February 2019 - ghc-tickets

[GHC] #15219: Implement UnliftedNewtypes proposal
by GHC 14 Feb '19

14 Feb '19

#15219: Implement UnliftedNewtypes proposal -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple UnliftedNewtypes | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The unlifted newtypes proposal is described here: https://github.com/ghc- proposals/ghc-proposals/blob/master/proposals/0013-unlifted-newtypes.rst I am going to be working on it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15219> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16317: HIE files don't include module import/export information
by GHC 14 Feb '19

14 Feb '19

#16317: HIE files don't include module import/export information -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- HIE files don't record information about import/exports. This blocks implementing LSIF files which need to know about imports/exports. Export information can be read from `tcg_exports`. Import information can be got from the `HscEnv` and looked up using `findImportedModule` I think. Would be good to target this for 8.8 if there is any time remaining. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16317> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16316: `-package-env=` in OPTIONS_GHC not supported
by GHC 14 Feb '19

14 Feb '19

#16316: `-package-env=` in OPTIONS_GHC not supported -------------------------------------+------------------------------------- Reporter: hvr | Owner: (none) Type: feature | Status: new request | Priority: high | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- I just realised we're missing an ingredient in order to support persistent package-environment workflows for standalone scripts: Consider the following use-cases: ---- 1. Script requires package environemnts disabled {{{#!hs #!/usr/bin/env runghc {-# OPTIONS_GHC -package-env=- #-} main = putStrLn "Hello World" }}} ---- 2. User manually maintains a package environment for scripts or teaching exercises (this is a quite common way to teach Haskell which I subscribe to, by letting students interact with ghc and ghci directly instead, and only properly introducing `cabal` lateron when it's actually needed) {{{ cabal v2-install --lib lens lens-aeson --package-env=lets-lens }}} and the scripts shall be using that custom named package environment: {{{#!hs #!/usr/bin/env runghc {-# OPTIONS_GHC -package-env=lets-lens #-} import Control.Lens main = do putStrLn "Hello Lens" -- ...lens using code... }}} ---- Currently both of these use-cases don't work because {{{ $ ghci-8.6.3 Main.hs GHCi, version 8.6.3: http://www.haskell.org/ghc/ :? for help Main.hs:3:16: error: unknown flag in {-# OPTIONS_GHC #-} pragma: -package-env=lets-lens | 3 | {-# OPTIONS_GHC -package-env=lets-lens #-} | ^^^^^^^^^^^^^^^^^^^^^^^^ }}} I do realise that it's tricky to support package-db related commands in `OPTIONS_GHC` but it'd nevertheless be quite important to support this in some way (possibly with some restrictions) in order to properly support the package-env based workflows (NB: the legacy user pkg-db based ones aren't available anymore in future cabal versions -- package-environments have completely replaced the legacy user-pkg db there). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16316> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16307: gloss-examples' fluid program takes close to an eternity to compile
by GHC 13 Feb '19

13 Feb '19

#16307: gloss-examples' fluid program takes close to an eternity to compile -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 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: -------------------------------------+------------------------------------- It has been over ten minutes and 16 GB of residency and `ghc` `master` still hasn't finished. We should investigate this; something seems very wrong. https://github.com/bgamari/gloss/tree/d863394df7b5a9400f2c2fae08fdbb07c91c6… -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16307> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16310: Program fails with "Impossible case alternative" when optimized
by GHC 13 Feb '19

