May 2017 - ghc-tickets

[GHC] #13651: Invalid redundant pattern matches with -XTypeFamilyDependencies
by GHC 06 May '17

06 May '17

#13651: Invalid redundant pattern matches with -XTypeFamilyDependencies -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple InjectiveFamilies | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code triggers a warning about a redundant pattern match for `foo`: {{{ {-# LANGUAGE TypeFamilies, TypeFamilyDependencies #-} type family F r s = f | f -> r s type instance F (Bar h (Foo r)) (Bar h (Foo s)) = Bar h (Bar r s) data Bar s b data Foo a foo :: (F cr cu ~ Bar h (Bar r u), F cu cs ~ Bar (Foo h) (Bar u s)) => Bar h (Bar r u) -> Bar (Foo h) (Bar u s) -> Foo (cr -> cs) foo = undefined }}} {{{ warning: [-Woverlapping-patterns] Pattern match is redundant In an equation for ‘foo’: foo = .. }}} This warning seems invalid to me: I'm not sure how a single definition could constitute a redundant pattern match. Moreover, if I try to address the warning by removing the "redundant" pattern, the code (of course) fails to compile because there is no accompanying binding for the signature of `foo`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13651> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12156: -fdefer-typed-holes causes panic on unbound variable
by GHC 06 May '17

06 May '17

#12156: -fdefer-typed-holes causes panic on unbound variable -------------------------------------+------------------------------------- Reporter: osa1 | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- {{{#!haskell module Main where main = do print v return () }}} Compile it without {{{-fdefer-typed-holes}}} and it fails as expected: {{{ ➜ hole_bug ghc --make Main.hs -fforce-recomp [1 of 1] Compiling Main ( Main.hs, Main.o ) Main.hs:4:11: error: Variable not in scope: v }}} Adding {{{-fdefer-typed-holes}}} is causing a panic instead of runtime error: {{{ ➜ hole_bug ghc --make Main.hs -fforce-recomp -fdefer-typed-holes [1 of 1] Compiling Main ( Main.hs, Main.o ) Main.hs:4:11: warning: [-Wtyped-holes] Variable not in scope: v ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): StgCmmEnv: variable not found $dShow_aKo local binds for: $trModule $trModule1_r16k $trModule2_r16s sat_s16x sat_s16z Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Tried with: 8.0.1, HEAD as of today. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12156> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9557: Deriving instances is slow
by GHC 06 May '17

06 May '17

#9557: Deriving instances is slow -------------------------------------+------------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Let's take [https://raw.githubusercontent.com/haskell-suite/haskell-src- exts/8e0153d33b66add96fd5606614ce7938d2029510/src/Language/Haskell/Exts/Annotated/Syntax.hs this file] (from haskell-src-exts) and build it with -O0. On my machine it takes 55s. If we remove deriving of all classes except Functor (which is the only one used by the module itself), the time will drop down to 4s. Different classes vary in their compile-time cost, but there's no single culprit. Among the costly ones are Generic, Data, Show, Ord. haskell-src-exts users are very annoyed by its long compile time, about 10 minutes, especially because we don't compile with -O0 by default. It would be nice to get this fixed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9557> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13622: Regression: can't export constructor when conflicting, qualified constructor is also in scope
by GHC 06 May '17

06 May '17

#13622: Regression: can't export constructor when conflicting, qualified constructor is also in scope -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 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: -------------------------------------+------------------------------------- I ran into this regression when trying to compile the `ersatz` library with GHC 8.2.1-rc1. Here is a minimized example: {{{#!hs module Bug (Bits(Bits)) where import qualified Data.Bits as Bits newtype Bits = Bits Int }}} Compiling this with GHC 8.0.2 works fine, but with 8.2.1-rc1, you get this error: {{{ l$ /opt/ghc/8.2.1/bin/ghci Bug.hs GHCi, version 8.2.0.20170422: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:1:13: error: • Ambiguous occurrence ‘Bits’ It could refer to either ‘Bits.Bits’, imported qualified from ‘Data.Bits’ at Bug.hs:3:1-34 or ‘Bits’, defined at Bug.hs:5:1 • In the export: Bits(Bits) | 1 | module Bug (Bits(Bits)) where | ^^^^^^^^^^ }}} Despite the fact that `Bits` isn't actually ambiguous, since the `Bits` from `Data.Bits` is qualified. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13622> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13653: Re-allocate byteArray lead internal error: evacuate: strange closure type 241
by GHC 06 May '17

06 May '17

#13653: Re-allocate byteArray lead internal error: evacuate: strange closure type 241 -------------------------------------+------------------------------------- Reporter: winter | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: None/Unknown (amd64) | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compile and run following code lead to {{{evacuate: strange closure type XXX}}} on GHC 7.10.3/8.0.2/head, which is unreasonable. But running in GHCi is fine. {{{ {-# LANGUAGE BangPatterns #-} {-# LANGUAGE MagicHash #-} {-# LANGUAGE UnboxedTuples #-} import qualified Data.List as List import GHC.Prim import Data.Primitive.ByteArray import GHC.Types import GHC.ST data Bytes = Bytes {-# UNPACK #-} !ByteArray -- payload {-# UNPACK #-} !Int -- s {-# UNPACK #-} !Int -- length packN :: Int -> [Word8] -> Bytes packN n0 ws0 = runST (newByteArray n0 >>= go 0 n0 ws0) where go :: Int -> Int -> [Word8] -> MutableByteArray s -> ST s Bytes go !i !n [] !mba = do ba <- unsafeFreezeByteArray mba return (Bytes ba 0 i) go !i !n (w:ws) !mba | i <= n = do writeByteArray mba i w go (i+1) n ws mba | otherwise = do let n' = (n + 1) `shiftL` 1 -- mba' <- newByteArray n' -- these dosen't work either -- copyMutableByteArray mba' 0 mba 0 i mba' <- resizeMutableByteArray mba n' writeByteArray mba' i w go (i+1) n' ws mba' resizeMutableByteArray :: MutableByteArray s -> Int -> ST s (MutableByteArray s) resizeMutableByteArray (MutableByteArray mba#) (I# i#) = ST (\ s# -> let (# s'#, mba'# #) = resizeMutableByteArray# mba# i# s# in (# s'#, MutableByteArray mba'# #) ) main = print $ packN 64 (List.replicate 8192 128) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13653> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5546: Documentation errors in Control.Exception.Base
by GHC 05 May '17

