March 2018 - ghc-tickets

[GHC] #9951: OverloadedLists breaks exhaustiveness check
by GHC 03 May '18

03 May '18

#9951: OverloadedLists breaks exhaustiveness check -------------------------------------+------------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE OverloadedLists #-} module Bug where f :: [a] -> () f x = case x of [] -> () (_:_) -> () }}} GHC reports: {{{ bug.hs:6:7: Warning: Pattern match(es) are non-exhaustive In a case alternative: Patterns not matched: [] }}} This is reproducible with 7.8 and 7.10rc1. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9951> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10116: Closed type families: Warn if it doesn't handle all cases
by GHC 03 May '18

03 May '18

#10116: Closed type families: Warn if it doesn't handle all cases -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Right now, I can do the following: data Foo = A | B type family Bar (n :: 'Foo) where Bar 'A = Int I would like to be warned if I write a partial type function like this because partial functions are almost always a mistake. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10116> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10393: Bogus warning with OverloadedLists
by GHC 03 May '18

03 May '18

#10393: Bogus warning with OverloadedLists -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE OverloadedLists #-} lgo :: [a] -> () lgo [] = () lgo (_:_) = () }}} I get {{{ /Users/rae/temp/Bug.hs:4:1: Warning: Pattern match(es) are non-exhaustive In an equation for ‘lgo’: Patterns not matched: [] }}} I don't know !OverloadedLists deeply, but that warning surely is confusing! Happens on both 7.8.3 and 7.10.1. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10393> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13091: Build broken on amd64 solaris 11
by GHC 02 May '18

02 May '18

#13091: Build broken on amd64 solaris 11 -------------------------------------+------------------------------------- Reporter: kgardas | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Build System | Version: 8.0.2 Keywords: | Operating System: Solaris Architecture: x86_64 | Type of failure: Building GHC (amd64) | failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ ===--- building phase 1 gmake --no-print-directory -f ghc.mk phase=1 phase_1_builds libraries/hpc/ghc.mk:3: libraries/hpc/dist-boot/build/.depend-v.haskell: No such file or directory compiler/ghc.mk:584: compiler/stage1/build/.depend-v.haskell: No such file or directory "/opt/ghc-7.10.2-amd64/bin/ghc" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -Wall -package-db libraries/bootstrapping.conf -hide-all- packages -i -iutils/hsc2hs/. -iutils/hsc2hs/dist/build -iutils/hsc2hs/dist/build/autogen -Iutils/hsc2hs/dist/build -Iutils/hsc2hs/dist/build/autogen -optP-include -optPutils/hsc2hs/dist/build/autogen/cabal_macros.h -package-id base-4.8.1.0-bcc57434d4c4ded429bd4c7561dc7931 -package-id containers-0.5.6.2-3bd9811190df2d727713a53a0942b5c9 -package-id directory-1.2.2.0-17006ecadb146c26f40f44f8704a6547 -package-id filepath-1.4.0.0-8fee9c13b5e42926cc01f6aa7c403c4b -package-id process-1.2.3.0-47082ea082854427d5ceb7c692692d3c -XHaskell2010 -no-user- package-db -rtsopts -odir utils/hsc2hs/dist/build -hidir utils/hsc2hs/dist/build -stubdir utils/hsc2hs/dist/build -c utils/hsc2hs/./Main.hs -o utils/hsc2hs/dist/build/Main.o "/opt/ghc-7.10.2-amd64/bin/ghc" -o utils/hsc2hs/dist/build/tmp/hsc2hs -hisuf hi -osuf o -hcsuf hc -static -H32m -O -Wall -package-db libraries/bootstrapping.conf -hide-all-packages -i -iutils/hsc2hs/. -iutils/hsc2hs/dist/build -iutils/hsc2hs/dist/build/autogen -Iutils/hsc2hs/dist/build -Iutils/hsc2hs/dist/build/autogen -optP- include -optPutils/hsc2hs/dist/build/autogen/cabal_macros.h -package-id base-4.8.1.0-bcc57434d4c4ded429bd4c7561dc7931 -package-id containers-0.5.6.2-3bd9811190df2d727713a53a0942b5c9 -package-id directory-1.2.2.0-17006ecadb146c26f40f44f8704a6547 -package-id filepath-1.4.0.0-8fee9c13b5e42926cc01f6aa7c403c4b -package-id process-1.2.3.0-47082ea082854427d5ceb7c692692d3c -XHaskell2010 -no-user- package-db -rtsopts -odir utils/hsc2hs/dist/build -hidir utils/hsc2hs/dist/build -stubdir utils/hsc2hs/dist/build -optl-optl- Wl,-m64 -static -H32m -O -Wall -package-db libraries/bootstrapping.conf -hide-all-packages -i -iutils/hsc2hs/. -iutils/hsc2hs/dist/build -iutils/hsc2hs/dist/build/autogen -Iutils/hsc2hs/dist/build -Iutils/hsc2hs/dist/build/autogen -optP-include -optPutils/hsc2hs/dist/build/autogen/cabal_macros.h -package-id base-4.8.1.0-bcc57434d4c4ded429bd4c7561dc7931 -package-id containers-0.5.6.2-3bd9811190df2d727713a53a0942b5c9 -package-id directory-1.2.2.0-17006ecadb146c26f40f44f8704a6547 -package-id filepath-1.4.0.0-8fee9c13b5e42926cc01f6aa7c403c4b -package-id process-1.2.3.0-47082ea082854427d5ceb7c692692d3c -XHaskell2010 -no-user- package-db -rtsopts utils/hsc2hs/dist/build/Main.o utils/hsc2hs/dist/build/C.o utils/hsc2hs/dist/build/Common.o utils/hsc2hs/dist/build/CrossCodegen.o utils/hsc2hs/dist/build/DirectCodegen.o utils/hsc2hs/dist/build/Flags.o utils/hsc2hs/dist/build/HSCParser.o utils/hsc2hs/dist/build/UtilsCodegen.o utils/hsc2hs/dist/build/Paths_hsc2hs.o ld: fatal: option '-optl-Wl,-m64' and option '-outils/hsc2hs/dist/build/tmp/hsc2hs' are multiple definitions collect2: error: ld returned 1 exit status gmake[1]: *** [utils/hsc2hs/dist/build/tmp/hsc2hs] Error 1 gmake: *** [all] Error 2 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13091> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11352: Allow applying type to label
by GHC 02 May '18

