February 2016 - ghc-tickets

[GHC] #10361: DeriveAnyClass does not fill in associated type defaults
by GHC 01 Aug '17

01 Aug '17

#10361: DeriveAnyClass does not fill in associated type defaults -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I would expect `test1` and `test2` below to typecheck. This is a reduced test case from trying to use `DeriveAnyClass` on the `Generic` class of the `generics-sop` package, which unfortunately fails due to this bug. {{{ {-# LANGUAGE DeriveAnyClass, StandaloneDeriving, TypeFamilies #-} module Test where class C1 a where type T1 a type instance T1 a = Char class C2 a where -- equivalent to C1 type T2 a type instance T2 a = Char class C3 a where -- equivalent to C1, C2 type T3 a type instance T3 a = Char data A = B deriving C1 deriving instance C2 A instance C3 A -- fails -- test1 :: T1 A -- test1 = 'x' -- fails -- test2 :: T2 A -- test2 = 'x' -- succeeds test3 :: T3 A test3 = 'x' }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10361> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10447: DeriveFoldable rejects instances with constraints in last argument of data type
by GHC 01 Aug '17

01 Aug '17

#10447: DeriveFoldable rejects instances with constraints in last argument of data type -------------------------------------+------------------------------------- Reporter: | Owner: RyanGlScott | Status: new Type: bug | Milestone: Priority: normal | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #8678 Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Currently, the {{{-XDeriveFoldable}}} extension will reject any derived {{{Foldable}}} instance for a data type where the last argument of the type constructor is constrained. For example, using this data type from [http://git.haskell.org/ghc.git/blob/9f968e97a0de9c2509da00f6337b612dd72a038… TcDeriv.hs] as inspiration: {{{#!hs {-# LANGUAGE DeriveFoldable, GADTs, StandaloneDeriving #-} module DeriveFoldableRejected where data T a b where T4 :: Ord b => b -> T a b T5 :: b -> T b b T6 :: T a (b,b) deriving instance Foldable (T a) }}} Compiling {{{DeriveFoldableRejected.hs}}} with GHC 7.10 will currently fail: {{{ DeriveFoldableRejected.hs:9:1: Can't make a derived instance of ‘Foldable (T a)’: Constructor ‘T4’ must be truly polymorphic in the last argument of the data type In the stand-alone deriving instance for ‘Foldable (T a)’ Failed, modules loaded: none. }}} I don't think this restriction needs to apply to {{{Foldable}}} instances. Unlike {{{Functor}}} and {{{Traversable}}} instances, which require the last argument to be truly universal, {{{Foldable}}} instances can get away without this. To demonstrate, here's a slightly modified {{{T}}} data type, without the constraints: {{{#!hs {-# LANGUAGE DeriveFoldable, GADTs, StandaloneDeriving #-} {-# OPTIONS_GHC -ddump-deriv #-} module DeriveFoldableLegal where data T a b where T45 :: b -> T a b T6 :: T a b deriving instance Foldable (T a) }}} The output of {{{-ddump-deriv}}} is: {{{ Derived instances: instance Data.Foldable.Foldable (DeriveFoldableRejected.T a_aDc) where Data.Foldable.foldr f_aDd z_aDe (DeriveFoldableRejected.T45 a1_aDf) = f_aDd a1_aDf z_aDe Data.Foldable.foldr f_aDg z_aDh DeriveFoldableRejected.T6 = z_aDh Data.Foldable.foldMap f_aDi (DeriveFoldableRejected.T45 a1_aDj) = f_aDi a1_aDj Data.Foldable.foldMap f_aDk DeriveFoldableRejected.T6 = GHC.Base.mempty }}} Copying this back into {{{DeriveFoldableRejected.hs}}} (after some cleanup): {{{#!hs {-# LANGUAGE DeriveFoldable, GADTs, StandaloneDeriving #-} module DeriveFoldableRejected where data T a b where T4 :: Ord b => b -> T a b T5 :: b -> T b b T6 :: T a (b,b) instance Foldable (T a) where foldr f z (T4 a) = f a z foldr f z (T5 a) = f a z foldr f z T6 = z foldMap f (T4 a) = f a foldMap f (T5 a) = f a foldMap f T6 = mempty }}} reveals that it will compile correctly with the generated code. Therefore, it seems like the check for universality in the last type argument shouldn't be used in {{{-XDeriveFoldable}}}. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10447> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10524: PolyKinds doesn't interact well with DeriveFunctor
by GHC 01 Aug '17

