January 2019 - ghc-tickets

[GHC] #15831: DerivingVia allows bogus implicit quantification in `via` type
by GHC 14 Jan '19

14 Jan '19

#15831: DerivingVia allows bogus implicit quantification in `via` type -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Keywords: deriving | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the following code: {{{#!hs {-# LANGUAGE DerivingVia #-} {-# LANGUAGE PolyKinds #-} module Bug where import Data.Functor.Const (Const(..)) import GHC.Exts (Any) newtype Age = MkAge Int deriving Eq via Const Int Any }}} This fails to compile with a spectacularly unhelpful error message: {{{ $ /opt/ghc/8.6.1/bin/ghc -ddump-deriv Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) ==================== Derived instances ==================== Derived class instances: instance GHC.Classes.Eq Bug.Age where (GHC.Classes.==) = GHC.Prim.coerce @((Data.Functor.Const.Const GHC.Types.Int (GHC.Types.Any :: k_a24l) :: TYPE GHC.Types.LiftedRep) -> (Data.Functor.Const.Const GHC.Types.Int (GHC.Types.Any :: k_a24l) :: TYPE GHC.Types.LiftedRep) -> GHC.Types.Bool) @(Bug.Age -> Bug.Age -> GHC.Types.Bool) (GHC.Classes.==) :: Bug.Age -> Bug.Age -> GHC.Types.Bool (GHC.Classes./=) = GHC.Prim.coerce @((Data.Functor.Const.Const GHC.Types.Int (GHC.Types.Any :: k_a24l) :: TYPE GHC.Types.LiftedRep) -> (Data.Functor.Const.Const GHC.Types.Int (GHC.Types.Any :: k_a24l) :: TYPE GHC.Types.LiftedRep) -> GHC.Types.Bool) @(Bug.Age -> Bug.Age -> GHC.Types.Bool) (GHC.Classes./=) :: Bug.Age -> Bug.Age -> GHC.Types.Bool Derived type family instances: Bug.hs:9:12: error: The exact Name ‘k’ is not in scope Probable cause: you used a unique Template Haskell name (NameU), perhaps via newName, but did not bind it If that's it, then -ddump-splices might be useful | 9 | deriving Eq | ^^ Bug.hs:9:12: error: The exact Name ‘k’ is not in scope Probable cause: you used a unique Template Haskell name (NameU), perhaps via newName, but did not bind it If that's it, then -ddump-splices might be useful | 9 | deriving Eq | ^^ Bug.hs:9:12: error: The exact Name ‘k’ is not in scope Probable cause: you used a unique Template Haskell name (NameU), perhaps via newName, but did not bind it If that's it, then -ddump-splices might be useful | 9 | deriving Eq | ^^ Bug.hs:9:12: error: The exact Name ‘k’ is not in scope Probable cause: you used a unique Template Haskell name (NameU), perhaps via newName, but did not bind it If that's it, then -ddump-splices might be useful | 9 | deriving Eq | ^^ }}} There are two things that are strange here: * Notice that in the derived `Eq` instance, there are references to `(GHC.Types.Any :: k_a24l)`, where `k_a24l` is completely free! This should never happen, and is almost surely the cause of the resulting volley of errors. * It's quite odd that we didn't reject this `deriving` clause outright //before// generating the derived code. In fact, if we explicitly mention the kind `k`: {{{#!hs newtype Age = MkAge Int deriving Eq via Const Int (Any :: k) }}} //Then// it's rejected properly: {{{ $ /opt/ghc/8.6.1/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:9:12: error: Type variable ‘k’ is bound in the ‘via’ type ‘Const Int (Any :: k)’ but is not mentioned in the derived class ‘Eq’, which is illegal | 9 | deriving Eq | ^^ }}} Something about implicit quantification must be sneaking by this validity check. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15831> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16181: ghc panic when using DerivingVia
by GHC 14 Jan '19