13 Feb '19

#16310: Program fails with "Impossible case alternative" when optimized -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Here's an (unfortunately rather large) program: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE InstanceSigs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE UndecidableInstances #-} module Main (main) where import Data.Kind (Type) import Data.Type.Equality ((:~:)(..)) import Unsafe.Coerce (unsafeCoerce) main :: IO () main = print $ traversableComposition @(M1 U1) @() @() @() @U1 @U1 sPureFun sPureFun (SM1 SU1) ----- sPureFun :: forall f a. SApplicative f => Sing (PureSym0 :: a ~> f a) sPureFun = singFun1 @PureSym0 sPure data family Sing (a :: k) data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type infixr 0 ~> type family Apply (f :: a ~> b) (x :: a) :: b data (.@#@$$$) :: forall a b c. (b ~> c) -> (a ~> b) -> a ~> c type instance Apply (f .@#@$$$ g) x = Apply f (Apply g x) newtype instance Sing (f :: k1 ~> k2) = SLambda (forall t. Sing t -> Sing (Apply f t)) type SingFunction1 f = forall t. Sing t -> Sing (Apply f t) singFun1 :: forall f. SingFunction1 f -> Sing f singFun1 f = SLambda f type SingFunction2 f = forall t. Sing t -> SingFunction1 (Apply f t) singFun2 :: forall f. SingFunction2 f -> Sing f singFun2 f = SLambda (\x -> singFun1 (f x)) ----- data U1 p = U1 data instance Sing (z :: U1 p) where SU1 :: Sing 'U1 newtype M1 f p = M1 (f p) data instance Sing (z :: M1 f p) where SM1 :: Sing x -> Sing ('M1 x) data M1Sym0 :: forall k (f :: k -> Type) (p :: k). f p ~> M1 f p type instance Apply M1Sym0 x = 'M1 x newtype Compose f g x = Compose (f (g x)) data ComposeSym0 :: forall k1 k2 (f :: k2 -> Type) (g :: k1 -> k2) (x :: k1). f (g x) ~> Compose f g x type instance Apply ComposeSym0 x = 'Compose x data instance Sing (z :: Compose f g a) where SCompose :: Sing x -> Sing ('Compose x) instance (PFunctor f, PFunctor g) => PFunctor (Compose f g) where type Fmap h ('Compose x) = 'Compose (Fmap (FmapSym1 h) x) instance (SFunctor f, SFunctor g) => SFunctor (Compose f g) where sFmap :: forall a b (h :: a ~> b) (x :: Compose f g a). Sing h -> Sing x -> Sing (Fmap h x) sFmap sh (SCompose sx) = SCompose (sFmap (singFun1 @(FmapSym1 h) (sFmap sh)) sx) instance (PApplicative f, PApplicative g) => PApplicative (Compose f g) where type Pure x = 'Compose (Pure (Pure x)) type 'Compose h <*> 'Compose x = 'Compose (Fmap (<*>@#@$) h <*> x) instance (SApplicative f, SApplicative g) => SApplicative (Compose f g) where sPure sx = SCompose (sPure (sPure sx)) SCompose sh %<*> SCompose sx = SCompose (sFmap (singFun2 @(<*>@#@$) (%<*>)) sh %<*> sx) instance PFunctor U1 where type Fmap _ _ = 'U1 instance SFunctor U1 where sFmap _ _ = SU1 instance VFunctor U1 where fmapCompose _ _ SU1 = Refl instance PFunctor f => PFunctor (M1 f) where type Fmap g ('M1 x) = 'M1 (Fmap g x) instance SFunctor f => SFunctor (M1 f) where sFmap sg (SM1 sx) = SM1 (sFmap sg sx) instance VFunctor f => VFunctor (M1 f) where fmapCompose sg sh (SM1 x) | Refl <- fmapCompose sg sh x = Refl instance PApplicative U1 where type Pure _ = 'U1 type _ <*> _ = 'U1 instance SApplicative U1 where sPure _ = SU1 _ %<*> _ = SU1 instance VApplicative U1 where applicativeHomomorphism _ _ = Refl applicativeFmap _ _ = Refl instance PTraversable U1 where type Traverse _ _ = Pure 'U1 instance STraversable U1 where sTraverse _ _ = sPure SU1 instance VTraversable U1 where traversableComposition :: forall p q r (f :: Type -> Type) (g :: Type -> Type) (h :: p ~> f q) (i :: q ~> g r) (x :: U1 p). (VApplicative f, VApplicative g) => Sing h -> Sing i -> Sing x -> Traverse (ComposeSym0 .