01 Aug '17

#10524: PolyKinds doesn't interact well with DeriveFunctor -------------------------------------+------------------------------------- Reporter: | Owner: RyanGlScott | Status: new Type: bug | Milestone: Priority: normal | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Using {{{PolyKinds}}} and {{{DeriveFunctor}}} in tandem on GHC 7.10.2-rc1 will cause a kind incompatibility in certain cases: {{{ GHCi, version 7.10.1.20150612: http://www.haskell.org/ghc/ :? for help λ> :set -XPolyKinds -XDeriveFunctor -ddump-deriv λ> newtype Compose f g a = Compose (f (g a)) deriving Functor ==================== Derived instances ==================== Derived instances: instance forall (k_axa :: BOX) (f_axb :: k_axa -> *) (g_axc :: * -> k_axa). (GHC.Base.Functor f_axb, GHC.Base.Functor g_axc) => GHC.Base.Functor (Ghci1.Compose f_axb g_axc) where GHC.Base.fmap f_axd (Ghci1.Compose a1_axe) = Ghci1.Compose (GHC.Base.fmap (GHC.Base.fmap f_axd) a1_axe) Generic representation: Generated datatypes for meta-information: Representation types: <interactive>:3:52: Kind incompatibility when matching types: f0 :: * -> * f :: k -> * Expected type: f (g b) Actual type: f0 (f1 b) Relevant bindings include a1 :: f (g a) (bound at <interactive>:3:52) fmap :: (a -> b) -> Compose f g a -> Compose f g b (bound at <interactive>:3:52) In the first argument of ‘Compose’, namely ‘fmap (fmap f) a1’ In the expression: Compose (fmap (fmap f) a1) When typechecking the code for ‘fmap’ in a derived instance for ‘Functor (Compose f g)’: To see the code I am typechecking, use -ddump-deriv }}} A workaround is to use {{{StandaloneDeriving}}}: {{{ λ> :set -XStandaloneDeriving λ> newtype Compose f g a = Compose (f (g a)) λ> deriving instance (Functor f, Functor g) => Functor (Compose f g) ==================== Derived instances ==================== Derived instances: instance (GHC.Base.Functor f_ayO, GHC.Base.Functor g_ayP) => GHC.Base.Functor (Ghci1.Compose f_ayO g_ayP) where GHC.Base.fmap f_ayQ (Ghci1.Compose a1_ayR) = Ghci1.Compose (GHC.Base.fmap (GHC.Base.fmap f_ayQ) a1_ayR) Generic representation: Generated datatypes for meta-information: Representation types: }}} This problem does not seem to occur in GHC HEAD, however: {{{ GHCi, version 7.11.20150608: http://www.haskell.org/ghc/ :? for help λ> :set -XPolyKinds -XDeriveFunctor -ddump-deriv λ> newtype Compose f g a = Compose (f (g a)) deriving Functor ==================== Derived instances ==================== Derived instances: instance forall (k_a148 :: BOX) (f_a149 :: k_a148 -> *) (g_a14a :: * -> k_a148). (GHC.Base.Functor f_a149, GHC.Base.Functor g_a14a) => GHC.Base.Functor (Ghci3.Compose f_a149 g_a14a) where GHC.Base.fmap f_a14b (Ghci3.Compose a1_a14c) = Ghci3.Compose (GHC.Base.fmap (GHC.Base.fmap f_a14b) a1_a14c) Generic representation: Generated datatypes for meta-information: Representation types: }}} Can this fix be backported in time for GHC 7.10.2? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10524> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10561: "deriving (Functor)" on a polykinded type produces ill-kinded instance
by GHC 01 Aug '17

