October 2017 - ghc-tickets

[GHC] #9725: Constraint deduction failure
by GHC 03 Oct '17

03 Oct '17

#9725: Constraint deduction failure -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: GHC Difficulty: Unknown | rejects valid program Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I get a strange error message like this {{{ [1 of 1] Compiling Main ( 08-10.hs, interpreted ) 08-10.hs:254:33: Could not deduce (KnownLoc (ent par1 a)) arising from a use of ‘Hidden'’ from the context (List ConfFamily ts) bound by the type signature for locAware :: List ConfFamily ts => (forall (i :: k). KnownLoc (ent par i) => ConfFamily (Facility (ent par i)) ts) -> Con ConfFamily (On ent par) at 08-10.hs:251:13-160 or from (ent par a ~ 'Monitor par1 mp, KnownLoc ('Monitor par1 mp)) bound by a pattern with constructor MonitorF :: forall (par :: Entity) (mp :: MonitorPoint). KnownLoc ('Monitor par mp) => String -> String -> Observer -> Bool -> Facility ('Monitor par mp), in an equation for ‘h’ at 08-10.hs:254:19-28 In the expression: Hidden' (d f) In an equation for ‘h’: h (Hide f@(MonitorF {})) = Hidden' (d f) In an equation for ‘locAware’: locAware descr = Abstr h where h :: (ent `On` par) -> ConfFamily (ent `On` par) ts h (Hide f@(MonitorF {})) = Hidden' (d f) d :: KnownLoc (ent par i) => Facility (ent par i) -> ConfFamily (Facility (ent par i)) ts d _ = descr Failed, modules loaded: none. }}} I have many language extensions active, such as, `DataKinds`, `ScopedTypeVariables`, etc. If somebody says this indeed looks like a bug, then I'll try to post a minimal reproduction case. ** My reasoning goes like this ** Here are the relevant facts that GHC figured out from a GADT pattern match: `(ent par a ~ 'Monitor par1 mp, KnownLoc ('Monitor par1 mp))` From this I discover these equalities: {{{ ent === 'Monitor (*) par === par1 (**) a === mp (***) }}} Substituring `(*)`^-1^ and `(***)`^-1^ into the given `KnownLoc ('Monitor par1 mp)` results in the desired `KnownLoc (ent par1 a)` Looks like a bug, right? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9725> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13819: GHC Panics
by GHC 03 Oct '17

03 Oct '17

#13819: GHC Panics -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE DeriveFunctor, TypeApplications #-} -- {-# Language ViewPatterns #-} -- {-# Language InstanceSigs, ViewPatterns, TupleSections, GeneralizedNewtypeDeriving, TemplateHaskell, LambdaCase #-} module D where import Data.Coerce import Control.Applicative newtype A a = A (IO a) deriving Functor instance Applicative A where pure = pure @(_ -> WrappedMonad A _) @(_ -> A _) pure instance Monad A where }}} causes a panic {{{ $ ghci -ignore-dot-ghci /tmp/a.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling D ( /tmp/a.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.3.20170605 for x86_64-unknown-linux): repSplitAppTys w0_a1xc[tau:4] WrappedMonad A w0_a1xe[tau:4] [] 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/types/Type.hs:809:9 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13819> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14308: GHC panic with invalid expression
by GHC 03 Oct '17

03 Oct '17

#14308: GHC panic with invalid expression ----------------------------------------+--------------------------------- Reporter: d6e | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- Hi, I recently discovered this expression causes GHC to panic. Shouldn't it handle this more gracefully? Perhaps saying something like "That expression is not valid. <Further Explanation>" Invalid expression: {{{#!hs g :: (a->b) a }}} {{{ Prelude> g :: (a->b) a ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-apple-darwin): repSplitAppTys a_a1Lz[sk:1] b_a1LA[sk:1] [] 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/types/Type.hs:808:9 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14308> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14110: GHC Panic on over-saturated associated type family
by GHC 03 Oct '17