02 May '18

#11352: Allow applying type to label -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE OverloadedLabels #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE DataKinds #-} import GHC.TypeLits import GHC.OverloadedLabels instance IsLabel "answer" Int where fromLabel _ = 42 answer :: IsLabel "answer" a => a answer = #answer }}} The follow works: {{{#!hs >>> answer @Int 42 }}} but fails with a label: {{{#!hs >>> #answer @Int <interactive>:...:1: error: • Cannot not apply expression of type ‘t0’ to a visible type argument ‘Int’ • In the expression: #answer @Int In an equation for ‘it’: it = #answer @Int }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11352> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14970: GHC.Err.errorWithoutStackTrace produces stack trace when profiling enabled
by GHC 02 May '18

02 May '18

#14970: GHC.Err.errorWithoutStackTrace produces stack trace when profiling enabled -------------------------------------+------------------------------------- Reporter: rotaerk | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 8.2.2 libraries/base | Keywords: | Operating System: Linux Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When you run 'error', it shows the usual stack trace. When you enable profiling with the -prof flag to ghc, and you run 'error', it shows the usual stack trace plus an additional prof-specific stack trace. When you run 'errorWithoutStackTrace' with profiling enabled, it strips the usual stack trace of 'error', but still displays the prof-specific stack trace. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14970> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11323: powerpc64: recomp015 fails with redundant linking
by GHC 01 May '18

01 May '18

#11323: powerpc64: recomp015 fails with redundant linking -------------------------------------+------------------------------------- Reporter: trommler | Owner: trommler Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.11 Keywords: | Operating System: Linux Architecture: powerpc64 | Type of failure: Compile-time Test Case: | performance bug driver/recomp15 | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ [1 of 1] Compiling Main ( Main.hs, Main.o ) Linking Main ... Running main... +Linking Main ... Running main... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11323> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14149: Tyepchecker generates top-level unboxed coercion
by GHC 27 Apr '18

27 Apr '18

#14149: Tyepchecker generates top-level unboxed coercion -------------------------------------+------------------------------------- Reporter: simonpj | 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: -------------------------------------+------------------------------------- Consider this code {{{ {-# OPTIONS_GHC -fdefer-out-of-scope-variables #-} module Foo where import Data.Coerce f :: Bool f = coerce (k :: Int) }}} It generates a lint error: {{{ *** Core Lint errors : in result of Desugar (after optimization) *** <no location info>: warning: [RHS of cobox_a11N :: (Int :: *) ~R# (Bool :: *)] The type of this binder is unlifted: cobox_a11N Binder's type: (Int :: *) ~R# (Bool :: *) *** Offending Program *** $trModule :: Module [LclIdX] $trModule = Module (TrNameS "main"#) (TrNameS "Foo"#) cobox_a11N :: (Int :: *) ~R# (Bool :: *) [LclId[CoVarId]] cobox_a11N = typeError @ ('TupleRep '[]) @ ((Int :: *) ~R# (Bool :: *)) "Foo.hs:8:5: error:\n\ \ \\226\\128\\162 Couldn't match representation of type \\226\\128\\152Int\\226\\128\\153 with that of \\226\\128\\152Bool\\226\\128\\153\n\ \ arising from a use of \\226\\128\\152coerce\\226\\128\\153\n\ \ \\226\\128\\162 In the expression: coerce (k :: Int)\n\ \ In an equation for \\226\\128\\152f\\226\\128\\153: f = coerce (k :: Int)\n\ \(deferred type error)"# f :: Bool [LclIdX] f = (typeError @ 'LiftedRep @ Int "Foo.hs:8:13: error: Variable not in scope: k :: Int\n\ \(deferred type error)"#) `cast` (cobox_a11N :: (Int :: *) ~R# (Bool :: *)) *** End of Offense *** }}} Reason: this rather hacky test in `TcUnify.buildImplication` {{{ ; if null skol_tvs && null given && (not deferred_type_errors || not (isTopTcLevel tc_lvl)) }}} did take account of `Opt_DeferOutOfScopeVariables`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14149> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14955: Musings on manual type class desugaring
by GHC 27 Apr '18