01 Aug '17

#10561: "deriving (Functor)" on a polykinded type produces ill-kinded instance -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Arose in #10524, and new since 7.10. {{{ rwbarton@morphism:/tmp$ ~/ghc/inplace/bin/ghc-stage2 --interactive GHCi, version 7.11.20150615: http://www.haskell.org/ghc/ :? for help Prelude> :set -XPolyKinds -XDeriveFunctor -ddump-deriv -fprint-explicit- kinds Prelude> newtype Compose f g a = Compose (f (g a)) deriving Functor ==================== Derived instances ==================== Derived instances: instance forall (k_and :: BOX) (f_ane :: k_and -> *) (g_anf :: * -> k_and). (GHC.Base.Functor f_ane, GHC.Base.Functor g_anf) => GHC.Base.Functor (Ghci1.Compose k_and * f_ane g_anf) where GHC.Base.fmap f_ang (Ghci1.Compose a1_anh) = Ghci1.Compose (GHC.Base.fmap (GHC.Base.fmap f_ang) a1_anh) Generic representation: Generated datatypes for meta-information: Representation types: Prelude> :i GHC.Base.Functor class Functor (f :: * -> *) where [...] }}} The context `(GHC.Base.Functor f_ane, GHC.Base.Functor g_anf)` is ill- kinded except when `k_and = *`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10561> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10835: Regression in standalone Data deriving for phantom types
by GHC 01 Aug '17

01 Aug '17

#10835: Regression in standalone Data deriving for phantom types -------------------------------------+------------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Thise code {{{#!hs {-# LANGUAGE DeriveDataTypeable, StandaloneDeriving, PolyKinds #-} module M where import Data.Data import Data.Typeable data Phantom t = Phantom deriving Typeable deriving instance Typeable t => Data (Phantom t) }}} compiles with 7.8.4 but not with 7.10.2. The error is {{{ data.hs:8:1: Could not deduce (Typeable Phantom) arising from the superclasses of an instance declaration from the context (Typeable t) bound by the instance declaration at data.hs:8:1-48 In the instance declaration for ‘Data (Phantom t)’ }}} PolyKinds here is a hack I came up with to make this compile with 7.8; but ideally, this code should compile whether PolyKinds is enabled or not. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10835> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11396: deriving Ix with custom ifThenElse causes "Bad call to tagToEnum#"
by GHC 01 Aug '17

01 Aug '17

#11396: deriving Ix with custom ifThenElse causes "Bad call to tagToEnum#" -------------------------------------+------------------------------------- Reporter: Lemming | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-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: -------------------------------------+------------------------------------- {{{ $ cat IfThenElseIx.hs {-# LANGUAGE RebindableSyntax #-} module IfThenElseIx where import Data.Ix (Ix, ) import Prelude ifThenElse :: Bool -> a -> a -> a ifThenElse True x _ = x ifThenElse False _ x = x data T = A | B deriving (Eq, Ord, Ix) $ ghci-8.0.0.20160109 IfThenElseIx.hs GHCi, version 8.0.0.20160109: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling IfThenElseIx ( IfThenElseIx.hs, interpreted ) IfThenElseIx.hs:13:35: error: • Bad call to tagToEnum# at type a_a2ky Specify the type by giving a type signature e.g. (tagToEnum# x) :: Bool • In the second argument of ‘ifThenElse’, namely ‘(GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#))’ In the expression: if (GHC.Prim.tagToEnum# (c# GHC.Prim.>=# a#)) then (GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#)) else False In a case alternative: c# -> if (GHC.Prim.tagToEnum# (c# GHC.Prim.>=# a#)) then (GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#)) else False When typechecking the code for ‘GHC.Arr.inRange’ in a derived instance for ‘Ix T’: To see the code I am typechecking, use -ddump-deriv Failed, modules loaded: none. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11396> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11174: Traversable can't be derived for datatypes with unboxed arguments
by GHC 01 Aug '17

