July 2018 - ghc-tickets

[GHC] #15206: Strictness annotations bind more tightly than doc strings on non-record data declarations
by GHC 10 Jul '18

10 Jul '18

#15206: Strictness annotations bind more tightly than doc strings on non-record data declarations -------------------------------------+------------------------------------- Reporter: harpocrates | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 (Parser) | 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): Phab:D4727 | Wiki Page: -------------------------------------+------------------------------------- Consider the following declaration: {{{#!hs data Point = Point -- ^ a 2D point !Int -- ^ x coord !Int -- ^ y coord }}} With `-haddock` enabled, the first field parses as {{{ ({ bad.hs:2:16-32 } (HsDocTy ({ bad.hs:2:16-19 } (HsBangTy (HsSrcBang (NoSourceText) (NoSrcUnpack) (SrcStrict)) ({ bad.hs:2:17-19 } (HsTyVar (NotPromoted) ({ bad.hs:2:17-19 } (Unqual {OccName: Int})))))) ({ bad.hs:2:21-32 } (HsDocString {FastString: " x coord"})))) }}} However, this is incorrect since further down the compilation pipeline, strictness and unpackedness annotations are only looked for at the top- level of a field (meaning the above example hits the `strictness annotation cannot appear nested inside a type` error). We want this instead: {{{ ({ bad.hs:2:16-32 } (HsBangTy (NoExt) (HsSrcBang (NoSourceText) (NoSrcUnpack) (SrcStrict)) ({ bad.hs:2:17-32 } (HsDocTy (NoExt) ({ bad.hs:2:17-19 } (HsTyVar (NoExt) (NotPromoted) ({ bad.hs:2:17-19 } (Unqual {OccName: Int})))) ({ bad.hs:2:21-32 } (HsDocString {FastString: " x coord"})))))) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15206> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14975: Refactor (Maybe Coercion)
by GHC 10 Jul '18

10 Jul '18

#14975: Refactor (Maybe Coercion) -------------------------------------+------------------------------------- Reporter: tdammers | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #11735 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As discussed here: https://phabricator.haskell.org/D4395#inline-34607 Define a type {{{#!hs data MCoercion = MRefl | MCo Coercion }}} This is isomorphic to {{{Maybe Coercion}}} but useful in a number of places, and super-helpful documentation. (eg {{{MRefl}}} is much more perspicuous than {{{Nothing}}}. Define this in {{{Coercion.hs}}} I think. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14975> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11070: Type-level arithmetic of sized-types has weaker inference power than in 7.8
by GHC 10 Jul '18

10 Jul '18

#11070: Type-level arithmetic of sized-types has weaker inference power than in 7.8 -------------------------------------+------------------------------------- Reporter: cactus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- Given the following definitions (just a copy of the relevant bits from sized-types 0.3.5.1, to keep this example self-contained): {{{ -- Copied from sized-types 0.3.5.1 data X0 = X0 data N1 = N1 data X0_ a = X0_ Integer data X1_ a = X1_ Integer type X1 = X1_ X0 type X2 = X0_ (X1_ X0) class Size ix instance Size X0 instance Size a => Size (X1_ a) instance Size a => Size (X0_ a) type family APP0 a type instance APP0 X0 = X0 type instance APP0 N1 = X0_ N1 type instance APP0 (X1_ a) = X0_ (X1_ a) type instance APP0 (X0_ a) = X0_ (X0_ a) type family APP1 a type instance APP1 X0 = X1_ X0 type instance APP1 N1 = N1 type instance APP1 (X1_ a) = X1_ (X1_ a) type instance APP1 (X0_ a) = X1_ (X0_ a) type family SUCC a type instance SUCC X0 = X1_ X0 type instance SUCC N1 = X0 type instance SUCC (X1_ a) = APP0 (SUCC a) type instance SUCC (X0_ a) = APP1 a type family ADD a b type instance ADD a X0 = a type instance ADD X0 a = a type instance ADD X0 N1 = N1 type instance ADD N1 N1 = APP0 N1 type instance ADD N1 (X1_ b) = APP0 b type instance ADD N1 (X0_ b) = APP1 (ADD N1 b) type instance ADD (X1_ a) N1 = APP0 a type instance ADD (X0_ a) N1 = APP1 (ADD a N1) type instance ADD (X1_ a) (X1_ b) = APP0 (SUCC (ADD a b)) type instance ADD (X1_ a) (X0_ b) = APP1 (ADD a b) type instance ADD (X0_ a) (X1_ b) = APP1 (ADD a b) type instance ADD (X0_ a) (X0_ b) = APP0 (ADD a b) type family NOT a type instance NOT X0 = N1 type instance NOT N1 = X0 type instance NOT (X1_ a) = APP0 (NOT a) type instance NOT (X0_ a) = APP1 (NOT a) type SUB a b = ADD a (SUCC (NOT b)) }}} The following module typechecks with GHC 7.8.3: {{{ data B w = B (&*) :: (Size n, Size n', Size (ADD n' n), n ~ SUB (ADD n' n) n', n' ~ SUB (ADD n' n) n) => [(a, B n)] -> [(b, B n')] -> [((a, b), B (ADD n' n))] mks &* args = undefined foo :: [((), B X1)] foo = [((), B)] bar :: [(((), ()), B X2)] bar = [((), B)] &* foo }}} However, it fails with GHC 7.10.2, with {{{ /tmp/GHCBug.hs:70:7: Couldn't match type ‘ADD X1 n0’ with ‘X0_ (X1_ X0)’ The type variable ‘n0’ is ambiguous Expected type: [(((), ()), B X2)] Actual type: [(((), ()), B (ADD X1 n0))] In the expression: [((), B)] &* foo In an equation for ‘bar’: bar = [((), B)] &* foo /tmp/GHCBug.hs:70:17: Occurs check: cannot construct the infinite type: n0 ~ ADD (ADD X1 n0) N1 The type variable ‘n0’ is ambiguous Expected type: SUB (ADD X1 n0) X1 Actual type: n0 In the expression: [((), B)] &* foo In an equation for ‘bar’: bar = [((), B)] &* foo Failed, modules loaded: none. }}} The workaround/solution is to change the definition of `bar`: {{{ bar :: [(((), ()), B X2)] bar = [((), B :: B X1)] &* foo }}} This second version typechecks with GHC 7.10.2. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11070> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13109: CUSK improvements
by GHC 10 Jul '18

