October 2018 - ghc-tickets

[GHC] #15594: --abi-hash with Backpack incorrectly loads modules from dependent packages
by GHC 11 Nov '18

11 Nov '18

#15594: --abi-hash with Backpack incorrectly loads modules from dependent packages -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Repro at: https://github.com/alexbiehl/cabal-backpack-register- repro/blob/master/src/Lib.hs -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15594> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15611: scope errors lie about what modules are imported
by GHC 11 Nov '18

11 Nov '18

#15611: scope errors lie about what modules are imported -------------------------------------+------------------------------------- Reporter: dmwit | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.2 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: -------------------------------------+------------------------------------- Here's Test.hs: {{{ module Test where }}} And here's a ghci session: {{{ % ghci Test.hs GHCi, version 8.4.2: http://www.haskell.org/ghc/ :? for help *Test> Test.foo <interactive>:1:1: error: Not in scope: ‘Test.foo’ No module named ‘Test’ is imported. }}} That "No module named ‘Test’ is imported." part seems blatantly wrong (and persists even if I explicitly `import Test` rather than using the implicit loading of the module). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15611> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11647: GHCi does not honour implicit `module Main (main) where` for re-exported `main`s
by GHC 11 Nov '18

11 Nov '18

#11647: GHCi does not honour implicit `module Main (main) where` for re-exported `main`s -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | 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: -------------------------------------+------------------------------------- Haskell2010 states: > An abbreviated form of module, consisting only of the module body, is permitted. If this is used, the header is assumed to be `module Main(main) where`. Consider the following two modules: {{{#!hs -- module Main (main) where import Main2 (main) }}} {{{#!hs module Main2 (main) where main :: IO () main = return () }}} A non-interactive GHC happily compiles `ghc --make Main`, however, GHCi fails with {{{ $ ghci Main.hs GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help unknown option: 'c' [1 of 2] Compiling Main2 ( Main2.hs, interpreted ) [2 of 2] Compiling Main ( Main.hs, interpreted ) Main.hs:1:1: The IO action ‘main’ is not exported by module ‘Main’ Failed, modules loaded: Main2. }}} For GHCi we need to uncomment the explicit `module Main (main) where` line to make it work. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11647> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15820: Document the proposals process in the GHC manual
by GHC 10 Nov '18

10 Nov '18

#15820: Document the proposals process in the GHC manual -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Documentation | Version: 8.6.1 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: -------------------------------------+------------------------------------- The ghc-proposals process has proved robust, in my opinion. We should explicitly state that such a process exists and point users to it from the manual. This came up as I was documenting the solution to #15743 in the manual. The end result there is very much a free design decision, and I wanted to invite readers to propose changes if they disagree with the design. But there's no good way to do so, currently. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15820> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9692: Template Haskell reification for Data Families is buggy?
by GHC 08 Nov '18

08 Nov '18

#9692: Template Haskell reification for Data Families is buggy? -------------------------------------+------------------------------------- Reporter: hpacheco | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: TemplateHaskell | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I have found an example where I think that the TH reification for data/newtype families is incorrect, in that if forgets non-instantiated type variables in instance declarations. For the attached example, it will infer the Info: {{{#!hs FamilyI (FamilyD DataFam TyFamReifyDefs.F [PlainTV a_1627399879,PlainTV b_1627399880] (Just StarT)) [DataInstD [] TyFamReifyDefs.F [ConT GHC.Types.Int] [NormalC TyFamReifyDefs.FInt [(NotStrict,VarT x_1627399881)]] []] }}} Note how the variable x is not declared in the body of the DataInstD. Since it does not need to have the same name as the family-declared variable, substituing is non-trivial this way... -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9692> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14179: "Conflicting family instance" error pretty prints data family instances poorly
by GHC 08 Nov '18