01 Aug '17

#11174: Traversable can't be derived for datatypes with unboxed arguments -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- Unlike `Functor` and `Foldable`, `Traversable` cannot be derived for datatypes that contain arguments with unboxed types. A simple example: {{{#!hs {-# LANGUAGE DeriveTraversable, MagicHash #-} import GHC.Prim (Int#) data IntHash a = IntHash Int# deriving (Functor, Foldable, Traversable) }}} The generated `Traversable` instance reveals the issue: {{{#!hs instance Traversable IntHash where traverse f (IntHash a1) = fmap IntHash (pure a1) }}} {{{ Couldn't match kind `*' with `#' When matching types a0 :: * Int# :: # Expected type: a0 -> IntHash b Actual type: Int# -> IntHash b In the first argument of `fmap', namely `IntHash' In the expression: fmap IntHash (pure a1) When typechecking the code for `traverse' in a derived instance for `Traversable IntHash': To see the code I am typechecking, use -ddump-deriv }}} We have to avoid calling `pure` on `a1`, since `pure` expects an argument with a `*`-kinded type, not a `#`-kinded one. One way to fix this would be restructuring the derived `traverse` implementation such that unboxed arguments are moved to the function initially lifted with `pure`, and doing nothing with them later. To better articulate what I mean, envision something like this: {{{#!hs data IntHash2 a = IntHash2 Int# a (IntHash2 a) Int# deriving (Functor, Foldable) }}} Then a derived `Traversable` instance that would typecheck would be: {{{#!hs instance Traversable IntHash2 where traverse f (IntHash2 a1 a2 a3 a4) = pure (\x2 x3 -> IntHash2 a1 x2 x3 a4) <*> f a2 <*> traverse f a3 }}} Conceptually, this doesn't sound hard to implement. The tricky part is figuring out how much of the existing `Functor`/`Foldable`/`Traversable` deriving machinery would need to be tweaked to make this work. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11174> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9020: Massive blowup of code size on trivial program
by GHC 31 Jul '17

31 Jul '17

#9020: Massive blowup of code size on trivial program ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The test `simplCore/should_compile/simpl015` was leading to massive compile times. This is weird: it looks like: {{{ main = do { return () ; return () ... hundreds more times ... ; return () } }}} It turns out that the cause was over-eager eta-expansion. Each `return ()` gives a top-level PAP thus {{{ lvl17 :: IO () lvl17 = returnIO () }}} But these definitions are then eta-expanded, thus: {{{ lvl17 = ((\eta. returnIO () |> sym g) eta) |> g where g :: State# RealWorld -> (# State# RealWorld, () #) ~ IO () }}} Now in general it makes sense to eta-expand through newtypes (as is done here), because it exposes more lambadas. But it really doesn't make sense to eta-expand a PAP like this. Fortunately the fix is easy: use `exprArity` rather than `manifestArity` in `SimplUtils.tryEtaExpandRhs`. The effect on `simpl015` is dramatic: compiler allocation drops from 6.6G to 812M; and residency drops from 1.8G to 45M. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9020> 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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[GHC] #10684: Error cascade when unrelated class derivation fails
by GHC 25 Jul '17

25 Jul '17

#10684: Error cascade when unrelated class derivation fails -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Pretty minor bug, but I thought I'd point it out: {{{ module A where import Data.Typeable data A = A deriving (Show, Typeable) data B = B A deriving (Show) }}} I get two errors when I expect one: {{{ A.hs:3:28: Can't make a derived instance of `Typeable A': You need -XDeriveDataTypeable to derive an instance for this class In the data declaration for `A' A.hs:4:24: No instance for (Show A) arising from the 'deriving' clause of a data type declaration Possible fix: add an instance declaration for (Show A) or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Show B) }}} The failed Typeable derivation also causes the Show derivation to fail, which causes an error later in the file. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10684> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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