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[GHC] #12716: Suggest ScopedTypeVariables when type variable not in scope
by GHC 19 Oct '16

19 Oct '16

#12716: Suggest ScopedTypeVariables when type variable not in scope -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | 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 recently wrote this: {{{ {-# LANGUAGE ExplicitForAll #-} {-# LANGUAGE TypeApplications #-} module B where f :: forall a. a -> a f x = id @a x }}} And was hornswoggled for the better part of five minutes for why "a" wasn't in scope. Answer: you need `ScopedTypeVariables`. A suggestion would be nice. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12716> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12140: Clarify Trac menus for new reporters
by GHC 19 Oct '16

19 Oct '16

#12140: Clarify Trac menus for new reporters -------------------------------------+------------------------------------- Reporter: goldfire | Owner: hvr Type: bug | Status: new Priority: normal | Milestone: Component: Trac & Git | 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: -------------------------------------+------------------------------------- An officemate of mine rarely posts bugs here. He finds the interface to posting a bug confusing. I have to say I agree, if I consider the perspective of an infrequent reporter. (The reason he rarely posts bugs is that he rarely has bugs to post, not because of the confusing interface.) Specifically, there are many fields to fill out when posting a bug. Some of these are important to us (`Version` probably being the most). Some are better for developers to set (`Milestone`, `Test case`). Some are less important (`Operating System` for a bug in the type-checker). Some are essentially ignored (`Type of failure`, in my experience). Yet a new reporter doesn't know any of this and will diligently try to fill out them all. Can we label the fields as to importance somehow? Mark some as advanced/dev only? Make some available only after posting the ticket (`Test case`, `Differential`)? I don't suppose there are masses of people out there trying to post bugs and stymied by this problem, but I do think we can clean this up a bit. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12140> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12733: Orphan hashes are not being propagated correctly
by GHC 19 Oct '16

19 Oct '16

#12733: Orphan hashes are not being propagated correctly -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Driver | 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: -------------------------------------+------------------------------------- In Phab:D2607, simonpj asked why we didn't also put class instances in the export hash. Why indeed. In the course of investigating, I discovered another bug in how we handle orphan recompilation. Unfortunately, this bug needs two packages to manifest. {{{ -- p/P.hs module P where instance Show (a -> b) where --instance Show (IO a) where -- q/Q.hs module Q where import P -- q/Q2.hs module Q2 where import Q }}} Put in some default Cabal files, with q depending on p, and then build the entire kaboodle. Then edit `p/P.hs` to uncomment the second orphan instance. Rebuild. {{{ ezyang@sabre:~/Dev/labs/orph$ cabal new-build q -w ghc-head In order, the following will be built (use -v for more details): - p-0.1.0.0 (lib) (file P.hs changed) - q-0.1.0.0 (lib) (dependency rebuilt) Preprocessing library p-0.1.0.0... [1 of 1] Compiling P ( P.hs, /srv/code/labs/orph/dist- newstyle/build/x86_64-linux/ghc-8.1.20161016/p-0.1.0.0/build/P.o ) P.hs:2:10: warning: [-Wmissing-methods] • No explicit implementation for either ‘showsPrec’ or ‘show’ • In the instance declaration for ‘Show (a -> b)’ P.hs:3:10: warning: [-Wmissing-methods] • No explicit implementation for either ‘showsPrec’ or ‘show’ • In the instance declaration for ‘Show (IO a)’ module Q2 where Preprocessing library q-0.1.0.0... [1 of 2] Compiling Q ( Q.hs, /srv/code/labs/orph/dist- newstyle/build/x86_64-linux/ghc-8.1.20161016/q-0.1.0.0/build/Q.o ) [P changed] ezyang@sabre:~/Dev/labs/orph$ }}} Notice: Q2 never got rebuilt. This is wrong wrong wrong: P changed, and we need to rebuild Q2! Here are the hashes for Q.hi before and after: {{{ -- Before interface Q 80120161016 interface hash: 2ffc06a1552565a73c888110ab4cf8df ABI hash: b2768862866252ea5a63401d2aa05aaa export-list hash: 092acc280445a8bcc96904afb8b766b0 orphan hash: 693e9af84d3dfcc71e640e005bdc5e2e flag hash: f01bb78d3c47152bc5253f256b2a60d3 -- After interface Q 80120161016 interface hash: 009db9e5ecbe49e36b7bf38e02087e75 ABI hash: b2768862866252ea5a63401d2aa05aaa export-list hash: 092acc280445a8bcc96904afb8b766b0 orphan hash: 693e9af84d3dfcc71e640e005bdc5e2e flag hash: f01bb78d3c47152bc5253f256b2a60d3 }}} The orphan hash didn't get updated. At the moment, when we compute the orphan hash, we only consider the orphan hashes from the home package. Here's the comment justifying it: {{{ -- the export hash of a module depends on the orphan hashes of the -- orphan modules below us in the dependency tree. This is the way -- that changes in orphans get propagated all the way up the -- dependency tree. We only care about orphan modules in the current -- package, because changes to orphans outside this package will be -- tracked by the usage on the ABI hash of package modules that we import. }}} It is true that we know to rebuild Q.hs when P.hs changes. But that is not much solace for Q2.hs... -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12733> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12411: GHC panic on TypeApplications + TemplateHaskell
by GHC 19 Oct '16

