July 2018 - ghc-tickets

[GHC] #15367: Misleading error message when unboxed tuples used in sums without -XUnboxedTuples
by GHC 12 Jul '18

12 Jul '18

#15367: Misleading error message when unboxed tuples used in sums without -XUnboxedTuples -------------------------------------+------------------------------------- Reporter: osa1 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- {{{ $ cat lib.hs {-# LANGUAGE UnboxedSums #-} module Lib where type Foo = (# (# Int, Int #) | Int #) $ ghc lib.hs [1 of 1] Compiling Lib ( lib.hs, lib.o ) lib.hs:5:1: error: • Illegal unboxed tuple type as function argument: (# Int, Int #) • In the type synonym declaration for ‘Foo’ | 5 | type Foo = (# (# Int, Int #) | Int #) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} But there's nothing illegal about this type, we just need to enable `UnboxedTuples`. The error message is misleading. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15367> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14164: GHC hangs on type family dependency
by GHC 12 Jul '18

12 Jul '18

#14164: GHC hangs on type family dependency -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- {{{#!hs {-# Language TypeOperators, DataKinds, PolyKinds, KindSignatures, TypeInType, GADTs, TypeFamilyDependencies #-} import Data.Kind type Cat a = a -> a -> Type data SubList :: Cat [a] where SubNil :: SubList '[] '[] Keep :: SubList xs ys -> SubList (x:xs) (x:ys) Drop :: SubList xs ys -> SubList xs (x:ys) type family UpdateWith (ys'::[a]) (xs::[a]) (pf::SubList ys xs) = (res :: [a]) | res -> pf ys' xs where UpdateWith '[] '[] SubNil = '[] UpdateWith (y:ys) '[] SubNil = y:ys -- UpdateWith '[] (_:_) (Keep _) = '[] UpdateWith (y:ys) (_:xs) (Keep rest) = y:UpdateWith ys xs rest -- UpdateWith ys (x:xs) (Drop rest) = x:UpdateWith ys xs rest }}} seems to loop forever on the "`Renamer/typechecker`" {{{ $ ghci -ignore-dot-ghci -v /tmp/u.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help Glasgow Haskell Compiler, Version 8.3.20170605, stage 2 booted by GHC version 8.0.2 [...] *** Parser [Main]: !!! Parser [Main]: finished in 1.31 milliseconds, allocated 0.651 megabytes *** Renamer/typechecker [Main]: [hangs] }}} while {{{#!hs type family UpdateWith (ys'::[a]) (xs::[a]) (pf::SubList ys xs) = (res :: [a]) | res -> pf ys' xs where UpdateWith '[] '[] SubNil = '[] UpdateWith (y:ys) '[] SubNil = y:ys UpdateWith '[] (_:_) (Keep _) = '[] }}} immediately gives {{{ $ ghc -ignore-dot-ghci /tmp/u.hs [1 of 1] Compiling Main ( /tmp/u.hs, /tmp/u.o ) /tmp/u.hs:14:3: error: • Type family equations violate injectivity annotation: UpdateWith '[] '[] 'SubNil = '[] -- Defined at /tmp/u.hs:14:3 forall a (xs :: [a]) (_1 :: [a]) (_2 :: a) (_3 :: SubList xs _1). UpdateWith '[] (_2 : _1) ('Keep _3) = '[] -- Defined at /tmp/u.hs:16:3 • In the equations for closed type family ‘UpdateWith’ In the type family declaration for ‘UpdateWith’ | 14 | UpdateWith '[] '[] SubNil = '[] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ /tmp/u.hs:16:3: error: • Type family equation violates injectivity annotation. Type and kind variables ‘_2’, ‘_1’, ‘xs’, ‘_3’ cannot be inferred from the right-hand side. Use -fprint-explicit-kinds to see the kind arguments In the type family equation: forall a (xs :: [a]) (_1 :: [a]) (_2 :: a) (_3 :: SubList xs _1). UpdateWith '[] (_2 : _1) ('Keep _3) = '[] -- Defined at /tmp/u.hs:16:3 • In the equations for closed type family ‘UpdateWith’ In the type family declaration for ‘UpdateWith’ | 16 | UpdateWith '[] (_:_) (Keep _) = '[] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14164> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15330: Error message prints invisible kind arguments in a visible matter
by GHC 11 Jul '18

