April 2018 - ghc-tickets

[GHC] #10087: DefaultSignatures: error message mentions internal name
by GHC 03 Aug '18

03 Aug '18

#10087: DefaultSignatures: error message mentions internal name -------------------------------------+------------------------------------- Reporter: | Owner: andreas.abel | Status: new Type: feature | Milestone: request | Version: 7.8.4 Priority: normal | Operating System: Unknown/Multiple Component: Compiler | Type of failure: Other (Type checker) | Blocked By: Keywords: | Related Tickets: Architecture: | Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE DefaultSignatures #-} class C a where reflexive :: a -> Bool default reflexive :: Eq a => a -> Bool reflexive x = x == x data D instance C D where -- /home/abel/play/haskell/bugs/DefaultSig.hs:10:10: -- No instance for (Eq D) arising from a use of ‘Main.$gdmreflexive’ -- In the expression: Main.$gdmreflexive -- In an equation for ‘reflexive’: reflexive = Main.$gdmreflexive -- In the instance declaration for ‘C D’ }}} Error looks odd: The user has not written $gdmreflexive in his code. TODO: Better error message. Maybe this should just trigger a warning that method {{{reflexive}}} is undefined for instance {{{D}}} of {{{C}}}. Like when I remove the default method. {{{ /home/abel/play/haskell/bugs/DefaultSig.hs:10:10: Warning: No explicit implementation for ‘reflexive’ In the instance declaration for ‘C D’ }}} It seems the semantics of a default signature is that each instance *must* implement this method. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10087> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12096: Attach stacktrace information to SomeException
by GHC 02 Aug '18

02 Aug '18

#12096: Attach stacktrace information to SomeException -------------------------------------+------------------------------------- Reporter: ndtimofeev | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | 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: -------------------------------------+------------------------------------- Now (base 4.9.0.0) ErrorCall contain field for stacktrace information and error fills it. If you add field for stacktrace information to SomeException {{{#!hs data SomeException where SomeExceptionWithLocation :: Exception e => String -> e -> SomeException pattern SomeException :: () => Exception e => e -> SomeException pattern SomeException err <- SomeExceptionWithLocation _ err where SomeException err = SomeExceptionWithLocation "" err }}} and will fills it in throw {{{#!hs throw :: (HasCallStack, Exception e) => e -> a throw e = unsafeDupablePerformIO $ do stack <- currentCallStack raise# (CallStackException e $ if stack /= [] then prettyCallStack ?callStack ++ "\n" ++ renderStack stack else prettyCallStack ?callStack) }}} it will be more useful for ghci users. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12096> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11759: can't decompose ghc.exe path
by GHC 02 Aug '18

02 Aug '18

#11759: can't decompose ghc.exe path --------------------------------------+---------------------------- Reporter: erisco | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: Other Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+---------------------------- {{{ erisco@ERICWIN C:\Users\erisco\haskell-platform-bin $ ghc.exe ghc.exe: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-unknown-mingw32): can't decompose ghc.exe path: "C:\\Users\\erisco\\haskell- platform-bin\\ghc.exe" }}} haskell-platform-bin is a symbolic directory link to "C:\Program Files\Haskell Platform\2014.2.0.0\bin". I did this so there would not be spaces in the path because this is causing other issues for me. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11759> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14928: TH eats 50 GB memory when creating ADT with multiple constructors
by GHC 01 Aug '18

01 Aug '18

#14928: TH eats 50 GB memory when creating ADT with multiple constructors -------------------------------------+------------------------------------- Reporter: YitzGale | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.2.2 Haskell | 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: -------------------------------------+------------------------------------- When TH creates a data type with multiple constructors, GHC consumes huge amounts of memory in what appears to be a highly superlinear manner. A common use case: in the Yesod web framework, localized strings are represented by constructors of a Messages data type, created by a TH splice. There is one constructor for each localized string on the site, possibly hundreds. The splice also creates a class instance for the data type whose method matches against all the constructors for each language for which localizations are provided; this may or may not play a role in the memory leak. This Trac ticket corresponds to this Yesod issue: https://github.com/yesodweb/yesod/issues/1487 Here are two reproductions, and one NON-reproduction: 1. A blank "hello world" Yesod web site, with 500 messages defined for about 30 languages. The single page displays the messages in the user's language. Compiling this program in GHC 8.2.2 (stackage lts-10.5) on Ubuntu 16.04 eats over 50 GB of memory. https://gitub.com/ygale/yesod-bug1487 2. @snoyberg has cut down this reproduction to avoid using any libraries not included with GHC. It is in the same repo, on the {{{snoyberg- master}}} branch. NON-reproduction: The code in this gist, which is similar to what is generated by the TH in the above reproductions, is compiled by GHC without the bat of an eyelash. This demonstrates that the bug requires TH to reproduce. https://gist.github.com/92347aa93d226e31f977a0b62b443aa7 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14928> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15063: T3001-2 fails on i386 Linux
by GHC 01 Aug '18