10 Jul '18

#13109: CUSK improvements -------------------------------------+------------------------------------- Reporter: simonpj | 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: -------------------------------------+------------------------------------- Inspired by looking at `RnTypes.bindLHsTyVarBndr`, and driven by #11592, Richard and I decided to make some improvements to the treatment of CUSKs. Here's a scrappy Skype dump as a memory-jogger; it is a memory-jogger, not a full description. Richard has notes too {{{ Richard Eisenberg: data F (x :: B a) data G (x :: C b) You have written a complete user-suppled kind signature, but the following variable is undetermined: a0 :: A Perhaps add a kind signature. Inferred kinds of user-written variables: b :: B a0 x :: C b SPJ claim: CUSKs should be handled INDIVIDUALLY and in isoloation, just like term-level type signatures SPJ claim: get rid of the "after the ::" side condition for data types (last bullet of HsDecls Note about CUSKs All of this should mean (SPJ claims) no need for dep_vars returns by bindHsQTyVar, bindLHsTyVarBnrds etc ToDo: clarify comments etc in bindLHStyVarBndr Related to D2914 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13109> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11282: Injectivity annotation fails in the presence of higher-rank use of constraint family
by GHC 09 Jul '18

09 Jul '18

#11282: Injectivity annotation fails in the presence of higher-rank use of constraint family -------------------------------------+------------------------------------- Reporter: goldfire | 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 | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE TypeFamilies, RankNTypes #-} module Bug where import GHC.Exts type family F a = r | r -> a type family G a :: Constraint meth :: (G a => F a) -> () meth = undefined }}} I get {{{ Bug.hs:10:9: error: • Could not deduce: F a ~ F a0 from the context: G a0 bound by the type signature for: meth :: G a0 => F a0 at Bug.hs:10:9-26 NB: ‘F’ is a type function, and may not be injective The type variable ‘a0’ is ambiguous • In the ambiguity check for ‘meth’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: meth :: (G a => F a) -> () }}} The presence of `G a` is critical for exhibiting this bug. If I replace `G a` with `Show a` the problem disappears. This one was actually encountered in an attempt to do Useful Work, not just idle typecheckery. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11282> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12928: Too easy to trigger CUSK condition using TH
by GHC 09 Jul '18

09 Jul '18

#12928: Too easy to trigger CUSK condition using TH -------------------------------------+------------------------------------- Reporter: int-index | Owner: Type: feature | Status: new request | Priority: high | Milestone: Component: Compiler | Version: 8.0.1 (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: -------------------------------------+------------------------------------- While trying to make `singletons` class promotion work with kind- polymorphic type variables, I've encountered a problem regarding CUSKs. Consider this class: {{{ $(promoteOnly [d| class Cls a where fff :: Proxy a -> () |]) }}} The generated TH (slightly simplified by hand) looks like this: {{{ type FffSym1 (t_alvm :: Proxy a1627472612) = Fff t_alvm data FffSym0 (l_alvn :: TyFun (Proxy a1627472612) ()) type instance Apply FffSym0 l_alvn = FffSym1 l_alvn class PCls a_alve where type Fff (arg_alvl :: Proxy a_alve) :: () }}} However, it fails to compile with the following error: {{{ cusk.hs:25:1: error: You have written a *complete user-suppled kind signature*, but the following variable is undetermined: k0 :: * Perhaps add a kind signature. Inferred kinds of user-written variables: a1627472612 :: k0 l_alvn :: TyFun (Proxy a1627472612) () }}} As suggested by the error message, we need to specify the kind in its entirety (write a proper CUSK). So to sidestep the issue, we can write {{{ data FffSym0 (l_alvn :: TyFun (Proxy (a1627472612 :: k)) ()) }}} and it'll work. However, this means that the TH code generator should perform some guesswork to modify kind annotations. It sounds like a minefield — too much can go wrong, so it'd be great to avoid doing so. Looking at the module `TcHsType` in the GHC sources, I see that the error is reported by the `kcHsTyVarBndrs` function: {{{ -- If there are any meta-tvs left, the user has -- lied about having a CUSK. Error. ; let (meta_tvs, good_tvs) = partition isMetaTyVar qkvs ; when (not (null meta_tvs)) $ report_non_cusk_tvs (qkvs ++ tc_tvs) }}} However, I don't see why we can't generalize over `meta_tvs` instead of reporting a failure. I asked on IRC #ghc and ezyang suggested that it should be sound. Below I attach a self-contained example that demonstrates the issue and has no dependencies except `base`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12928> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14091: When PolyKinds is on, suggested type signatures seem to require TypeInType
by GHC 09 Jul '18