05 May '17

#5546: Documentation errors in Control.Exception.Base -------------------------------------+------------------------------------- Reporter: bit | Owner: (none) Type: bug | Status: new Priority: high | Milestone: ⊥ Component: libraries/base | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bezirg): * owner: simonmar => (none) * status: closed => new * version: 7.2.1 => 8.0.1 * resolution: fixed => * milestone: 7.4.1 => ⊥ -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5546#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5546: Documentation errors in Control.Exception.Base
by GHC 05 May '17

05 May '17

#5546: Documentation errors in Control.Exception.Base -------------------------------------+------------------------------------- Reporter: bit | Owner: simonmar Type: bug | Status: closed Priority: high | Milestone: 7.4.1 Component: libraries/base | Version: 7.2.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bezirg): In the documentation of [https://hackage.haskell.org/package/base-4.9.1.0/docs/Control- Exception.html Control.Exception] of base 4.9.10 there is still a link to non-existing ''forkIOUnmasked'' function: > To create a a new thread in an unmasked state use forkIOUnmasked. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5546#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11799: Legend for hpc markup colors
by GHC 05 May '17

05 May '17

#11799: Legend for hpc markup colors -------------------------------------+------------------------------------- Reporter: drathier | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Test Suite | Version: 7.10.3 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: -------------------------------------+------------------------------------- The hpc markup colors are not documented anywhere. Coming from an imperative background, red means never executed and green means executed at least once. Here, green means always true, red means always false, yellow means never executed. Adding a one-line legend at the top of the output file(s) describing the colours would help a lot. Suggesting `never executed` `always true` and `always false` on a single line at the top with the same yellow, green and red background as the respective highlighted code would have. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11799> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11616: Kinds aren't instantiated
by GHC 05 May '17

05 May '17

#11616: Kinds aren't instantiated -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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 TypeInType, AllowAmbiugousTypes #-} class Whoami a where whoami :: String instance Whoami Int where whoami = "int" instance Whoami Bool where whoami = "[y/n]" instance Whoami Maybe where whoami = "call me maybe" }}} we can write {{{ >>> whoami @Type @Int "int" >>> whoami @Type @Bool "[y/n]" >>> whoami @(Type -> Type) @Maybe "call me maybe" }}} Attempting to specialise `whoami` to `Type` we can't simply write `whoamiType = whoami @Type` as one might expect. To start we define a synonym: {{{ $ ghci -ignore-dot-ghci /tmp/t17q.hs GHCi, version 8.1.20160117: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/t17q.hs, interpreted ) Ok, modules loaded: Main. *Main> whoami2 = whoami <interactive>:1:1: error: • Ambiguous type variable ‘a0’ arising from a use of ‘whoami’ prevents the constraint ‘(Whoami a0)’ from being solved. Probable fix: use a type annotation to specify what ‘k0’, ‘a0’ should be. These potential instances exist: three instance involving out-of-scope typess (use -fprint-potential-instances to see them all) • When instantiating ‘whoami2’, initially inferred to have this overly-general type: forall k (a :: k). Whoami a => String NB: This instantiation can be caused by the monomorphism restriction. }}} Using the “overly-general” inferred type `whoami :: forall k (a :: k). Whoami a => String` fails: {{{#!hs -- • Could not deduce (Whoami a0) arising from a use of ‘whoami’ -- from the context: Whoami a -- bound by the type signature for: -- whoami2 :: Whoami a => String -- at /tmp/t17q.hs:20:1-44 -- The type variable ‘a0’ is ambiguous -- These potential instances exist: -- three instance involving out-of-scope typess -- (use -fprint-potential-instances to see them all) -- • In the expression: whoami -- In an equation for ‘whoami2’: whoami2 = whoami whoami2 :: forall k (a :: k). Whoami a => String whoami2 = whoami }}} so we need `TypeApplications`: {{{#!hs whoami2 :: forall k (a :: k). Whoami a => String whoami2 = whoami @_ @a }}} and then we can write: {{{#!hs whoamiType :: forall (a :: Type). Whoami a => String whoamiType = whoami @_ @a }}} and we can write as intended: {{{ >>> whoamiType @Int "int" >>> whoamiType @Bool "[y/n]" }}} Is there a reason one cannot write: {{{#!hs whoami2 = whoami whoamiType = whoami @Type }}} ---- As a side note, what is the difference between {{{#!hs -- >>> :set -fprintf-explicit-foralls -- >>> :kind Whoami1 -- Whoami1 :: forall {k}. k -> Constraint -- >>> :kind Whoami2 -- Whoami2 :: forall k. k -> Constraint class Whoami1 a class Whoami2 (a :: k) }}} Is there a snippet of code that highlights differences -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11616> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13632: Frontend plugin arguments are reversed
by GHC 05 May '17

05 May '17

#13632: Frontend plugin arguments are reversed -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHC API | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: frontend01 | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The arguments passed to a frontend plugin are passed in the opposite order to that with which they were passed to the command line. I will attach a diff that modifies the frontend01 test to exhibit the error. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13632> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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