August 2017 - ghc-tickets

[GHC] #9756: Warn about unnecessary unsafeCoerce
by GHC 05 Sep '17

05 Sep '17

#9756: Warn about unnecessary unsafeCoerce -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.9 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- `unsafeCoerce` has been around a lot longer than `coerce`, so older code tends to use it even if `coerce` could do the job. It would be nice if the type checker could produce a warning when it detected such a situation. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9756> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13779: Add more signature suppression control for dumps
by GHC 05 Sep '17

05 Sep '17

#13779: Add more signature suppression control for dumps -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.4.1 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: -------------------------------------+------------------------------------- I tend to find some type signatures essential when reading Core. However, `Generic`-heavy code can produce extremely large signatures. I suspect one or both of the following additional options could help: 1. An option to suppress non-top-level signatures, leaving top-level ones alone. 2. An option to suppress phantom type arguments in signatures. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13779> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13182: Rethinking dataToTag#
by GHC 05 Sep '17

05 Sep '17

#13182: Rethinking dataToTag# -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 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: -------------------------------------+------------------------------------- We currently use a primop `dataToTag#` that requires some careful handling because it can only be applied to something that has already been evaluated. We (now) mark it `can_fail` to prevent it from floating out, and then add a fix-up pass in CorePrep just in case things went wrong. Could we do something simpler? Suppose we had {{{#!hs -- The real primop, preferably not exported from *anywhere*, but at least documented as never to be used outside GHC. secretDataToTag# :: a -> Int# -- A wired-in safe version dataToTag# :: a -> Int# dataToTag# !a = secretDataToTag# a {-# NOINLINE dataToTag# #-} }}} Then `dataToTag#` could be inlined in CorePrep, just like `runRW#`. === Questions === How would this interact with float out? It should be perfectly safe to float out when its argument is known to be forced, but it seems likely we'll run into let/app invariant failures. What RULES do we (or should we) have for `dataToTag#`? How will this change affect them? My vague recollection is that we don't have any, but it would be pretty nice to apply something equivalent to case-of-known- constructor. Whenever `dataToTag#` is applied to a known constructor, we should be able to evaluate it. The earlier we do this the better it will inform simplification. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13182> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14131: Difference between newtype and newtype instance
by GHC 05 Sep '17

05 Sep '17

#14131: Difference between newtype and newtype instance -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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 works {{{#!hs {-# Language RankNTypes, PolyKinds, GADTs #-} newtype Nat :: (k -> *) -> (k -> *) -> * where Nat :: (forall xx. f xx -> g xx) -> Nat f g }}} but this {{{#!hs {-# Language RankNTypes, PolyKinds, GADTs, TypeFamilies #-} data family Nat :: k -> k -> * newtype instance Nat :: (k -> *) -> (k -> *) -> * where Nat :: (forall xx. f xx -> g xx) -> Nat f g }}} fails on GHC 8.3.20170815, and requires a `forall k.` to work {{{ $ ./ghc-stage2 -ignore-dot-ghci --interactive /tmp/kind.hs GHCi, version 8.3.20170815: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/kind.hs, interpreted ) /tmp/kind.hs:5:26: error: Not in scope: type variable ‘k’ | 5 | newtype instance Nat :: (k -> *) -> (k -> *) -> * where | ^ /tmp/kind.hs:5:38: error: Not in scope: type variable ‘k’ | 5 | newtype instance Nat :: (k -> *) -> (k -> *) -> * where | ^ Failed, 0 modules loaded. }}} Related to #12369? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14131> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13985: GHC 8.0 regression: ‘k’ is not in scope during type checking, but it passed the renamer
by GHC 05 Sep '17