@#@$$$ FmapSym1 i .@#@$$$ h) x :~: 'Compose (Fmap (TraverseSym1 i) (Traverse h x)) traversableComposition _ si _ | Refl <- applicativeHomomorphism @f sTraverseI sU1q , Refl <- applicativeFmap @f sTraverseI (sPure sU1q) = Refl where sTraverseI :: Sing (TraverseSym1 i :: U1 q ~> g (U1 r)) sTraverseI = singFun1 (sTraverse si) sU1q :: Sing ('U1 :: U1 q) sU1q = SU1 instance PTraversable f => PTraversable (M1 f) where type Traverse g ('M1 x) = Fmap M1Sym0 (Traverse g x) instance STraversable f => STraversable (M1 f) where sTraverse sg (SM1 sx) = sFmap (singFun1 @M1Sym0 SM1) (sTraverse sg sx) instance VTraversable f => VTraversable (M1 f) where traversableComposition :: forall p q r (cf :: Type -> Type) (cg :: Type -> Type) (h :: p ~> cf q) (i :: q ~> cg r) (x :: M1 f p). (VApplicative cf, VApplicative cg) => Sing h -> Sing i -> Sing x -> Traverse (ComposeSym0 .@#@$$$ FmapSym1 i .@#@$$$ h) x :~: 'Compose (Fmap (TraverseSym1 i) (Traverse h x)) traversableComposition sh si (SM1 (sfp :: Sing fp)) | Refl <- traversableComposition sh si sfp , Refl <- fmapCompose @cf (singFun1 @(FmapSym1 M1Sym0) (sFmap sM1Fun)) sTraverseIFun sTraverseHIp , Refl <- -- Fmap (FmapSym1 M1Sym0 .@#@$$$ TraverseSym1 i) (Traverse h fp) -- :~: Fmap (TraverseSym1 i .@#@$$$ M1Sym0) (Traverse h fp) Refl @FmapSym0 `apply` funExt @(f q) @(cg (M1 f r)) @(FmapSym1 M1Sym0 .@#@$$$ TraverseSym1 i) @(TraverseSym1 i .@#@$$$ M1Sym0) lemma `apply` Refl @(Traverse h fp) , Refl <- fmapCompose @cf sTraverseIFun sM1Fun sTraverseHIp = Refl where lemma :: forall (z :: f q). Sing z -> Fmap M1Sym0 (Traverse i z) :~: Traverse i (Apply M1Sym0 z) lemma _ = Refl sM1Fun :: forall z. Sing (M1Sym0 :: f z ~> M1 f z) sM1Fun = singFun1 SM1 sTraverseHIp :: Sing (Traverse h fp) sTraverseHIp = sTraverse sh sfp sTraverseIFun :: forall hk. STraversable hk => Sing (TraverseSym1 i :: hk q ~> cg (hk r)) sTraverseIFun = singFun1 (sTraverse si) ----- class PFunctor (f :: Type -> Type) where type Fmap (g :: a ~> b) (x :: f a) :: f b data FmapSym0 :: forall f a b. (a ~> b) ~> f a ~> f b data FmapSym1 :: forall f a b. (a ~> b) -> f a ~> f b type instance Apply FmapSym0 f = FmapSym1 f type instance Apply (FmapSym1 f) x = Fmap f x class SFunctor (f :: Type -> Type) where sFmap :: forall a b (g :: a ~> b) (x :: f a). Sing g -> Sing x -> Sing (Fmap g x) class (PFunctor f, SFunctor f) => VFunctor f where fmapCompose :: forall a b c (g :: b ~> c) (h :: a ~> b) (x :: f a). Sing g -> Sing h -> Sing x -> Fmap g (Fmap h x) :~: Fmap (g .@#@$$$ h) x class PFunctor f => PApplicative f where type Pure (x :: a) :: f a type (g :: f (a ~> b)) <*> (x :: f a) :: f b infixl 4 <*> data PureSym0 :: forall (f :: Type -> Type) a. a ~> f a type instance Apply PureSym0 x = Pure x data (<*>@#@$) :: forall (f :: Type -> Type) a b. f (a ~> b) ~> f a ~> f b data (<*>@#@$$) :: forall (f :: Type -> Type) a b. f (a ~> b) -> f a ~> f b type instance Apply (<*>@#@$) f = (<*>@#@$$) f type instance Apply ((<*>@#@$$) f) x = f <*> x class SFunctor f => SApplicative f where sPure :: forall a (x :: a). Sing x -> Sing (Pure x :: f a) (%<*>) :: forall a b (g :: f (a ~> b)) (x :: f a). Sing g -> Sing x -> Sing (g <*> x) class (PApplicative f, SApplicative f, VFunctor f) => VApplicative f where applicativeHomomorphism :: forall a b (g :: a ~> b) (x :: a). Sing g -> Sing x -> (Pure g <*> Pure x) :~: (Pure (g `Apply` x) :: f b) applicativeFmap :: forall a b (g :: a ~> b) (x :: f a). Sing g -> Sing x -> Fmap g x :~: (Pure g <*> x) class PFunctor t => PTraversable