November 2017 - ghc-tickets

[GHC] #14203: GHC-inferred type signature doesn't actually typecheck
by GHC 03 Nov '17

03 Nov '17

#14203: GHC-inferred type signature doesn't actually typecheck -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 (Type checker) | Keywords: TypeInType, | Operating System: Unknown/Multiple TypeFamilies | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This code typechecks: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Kind data TyFun :: * -> * -> * type a ~> b = TyFun a b -> * infixr 0 ~> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2 data family Sing :: k -> * data Sigma (a :: *) :: (a ~> *) -> * where MkSigma :: forall (a :: *) (p :: a ~> *) (x :: a). Sing x -> Apply p x -> Sigma a p data instance Sing (z :: Sigma a p) where SMkSigma :: Sing sx -> Sing px -> Sing (MkSigma sx px) }}} I was curious to know what the full type signature of `SMkSigma` was, so I asked GHCi what the inferred type is: {{{ λ> :i SMkSigma data instance Sing z where SMkSigma :: forall a (p :: a ~> *) (x :: a) (sx :: Sing x) (px :: Apply p x). (Sing sx) -> (Sing px) -> Sing ('MkSigma sx px) }}} I attempted to incorporate this newfound knowledge into the program: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Kind data TyFun :: * -> * -> * type a ~> b = TyFun a b -> * infixr 0 ~> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2 data family Sing :: k -> * data Sigma (a :: *) :: (a ~> *) -> * where MkSigma :: forall (a :: *) (p :: a ~> *) (x :: a). Sing x -> Apply p x -> Sigma a p data instance Sing (z :: Sigma a p) where SMkSigma :: forall a (p :: a ~> *) (x :: a) (sx :: Sing x) (px :: Apply p x). Sing sx -> Sing px -> Sing (MkSigma sx px) }}} But to my surprise, adding this inferred type signature causes the program to no longer typecheck! {{{ GHCi, version 8.3.20170907: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:23:31: error: • Expected kind ‘Apply p0 x’, but ‘px’ has kind ‘Apply p1 x’ • In the first argument of ‘Sing’, namely ‘px’ In the type ‘Sing px’ In the definition of data constructor ‘SMkSigma’ | 23 | Sing sx -> Sing px -> Sing (MkSigma sx px) | ^^ }}} I'm showing the output of GHC HEAD here, but this bug can be reproduced all the way back to GHC 8.0.1. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14203> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14417: Overly specific instances may not be resolved
by GHC 03 Nov '17

03 Nov '17

#14417: Overly specific instances may not be resolved -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.3 (Type checker) | 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} class A x class A x => B x class A x => C x instance B x => C x }}} produces {{{ BrokenSuper.hs:8:10: error: • Could not deduce (A x) arising from the superclasses of an instance declaration from the context: B x bound by the instance declaration at BrokenSuper.hs:8:10-19 Possible fix: add (A x) to the context of the instance declaration • In the instance declaration for ‘C x’ | 8 | instance B x => C x }}} This was noticed in [https://stackoverflow.com/questions/47093627/can-not- deduce-superclass this SO question] and reduced by Daniel Wagner. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14417> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5889: -fno-prof-count-entries leads to linking errors
by GHC 03 Nov '17

03 Nov '17

#5889: -fno-prof-count-entries leads to linking errors -------------------------------------+------------------------------------- Reporter: akio | Owner: bgamari Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): > However, the tick remains in the unfolding * Why? If it is dropped in the RHS why isn't it dropped in the unfolding too? * Also, when that unfolding is later inlined at a call site, why isn't the tick eliminated then? Still, I suppose alternative (2) in comment:10 is also a plausible belt- and-braces approach. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5889#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10577: Use empty cases where appropriate when deriving instances for empty types
by GHC 02 Nov '17

02 Nov '17

#10577: Use empty cases where appropriate when deriving instances for empty types -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- In some sense the correct instance for {{{ data X deriving instance Eq X }}} is not (what GHC currently produces) {{{ instance Eq X where (==) = error "Void ==" }}} but rather {{{ instance Eq X where a == b = case a of {} -- using the EmptyCase extension }}} See comments starting at ticket:7401#comment:28 for justification. The list of classes that GHC can currently derive is * Eq, Ord, Enum, Bounded, Show, Read (Haskell 2010 Report) * Functor, Foldable, Traversable, Typeable, Generic, Data, "any class" (`-XDerive*`) Deriving Enum and Bounded is not currently allowed for empty data types. The `showList` method of Show and the whole Read instance are easy and already implemented correctly. All the remaining methods of Haskell 2010 derivable type classes take at least one argument of the instance head type `a`. I propose that all these methods be defined as an empty case on the first such argument. Similarly in Functor, Foldable and Traversable, each method has a single argument of the form `t _` where `t :: * -> *` is the instance head type, and the method should be defined as an empty case on that argument. In all these cases so far, the derived methods for a non-empty type would, at the outermost level, be a (non-empty) case on that first argument, or the equivalent (series of pattern matches, one for each constructor), so the use of an empty case is justified for an empty type. Typeable does not care about the values or even the kind of the type at all, so it's not relevant here. Generic and especially Data are above my pay grade, but generally I expect that methods which are normally defined by case analysis on an argument of the instance head type should be defined by an empty case, and methods that (sometimes) produce a value of the instance head type should do whatever they normally do when unable to produce such a value (like `readsPrec` returning an empty list, or `read` calling `error` (if `read` were actually a method of `Read`)). `DeriveAnyClass` doesn't generate any new code, so like Typeable it's not relevant. None of this behavior is specified by the Haskell 2010 Report, which disallows deriving any class for a type with no constructors; but see #7401. So, we are entitled to do what we think is best here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10577> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so.
by GHC 02 Nov '17