11 Jul '18

#15330: Error message prints invisible kind arguments in a visible matter -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 (Type checker) | Keywords: TypeInType | 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: -------------------------------------+------------------------------------- Consider the following program: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind import Data.Proxy data T :: forall a. a -> Type f1 :: Proxy (T True) f1 = "foo" f2 :: forall (t :: forall a. a -> Type). Proxy (t True) f2 = "foo" }}} This program doesn't typecheck (for good reason). The error messages, however, are a bit iffy: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:11:6: error: • Couldn't match expected type ‘Proxy (T 'True)’ with actual type ‘[Char]’ • In the expression: "foo" In an equation for ‘f1’: f1 = "foo" | 11 | f1 = "foo" | ^^^^^ Bug.hs:15:6: error: • Couldn't match expected type ‘Proxy (t Bool 'True)’ with actual type ‘[Char]’ • In the expression: "foo" In an equation for ‘f2’: f2 = "foo" • Relevant bindings include f2 :: Proxy (t Bool 'True) (bound at Bug.hs:15:1) | 15 | f2 = "foo" | ^^^^^ }}} Note that in the error message for `f1`, the type `T 'True` is printed correctly—the invisible `Bool` argument is omitted. However, in the error message for `f2`, this is not the case, as the type `t Bool 'True` is printed. That `Bool` is an invisible argument as well, and should not be printed without the use of, say, `-fprint-explicit-kinds`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15330> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15352: False kind errors with implicitly bound kinds in GHC 8.6
by GHC 11 Jul '18

11 Jul '18

#15352: False kind errors with implicitly bound kinds in GHC 8.6 -------------------------------------+------------------------------------- Reporter: aaronvargo | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 (Type checker) | 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: -------------------------------------+------------------------------------- This could be related to #15343. The following code fails to compile with GHC 8.6.0.20180627, but does compile with 8.4: {{{#!hs {-# LANGUAGE TypeInType #-} -- or PolyKinds {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeFamilies #-} import Data.Kind class C (x :: Type) (y :: k) where type F y }}} {{{ • Expected a type, but ‘k’ has kind ‘k’ • In the kind ‘k’ | 7 | class C (x :: Type) (y :: k) where | ^ }}} Yet all of the following slightly different examples still do compile: {{{#!hs -- remove `x` class C0 (y :: k) where type F0 y -- remove `F` class C1 (x :: Type) (y :: k) -- remove the kind annotation from `x` class C2 x (y :: k) where type F2 y -- switch the order of `x` and `y` class C3 (y :: k) (x :: Type) where type F3 y -- make `k` an explicit parameter, with or without a kind annotation class C4 k (x :: Type) (y :: k) where type F4 y class C5 (k :: Type) (x :: Type) (y :: k) where type F5 y -- add a new parameter *with no kind annotation* class C6 z (x :: Type) (y :: k) where type F6 y }}} Here's also my original example which failed to compile: {{{#!hs type Hom k = k -> k -> Type type family Ob (p :: Hom k) :: k -> Constraint class ( obP ~ Ob p , opP ~ Dom p , obQ ~ Ob q , opQ ~ Dom q , p ~ Dom f , q ~ Cod f ) => Functor' (obP :: i -> Constraint) (opP :: Hom i) (p :: Hom i) (obQ :: j -> Constraint) (opQ :: Hom j) (q :: Hom j) (f :: i -> j) where type Dom f :: Hom i type Cod f :: Hom j }}} {{{ • Expected a type, but ‘j’ has kind ‘k’ • In the first argument of ‘Hom’, namely ‘j’ In the kind ‘Hom j’ | 34 | type Cod f :: Hom j | ^ }}} The only way I can find to make this one compile is to make `i` and `j` explicit parameters with explicit kinds: {{{#!hs class ( obP ~ Ob p , opP ~ Dom p , obQ ~ Ob q , opQ ~ Dom q , p ~ Dom f , q ~ Cod f ) => Functor' (i :: Type) (j :: Type) (obP :: i -> Constraint) (opP :: Hom i) (p :: Hom i) (obQ :: j -> Constraint) (opQ :: Hom j) (q :: Hom j) (f :: i -> j) where type Dom f :: Hom i type Cod f :: Hom j }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15352> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15354: QuantifiedConstraints not fully described in manual
by GHC 10 Jul '18