05 Sep '17

#13985: GHC 8.0 regression: ‘k’ is not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: TypeFamilies | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: #13738 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE PolyKinds #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} module Bug where import Data.Proxy data family Fam data instance Fam = MkFam (forall (a :: k). Proxy a) }}} On GHC 8.0.1, 8.0.2, 8.2.1, and HEAD, this fails with a GHC internal error: {{{ $ /opt/ghc/8.2.1/bin/ghci Bug.hs GHCi, version 8.2.0.20170704: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:9:41: error: • GHC internal error: ‘k’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [r1vy :-> APromotionErr FamDataConPE] • In the kind ‘k’ In the type ‘(forall (a :: k). Proxy a)’ In the definition of data constructor ‘MkFam’ | 9 | data instance Fam = MkFam (forall (a :: k). Proxy a) | ^ }}} This is a regression, since on GHC 7.10.3, it did not crash: {{{ $ /opt/ghc/7.10.3/bin/ghci Bug.hs GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:9:21: Data constructor ‘MkFam’ has existential type variables, a context, or a specialised result type MkFam :: forall (k :: BOX). (forall (k :: BOX) (a :: k). Proxy a) -> Fam (Use ExistentialQuantification or GADTs to allow this) In the definition of data constructor ‘MkFam’ In the data instance declaration for ‘Fam’ }}} This smells like #13738, but no `TypeApplications` are involved here, so I decided to open a separate ticket to be safe. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13985> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9574: GHC Panic: No Skolem Info
by GHC 05 Sep '17

05 Sep '17

#9574: GHC Panic: No Skolem Info -------------------------------------+------------------------------------- Reporter: ian_mi | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- GHC 7.8.3 and from git both panic with Couldn't match kind ‘o1’ with ‘(,) o o’ ‘o1’ is untouchable inside the constraints (Object (c :><: c) a) bound by a type expected by the context: Object (c :><: c) a => Tagged a (c (FMap (ProductF c) a) (FMap (Proj2 c c) a)) at Product.hs:35:9-15ghc: panic! (the 'impossible' happened) (GHC version 7.9.20140908 for x86_64-unknown-linux): No skolem info: o1_a6XS I have not yet attempted to reduce the problem at all. The offending code is the use of fmap here: {{{#!hs proj2 :: forall (c :: o -> o -> *). ProductCategory c => NatTr (c :><: c) c (ProductF c) (Proj2 c c) proj2 = NatTr t where NatTr t = fmap (CompF Proj2 IdentityF) e e :: NatTr (c :><: c) (c :><: c) (Comp ('KProxy :: KProxy o) (Diag c) (ProductF c)) (IdentityF (c :><: c)) e = counit }}} fmap is defined as {{{#!hs fmap :: forall f (a :: o1) (b :: o1). Functor f ('KProxy :: KProxy (o1 -> o2)) => f -> Domain f a b -> Codomain f (FMap f a :: o2) (FMap f b :: o2) fmap _ = proxy morphMap (Proxy :: Proxy f) }}} while CompF is defined by {{{#!hs data CompF f g (k :: KProxy (o3 -> o4, o1 -> o2)) where CompF :: (Functor f ('KProxy :: KProxy (o3 -> o4)), Functor g ('KProxy :: KProxy (o1 -> o2))) => f -> g -> CompF f g ('KProxy :: KProxy (o3 -> o4, o1 -> o2)) }}} This makes some sense because there is a functional dependency between the functor and the kind proxy. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9574> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13988: GADT constructor with kind equality constraint quantifies unused existential type variables
by GHC 05 Sep '17

05 Sep '17

#13988: GADT constructor with kind equality constraint quantifies unused existential type variables -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Reproducible with GHC 8.0.1., 8.0.2, 8.2.1, or HEAD (but I'll use GHC 8.2.1 to show the results of `:type +v`): {{{ $ /opt/ghc/8.2.1/bin/ghci GHCi, version 8.2.0.20170704: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci λ> :set -XTypeInType -XGADTs -fprint-explicit-foralls λ> import Data.Kind λ> data Foo (a :: k) where MkFoo :: (k ~ Type) => Foo (a :: k) λ> :type +v MkFoo MkFoo :: forall k1 (a :: k1) k2 (k3 :: k2). k1 ~ * => Foo a }}} Note that `MkFoo` quantifies two extra existential type variables, `k2` and `k3` which are completely unused! Note that this does not occur if the `MkFoo` constructor uses an explicit `forall`: {{{ λ> :set -XScopedTypeVariables λ> data Foo (a :: k) where MkFoo :: forall k (a :: k). (k ~ Type) => Foo (a :: k) λ> :type +v MkFoo MkFoo :: forall k (a :: k). k ~ * => Foo a }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13988> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13105: Allow type families in RuntimeReps
by GHC 04 Sep '17