09 Jul '18

#14091: When PolyKinds is on, suggested type signatures seem to require TypeInType -------------------------------------+------------------------------------- Reporter: jberryman | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- We compile the following with -Wall {{{ {-# LANGUAGE PolyKinds #-} import Data.Bits import Data.Word data Hash128 a = Hash128 { hashWord128_0 :: !Word64, hashWord128_1 :: !Word64 } deriving (Show, Read, Eq) -- These instances copied from 'FixedPoint-simple': instance FiniteBits (Hash128 a) where finiteBitSize ~(Hash128 a b) = finiteBitSize a + finiteBitSize b instance Bits (Hash128 a) where popCount (Hash128 h l) = popCount h + popCount l bit i | i >= 64 = Hash128 (bit $ i - 64) 0 | otherwise = Hash128 0 (bit i) complement = pointwise complement (.&.) = pointwise2 (.&.) (.|.) = pointwise2 (.|.) xor = pointwise2 xor setBit (Hash128 h l) i | i >= 64 = Hash128 (setBit h (i - 64)) l | otherwise = Hash128 h (setBit l i) shiftL (Hash128 h l) i | i > finiteBitSize l = shiftL (Hash128 l 0) (i - finiteBitSize l) | otherwise = Hash128 ((h `shiftL` i) .|. (l `shiftR` (finiteBitSize l - i))) (l `shiftL` i) shiftR (Hash128 h l) i | i > finiteBitSize h = shiftR (Hash128 0 h) (i - finiteBitSize h) | otherwise = Hash128 (h `shiftR` i) ((l `shiftR` i) .|. h `shiftL` (finiteBitSize h - i)) isSigned _ = False testBit (Hash128 h l) i | i >= finiteBitSize l = testBit h (i - finiteBitSize l) | otherwise = testBit l i rotateL w i = shiftL w i .|. shiftR w (128 - i) rotateR w i = shiftR w i .|. shiftL w (128 - i) bitSize _ = 128 bitSizeMaybe _ = Just 128 pointwise op (Hash128 a b) = Hash128 (op a) (op b) pointwise2 op (Hash128 a b) (Hash128 c d) = Hash128 (op a c) (op b d) }}} get a warning like: {{{ Top-level binding with no type signature: pointwise2 :: forall k1 k2 k3 (a1 :: k2) (a2 :: k1) (a3 :: k3). (Word64 -> Word64 -> Word64) -> Hash128 a1 -> Hash128 a2 -> Hash128 a3 }}} but that's not a valid signature. Pasting it in causes GHC to suggest RankNTypes with an error, and then to suggest TypeInType, at which point it compiles. I want to just be able to paste in the signature from the warning. Related to #6065 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14091> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15337: Warning not showing up when deprecated variable is explicitly imported
by GHC 09 Jul '18

09 Jul '18

#15337: Warning not showing up when deprecated variable is explicitly imported -------------------------------------+------------------------------------- Reporter: alanasp | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: deprecation | Operating System: Unknown/Multiple warning | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In the case below a deprecation warning does not show up. {{{#!hs {- ModuleA -} module ModuleA where {-# DEPRECATED func "func is deprecated" #-} func :: Int func = 42 {- ModuleB -} module ModuleB where import ModuleA(func) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15337> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15356: Template Haskell should turn off RebindableSyntax in quotes
by GHC 08 Jul '18

08 Jul '18

#15356: Template Haskell should turn off RebindableSyntax in quotes -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Template | Version: 8.4.3 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: -------------------------------------+------------------------------------- If I say {{{#!hs {-# LANGUAGE RebindableSyntax, TemplateHaskellQuotes #-} module Bug ( quote ) where quote = [| if 5>3 then 'x' else 'y' |] }}} GHC complains that `ifThenElse` and `fromInteger` are not in scope. If I then bring these into scope somehow, then the resulting quote does not use them. I think it's correct that the resulting quote doesn't use the rebindable syntax -- a quote should just stand for a convenient way or writing the TH AST. But then we shouldn't complain about missing rebindable syntax bits inside of a quote. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15356> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15311: MCoercion lacks an Outputable instance
by GHC 08 Jul '18

08 Jul '18

#15311: MCoercion lacks an Outputable instance -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: newcomer | 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 should be an outputable instance for `MCoercion` so it can be printed when debugging. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15311> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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