June 2016 - ghc-tickets

[GHC] #11825: Pretty printer doesn't display functional dependency with ‘→’
by GHC 25 Aug '16

25 Aug '16

#11825: Pretty printer doesn't display functional dependency with ‘→’ -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: GHCi | Version: 7.10.3 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: -------------------------------------+------------------------------------- {{{ % ghci -ignore-dot-ghci GHCi, version 8.1.20160117: http://www.haskell.org/ghc/ :? for help Prelude> :set -XUnicodeSyntax Prelude> import Control.Monad.Free Prelude Control.Monad.Free> :set -XUnicodeSyntax Prelude Control.Monad.Free> :i MonadFree class Monad m => MonadFree (f :: * -> *) (m :: * -> *) | m -> f where wrap :: f (m a) -> m a default wrap :: (m ~ t n, Control.Monad.Trans.Class.MonadTrans t, MonadFree f n, Functor f) => f (m a) -> m a -- Defined in ‘Control.Monad.Free.Class’ instance [safe] Functor f => MonadFree f (Free f) -- Defined in ‘Control.Monad.Free’ Prelude Control.Monad.Free> }}} should be {{{ class Monad m => MonadFree (f :: * -> *) (m :: * -> *) | m → f where }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11825> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12041: GHC panics on "print_equality ~"
by GHC 25 Aug '16

25 Aug '16

#12041: GHC panics on "print_equality ~" -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: 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: -------------------------------------+------------------------------------- {{{#!hs {-# Language PolyKinds, TypeFamilies #-} import Data.Kind class Category (p :: i -> i -> Type) where type Ob p :: i -> Constraint data I a b instance Category I where type Ob I = (~) Int }}} fails with {{{ $ ghci -ignore-dot-ghci /tmp/Error.hs GHCi, version 8.1.20160503: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/Error.hs, interpreted ) /tmp/Error.hs:10:15: error:ghc: panic! (the 'impossible' happened) (GHC version 8.1.20160503 for x86_64-unknown-linux): print_equality ~ Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12041> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11833: GHC can't derive polykinded instance of polykinded typeclass for newtype that requires a class constraint
by GHC 25 Aug '16

25 Aug '16

#11833: GHC can't derive polykinded instance of polykinded typeclass for newtype that requires a class constraint -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: #8865 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC chokes when trying to derive the following: {{{#!hs {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE PolyKinds #-} module Example where class Category (cat :: k -> k -> *) where catId :: cat a a catComp :: cat b c -> cat a b -> cat a c newtype T (c :: * -> * -> *) a b = MkT (c a b) deriving Category }}} with the following error: {{{ $ /opt/ghc/8.0.1/bin/ghc Example.hs -fprint-explicit-kinds [1 of 1] Compiling Example ( Example.hs, Example.o ) Example.hs:9:57: error: • No instance for (Category * c) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself • When deriving the instance for (Category * (T c)) }}} I know what is happening. Unlike in #8865, where we were deriving `Category` for a concrete type like `Either`, in the above example we are attempting to derive an instance of the form: {{{#!hs instance Category * c => Category (T * c) where ... }}} (using `-fprint-explicit-kinds` syntax). But `validDerivPred` is checking if `sizePred (Category * c)` equals the number of free type variables in `Category * c`. But note that `sizePred` counts both type variables //and// type constructors, and `*` is a type constructor! So `validDerivPred` erroneously rejects the above instance. To fix this behavior, I think we just need to change `validDerivPred` to only consider the //visible// arguments of `Category` (i.e., only `c`). This should be a pretty easy fix - patch incoming. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11833> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11484: Type synonym using -XTypeInType can't be spliced with TH
by GHC 25 Aug '16