14 Jan '19

#16181: ghc panic when using DerivingVia -------------------------------------+------------------------------------- Reporter: chessai | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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 following program results in a ghc panic: {{{#!hs {-# LANGUAGE DerivingVia #-} import Data.Functor.Const (Const(..)) import Data.Functor.Classes newtype FlipConst a b = FlipConst b deriving (Show1, Eq1) via (Const b) }}} Here is the output of the compile: {{{#!sh test/Spec/Contravariant.hs:52:13: error: • No instance for (Show b) arising from the 'deriving' clause of a data type declaration Possible fix: add (Show b) to the context of the deriving clause for ‘Show1 (FlipConst a)’ or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself • When deriving the instance for (Show1 (FlipConst a)) | 52 | deriving (Show1, Eq1) via (Const b) | ^^^^^ test/Spec/Contravariant.hs:52:13: error:ghc: panic! (the 'impossible' happened) (GHC version 8.6.3 for x86_64-unknown-linux): No skolem info: [b_a3eO] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcErrors.hs:2891:5 in ghc:TcErrors Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I'm using GHC 8.6.3 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16181> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16151: GHC 8.6 build failure on ARM
by GHC 14 Jan '19

14 Jan '19

#16151: GHC 8.6 build failure on ARM --------------------------------+---------------------------------------- Reporter: dustin | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Linux Architecture: arm | Type of failure: Building GHC failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------+---------------------------------------- I'm attempting to build the ghc-8.6 branch on ARM linux. I have GHC 8.2.2 and LLVM 6.0.1 installed. My only build.mk change is to set BuildFlavour=quick I've made it as far as "final phase" where I get the following failure: {{{ ===--- building final phase /usr/bin/make --no-print-directory -f ghc.mk phase=final all "inplace/bin/ghc-stage1" -static -O0 -H64m -Wall -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist- ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -DFS_NAMESPACE=rts -this-unit-id rts -optc-D NOSMP -dcmm-lint -i -irts -irts/dist/build -Irts/dist/build -irts/dist/build/./autogen -Irts/dist/build/./autogen -O2 -Wcpp-undef -Wnoncanonical-monad-instances -c rts/StgStartup.cmm -o rts/dist/build/StgStartup.o /tmp/ghc154171_0/ghc_8.s: Assembler messages: /tmp/ghc154171_0/ghc_8.s:32:0: error: Error: selected processor does not support `movw r7,:lower16:stg_enter_info' in ARM mode | 32 | movw r7, :lower16:stg_enter_info | ^ /tmp/ghc154171_0/ghc_8.s:33:0: error: Error: selected processor does not support `movt r7,:upper16:stg_enter_info' in ARM mode | 33 | movt r7, :upper16:stg_enter_info | ^ /tmp/ghc154171_0/ghc_8.s:231:0: error: Error: selected processor does not support `movw r2,#32512' in ARM mode | 231 | movw r2, #32512 | ^ /tmp/ghc154171_0/ghc_8.s:233:0: error: Error: selected processor does not support `movt r2,#640' in ARM mode | 233 | movt r2, #640 | ^ `gcc' failed in phase `Assembler'. (Exit code: 1) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16151> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15010: Application (warp) server crashing periodically with "TSO object entered"
by GHC 14 Jan '19

14 Jan '19

#15010: Application (warp) server crashing periodically with "TSO object entered" -------------------------------------+------------------------------------- Reporter: ramirez7 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.3 Component: Runtime | Version: 8.0.2 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: -------------------------------------+------------------------------------- We are seeing one of our warp servers periodically crash with the following error: {{{ Apr 06 10:44:28 stdouterr.log: binary-name-elided: internal error: TSO object entered! Apr 06 10:44:28 stdouterr.log: (GHC version 8.0.2 for x86_64_unknown_linux) }}} We are sometimes seeing CPU/memory spikes concurrently with this error, but not always. We are running very similar servers for other applications and they are '''not''' experiencing this error. But this server is one of our highest- load ones. Other tickets I found with this error: * https://ghc.haskell.org/trac/ghc/ticket/12383 * https://ghc.haskell.org/trac/ghc/ticket/8316 But these seem to be happening in ghci and ghc itself, not in a binary compiled by ghc. Questions I have: * What exactly is this error? * Is there anything else we can do on our side to help debug? Any artifacts that should be produced upon crash? * Should we consider upgrading our GHC version from 8.0.2 to get a bugfix? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15010> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14645: Allow type family in data family return kind
by GHC 14 Jan '19