08 Nov '18

#14179: "Conflicting family instance" error pretty prints data family instances poorly -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 (Type checker) | Keywords: TypeFamilies | 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: -------------------------------------+------------------------------------- This can be observed on GHC 8.0.1 or later: {{{#!hs {-# LANGUAGE TypeFamilies #-} module Bug where data family Fam a data instance Fam Int data instance Fam Int }}} {{{ $ /opt/ghc/8.2.1/bin/ghci Bug.hs GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:5:15: error: Conflicting family instance declarations: Fam Int = -- Defined at Bug.hs:5:15 Fam Int = -- Defined at Bug.hs:6:15 | 5 | data instance Fam Int | ^^^ }}} Notice how GHC attempts to pretty-print the RHS by using a `=` symbol, but there is no RHS! This gets even more confusing with this program, which requires GHC HEAD: {{{#!hs {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeFamilies #-} module Bug where data family Fam :: k -> * data instance Fam :: * -> * data instance Fam :: * -> * }}} {{{ $ ghc5/inplace/bin/ghc-stage2 --interactive Bug.hs GHCi, version 8.3.20170818: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:6:15: error: Conflicting family instance declarations: Fam = -- Defined at Bug.hs:6:15 Fam = -- Defined at Bug.hs:7:15 | 6 | data instance Fam :: * -> * | ^^^ }}} Not only is there no RHS, but the kind signatures of each instance aren't printed either. This is an issue, since the entire reason why the two instances conflict are because of their kinds! We should rethink how data family instances are pretty printer here to avoid this issue. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14179> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11335: Add instance (Ix a, Read a, Read b) => Read (UArray a b)
by GHC 08 Nov '18

08 Nov '18

#11335: Add instance (Ix a, Read a, Read b) => Read (UArray a b) -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: libraries | Version: 7.8.3 (other) | Keywords: array | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `Array` has `Eq`, `Ord`, `Show` and `Read` instances but `UArray` only has `Eq`, `Ord` and `Show`. Add the missing `Read` instance. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11335> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13933: Support Typeable instances for types with coercions
by GHC 07 Nov '18

07 Nov '18

#13933: Support Typeable instances for types with coercions -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Keywords: TypeInType, | Operating System: Unknown/Multiple Typeable | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If I say {{{#!hs {-# LANGUAGE GADTs, TypeApplications, TypeInType #-} module Bug where import Type.Reflection data G a where MkG :: a ~ Bool => G a rep = typeRep @MkG }}} I get {{{ Bug.hs:10:7: error: • No instance for (Typeable <>) arising from a use of ‘typeRep’ • In the expression: typeRep @MkG In an equation for ‘rep’: rep = typeRep @MkG | 10 | rep = typeRep @MkG | }}} First off, the error message is confusing, mentioning the mysterious `<>`. But more importantly, it would be nice if the `Typeable` mechanism supported coercions. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13933> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15710: Should accept a type that needs coercion quantification
by GHC 07 Nov '18

07 Nov '18

#15710: Should accept a type that needs coercion quantification -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 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 {{{ f :: forall k (f :: k) (x :: k1). (k ~ (k1 -> *)) => f x f = error "uk" }}} Should we accept it? Now that we have coercion quantification (Trac #15497), I think the answer should be yes, with the elaborated signature being {{{ f :: forall k (f::k) (x::k1). forall (co :: k ~# (k1->*)). (f |> co) x }}} But there is a problem: the user wrote `k ~ (k1 -> *)`, and that's a boxed value that we can't take apart in types. I'm not sure what to do here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15710> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11008: GND with Type Families
by GHC 07 Nov '18

07 Nov '18

#11008: GND with Type Families -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- In the following code: {{{ {-# LANGUAGE TypeFamilies, FlexibleContexts, UndecidableInstances #-} class C r type family F r newtype Foo r = Foo r instance (C (F r), Eq r) => Eq (Foo r) newtype Bar r = Bar (Foo r) deriving (Eq) }}} GHC produces the error {{{ No instance for (C (F r)) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Eq (Bar r)) }}} If I enable `StandaloneDeriving`, I am able to derive the instance: `deriving instance (Eq (Foo r)) => Eq (Bar r)` [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/deriving.ht… #newtype-deriving The docs] indicate that this is exactly the instance that should be generated by GND for `newtype T v1..vn = MkT (t vk+1..vn) deriving (C t1..tj)`, where my code uses the following parameters: {{{ T = Bar v1 = r n = 1 MkT = Bar t = Foo r k= 1 C = Eq j = 0 }}} and all of the conditions enumerated in the docs seem to be met. Furthermore, `Bar` seems to fit squarely into the format of `data T1` in section 7.5.1 of the same documentation, which indicates it should not need `StandaloneDeriving`. It seems that the type family constraint on the `Eq` instance for `Foo` is causing the problem, but it's not clear why I'm forced to write a standalone instance that is identical to the one that should be generated by GND. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11008> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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