19 Oct '16

#12411: GHC panic on TypeApplications + TemplateHaskell -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple TypeApplications, TemplateHaskell | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This fails {{{ $ ghci -XTemplateHaskell -ignore-dot-ghci GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> import Control.Lens Prelude Control.Lens> data A = B { _int :: Int } Prelude Control.Lens> pure @Q []; makeLenses ''A ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): tcMonoExpr _ Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Prelude Control.Lens> }}} sorry, don't have time for more detail -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12411> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12688: derived Show instances aren't protected from RebindableSyntax+OverloadedStrings
by GHC 19 Oct '16

19 Oct '16

#12688: derived Show instances aren't protected from RebindableSyntax+OverloadedStrings -------------------------------------+------------------------------------- Reporter: daviddarais | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple rebindablesyntax | overloadedstrings deriving show | string | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When using both `RebindableSyntax` and `OverloadedStrings`, `deriving (Show)` no longer works. Example program: {{{#!hs {-# LANGUAGE RebindableSyntax, OverloadedStrings #-} module Bug where import Prelude (String,Show(..)) newtype Text = Text String fromString :: String -> Text fromString = Text x :: Text x = "x" newtype Foo = Foo () deriving (Show) }}} In this example, `fromString` is redefined to return a type different from `[Char]`. The example `x` typechecks due to to the `RebindableSyntax` and `OverloadedStrings` extensions. However, the generated code for the `deriving (Show)` instance for Foo does not typecheck, and ghc gives a code generation error: {{{#!hs error: • Couldn't match type ‘Text’ with ‘[GHC.Types.Char]’ Expected type: String Actual type: Text • In the first argument of ‘GHC.Show.showString’, namely ‘"Foo "’ In the first argument of ‘(GHC.Base..)’, namely ‘(GHC.Show.showString "Foo ")’ In the second argument of ‘GHC.Show.showParen’, namely ‘((GHC.Base..) (GHC.Show.showString "Foo ") (showsPrec 11 b1))’ When typechecking the code for ‘showsPrec’ in a derived instance for ‘Show Foo’: To see the code I am typechecking, use -ddump-deriv }}} A solution would be to protect the code generated by `deriving (Show)` from `OverloadedStrings` and `RebindableSyntax` extensions. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12688> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12562: GHC panic on rebuild (idInfo r_XsTP)
by GHC 19 Oct '16

19 Oct '16

#12562: GHC panic on rebuild (idInfo r_XsTP) -------------------------------------+------------------------------------- Reporter: cocreature | Owner: 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: -------------------------------------+------------------------------------- First of all let me apologize for the terrible testcase. I tried to find a smaller one (and am still trying) but haven’t managed to do so. The good news is that at least for me it’s reproducible === Steps to reproduce === {{{ git clone 'git@github.com:bscarlet/llvm-general.git' -b llvm-3.8 cd llvm-general cabal new-build llvm-general curl -s https://gist.githubusercontent.com/cocreature/c6807d7906756a2d58b8fe774141b… > out.patch git apply out.patch cabal new-build llvm-general }}} The patch just adds a newline somewhere to create a rebuild. I’ve seen this panic for completely different changes (all in this project) so I don’t think the change matters. I’ve also seen this panic with stack, cabal new-build and cabal build (using sandboxes). === Output === {{{ In order, the following will be built (use -v for more details): llvm-general-3.8.0.0 Preprocessing library llvm-general-3.8.0.0... [84 of 92] Compiling LLVM.General.Internal.Module ( src/LLVM/General/Internal/Module.hs, /home/moritz/tmp/llvm-general/dist- newstyle/build/llvm-general-3.8.0.0/build/LLVM/General/Internal/Module.o ) [85 of 92] Compiling LLVM.General.Module ( src/LLVM/General/Module.hs, /home/moritz/tmp/llvm-general/dist-newstyle/build/llvm- general-3.8.0.0/build/LLVM/General/Module.o ) [LLVM.General.Internal.Module changed] [89 of 92] Compiling LLVM.General.Internal.PassManager ( src/LLVM/General/Internal/PassManager.hs, /home/moritz/tmp/llvm-general /dist-newstyle/build/llvm- general-3.8.0.0/build/LLVM/General/Internal/PassManager.o ) [TH] ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): idInfo r_XsTP Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} === Comments === In this case this can be resolved by running cabal new-build again. However I’ve also had cases where this didn’t fix it and I had to blow away dist-newstyle. I haven’t yet managed to find a reproducible testcase for the latter. Matthew Pickering mentioned that he encountered this (or a similar) bug while building GHC. I tried core-lint but that didn’t help. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12589: GHC panic with defer-typed-holes
by GHC 19 Oct '16