01 Aug '18

#15063: T3001-2 fails on i386 Linux -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Profiling | Version: 8.2.2 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 `T3001-2` testcase fails on i386/Linux: {{{ Wrong exit code for T3001-2(prof_hb)(expected 0 , actual 134 ) Stderr ( T3001-2 ): T3001-2: internal error: Invalid object in processHeapClosureForDead(): 7 (GHC version 8.5.20180419 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted *** unexpected failure for T3001-2(prof_hb) }}} Closure type 7 is `CONSTR_NOCAF`, which is indeed invalid. Tracking this down will take some debugging. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15063> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14346: 8.2.1 regression: heap corruption after safe foreign calls
by GHC 01 Aug '18

01 Aug '18

#14346: 8.2.1 regression: heap corruption after safe foreign calls -------------------------------------+------------------------------------- Reporter: andrewchen | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Runtime | Version: 8.2.1 System | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Test case: (compile with ghc 8.2.1 and -threaded option) {{{#!haskell module Main where import Control.Concurrent import Control.Monad import Data.Word import Foreign.Marshal.Alloc import Foreign.Ptr import Foreign.Storable foreign import ccall safe "test" c_test :: Ptr Word32 -> IO () main :: IO () main = do replicateM_ 1000 $ threadDelay 1000 _ <- forkIO $ forever $ threadDelay 100 allocaBytes 4 $ \p -> forever $ do c_test p x <- peek p unless (x == 0xDEADBEEF) $ putStrLn "value mismatch" }}} {{{#!c void test(unsigned int *buf) { *buf = 0xDEADBEEF; } }}} On my machine, it detects a few value mismatches before crashing with sigsegv. {{{ $ time ./.stack-work/install/x86_64-linux- nopie/nightly-2017-10-10/8.2.1/bin/bug value mismatch value mismatch value mismatch value mismatch zsh: segmentation fault (core dumped) ./.stack-work/install/x86_64-linux- nopie/nightly-2017-10-10/8.2.1/bin/bug ./.stack-work/install/x86_64-linux-nopie/nightly-2017-10-10/8.2.1/bin/bug 2.11s user 0.25s system 66% cpu 3.543 total }}} I believe this is what is causing crashes in xmobar. See discussion: https://github.com/jaor/xmobar/issues/310. Note that the crash in xmobar still happens without -threaded option, while this example only breaks when compiled with -threaded. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14346> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12030: GHCi Proposal: Display (Data.Kind.)Type instead of *
by GHC 31 Jul '18