10 Jul '18

#15354: QuantifiedConstraints not fully described in manual -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Documentation | Version: 8.5 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 pointed out in comment:4:ticket:15351, the section in the manual on `-XQuantifiedConstraints` says that an `=>` is essential in a quantified constraint. However, the following is accepted: {{{#!hs class C a foo :: (forall x. C x) => () foo = () }}} Note that there is no `=>` in the quantified constraint. We need to update the manual accordingly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15354> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14929: Program compiled with -O2 exhibits much worse performance
by GHC 10 Jul '18

10 Jul '18

#14929: Program compiled with -O2 exhibits much worse performance -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- A user on reddit reports that compiling the program with `-O2` makes his program use a lot more memory. https://www.reddit.com/r/haskell/comments/84qovv/an_example_of_code_where_g… It runs in constant memory without `-O2` and leaks memory with `-O2. It seems worth investigating as the example is quite small (< 1000 lines) and self-contained. https://github.com/luispedro/TestingNGLESS -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14929> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15339: Add function equality instance for finite functions to base
by GHC 10 Jul '18

10 Jul '18

#15339: Add function equality instance for finite functions to base -------------------------------------+------------------------------------- Reporter: madgen | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: | Version: 8.4.3 libraries/base | Keywords: base, | Operating System: Unknown/Multiple equality, function | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If the input type is bounded and enumerable and the result type can be compared for equality, functions can be checked for equality. Basically this instance: {{{#!hs instance (Bounded a, Enum a, Eq b) => Eq (a -> b) where f == g = all (\x -> f x == g x) [ minBound..maxBound ] }}} I often work with functions with finite domains and find [(a,b)] awkward. I thought this is generic enough that it might belong to base. I'd also submit a patch, but I couldn't quite figure out where it should live. GHC.Base doesn't have Enum and Bounded; Enum is not where -> or Eq are declared; Eq is not declared anywhere; and Data.Function is only for combinators. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15339> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14174: GHC panic with TypeInType and type family
by GHC 10 Jul '18

10 Jul '18

#14174: GHC panic with TypeInType and type family -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.2 Component: Compiler | Version: 8.2.1 (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: -------------------------------------+------------------------------------- This rather simple type family, {{{#!hs {-# LANGUAGE TypeFamilies, TypeOperators, TypeInType #-} module GenWhoops where import GHC.Generics type family GenComp k (x :: k) (y :: k) :: Ordering where GenComp ((x :+: y) p) ('L1 x) ('L1 y) = GenComp (x p) x y }}} produces the following panic: {{{ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.3.20170828 for x86_64-unknown-linux): piResultTy k_a1LK[tau:1] p_a1Lz[sk:1] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:949:35 in ghc:Type }}} This happens with both GHC 8.2.1 and something very close to HEAD. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14174> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12050: Allow haddock comments on non-record types
by GHC 10 Jul '18

10 Jul '18

#12050: Allow haddock comments on non-record types -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 (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: -------------------------------------+------------------------------------- There are a variety of cases I have found myself wanting to place haddock documentation on fields of non-record data types rather often in the past. The syntax for this might look like, {{{#!hs data Foo = Foo -- ^ A foo Int -- ^ how big is the foo? String -- ^ the name of the foo }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12050> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8822: Allow -- ^ Haddock syntax on record constructors
by GHC 10 Jul '18

10 Jul '18

#8822: Allow -- ^ Haddock syntax on record constructors -------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Parser) | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- Original ticket is on Haddock Trac [http://trac.haskell.org/haddock/ticket/144 here] which I'm opening here as it requires lexer/parser changes. The idea is that given something like {{{ -- | A tree with labeled internal nodes data Tree = Empty -- ^ Leaf | Branch -- ^ Internal node { label :: a -- ^ Node label , subtrees :: [Tree] -- ^ List of subtrees } }}} we'd like it to parse as the user would expect instead of failing. We're currently forced to do something like {{{ -- | A tree with labeled internal nodes data Tree = Empty -- ^ Leaf | -- | Internal node Branch { label :: a -- ^ Node label , subtrees :: [Tree] -- ^ List of subtrees } }}} which is quite ugly. I can't think of a reason why the first form wouldn't be allowed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8822> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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