25 Aug '16

#11484: Type synonym using -XTypeInType can't be spliced with TH -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1-rc1 Haskell | Keywords: TypeInType | 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: -------------------------------------+------------------------------------- The following code compiles: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE TypeInType #-} {-# OPTIONS_GHC -ddump-splices #-} module Foo where import Data.Kind type TySyn (k :: *) (a :: k) = () -- $([d| type TySyn2 (k :: *) (a :: k) = () |]) }}} But uncomment the last line, and it doesn't compile: {{{ $ /opt/ghc/head/bin/ghc Foo.hs [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) Foo.hs:10:3-43: Splicing declarations [d| type TySyn2_aBH (k_aBI :: *) (a_aBJ :: k_aBI) = () |] ======> type TySyn2_a4BF (k_a4BG :: Type) (a_a4BH :: k_a4BG) = () Foo.hs:10:3: error: • Couldn't match expected kind ‘GHC.Prim.Any’ with actual kind ‘k1’ • In the type declaration for ‘TySyn2’ Foo.hs:10:3: error: • Kind variable ‘k_a4BG’ is implicitly bound in datatype ‘TySyn2’, but does not appear as the kind of any of its type variables. Perhaps you meant to bind it (with TypeInType) explicitly somewhere? Type variables with inferred kinds: k_a4BG (a_a4BH :: GHC.Prim.Any) • In the type declaration for ‘TySyn2’ }}} There are two issues here: 1. The error message claims that `TySyn2` is a datatype when it is actually a type synonym. This should be easy enough to fix; just change [http://git.haskell.org/ghc.git/blob/89bdac7635e6ed08927d760aa885d3e7ef3edb8… the code] that throws the error message to invoke [http://git.haskell.org/ghc.git/blob/89bdac7635e6ed08927d760aa885d3e7ef3edb8… tyConFlavour]. 2. For some reason, the type variable `a` in `TySyn2` fails to kind-check. Somehow, an `Any` got in there, but I'm not sure where it snuck in. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11484> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11976: Error message mentions impredicative polymorphism
by GHC 25 Aug '16

25 Aug '16

#11976: Error message mentions impredicative polymorphism -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- When we apply `Lens` to too many arguments in the `:kind` command we get a sensible error message {{{ ghci> type Lens s a = forall f. Functor f => (a -> f a) -> (s -> f s) ghci> :kind Lens _ _ Lens _ _ :: * ghci> :kind Lens _ _ _ <interactive>:1:1: error: • Expecting one fewer argument to ‘Lens t0 t1’ Expected kind ‘k0 -> k1’, but ‘Lens t0 t1’ has kind ‘*’ • In the type ‘Lens _ _ _’ }}} but use the same in a type signature or annotation and it complains about impredicative polymorphism {{{ ghci> :t undefined :: Lens _ _ _ <interactive>:1:1: error: • Illegal polymorphic type: Lens _ _1 GHC doesn't yet support impredicative polymorphism • In the expression: undefined :: Lens _ _ _ ghci> a :: Lens _ _ _; a = undefined <interactive>:6:1: error: Illegal polymorphic type: Lens _ _1 GHC doesn't yet support impredicative polymorphism }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11976> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11941: stage restriction mentioned when an identifier is out of scope
by GHC 25 Aug '16

25 Aug '16

#11941: stage restriction mentioned when an identifier is out of scope -------------------------------------+------------------------------------- Reporter: aavogt | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE TemplateHaskell #-} import Data.Monoid const (return []) $ mempty { getFrst = Just () } }}} {{{ typeErrBug.hs:5:21: error: • GHC stage restriction: ‘getFrst’ is used in a top-level splice, quasi-quote, or annotation, and must be imported, not defined locally • In the second argument of ‘($)’, namely ‘mempty {getFrst = Just ()}’ In the expression: const (return []) $ mempty {getFrst = Just ()} typeErrBug.hs:5:30: error: Not in scope: ‘getFrst’ Perhaps you meant one of these: ‘getFirst’ (imported from Data.Monoid), ‘getLast’ (imported from Data.Monoid) }}} The stage restriction error shouldn't be mentioned: `getFrst` isn't defined at all while the "not defined locally" phrase says it's defined (in the wrong spot). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11941> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11947: GHC mistakenly warns about type defaulting in the presence of -XTypeApplications
by GHC 25 Aug '16

