April 2018 - ghc-tickets

[GHC] #14471: Certain do blocks cause TH to barf when ApplicativeDo is enabled
by GHC 12 Jul '18

12 Jul '18

#14471: Certain do blocks cause TH to barf when ApplicativeDo is enabled -------------------------------------+------------------------------------- Reporter: lexi.lambda | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.2.1 Haskell | Keywords: | 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 fails with an error: {{{#!hs {-# LANGUAGE ApplicativeDo #-} {-# LANGUAGE TemplateHaskell #-} main = $([|do return () return () return ()|]) }}} {{{ Exotic.hs:4:12: error: Exotic statement not (yet) handled by Template Haskell [return (); return (), return ()] }}} It only happens when `ApplicativeDo` is enabled. Furthermore, while this example is extremely minimal, this issue isn’t restricted to `ApplicativeDo`’s special handling of `return`. The following example produces the same error: {{{#!hs {-# LANGUAGE ApplicativeDo #-} {-# LANGUAGE TemplateHaskell #-} main = $([|do getLine getLine getLine|]) }}} {{{ Exotic.hs:4:12: error: Exotic statement not (yet) handled by Template Haskell [getLine; getLine, getLine] }}} This ''doesn’t'' happen with fewer than three statements in the `do` block, but it ''does'' happen with more. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14471> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15061: print022 testcase fails on i386
by GHC 12 Jul '18

12 Jul '18

#15061: print022 testcase fails on i386 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.1 Component: GHCi | 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: -------------------------------------+------------------------------------- CircleCI's i386 way is showing this failure of `print002` in the `ghci` way, {{{ Actual stderr output differs from expected: --- /dev/null 2018-04-18 16:05:23.479353000 +0000 +++ ./ghci.debugger/scripts/print022.run/print022.run.stderr.normalised 2018-04-19 13:53:47.685662431 +0000 @@ -0,0 +1 @@ +*** Exception: Prelude.chr: bad argument: 1493110744 *** unexpected failure for print022(ghci) }}} This is a bit frightening as it suggests that there is memory unsafety here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15061> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14808: GHC HEAD regression: GADT constructors no longer quantify tyvars in topological order
by GHC 12 Jul '18

12 Jul '18

#14808: GHC HEAD regression: GADT constructors no longer quantify tyvars in topological order -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.1 Component: Compiler | Version: 8.5 (Type checker) | Keywords: GADTs | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #14529, #14796 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Originally noticed in #14796. This program: {{{#!hs {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeApplications #-} module Bug where import Data.Kind data ECC ctx f a where ECC :: ctx => f a -> ECC ctx f a f :: [()] -> ECC () [] () f = ECC @() @[] @() }}} Typechecks in GHC 8.2.2 and 8.4.1, but not in GHC HEAD: {{{ $ ~/Software/ghc2/inplace/bin/ghc-stage2 Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:12:5: error: • Couldn't match type ‘()’ with ‘[]’ Expected type: [()] -> ECC (() :: Constraint) [] () Actual type: () [] -> ECC (() :: Constraint) () [] • In the expression: ECC @() @[] @() In an equation for ‘f’: f = ECC @() @[] @() | 12 | f = ECC @() @[] @() | ^^^^^^^^^^^^^^^ Bug.hs:12:10: error: • Expected kind ‘* -> *’, but ‘()’ has kind ‘*’ • In the type ‘()’ In the expression: ECC @() @[] @() In an equation for ‘f’: f = ECC @() @[] @() | 12 | f = ECC @() @[] @() | ^^ Bug.hs:12:14: error: • Expecting one more argument to ‘[]’ Expected a type, but ‘[]’ has kind ‘* -> *’ • In the type ‘[]’ In the expression: ECC @() @[] @() In an equation for ‘f’: f = ECC @() @[] @() | 12 | f = ECC @() @[] @() | ^^ }}} This is because the order of type variables for `ECC` has changed between GHC 8.4.1 and HEAD. In 8.4.1, it's {{{ $ /opt/ghc/8.4.1/bin/ghci Bug.hs -XTypeApplications -fprint-explicit- foralls GHCi, version 8.4.0.20180209: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Ok, one module loaded. λ> :type +v ECC ECC :: forall (ctx :: Constraint) (f :: * -> *) a. ctx => f a -> ECC ctx f a }}} In GHC HEAD, however, it's: {{{ $ ~/Software/ghc2/inplace/bin/ghc-stage2 --interactive Bug.hs -XTypeApplications -fprint-explicit-foralls GHCi, version 8.5.20180213: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Ok, one module loaded. λ> :type +v ECC ECC :: forall (f :: * -> *) a (ctx :: Constraint). ctx => f a -> ECC ctx f a }}} This regression was introduced in fa29df02a1b0b926afb2525a258172dcbf0ea460 (Refactor ConDecl: Trac #14529). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14808> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8581: Add support for explicitly-bidirectional pattern synonyms
by GHC 12 Jul '18

12 Jul '18

#8581: Add support for explicitly-bidirectional pattern synonyms ------------------------------------+------------------------------------- Reporter: cactus | Owner: cactus Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: 5144 | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Some patterns cannot, by themselves, be turned over into an expression, so they have to be defined as unidirectional. Maybe the most trivial example would be {{{ pattern P -> _ }}} Sometimes, however, it would be desirable to give an explicit way of turning these pattern synonyms into expressions. The PatternSynonyms wiki page has this example: {{{ import qualified Data.Sequence as Seq pattern Empty -> (Seq.viewl -> Seq.EmptyL) pattern x :< xs -> (Seq.viewl -> x Seq.:< xs) pattern xs :> x -> (Seq.viewr -> xs Seq.:> x) }}} It would make a ton of sense to be able to use this cons/snoc notation as "constructors" for `Seq`s. The proposed syntax for this {{{ pattern x :< xs -> (Seq.viewl -> x Seq.:< xs) where x :< xs = x Seq.<| xs }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8581> 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] #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] #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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[GHC] #14975: Refactor (Maybe Coercion)
by GHC 10 Jul '18

10 Jul '18

#14975: Refactor (Maybe Coercion) -------------------------------------+------------------------------------- Reporter: tdammers | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #11735 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As discussed here: https://phabricator.haskell.org/D4395#inline-34607 Define a type {{{#!hs data MCoercion = MRefl | MCo Coercion }}} This is isomorphic to {{{Maybe Coercion}}} but useful in a number of places, and super-helpful documentation. (eg {{{MRefl}}} is much more perspicuous than {{{Nothing}}}. Define this in {{{Coercion.hs}}} I think. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14975> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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