19 Oct '16

#12589: GHC panic with defer-typed-holes -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: 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: -------------------------------------+------------------------------------- Does this still happen in HEAD? {{{#!hs import qualified GHC.Generics as GHC import Generics.SOP import Generics.SOP.TH import Data.Proxy gminbound' :: (Generic a, Code a ~ (xs:xss), All2 Bounded (Code a)) => a gminbound' = minBound & I & hcpure (Proxy @Bounded) & apInjs_POP & head & to }}} Fails but doesn't crash with {{{ $ ghci -ignore-dot-ghci -XTypeApplications -XTypeOperators -XDataKinds -XGADTs -XFlexibleContexts /tmp/tX96.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/tX96.hs, interpreted ) /tmp/tX96.hs:8:3: error: Variable not in scope: (&) :: t4 -> (a0 -> I a0) -> t3 /tmp/tX96.hs:9:3: error: Variable not in scope: (&) :: t3 -> t5 -> t2 /tmp/tX96.hs:10:3: error: Variable not in scope: (&) :: t2 -> (POP f1 xss0 -> [SOP f1 xss0]) -> t1 /tmp/tX96.hs:11:3: error: Variable not in scope: (&) :: t1 -> ([a1] -> a1) -> t0 /tmp/tX96.hs:12:3: error: Variable not in scope: (&) :: t0 -> (Rep a2 -> a2) -> a Failed, modules loaded: none. Prelude> }}} but crashes with `-fdefer-typed-holes` {{{ $ ghci -ignore-dot-ghci -fdefer-typed-holes -XTypeApplications -XTypeOperators -XDataKinds -XGADTs -XFlexibleContexts /tmp/tX96.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/tX96.hs, interpreted ) /tmp/tX96.hs:8:3: warning: [-Wtyped-holes] Variable not in scope: (&) :: t4 -> (a0 -> I a0) -> t3 /tmp/tX96.hs:9:3: warning: [-Wtyped-holes] Variable not in scope: (&) :: t3 -> t5 -> t2 /tmp/tX96.hs:10:3: warning: [-Wtyped-holes] Variable not in scope: (&) :: t2 -> (POP f1 xss0 -> [SOP f1 xss0]) -> t1 /tmp/tX96.hs:11:3: warning: [-Wtyped-holes] Variable not in scope: (&) :: t1 -> ([a1] -> a1) -> t0 /tmp/tX96.hs:12:3: warning: [-Wtyped-holes] Variable not in scope: (&) :: t0 -> (Rep a2 -> a2) -> a ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): opt_univ fell into a hole {aabX} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} ---- More minimal example, still requires [https://hackage.haskell.org/package /generics-sop-0.2.2.0 generics-sop]: {{{#!hs import Generics.SOP a = minBound & hcpure (Proxy @Bounded) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12589> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12676: Panic with piResultTys1 again
by GHC 19 Oct '16

19 Oct '16

#12676: Panic with piResultTys1 again -------------------------------------+------------------------------------- Reporter: pjmagni | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: #12634 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The code {{{#!hs {-# LANGUAGE RankNTypes, TypeFamilies #-} module Panic where class C a where data T a panic :: (forall s . T a) -> () instance C () where data T () = T panic T = () }}} produces the output {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): piResultTys1 R:T() [Any] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12676> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12698: GHC panic on pattern synonym
by GHC 19 Oct '16