25 Aug '16

#11947: GHC mistakenly warns about type defaulting in the presence of -XTypeApplications -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This code: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} module Main (main) where theFloatDigits :: forall a. RealFloat a => Int theFloatDigits = floatDigits (undefined @_ @a) main :: IO () main = print (theFloatDigits @Double, theFloatDigits @Float) }}} erroneously produces this warning: {{{ $ /opt/ghc/8.0.1/bin/runghc -Wall TheFloatDigits.hs TheFloatDigits.hs:6:19: warning: [-Wtype-defaults] • Defaulting the following constraint to type ‘Double’ RealFloat a0 • In the ambiguity check for ‘theFloatDigits’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: theFloatDigits :: forall a. RealFloat a => Int (53,24) }}} GHC's claim that `a0` was defaulted to `Double` is clearly bogus, since `theFloatDigits` outputs different answers for `Double` and `Float`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11947> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11072: Runtime linker doesn't search for DLLs referenced in import libraries on Windows
by GHC 25 Aug '16

25 Aug '16

#11072: Runtime linker doesn't search for DLLs referenced in import libraries on Windows -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Phyx- Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2-rc2 (Linking) | Keywords: | Operating System: Windows Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (This is adapted from the comments [https://github.com/bos/text- icu/issues/12#issuecomment-154452774 here].) On Windows, the GHC runtime linker only searches for DLLs that have the same names as the import libraries passed to `-l`. This can sometimes create problems, since a library name could be different from the DLL it needs. `text-icu` provides an example of this, since it needs the extra libraries `icuuc`, `icudt`, and `icuin`. However, if you download the [http://site .icu-project.org/download/56#TOC-ICU4C-Download official ICU 56 binaries], they are distributed with DLLs named `icuuc56.dll`, `icudt56.dll`, and `icuin56.dll`, rather than `icuuc.dll`, `icudt.dll`, and `icuin.dll`. This doesn't create any trouble for the linker at compile-time. In fact, if you compile this program {{{#!hs -- TextICU.hs import Data.Text.ICU.Break main = print Kana }}} with `ghc TextICU.hs` and then run `cygcheck ./TextICU.hs` without having the ICU4C `bin64` folder in your `PATH`, it ''appears'' to search for the right DLLs: {{{ $ cygcheck ./TextICU.hs ... cygcheck: track_down: could not find icuin56.dll cygcheck: track_down: could not find icuuc56.dll }}} But actually running the code reveals a different story: {{{ $ runghc TextICU.hs TextICU.hs: icuuc: The specified module could not be found. TextICU.hs: <command line>: can't load .so/.DLL for: icuuc.dll (addDLL: could not load DLL) }}} This demonstrates that the runtime linker behaves differently; it is dependent on what the linked libraries' names are. To confirm this, you can recompile `text-icu` with the following changes to `text-icu.cabal`: {{{ extra-libraries: icuuc56 if os(mingw32) extra-libraries: icuin56 icudt56 }}} Also make symlinks named `icuuc56.lib`, `icuin56.lib`, and `icudt56.lib` that refer to `icuuc.lib`, `icuin.lib`, and `licudt.lib`, respectively, in the ICU4C `lib64` directory. Now `cygcheck` and `ghc` agree on which DLLs to use: {{{ $ ghc TextICU.hs $ cygcheck ./TextICU.exe ... cygcheck: track_down: could not find icuin56.dll cygcheck: track_down: could not find icuuc56.dll $ runghc TextICU.hs TextICU.hs: icuuc56: The specified module could not be found. TextICU.hs: <command line>: can't load .so/.DLL for: icuuc56.dll (addDLL: could not load DLL) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11072> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12072: GHC panic on type wildcard in left-hand side of data family
by GHC 25 Aug '16

25 Aug '16

#12072: GHC panic on type wildcard in left-hand side of data family -------------------------------------+------------------------------------- Reporter: andreash | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While playing around with data families I received the following output by ghc/ghci: {{{ ghc: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-linux): rnHsTyKi HsWildcardTy Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I had accidentally left a wildcard `_` on the left-hand side of a data instance definition. To reproduce enter the following code into a file and try to load that file into ghci, or try to compile it with ghc: {{{#!hs data family Bug x data instance Bug _ = Bug }}} The expected behavior would be a (non-panic) error message of some sort. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12072> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12165: Multiple pattern type signatures accepted
by GHC 25 Aug '16

25 Aug '16

#12165: Multiple pattern type signatures accepted -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This hogwash is accepted: {{{ pattern P :: a -> b -> Maybe (a,b) pattern P :: foo => bar => blah -> urgh pattern P x y = Just (x, y) }}} A little experimentation shows that only the first pattern signature is examined. Others are accepted and ignored. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12165> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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