27 Apr '18

#14955: Musings on manual type class desugaring -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: SpecConstr | 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 recently wrote a short post explaining why manual type class desugaring was different to actually writing a type class because of how they are optimised. http://mpickering.github.io/posts/2018-03-20-recordsvstypeclasses.html I implement 4 different equivalent programs which are all optimised differently. I paste the whole file below as it is not very big. Implementation 1 is in terms of a type class. Implementation 2 is in terms of explicit dictionary passing. Implementation 3 wraps a dictionary in a type class Implementation 4 wraps a dictionary in a type class with an additional dummy argument. Naively, a user would expect all 4 implementations to be as fast as each other. {{{ {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE AllowAmbiguousTypes #-} module Prop where import Prelude (Bool(..), (||), (&&)) -- Implementation 1 class Prop r where or :: r -> r -> r and :: r -> r -> r true :: r false :: r instance Prop Bool where or = (||) and = (&&) true = True false = False -- Implementation 2 data PropDict r = PropDict { dor :: r -> r -> r , dand :: r -> r -> r , dtrue :: r , dfalse :: r } boolDict = PropDict { dor = (||) , dand = (&&) , dtrue = True , dfalse = False } -- Implementation 3 class PropProxy r where propDict :: PropDict r instance PropProxy Bool where propDict = boolDict -- Implementation 4 class PropProxy2 r where propDict2 :: PropDict r dummy :: () instance PropProxy2 Bool where propDict2 = boolDict dummy = () ors :: Prop r => [r] -> r ors [] = true ors (o:os) = o `or` ors os {-# INLINABLE ors #-} dors :: PropDict r -> [r] -> r dors pd [] = dtrue pd dors pd (o:os) = dor pd o (dors pd os) pors :: PropProxy r => [r] -> r pors [] = dtrue propDict pors (o:os) = dor propDict o (pors os) {-# INLINABLE pors #-} porsProxy :: PropProxy2 r => [r] -> r porsProxy [] = dtrue propDict2 porsProxy (o:os) = dor propDict2 o (porsProxy os) {-# INLINABLE porsProxy #-} }}} Then using the 4 different implementations of `ors` in another module implementations 1 and 4 are fast whilst 2 and 3 are slow. https://github.com/mpickering/rtcwrao-benchmarks/blob/master/Prop2.hs {{{ benchmarking tc/Implementation 1 time 3.510 ms (3.509 ms .. 3.512 ms) 1.000 R² (1.000 R² .. 1.000 R²) mean 2.976 ms (2.886 ms .. 3.060 ms) std dev 241.1 μs (195.4 μs .. 293.1 μs) variance introduced by outliers: 51% (severely inflated) benchmarking tc/Implementation 2 time 25.05 ms (21.16 ms .. 30.43 ms) 0.912 R² (0.849 R² .. 0.984 R²) mean 19.18 ms (16.20 ms .. 21.45 ms) std dev 5.627 ms (4.710 ms .. 6.618 ms) variance introduced by outliers: 89% (severely inflated) benchmarking tc/Implementation 3 time 20.06 ms (15.33 ms .. 23.57 ms) 0.856 R² (0.755 R² .. 0.934 R²) mean 18.43 ms (16.92 ms .. 19.85 ms) std dev 3.490 ms (3.003 ms .. 4.076 ms) variance introduced by outliers: 74% (severely inflated) benchmarking tc/Implementation 4 time 3.498 ms (3.484 ms .. 3.513 ms) 1.000 R² (1.000 R² .. 1.000 R²) mean 3.016 ms (2.935 ms .. 3.083 ms) std dev 205.7 μs (162.6 μs .. 261.8 μs) variance introduced by outliers: 42% (moderately inflated) }}} I compiled the module with `-O2`. If I turn off `-fno-worker-wrapper` and `-fno-spec-constr` then implementation 3 is also fast. Implementation 2 is always slow. This ticket is querying what could be done to improve the robustness of these different refactorings. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14955> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14421: LambdaCase should be suggested if it is used but not enabled
by GHC 27 Apr '18

27 Apr '18

#14421: LambdaCase should be suggested if it is used but not enabled -------------------------------------+------------------------------------- Reporter: tomjaguarpaw | 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 I try to make a multiparameter typeclass GHC (well, GHCi here) advises me to turn on {{{MultiParamTypeClasses}}} {{{ Prelude> class C a b where ... (Use MultiParamTypeClasses to allow multi-parameter classes) }}} But if I try to use {{{\case}}} it doesn't give me a helpful suggestion {{{ Prelude> :t \case (_,_) -> () <interactive>:1:2: error: parse error on input ‘case’ }}} Could it? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14421> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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