31 Jul '18

#12030: GHCi Proposal: Display (Data.Kind.)Type instead of * -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: GHCi | Version: 8.1 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: -------------------------------------+------------------------------------- This is premature but what the darn, {{{ >>> :kind Maybe Maybe :: Type -> Type >>> :kind StateT StateT :: Type -> (Type -> Type) -> Type -> Type >>> :kind Eq Eq :: Type -> Constraint >>> :info Functor class Functor (f :: Type -> Type) where ... }}} `*` throws students off and makes it seem scarier than it is. Symbols are harder to search for in general and to understand without documentation, `Type` on the other hand is descriptive. There are valid arguments against displaying `Type`: 1. It's a recent feature subject to change. 2. Although symbols are more difficult to search for, `*` is established in educational materials, logs, blogs and questions. 3. By default `Type` is not in scope so a user cannot ask for information in GHCi. `*` is established and searching for “Haskell asterisk” yields a lot resources but [https://support.google.com/websearch/answer/2466433?hl=en ‘*’ is also a wildcard] in Google and ignored by GitHub. With time `Type` would be a good search term but currently it's chicken-and-the-egg. Previous versions of GHCi error on `:kind *` and `:info *` only shows multiplication so that wouldn't be a huge difference but we can qualify by default: {{{ >>> :kind Maybe Maybe :: Data.Kind.Type -> Data.Kind.Type >>> :kind StateT StateT :: Data.Kind.Type -> (Data.Kind.Type -> Data.Kind.Type) -> Data.Kind.Type -> Data.Kind.Type >>> :kind Eq Eq :: Data.Kind.Type -> Constraint >>> :info Functor class Functor (f :: Data.Kind.Type -> Data.Kind.Type) where ... }}} or display `*` normally and only when `TypeInType` is set do we display `Type`. I don't love it (and love `GHC.Types.Type` slightly less) but there is a precedent for unqualified names, browsing the Prelude for example: {{{#!hs ($) :: forall (r :: GHC.Types.RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b undefined :: forall (r :: GHC.Types.RuntimeRep) (a :: TYPE r). GHC.Stack.Types.HasCallStack => a }}} __If__ the consensus is that this will happen sometime down the line consider that each passing release means many more books and blog posts get written using `*`. I wasn't planning on resulting to scare tactics but [https://www.peoria.com/spaw/spawimages/members/member60763/shoot_this_dog.j… here we are]... ---- If needed a migration plan can be drafted like the Semigroup/FTP/AMP/BBP/MonadFail/expanding Float/... proposals, possibly culminating in `Type` fully replacing `*` and being imported by default. I'm sure there are some further reaching consequences to this and better arguments against. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12030> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10056: Inconsistent precedence of ~
by GHC 30 Jul '18

30 Jul '18

#10056: Inconsistent precedence of ~ -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 (Parser) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following compiles as expected: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family Foo a b f :: (Foo a b ~ Int) => a -> b -> b f = error "" }}} but this fails: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family a \\ b f :: (a \\ b ~ Int) => a -> b -> b f = error "" }}} with the error > "The second argument of `(\\)` should have kind `*`, but `b ~ Int` has kind `Constraint`." Thus the first example is being parsed as `(Foo a b) ~ Int`, while the second is parsed as `a \\ (b ~ Int)`. I believe the second example should compile, i.e. `(\\)` and `Foo` should have the same precedence, both of which are higher than `(~)`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10056> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14873: GHC HEAD regression (piResultTy)
by GHC 30 Jul '18

30 Jul '18

#14873: GHC HEAD regression (piResultTy) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.5 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (Originally noticed [https://travis- ci.org/goldfirere/singletons/jobs/347945148#L1179 here].) The following program typechecks on GHC 8.2.2 on GHC 8.4.1, but panics on GHC HEAD: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Kind (Type) data family Sing (a :: k) newtype instance Sing (f :: k1 ~> k2) = SLambda { applySing :: forall t. Sing t -> Sing (Apply f t) } data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type infixr 0 ~> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2 class SingI (a :: k) where sing :: Sing a data ColSym1 :: f a -> a ~> Bool type instance Apply (ColSym1 x) y = Col x y class PColumn (f :: Type -> Type) where type Col (x :: f a) (y :: a) :: Bool class SColumn (f :: Type -> Type) where sCol :: forall (x :: f a) (y :: a). Sing x -> Sing y -> Sing (Col x y :: Bool) instance (SColumn f, SingI x) => SingI (ColSym1 (x :: f a) :: a ~> Bool) where sing = SLambda (sCol (sing @_ @x)) }}} {{{ $ /opt/ghc/head/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.5.20180201 for x86_64-unknown-linux): piResultTy k_aZU[tau:1] (a_aW8[sk:1] |> <*>_N) Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:947:35 in ghc:Type }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14873> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13451: Bind implicit parameter in patterns
by GHC 30 Jul '18

30 Jul '18

#13451: Bind implicit parameter in patterns -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple ImplicitParams | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Is there any reason why variables for `ImplicitParams` can't be bound in patterns, so you can write {{{#!hs data Exp = Val Int | Op Op Exp Exp data Op = Add | Mul data Protect where Protect :: (?op :: Op) => Protect protectOp :: Exp -> Maybe Protect protectOp (Op ?op _ _) = Just Protect protectOp _ = Nothing }}} instead of {{{#!hs protectOp :: Exp -> Maybe Protect protectOp (Op op _ _) = Just Protect where ?op = op protectOp _ = Nothing }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13451> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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