t where type Traverse (g :: a ~> f b) (x :: t a) :: f (t b) data TraverseSym1 :: forall t f a b. (a ~> f b) -> t a ~> f (t b) type instance Apply (TraverseSym1 f) x = Traverse f x class SFunctor t => STraversable t where sTraverse :: forall f a b (g :: a ~> f b) (x :: t a). SApplicative f => Sing g -> Sing x -> Sing (Traverse g x) class (PTraversable t, STraversable t, VFunctor t) => VTraversable t where traversableComposition :: forall a b c (f :: Type -> Type) (g :: Type -> Type) (h :: a ~> f b) (i :: b ~> g c) (x :: t a). (VApplicative f, VApplicative g) => Sing h -> Sing i -> Sing x -> Traverse (ComposeSym0 .@#@$$$ FmapSym1 i .@#@$$$ h) x :~: 'Compose (Fmap (TraverseSym1 i) (Traverse h x)) ----- funExt :: forall a b (f :: a ~> b) (g :: a ~> b). (forall (x :: a). Sing x -> Apply f x :~: Apply g x) -> f :~: g funExt _ = axiom apply :: f :~: g -> a :~: b -> Apply f a :~: Apply g b apply Refl Refl = Refl axiom :: a :~: b axiom = unsafeCoerce Refl }}} When compiled without optimization, this program prints "`Refl`", as you would expect: {{{ $ /opt/ghc/8.6.3/bin/ghc -O0 Bug.hs -fforce-recomp [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... $ ./Bug Refl }}} However, when compiled with optimizations, it starts failing at runtime! {{{ $ /opt/ghc/8.6.3/bin/ghc -O Bug.hs -fforce-recomp [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... $ ./Bug Bug: Impossible case alternative }}} This behavior can be observed on all versions of GHC from 8.2.2 to HEAD. Interestingly, this program passes `-dcore-lint` on GHC 8.4.4 through HEAD, but on GHC 8.2.2, it fails `-dcore-lint`: {{{ $ /opt/ghc/8.6.3/bin/ghc -O Bug.hs -fforce-recomp -dcore-lint [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... $ /opt/ghc/8.2.2/bin/ghc -O Bug.hs -fforce-recomp -dcore-lint [1 of 1] Compiling Main ( Bug.hs, Bug.o ) *** Core Lint errors : in result of Simplifier *** <no location info>: warning: In a case alternative: (Refl cobox_a1UV :: (FmapSym0 :: (TyFun (f1_X2dk b_a2aC ~> g_a2aF (M1 f1_X2dk c_a2aD)) (f_a2aE (f1_X2dk b_a2aC) ~> f_a2aE (g_a2aF (M1 f1_X2dk c_a2aD))) -> *)) ~# (FmapSym0 :: (TyFun (f1_X2dk b_a2aC ~> g_a2aF (M1 f1_X2dk c_a2aD)) (f_a2aE (f1_X2dk b_a2aC) ~> f_a2aE (g_a2aF (M1 f1_X2dk c_a2aD))) -> *))) No alternatives for a case scrutinee in head-normal form: ($WRefl @ Any @ Any) `cast` (((:~:) (UnsafeCo nominal Any (f b ~> g (M1 f c))) (UnsafeCo nominal Any (FmapSym1 M1Sym0 .@#@$$$ TraverseSym1 i)) (UnsafeCo nominal Any (TraverseSym1 i .@#@$$$ M1Sym0)))_R :: ((Any :~: Any) :: *) ~R# (((FmapSym1 M1Sym0 .@#@$$$ TraverseSym1 i_a2aH) :~: (TraverseSym1 i_a2aH .@#@$$$ M1Sym0)) :: *)) }}} (The full Core Lint error is absolutely enormous, so I'll post it as a separate attachment.) The one thing about this program that might be considered strange is the use of `axiom = unsafeCoerce Refl`. I believe this should be a perfectly safe use of `unsafeCoerce`, but nevertheless, there is always the possibility that GHC is doing something unsightly when optimizing it. As one curiosity, if you mark `axiom` as `NOINLINE`, then the program produces a different result: {{{ $ /opt/ghc/8.6.3/bin/ghc -O Bug.hs -fforce-recomp -dcore-lint [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... $ ./Bug }}} The program simply prints a newline, for some odd reason. (It doesn't appear to throw an exception either, since `echo $?` yields `0`.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16310> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16247: GHC 8.6 Core Lint regression (Kind application error)
by GHC 12 Feb '19

