June 2017 - ghc-tickets

[GHC] #12949: Pattern coverage mistake
by GHC 06 Apr '18

06 Apr '18

#12949: Pattern coverage mistake -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I disabled syntax highlighting below; the bugs highlighting single quotes made the code unreadable. {{{ {-# LANGUAGE DataKinds, TypeFamilies, GADTs, TypeOperators, ScopedTypeVariables, ConstraintKinds, StandaloneDeriving #-} {-# OPTIONS_GHC -Wall #-} import Data.Constraint import Data.Type.Bool -- Bool singletons data Boolly b where Falsey :: Boolly 'False Truey :: Boolly 'True deriving instance Show (Boolly b) class KnownBool b where knownBool :: Boolly b instance KnownBool 'False where knownBool = Falsey instance KnownBool 'True where knownBool = Truey -- OrRel a b r expresses all the usual implications inherent -- in the statement that r ~ (a || b). type OrRel (a :: Bool) (b :: Bool) (r :: Bool) :: Constraint = (r ~ (a || b), If r (If (Not a) (b ~ 'True) (() :: Constraint), If (Not b) (a ~ 'True) (() :: Constraint)) (a ~ 'False, b ~ 'False)) -- Given known Bools, their disjunction is also known abr :: forall a b r p1 p2 . (OrRel a b r, KnownBool a, KnownBool b) => p1 a -> p2 b -> Dict (KnownBool r) abr _ _ = case knownBool :: Boolly a of Truey -> Dict Falsey -> case knownBool :: Boolly b of Truey -> Dict -- Problematic match Falsey -> Dict }}} The trouble is that GHC warns that the problematic match is redundant, which it is not. If I remove it, GHC ''fails'' to warn that the patterns are incomplete, which they are. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12949> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12938: Polykinded associated type family rejected on false pretenses
by GHC 04 Apr '18

04 Apr '18

#12938: Polykinded associated type family rejected on false pretenses -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If I say {{{ class HasRep a where type Rep a :: TYPE r }}} I get {{{ • Kind variable ‘r’ is implicitly bound in datatype ‘Rep’, but does not appear as the kind of any of its type variables. Perhaps you meant to bind it (with TypeInType) explicitly somewhere? Type variables with inferred kinds: a • In the class declaration for ‘HasRep’ }}} This definition should be accepted, though, as `r` is just an invisible parameter to the associated type family. (I don't know how ''useful'' this is, but it's not bogus.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12938> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12742: Instantiation of invisible type family arguments is too eager
by GHC 04 Apr '18

04 Apr '18

#12742: Instantiation of invisible type family arguments is too eager -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 module looks, to me, like it should be accepted: {{{ {-# LANGUAGE TypeInType, RankNTypes, TypeFamilies #-} module Bug where import Data.Kind type family F :: forall k2. (k1, k2) data T :: (forall k2. (Bool, k2)) -> Type type S = T F }}} But it's not. The problem is that `TcHsType.handle_tyfams` eagerly instantiates ''all'' invisible arguments to a type family at every occurrence. Instead, it should instantiate only those that are counted in the TF's arity -- that is, those "before the colon". Will fix. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12742> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13845: Runtime linker too eagerly checks for symbol names
by GHC 04 Apr '18

04 Apr '18

#13845: Runtime linker too eagerly checks for symbol names -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 8.0.1 System (Linker) | 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 discovered this bug in https://github.com/haskell- foundation/foundation/issues/326. Take this file: {{{#!hs module Main (main) where foreign import ccall "notAThing" notAThing :: IO () main :: IO () main = putStrLn "Hello, World!" }}} Compiling and running this file works without issue. But if you try to use the runtime linker, things go haywire: {{{ $ C:\Users\RyanGlScott\Software\ghc\inplace\bin\runghc Bug.hs ghc-stage2.exe: ^^ Could not load 'notAThing', dependency unresolved. See top entry above. Bug.hs: ByteCodeLink: can't find label During interactive linking, GHCi couldn't find the following symbol: notAThing This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org }}} This isn't just limited to Windows, since the same thing happens on Linux. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13845> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13330: forkIO has inconsistent behavior under optimization
by GHC 04 Apr '18

04 Apr '18

#13330: forkIO has inconsistent behavior under optimization -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Core | Version: 8.1 Libraries | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Troubleshooting the T4030 failure in SimonPJ's early-inline branch, Reid and I discovered that the problem showed up when the argument to `forkIO` was obviously bottom. He came up with a tiny test case that fails without Simon's changes: {{{#!hs main = forkIO undefined >> threadDelay 1000000 }}} It looks like the trouble is in the definition of `forkIO`: {{{#!hs forkIO :: IO () -> IO ThreadId forkIO action = IO $ \ s -> case (fork# action_plus s) of (# s1, tid #) -> (# s1, ThreadId tid #) where action_plus = catchException action childHandler }}} This seems to run into the trouble with `catchException` and strictness explained in `GHC.IO`. It would appear that the conservative fix would be to replace `catchException` with `catch`. Personally, I find it a bit surprising that `forkIO` doesn't force its `IO` argument before forking, but changing that behavior could break working code. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13330> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10016: UNPACK support for existentials
by GHC 03 Apr '18