04 Sep '17

#13105: Allow type families in RuntimeReps -------------------------------------+------------------------------------- Reporter: goldfire | Owner: 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: -------------------------------------+------------------------------------- Conal Elliott provided me with this puzzle: {{{ type family RepRep a ∷ RuntimeRep class HasRep a where type Rep a ∷ TYPE (RepRep a) repr ∷ a → Rep a abst ∷ Rep a → a type instance RepRep Int = IntRep instance HasRep Int where type Rep Int = Int# abst n = I# n repr (I# n) = n }}} I think we should accept. However, doing so (even with my solution to #12809 complete) is hard, because we frequently consult a kind in order to determine a runtime representation. When that kind is `TYPE (RepRep Int)`, the code generator throws up its arms in despair. The solution here is either to teach the code generator how to normalise types (requiring propagating the `FamInstEnvs`) or to do a whole-program transformation at some point (zonker? desugarer? maybe we can wait until !CorePrep or even unarisation?) to change ids whose types have kinds like `TYPE (RepRep Int)` into ids with types with kinds like `TYPE IntRep`. But I don't want to let this hold me up at the moment, so I'm posting here as a reminder to revisit this problem. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13105> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12708: RFC: Representation polymorphic Num
by GHC 04 Sep '17

04 Sep '17

#12708: RFC: Representation polymorphic Num -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Core | Version: 8.0.1 Libraries | 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 can create a GHC proposal for this but I need a sanity check first {{{#!hs import Prelude hiding (Num (..)) import qualified Prelude as P import GHC.Prim import GHC.Types class Num (a :: Type k) where (+) :: a -> a -> a (-) :: a -> a -> a (*) :: a -> a -> a negate :: a -> a abs :: a -> a signum :: a -> a fromInteger :: Integer -> a instance Num Int# where (+) :: Int# -> Int# -> Int# (+) = (+#) (-) :: Int# -> Int# -> Int# (-) = (-#) (*) :: Int# -> Int# -> Int# (*) = (*#) negate :: Int# -> Int# negate = negateInt# ... fromInteger :: Integer -> Int# fromInteger (fromInteger -> I# int) = int instance Num Double# where (+) :: Double# -> Double# -> Double# (+) = (+##) (-) :: Double# -> Double# -> Double# (-) = (-##) (*) :: Double# -> Double# -> Double# (*) = (*##) negate :: Double# -> Double# negate = negateDouble# ... fromInteger :: Integer -> Double# fromInteger (fromInteger -> D# dbl) = dbl }}} Note how the `fromInteger` views aren't qualified? That's because we can branch on the kind and all of a sudden, all instances of old `Num` are instances of our `Num` {{{#!hs instance P.Num a => Num (a :: Type) where (+) = (P.+) (-) = (P.-) (*) = (P.*) negate = P.negate abs = P.abs signum = P.signum fromInteger = P.fromInteger }}} ---- Same with `Show` etc. etc. {{{#!hs class Show (a :: TYPE k) where show :: (a :: TYPE k) -> String instance P.Show a => Show (a :: Type) where show :: (a :: Type) -> String show = P.show instance Show Int# where show :: Int# -> String show int = show (I# int) instance Show Double# where show :: Double# -> String show dbl = show (D# dbl) }}} ---- What effects would this have? They are even printed the same by default {{{#!hs >>> :kind Prelude.Num Prelude.Num :: * -> Constraint >>> :kind Main.Num Main.Num :: * -> Constraint >>> :set -fprint-explicit-runtime-reps >>> :kind Main.Num Main.Num :: TYPE k -> Constraint }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12708> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13956: ghc panic compiling lame-0.1.1
by GHC 03 Sep '17

03 Sep '17

#13956: ghc panic compiling lame-0.1.1 -------------------------------------+------------------------------------- Reporter: uznx | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compiling the package lame-0.1.1 using cabal, with profiling: [2 of 2] Compiling Codec.Audio.LAME ( Codec/Audio/LAME.hs, dist/build/Codec/Audio/LAME.p_o ) ghc: panic! (the 'impossible' happened) (GHC version 8.2.0.20170704 for x86_64-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone lvl_soT9 To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 504681 Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/simplCore/SimplMonad.hs:199:31 in ghc:SimplMonad Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug This is a regression; the package compiles fine with GHC 8.0.2 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13956> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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