12 Feb '19

#16247: GHC 8.6 Core Lint regression (Kind application error) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler | Version: 8.6.3 (Type checker) | Keywords: TypeInType | 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: -------------------------------------+------------------------------------- The following program produces a Core Lint error on GHC 8.6.3 and HEAD: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind data SameKind :: forall k. k -> k -> Type data Foo :: forall a k (b :: k). SameKind a b -> Type where MkFoo :: Foo sameKind }}} {{{ $ /opt/ghc/8.6.3/bin/ghc Bug.hs -dcore-lint [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) *** Core Lint errors : in result of CorePrep *** <no location info>: warning: In the type ‘forall k (a :: k) k (b :: k) (sameKind :: SameKind a b). Foo sameKind’ Kind application error in type ‘SameKind a_aWE b_aWG’ Function kind = forall k. k -> k -> * Arg kinds = [(k_aWF, *), (a_aWE, k_aWD), (b_aWG, k_aWF)] Fun: k_aWF (a_aWE, k_aWD) *** Offending Program *** <elided> MkFoo :: forall k (a :: k) k (b :: k) (sameKind :: SameKind a b). Foo sameKind }}} (Confusingly, the type of `MkFoo` is rendered as `forall k (a :: k) k (b :: k) (sameKind :: SameKind a b). Foo sameKind` in that `-dcore-lint` error, but I think it really should be `forall k1 (a :: k1) k2 (b :: k2) (sameKind :: SameKind a b). Foo sameKind`.) On GHC 8.4.4 and earlier, this simply produces an error message: {{{ $ /opt/ghc/8.4.4/bin/ghc Bug.hs -dcore-lint [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:9:13: error: • These kind and type variables: a k (b :: k) are out of dependency order. Perhaps try this ordering: k (a :: k) (b :: k) • In the kind ‘forall a k (b :: k). SameKind a b -> Type’ | 9 | data Foo :: forall a k (b :: k). SameKind a b -> Type where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16247> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16305: When should -Wmissed-specializations fire?
by GHC 12 Feb '19