03 Apr '18

#10016: UNPACK support for existentials -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.4 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Consider {{{ data Foo = forall a. Show a => Foo !a !a data Bar = Bar {-# UNPACK #-} !Foo }}} The UNPACK pragma should really be able to unpack the `Foo` field, so that (implementation-wise) it would be as if you'd declared `Bar` thus: {{{ data Bar = forall a. Show a => Bar !a !a }}} But currently we get {{{ Ignoring unusable UNPACK pragma on the first argument of ‘Bar’ }}} Suggested by Nicholas Clarke [https://www.haskell.org/pipermail/glasgow- haskell-users/2015-January/025590.html here]. Vaguely related tickets: #7647, #9214. But unlike those ones, this one looks quite feasible to me. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10016> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11186: Give strong preference to type variable names in scope when reporting hole contexts
by GHC 02 Apr '18

02 Apr '18

#11186: Give strong preference to type variable names in scope when reporting hole contexts -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (Type checker) | Keywords: typed-holes | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When using `ScopedTypeVariables` with typed holes, I want GHC to bend over backwards to preserve the names of type variables that the user has chosen to bring into scope. I can't immediately reproduce the situations I've run into recently where that hasn't happened, but sometimes I've had a signature like {{{#!hs foo :: forall bar . ... foo = ... _ ... }}} and yet the typed hole message shows that `bar` has been lost in unification and replaced by some unrelated name. I would very much prefer if this never happened. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11186> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10954: Add class/context information to typed hole relevant bindings
by GHC 02 Apr '18

02 Apr '18

#10954: Add class/context information to typed hole relevant bindings -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #9479 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC's typed hole messages don't currently include any known context information for relevant bindings. For example: {{{#!hs bar :: a ~ b => a -> b -> Int bar x y = _ }}} gets me {{{ Found hole ‘_’ with type: Int Relevant bindings include y :: b (bound at <interactive>:8:42) x :: a (bound at <interactive>:8:40) bar :: a -> b -> Int (bound at <interactive>:8:36) In the expression: _ In an equation for ‘bar’: bar x y = _ }}} The types `a` and `b` are not unified, and the `a ~ b` constraint is not shown. {{{#!hs foo :: Show a => a -> Int foo x = _ }}} gets me {{{ Found hole ‘_’ with type: Int Relevant bindings include x :: a (bound at <interactive>:4:36) foo :: a -> Int (bound at <interactive>:4:32) In the expression: _ In an equation for ‘foo’: foo x = _ }}} The `Show` constraint is lost. === What I want === I'd like context information for all type variables in known bindings, so I can see all the pieces available to help me fill in the hole. === Related ticket === In #9479, Dominique Devriese wants to see any constraints ''on'' an ambiguously-typed hole. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10954> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10267: Add support for typed holes in Template Haskell
by GHC 02 Apr '18

02 Apr '18

#10267: Add support for typed holes in Template Haskell -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.10.1 Component: Template | Operating System: Unknown/Multiple Haskell | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I want to be able to work with typed holes using Template Haskell. These are currently rejected: {{{#!hs [d| i :: a -> a i x = _ |] }}} {{{ Expression form not (yet) handled by Template Haskell _ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10267> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10822: GHC inconsistently handles \\?\ for long paths on Windows
by GHC 31 Mar '18

31 Mar '18

#10822: GHC inconsistently handles \\?\ for long paths on Windows -------------------------------------+------------------------------------- Reporter: snoyberg | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Windows Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- To demonstrate what I mean first: {{{ >ghc-pkg init \\?\c:\Users\michael\Desktop\some-pkg-db >dir \\?\c:\Users\Michael\Desktop\some-pkg-db Volume in drive \\?\c: is Windows8_OS Volume Serial Number is CEF7-874D Directory of \\?\c:\Users\Michael\Desktop\some-pkg-db 09/01/2015 09:38 AM <DIR> . 09/01/2015 09:38 AM <DIR> .. 09/01/2015 09:38 AM 40 package.cache 1 File(s) 40 bytes 2 Dir(s) 5,907,509,248 bytes free >ghc -package-db \\?\c:\Users\Michael\Desktop\some-pkg-db ghc: can't find a package database at \\?\c:\Users\Michael\Desktop\some- pkg-db }}} The problem: on Windows by default, paths are limited to 260 characters, which can become a real problem in practice when dealing with the standard library path hierarchy the Cabal library uses and any package with a decent name length. This was a real problem in practice, see: https://github.com/haskell/cabal/issues/2502 Windows has a workaround for this: you can prefix an absolute path with \\?\, see: https://msdn.microsoft.com/en- us/library/windows/desktop/aa365247%28v=vs.85%29.aspx#maxpath It would be very useful if such paths worked with GHC, but currently they do not. I don't yet know how deep the problem is. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10822> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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