joins: 0/0} absV :: forall r a. V1 r -> a absV = \ (@ r_a2Hy) (@ a_a2Hz) (x_a1fi :: V1 r_a2Hy) -> case x_a1fi of { } -- RHS size: {terms: 4, types: 7, coercions: 0, joins: 0/0} lvl_r2IF :: forall x. V1 x -> Void lvl_r2IF = \ (@ x_a2HP) (eta_B1 :: V1 x_a2HP) -> absV eta_B1 }}} I suppose I could add `GHC.Generics.Absurd` just to write the `absV` function for `Generic` and `Generic1` deriving, but that seems more than a little silly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13468> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12104: Type families, `TypeError`, and `-fdefer-type-errors` cause "opt_univ fell into a hole"
by GHC 29 Apr '17

29 Apr '17

#12104: Type families, `TypeError`, and `-fdefer-type-errors` cause "opt_univ fell into a hole" -------------------------------------+------------------------------------- Reporter: antalsz | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: TypeFamilies, | Operating System: MacOS X CustomTypeErrors | Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If I create a type family – open or closed – with a case that evaluates to a `TypeError`, and define a top-level binding with this type, loading the file with `-fdefer-type-errors` enabled (or via `:load!`/`:reload!`) panics GHC with "opt_univ fell into a hole". (And if I used `:load!` or `:reload!`, `-fdefer-type-errors` doesn't get unset.) A minimal example: {{{#!hs {-# LANGUAGE TypeFamilies, DataKinds, UndecidableInstances #-} import GHC.TypeLits type family F a where F a = TypeError (Text "error") err :: F () err = () }}} results in the panic {{{ ….hs:9:7: warning: [-Wdeferred-type-errors] • error • In the expression: () In an equation for ‘err’: err = () ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): opt_univ fell into a hole {a4Va} }}} Adding more cases to the type family, or making it open, still cause the crash. This holds whether the error case is a final catch-all case, or something more like {{{#!hs type family F a where F () = TypeError (Text "error") F a = () }}} Just using a type synonym for `F` doesn't cause a panic, however, and nor does giving `err` the type `TypeError (Text "error")` directly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12104> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13603: Can't resolve levity polymorphic superclass
by GHC 28 Apr '17

28 Apr '17

#13603: Can't resolve levity polymorphic superclass -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple LevityPolymorphism, TypeInType | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This works {{{#!hs {-# Language PolyKinds, TypeInType #-} import GHC.Exts (TYPE, RuntimeRep) class A (a :: TYPE rep) class A a => B (a :: TYPE rep) instance A b => A (a -> (b :: TYPE rep)) instance B b => B (a -> b) }}} but the moment you add (`b :: TYPE rep`) to the last line it stops working {{{#!hs -- t3I7.hs:9:10-40: error: … -- • Could not deduce (A b) -- arising from the superclasses of an instance declaration -- from the context: B b -- bound by the instance declaration at /tmp/t3I7.hs:9:10-40 -- • In the instance declaration for ‘B (a -> b)’ -- Compilation failed. {-# Language PolyKinds, TypeInType #-} import GHC.Exts (TYPE, RuntimeRep) class A (a :: TYPE rep) class A a => B (a :: TYPE rep) instance A b => A (a -> (b :: TYPE rep)) instance B b => B (a -> (b :: TYPE rep)) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13603> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13628: Confusing error message with TypeApplications already enabled
by GHC 28 Apr '17

28 Apr '17

#13628: Confusing error message with TypeApplications already enabled -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 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: -------------------------------------+------------------------------------- I have `{-# LANGUAGE TypeApplications #-}` in my file, and accidentally wrote a typo: `myFunction@a` (missing space, intended was `myFunction @a`). GHC 8.0.2 outputs: {{{ Pattern syntax in expression context: myFunction@a Did you mean to enable TypeApplications? }}} I already have TypeApplications on, why does GHC suggest this? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13628> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11821: Internal error: not in scope during type checking, but it passed the renamer
by GHC 28 Apr '17