03 Oct '17

#14110: GHC Panic on over-saturated associated type family -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- If we over-saturate a type family {{{#!hs {-# Language TypeFamilies, ScopedTypeVariables, PolyKinds, DataKinds #-} import Data.Kind class R (c :: k -> Constraint) where type R_ (c :: k -> Constraint) :: k -> Type instance R Eq where type R_ Eq a = a -> a -> Bool }}} we get {{{ $ ghci -ignore-dot-ghci test.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( test.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.3.20170605 for x86_64-unknown-linux): repSplitAppTys a_a2qu[sk:1] a_a2qu[sk:1] -> Bool [] 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/types/Type.hs:809:9 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14110> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14232: Invalid type signature prokoves error in GHCi
by GHC 03 Oct '17

03 Oct '17

#14232: Invalid type signature prokoves error in GHCi -------------------------------------+------------------------------------- Reporter: walling | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.2.1 Keywords: | Operating System: MacOS X Architecture: x86_64 | Type of failure: Poor/confusing (amd64) | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I create and save a file with the following content (notice the missing arrow `->`): {{{#!hs f :: (String -> a) String -> a f g s = g s }}} ... it outputs this snippet in GHCi (copy-pasted from terminal): {{{ $ ghci bug.hs GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( Playground/bug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-apple-darwin): repSplitAppTys String a_a1pl[sk:1] [] 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/types/Type.hs:808:9 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > Leaving GHCi. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14232> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14306: pretty-printer missing parens for infix class declaration
by GHC 03 Oct '17

03 Oct '17

#14306: pretty-printer missing parens for infix class declaration -------------------------------------+------------------------------------- Reporter: alanz | 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: #14289 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs class (a `C` b) c }}} Is pretty printed as {{{#!hs class a `C` b c }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14306> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12759: Latest Debian GCC breajs GHC
by GHC 02 Oct '17

02 Oct '17

#12759: Latest Debian GCC breajs GHC ----------------------------------------+-------------------------- Reporter: erikd | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux Architecture: Unknown/Multiple | Type of failure: Other Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+-------------------------- Just got `gcc (Debian 6.2.0-9) 6.2.0 20161019` in a recent upgrade (Debian Testing) and now: {{{ > cat hello.hs main :: IO () main = putStrLn "Hello" > ghc hello.hs -o hello [1 of 1] Compiling Main ( hello.hs, hello.o ) Linking hello ... /usr/bin/ld: hello.o: relocation R_X86_64_32S against symbol `stg_bh_upd_frame_info' \ can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: /usr/lib/ghc-8.0/lib/base-4.9.0.0/libHSbase-4.9.0.0.a(Base__166.o): \ relocation R_X86_64_32S against symbol `stg_bh_upd_frame_info' can not be used when \ making a shared object; recompile with -fPIC .... }}} The previous version of gcc in Debian Testing (gcc (Debian 6.2.0-6) 6.2.0 20161010) is fine. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12759> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13884: To an automatic compilation of file-header LANGUAGE pragmas in GHC.
by GHC 02 Oct '17