19 Oct '16

#12698: GHC panic on pattern synonym -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# Language ViewPatterns, TypeOperators, KindSignatures, PolyKinds, TypeInType, StandaloneDeriving, GADTs, RebindableSyntax, RankNTypes, LambdaCase, PatternSynonyms, TypeApplications #-} import GHC.Types import Prelude hiding ( fromInteger ) import Data.Type.Equality import Data.Kind import qualified Prelude class Ty (a :: k) where ty :: T a instance Ty Int where ty = TI instance Ty Bool where ty = TB instance Ty a => Ty [a] where ty = TA TL ty instance Ty [] where ty = TL instance Ty (,) where ty = TP data AppResult (t :: k) where App :: T a -> T b -> AppResult (a b) data T :: forall k. k -> Type where TI :: T Int TB :: T Bool TL :: T [] TP :: T (,) TA :: T f -> T x -> T (f x) deriving instance Show (T a) splitApp :: T a -> Maybe (AppResult a) splitApp = \case TI -> Nothing TB -> Nothing TL -> Nothing TP -> Nothing TA f x -> Just (App f x) data (a :: k1) :~~: (b :: k2) where HRefl :: a :~~: a eqT :: T a -> T b -> Maybe (a :~~: b) eqT a b = case (a, b) of (TI, TI) -> Just HRefl (TB, TB) -> Just HRefl (TL, TL) -> Just HRefl (TP, TP) -> Just HRefl pattern List :: () => [] ~~ b => T b pattern List <- (eqT (ty @(Type -> Type) @[]) -> Just HRefl) where List = ty pattern Int :: () => Int ~~ b => T b pattern Int <- (eqT (ty @Type @Int) -> Just HRefl) where Int = ty pattern (:<->:) :: () => fx ~ f x => T f -> T x -> T fx pattern f :<->: x <- (splitApp -> Just (App f x)) where f :<->: x = TA f x pattern Foo <- List :<->: Int }}} Using GHCi version 8.1.20160930: {{{ G$ ./ghc-stage2 -ignore-dot-ghci --interactive /tmp/td2W.hs GHCi, version 8.1.20160930: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/td2W.hs, interpreted ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160930 for x86_64-unknown-linux): ASSERT failed! k1_a2mO k1_a2mO [TCvSubst In scope: InScope {k_a2mM fx_a2mN f_a2mP x_a2mQ rep_a2ny r_a2nz scrut_a2nB $cshowsPrec_a2ob $cshow_a2p1 $cshowList_a2p8 $cty_a2pi $cty_a2po $cty_a2pw $cty_a2pJ $cty_a2pP splitApp eqT $fTy(->)(,) $fTy(->)[] $fTyTYPE[] $fTyTYPEBool $fTyTYPEInt $fShowT $mList $bList $mInt $bInt $m:<->: $b:<->:} Type env: [a2mN :-> fx_a2mN, a2mP :-> f_a2mP, a2mQ :-> x_a2mQ, a2nz :-> r_a2nz] Co env: []] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1125:22 in ghc:Outputable assertPprPanic, called at compiler/types/TyCoRep.hs:2318:46 in ghc:TyCoRep Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in ghc:Outputable pprPanic, called at compiler/utils/Outputable.hs:1123:5 in ghc:Outputable assertPprPanic, called at compiler/types/TyCoRep.hs:2318:46 in ghc:TyCoRep Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12698> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12653: reexported-modules sometimes gets mangled, causes problems for bootstrap
by GHC 19 Oct '16

19 Oct '16

#12653: reexported-modules sometimes gets mangled, causes problems for bootstrap -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: highest | Milestone: 8.0.2 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: -------------------------------------+------------------------------------- There is a pretty bad bug in Cabal 1.24's support for reexported modules (https://github.com/haskell/cabal/pull/3906) which means that, under some circumstances, Cabal library will output `reexported-modules` in a form that ghc-pkg will misinterpret. The particular instance I've seen is GHC's build system incorrectly concluding that GHC.Lexeme is provided by ghc- boot rather than ghc-boot-th (because the reexport wasn't parsed correctly). It does not actually seem possible to work around this given a GHC 8.0.1 bootstrap, because we need to register ghc-boot using the bootstrapping ghc-pkg, which will output the package configuration in mangled form. So my advice is: 1. Fix this bug for GHC 8.0.2, so that at least 8.0.2 bootstrap will work even if we have reexported modules in the bootstrap libraries 2. Stop using reexports in ghc-boot; they're not being used for any good reason and will help avoid the bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12653> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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