14 Jan '19

#14645: Allow type family in data family return kind -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1-alpha1 Keywords: TypeInType, | Operating System: Unknown/Multiple TypeFamilies | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC currently allows {{{#!hs data family DF1 :: k1 -> k2 }}} where it's expected (and checked) that all data ''instances'' have a return kind of `Type`. (Perhaps `k2` expands to `Type -> Type`, for example.) However, it rejects {{{#!hs type family TF (x :: Type) :: Type data family DF2 :: x -> TF x }}} when that's clearly just as sensible as the first definition. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14645> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16177: Rename Q (TExp a) to Code a
by GHC 14 Jan '19

14 Jan '19

#16177: Rename Q (TExp a) to Code a -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Template | Version: 8.6.3 Haskell | Keywords: | Operating System: Unknown/Multiple TypedTemplateHaskell | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I propose that we modify the typed template haskell API so that quoting an expression of type `t` results in a value of type `Code t` rather than `Q (TExp a)` and the splice construct requires an argument of type `Code a` to produce a value of type `a`. The definition of `Code` is as follows. {{{ newtype Code a = Code (Q (TExp a)) }}} There are two good reasons to do this. 1. `Q (TExp a)` is ugly and leaks implementation details to the user. Using effects from the `Q` monad is unsafe and against the principle of staged programming. 2. Writing instances for `Q (TExp a)` is quite difficult. It's much easier when the newtype is defined but at the cost of constant wrapping and unwrapping. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16177> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15839: DerivingStrategies defaulting warning has no associated enable/suppress flag
by GHC 14 Jan '19

14 Jan '19

#15839: DerivingStrategies defaulting warning has no associated enable/suppress flag -------------------------------------+------------------------------------- Reporter: tejon | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When `DerivingStrategies`, `DeriveAnyClass` and `GeneralizedNewtypeDeriving` are enabled together, an instance that could be derived with either `newtype` or `anyclass` throws a warning when no strategy is specified. It appears to be impossible to suppress this warning. Even `-w` doesn't work! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15839> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16054: Unable to build stage3 with hadrian
by GHC 14 Jan '19

14 Jan '19

#16054: Unable to build stage3 with hadrian -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- It seems that stage3 is unsupported by hadrian. I am trying to build the target `_build/stage2/bin/ghc` but it is reported as an unknown program. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16054> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16175: wrong wording (and possibly wrong location) in parse error message for "do $ bar"
by GHC 13 Jan '19

13 Jan '19

#16175: wrong wording (and possibly wrong location) in parse error message for "do $ bar" -------------------------------------+------------------------------------- Reporter: j.waldmann | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- Not a bug, as GHC correctly rejects an invalid program. Still - {{{ Prelude> foo x = do $ bar ; return () <interactive>:1:20: error: Parse error: module header, import declaration or top-level declaration expected. }}} Of the three suggestions, only "top-level declaration" can actually happen here (as this also happens deep inside a module). For reference, * ghc-7.10 : "parse error on input ‘=’" * ghc-8.0 : "naked expression at top level" * ghc-8.2 and later: as above I think the wording was introduced with https://ghc.haskell.org/trac/ghc/ticket/12146 Anyway one could also think that the actual error happened earlier, since after removing "return ()" as suggested by the error message, we get {{{ Prelude> foo x = do $ bar <interactive>:1:9: error: Empty 'do' block }}} so GHC could also use this as the original error message? By putting "; return ()" at the end, the 'do' block does not become non-empty? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16175> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16089: seq is not cooperating with :sprint in GHCi as expected
by GHC 13 Jan '19

13 Jan '19

#16089: seq is not cooperating with :sprint in GHCi as expected -------------------------------------+------------------------------------- Reporter: radrow | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.6.3 Keywords: seq sprint | Operating System: Linux strictness | Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I was playing around with strictness and performed following test: {{{#!hs Prelude> x = [True, False] Prelude> :sprint x x = _ Prelude> x `seq` True True Prelude> :sprint x x = _ }}} I completely don't understand why `x = _` at this moment. `seq` must evaluate one level of `x` achieving `x = True : _` to ensure that it is not `undefined`, so why is this information lost? I am testing it on GHCi version 8.6.3, but it is not reproducible on other versions (checked on 8.4.4, 8.2.2 and 7._._). I have asked about it on SO, so if this behavior is intended I kindly ask for explaination here [https://stackoverflow.com/questions/53898220 /sprint-and-seq-together-missing-evaluation] to let others know. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16089> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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