02 Nov '17

#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: (none) Type: feature request | Status: closed Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 7.6.1 Resolution: fixed | Keywords: deriving, | newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | deriving/should_run/T7401, | deriving/should_run/T7401_fail Blocked By: | Blocking: Related Tickets: #10577, #13117 | Differential Rev(s): Phab:D4047 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: patch => closed * testcase: => deriving/should_run/T7401, deriving/should_run/T7401_fail * resolution: => fixed * milestone: => 8.4.1 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:54> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5889: -fno-prof-count-entries leads to linking errors
by GHC 02 Nov '17

02 Nov '17

#5889: -fno-prof-count-entries leads to linking errors -------------------------------------+------------------------------------- Reporter: akio | Owner: bgamari Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Thanks, a testcase would be great! Indeed I didn't notice `Note [inline sccs]`. It's surprising that this bug wasn't spotted earlier given that this could happen for any binding, not just those marked as INLINE (since GHC may decide on its own to expose an unfolding). I guess `-fno-prof-count-entries` doesn't see much use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5889#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14412: Can't run tests with sdist -> bindist -> test
by GHC 02 Nov '17

02 Nov '17

#14412: Can't run tests with sdist -> bindist -> test -------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Build System | 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 you want to make source dist, compile it into bindist then run tests with the bindist, it fails. {{{ mk/get-win32-tarballs.sh download all ./boot ./configure "$@" make sdist mkdir -p sdist-build-dir pushd sdist-build-dir shopt -s extglob tar xvfJ ../sdistprep/ghc-*+([[:digit:]])-src.tar.xz sdist-build-dir cd ghc-* ./boot ./configure "$@" make -j$THREADS make binary-dist popd mkdir -p bdist-test-dir pushd bdist-test-dir tar xvfJ ../sdist-build-dir/ghc-*/ghc-*.tar.xz tar xvfJ ../sdistprep/ghc*testsuite.tar.xz cd ghc-* ./configure make test }}} I do not have the failure error on hand but it had to do with Haddock trying to read its version from .cabal file which was not included in the bindist/sdist. I have communicated this problem to Ben at the time and this ticket is just to track progress. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14412> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5889: -fno-prof-count-entries leads to linking errors
by GHC 02 Nov '17

02 Nov '17

#5889: -fno-prof-count-entries leads to linking errors -------------------------------------+------------------------------------- Reporter: akio | Owner: bgamari Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): What a great diagnosis. I will construct a test case for this next week if you have not already done so. Note [inline sccs] in Coverage.hs seems relevant. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5889#comment:11> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10871: Implement "buildable" interface files which can be directly compiled without source
by GHC 02 Nov '17

02 Nov '17

#10871: Implement "buildable" interface files which can be directly compiled without source -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- A fat interface file is like a normal hi file, but with extra information so that GHC can *recompile* the associated module without having to parse, rename and typecheck the source code again. The proposed command-line interface is something like (subject to bikeshedding): {{{ ghc -c A.hs -fno-code -fwrite-buildable-interface # produces a .hi-build file, then ghc -c A.hi-build # completes building, as if ghc -c A.hs had been called }}} The primary motivation for this is to support partially compiling indefinite packages, which cannot be compiled to object code due to the fact that some of the dependencies haven't been provided yet. However, there are some other cases where this might be useful: 1. Supercompilation requires having the source of all bindings, buildable interfaces can make this information available, even beyond what storing inlinings might provide 2. A buildable interface file can be used to build variants of a source, e.g. profiling and optimization, even "on the fly" by GHC if necessary. And maybe more we haven't thought of yet. The primary function you need to implement is a function from `ModIface`/`ModDetails` to `TcGblEnv`, which can then be fed to the desugarer. I'm looking at what things we need to add to `ModIface` to support this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10871> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5889: -fno-prof-count-entries leads to linking errors
by GHC 02 Nov '17

02 Nov '17

#5889: -fno-prof-count-entries leads to linking errors -------------------------------------+------------------------------------- Reporter: akio | Owner: bgamari Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * cc: Jaffacake (added) Comment: Off the top of my head I see a few general directions for fixing this: 1. Be less aggressive about dropping "useless" ticks 2. Ensure that during codegen we look for SCCs in unfoldings as well as the RHS itself -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5889#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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