02 Oct '17

#13884: To an automatic compilation of file-header LANGUAGE pragmas in GHC. -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I wrote this little piece of code to show that the compiler could very well execute the pragma by itself without being ordered to do so.\\ {{{ module Testfoo where import Language.Haskell.TH.Lib import Data.Kind tup = $(tupE $ take 4 $ cycle [ [| "hi" |] , [| 5 |] ]) data T = MkT (forall a. [a] -> [a]) answer_read = show (read @Int "3") data Foo (a :: Type) (b :: Type) where MkFoo :: (a ~ Int, b ~ Char) => Foo a b data family Song (a :: k) }}} By compiling the code without the Pragmas, GHC responds:\\ * 1) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:13:7: error: parse error on input `$' Perhaps you intended to use TemplateHaskell\\ * 2) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:15:23: error: Illegal symbol '.' in type Perhaps you intended to use {{{RankNTypes}}} or a similar language extension to enable explicit-forall syntax: forall <tvs>.<type>\\ * 3) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:19:16: error: Illegal kind signature: `Type' Perhaps you intended to use KindSignatures In the data type declaration for `Foo' testfoo.hs:19:28: error: Illegal kind signature: `Type' Perhaps you intended to use KindSignatures In the data type declaration for `Foo' testfoo.hs:22:1: error: Unexpected kind variable `k' Perhaps you intended to use {{{PolyKinds}}} In the declaration for type family `Song' testfoo.hs:22:24: error: Illegal kind signature: `k' Perhaps you intended to use KindSignatures In the declaration for type family `Song'\\ * 4) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:18:21: error: Pattern syntax in expression context: read@Int Did you mean to enable {{{TypeApplications}}}?\\ * 5) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:20:1: error: * Illegal generalised algebraic data declaration for `Foo' (Use {{{GADTs}}} to allow GADTs) * In the data declaration for `Foo'\\ * 6) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) testfoo.hs:23:1: error: * Illegal family declaration for `Song' Use {{{TypeFamilies}}} to allow indexed type families * In the data family declaration for `Song'\\ * 7) c:\Testghc>ghc testfoo.hs [1 of 1] Compiling Testfoo ( testfoo.hs, testfoo.o ) c:\Testghc>\\ Here is the code once completed. {{{ {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeFamilies #-} module Testfoo where import Language.Haskell.TH.Lib import Data.Kind tup = $(tupE $ take 4 $ cycle [ [| "hi" |] , [| 5 |] ]) data T = MkT (forall a. [a] -> [a]) answer_read = show (read @Int "3") data Foo (a :: Type) (b :: Type) where MkFoo :: (a ~ Int, b ~ Char) => Foo a b data family Song (a :: k) }}} As you may notice, GHC suggests the appropriate pragma.\\ If we add manually in the code the Pragmas one after the other and we arrive at the end, the code is fully compiled without error.\\ The compiler could do this alone.\\ We could test it using a "-auto" option on the compiler command line.\\ This is a start to the compiler automation technology, what do you think of that? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13884> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9198: large performance regression in type checker speed in 7.8
by GHC 02 Oct '17

02 Oct '17

#9198: large performance regression in type checker speed in 7.8 -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: Compile-time Architecture: Unknown/Multiple | performance bug Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- it was recently demonstrated on the haskell-cafe mailing list that the following code takes measurably longer to type check in GHC 7.8.2 than in GHC 7.6. http://www.haskell.org/pipermail/haskell-cafe/2014-June/114562.html the program example is as follows {{{ begin cont = cont (return ()) a m =cont (m >> putstrn "a") end m = m main = begin a a a a a a a a a a a a a a a a a end }}} takes about a second to type check in ghc 7.8, and is "instant" in 7.6 () each additional a doubles the time to type check the program {{{ main = begin a a a a a a a a a a a a a a a a a a a a a a a a end }}} takes longer than I have the patience to wait :) (so more than 5 seconds) the author of the email notes that a related program {{{ main = id id id id id id id id id id id id id id id id id id id id id id (return ()) }}} has the exponential complexity in both 7.8.2 and 7.6.2 This It could very well be that some of the type checker changes between 7.8 and 7.6 enlarged the space of programs that trip up exponential worst case behavior, but one way or another understanding *why* this happened -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9198> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13397: Optimise calls to tagToEnum#
by GHC 02 Oct '17

02 Oct '17

#13397: Optimise calls to tagToEnum# -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) 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: -------------------------------------+------------------------------------- Ever since we started using `Int#` to represent booleans unboxed (see [wiki:PrimBool]) we have had lots of code looking like {{{ case tagToEnum# (a ># b) of False -> e1 True -> e2 }}} It would be better (less code to optimise, more straightforward, more direct) to optimise this to {{{ case a ># b of DEFAULT -> e1 1# -> e2 }}} Happily, we already have a nice spot to do so: the `caseRules` function in `SimplUtils`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13397> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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