12 Feb '19

#16305: When should -Wmissed-specializations fire? -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 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: -------------------------------------+------------------------------------- While working on a fix for #16282, I noticed: 1. that `-Wmissed-specializations` doesn't fire when the docs say it should 2. that the "probable fix" suggested when a warning does fire is highly suspect {{{ import Data.Map main :: IO () main = do let m = [] :: [Map String Bool] mapM_ print m }}} With GHC 8.4.3, 8.6.3, and HEAD: `ghc -O2 -Wmissed-specializations Main.hs` does *not* issue any warnings. However, `ghc -O2 -Wall-missed-specializations Main.hs` *does* create a warning: {{{ Main.hs: warning: [-Wall-missed-specialisations] Could not specialise imported function ‘Data.Map.Internal.$w$cshowsPrec’ when specialising ‘Data.Map.Internal.$fShowMap_$cshowsPrec’ Probable fix: add INLINABLE pragma on ‘Data.Map.Internal.$w$cshowsPrec’ }}} The docs for `-Wmissed-specializations` say, "warn when specialisation of an imported, overloaded function fails." Since `showsPrec` is an imported function, it seems that a warning should have been issued with `-Wmissed- specs`. My reading of the docs is that `-Wall-missed-specs` should output everything `-Wmissed-specs` does, along with any *local* overloaded and unspecialized functions. Moreover, the "Probable fix" is suspect. A warning recommending an `INLINABLE` pragma is issued depending on the output of `warnMissedSpec` in specialise/Specialise.hs. For `-Wall-missed-specs`, `warnMissedSpec` doesn't check if an INLINABLE pragma is already present, so the fix could be redundant. For `-Wmissed-specs`, `warnMissedSpecs` *only* issues a warning if there *is* any inline pragma (of one sort of another) on all the callers, making the `probable fix` definitely redundant. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16305> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16309: Flag to instruct GHC not to use an environment file
by GHC 12 Feb '19

12 Feb '19

#16309: Flag to instruct GHC not to use an environment file -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- As the [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.ht… #package-environments user manual] document, GHC looks for environment files in the current directory to tell it what packages to look for. There seems to be no way to disable this behavior (short of deleting or renaming the environment file). This causes trouble for me, as I expect `ghci` to mean the same thing no matter where I say it. Can we add a flag (perhaps `-no-package-env`) that tells GHC not to look for an environment file? Note that specifying a dummy package environment file doesn't work because we can't suppress the implicit `-hide-all- packages` that is triggered whenever using a package environment. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16309> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16308: testsuite driver is sensitive to registration of multiple boot package versions
by GHC 12 Feb '19

12 Feb '19

#16308: testsuite driver is sensitive to registration of multiple boot package versions -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- Currently `testsuite/tests/Makefile` generates the `--rootdir` flags to be passed by `runtests.py` by looking at the output of `ghc-pkg list`. In the case that the user has recently bumped their submodules this list may contain multiple versions of the same package. This will then result in the same `library/$LIB/tests` directory being passed to the testsuite driver more than once. The testsuite driver will then squawk a "There are multiple tests with this name" warning. It took a few minutes for Simon and I to work out why this was. We should do better here (at least in Hadrian). Either by: * Teaching the testsuite driver to deduplicate the `--rootdir` list * Using a more robust source for the list of tested packages -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16308> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16051: Cross compilation broken under Hadrian
by GHC 12 Feb '19

12 Feb '19

#16051: Cross compilation broken under Hadrian -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.8.1 Component: Build System | Version: 8.7 (Hadrian) | 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: -------------------------------------+------------------------------------- Hadrian falls over essentially immediately when cross-compiling: {{{ $ ./boot $ ./configure --target=aarch64-linux-gnu $ hadrian/build.cabal.sh -j32 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16051> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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