28 Apr '17

#11821: Internal error: not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: darchon | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc3 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: -------------------------------------+------------------------------------- While trying to get the singletons package to compile on GHC8 (https://github.com/goldfirere/singletons/pull/142) I encountered the following error while trying to track down a bug: {{{ [1 of 1] Compiling NotInScope ( NotInScope.hs, interpreted ) NotInScope.hs:22:20: error: • GHC internal error: ‘b’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [a1lm :-> Type variable ‘b’ = b, a1lA :-> Type variable ‘l1’ = l1, a1lB :-> Type variable ‘l2’ = l2, a1lC :-> Type variable ‘l3’ = l3, a1lE :-> Type variable ‘a’ = a, a1lF :-> Type variable ‘l4’ = l4, r1aq :-> ATcTyCon Lgo, r1aG :-> ATcTyCon Lgo1, r1aI :-> ATcTyCon Lgo2] • In the kind ‘b’ In the definition of data constructor ‘Lgo1KindInference’ In the data declaration for ‘Lgo1’ }}} for the following code: {{{ {-# LANGUAGE RankNTypes, DataKinds, PolyKinds, GADTs, TypeFamilies, UndecidableInstances #-} module NotInScope where import Data.Proxy type KindOf (a :: k) = ('KProxy :: KProxy k) data TyFun :: * -> * -> * type family Apply (f :: TyFun k1 k2 -> *) (x :: k1) :: k2 data Lgo2 l1 l2 l3 (l4 :: b) (l5 :: TyFun [a] b) = forall (arg :: [a]) . KindOf (Apply (Lgo2 l1 l2 l3 l4) arg) ~ KindOf (Lgo l1 l2 l3 l4 arg) => Lgo2KindInference data Lgo1 l1 l2 l3 (l4 :: TyFun b (TyFun [a] b -> *)) = forall (arg :: b) . KindOf (Apply (Lgo1 l1 l2 l3) arg) ~ KindOf (Lgo2 l1 l2 l3 arg) => Lgo1KindInference type family Lgo f z0 xs0 (a1 :: b) (a2 :: [a]) :: b where Lgo f z0 xs0 z '[] = z Lgo f z0 xs0 z ('(:) x xs) = Apply (Apply (Lgo1 f z0 xs0) (Apply (Apply f z) x)) xs }}} Note that the above code works fine in GHC 7.10.2. There are two options to make the code compile on GHC8-rc3: * Remove the kind annotations on the {{{forall arg .}}} binders * Or make the following changes using TypeInType: {{{ {-# LANGUAGE RankNTypes, DataKinds, PolyKinds, GADTs, TypeFamilies, UndecidableInstances, TypeInType #-} module NotInScope where import Data.Proxy import GHC.Types type KindOf (a :: k) = ('KProxy :: KProxy k) data TyFun :: * -> * -> * type family Apply (f :: TyFun k1 k2 -> *) (x :: k1) :: k2 data Lgo2 a b l1 l2 l3 (l4 :: b) (l5 :: TyFun [a] b) = forall (arg :: [a]) . KindOf (Apply (Lgo2 a b l1 l2 l3 l4) arg) ~ KindOf (Lgo a b l1 l2 l3 l4 arg) => Lgo2KindInference data Lgo1 a b l1 l2 l3 (l4 :: TyFun b (TyFun [a] b -> *)) = forall (arg :: b) . KindOf (Apply (Lgo1 a b l1 l2 l3) arg) ~ KindOf (Lgo2 a b l1 l2 l3 arg) => Lgo1KindInference type family Lgo a b f z0 xs0 (a1 :: b) (a2 :: [a]) :: b where Lgo a b f z0 xs0 z '[] = z Lgo a b f z0 xs0 z ('(:) x xs) = Apply (Apply (Lgo1 a b f z0 xs0) (Apply (Apply f z) x)) xs }}} I'm sorry I didn't create a smaller test case. Let me know if one is required and I'll try. The error seems to be related to the recursive aspect of the three definitions and how implicit kind variables are handled in ghc8. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11821> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13560: Windows binary distributions have absolute paths from the build environment in the `settings` file
by GHC 28 Apr '17

28 Apr '17

#13560: Windows binary distributions have absolute paths from the build environment in the `settings` file -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-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: -------------------------------------+------------------------------------- The GHC 8.2.1-rc1 binary distribution for Windows has the absolute path to `gcc` from the build environment in its `settings` file, {{{ ... ("C compiler command", "C:/msys64/home/drydock/bin- dist-8.2.0.20170404-MINGW64_NT-6.3/ghc/inplace/mingw/bin/gcc.exe"), ... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13560> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13611: Segfault due to levity polymorphism of mkWeak#
by GHC 28 Apr '17

28 Apr '17

#13611: Segfault due to levity polymorphism of mkWeak# -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- This code segfaults: {{{ {-# LANGUAGE MagicHash, UnboxedTuples #-} import GHC.Prim import GHC.Types main = do let local = () let null = 0## :: Word# let triple = (# local, null, null #) IO (\s -> case mkWeakNoFinalizer# triple () s of (# s, r #) -> (# s, () #)) }}} The problem is that `mkWeakNoFinalizer#` has a levity polymorphic type for its first argument, but the implementation really requires the first argument to be a pointer. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13611> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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