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[GHC] #14300: FreeBSD 10.3 toolchain is terribly broken
by GHC 06 Oct '17

06 Oct '17

#14300: FreeBSD 10.3 toolchain is terribly broken -------------------------------------+------------------------------------- Reporter: bgamari | 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: #13974 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- == `ld.bfd` with `SplitSections=NO` Fails in the final bindist test with, {{{ /usr/bin/install -c -m 755 libraries/gen_contents_index "/usr/home/ben /bin- dist-8.2.1.20170929-FreeBSD/test/inst/share/doc/ghc-8.2.1.20170929/html/libraries/" [1 of 1] Compiling Main ( /usr/home/ben/bin- dist-8.2.1.20170929-FreeBSD/test/hi.hs, /usr/home/ben/bin- dist-8.2.1.20170929-FreeBSD/test/hi.o ) Linking /usr/home/ben/bin-dist-8.2.1.20170929-FreeBSD/test/hi ... /usr/bin/ld: Base__199.o: access beyond end of merged section (-24) /usr/bin/ld: Base__201.o: access beyond end of merged section (-24) ... }}} == `ld.bfd` with `SplitSections=YES` fails with, {{{ ... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14300> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14326: Panic on COMPLETE pragma with mismatched type variable order
by GHC 05 Oct '17

05 Oct '17

#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The motivating example is to allow patterns with phantom types to interact nicely with TypeApplications, so in the below we can do `L @Int :: a -> L a Int` to specify the phantom. {{{#!hs data E a b = L' a | R b pattern L :: forall b a. a -> E a b pattern L a = L' a {-# COMPLETE L, R #-} }}} The compiler balks {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-linux): mkOneConFull: Not TyConApp: c_a50V Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/deSugar/Check.hs:976:30 in ghc:Check Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14326> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14279: Type families interfere with specialisation rewrite rules
by GHC 05 Oct '17

05 Oct '17

#14279: Type families interfere with specialisation rewrite rules -------------------------------------+------------------------------------- Reporter: IvanTimokhin | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the attached file, in particular the function {{{#!hs vinr :: Length as -> VSum bs -> VSum (as ++ bs) }}} its specialised version {{{#!hs vinr0 :: Length '[] -> VSum as -> VSum as }}} and the rewrite rule {{{#!hs {-# RULES "vinr/0" vinr = vinr0 #-} }}} According to [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_ext… the relevant section of GHC user guide], `vinr` should be replaced with `vinr0` whenever the types match. However, the resulting Core for `test` contains the following (compiled with `ghc -O2`): {{{#!hs Test.test1 = case extractIdx @ 'Z @ '[Int] @ Int (Test.$WIZ @ Int @ '[]) Test.test2 of { Left other_aZf -> Test.$wvinl @ Length @ '[Int] @ (Remove 'Z '[Int]) other_aZf; Right x_aZg -> vinr @ (Remove 'Z '[Int]) @ '[Int] (Test.$WLZ `cast` ((Length (Sym (Test.D:R:Remove[0] <Int>_N <'[]>_N)))_R :: (Length '[] :: *) ~R# (Length (Remove 'Z '[Int]) :: *))) (Test.VInL @ '[Int] @ Int @ '[] @~ (<'[Int]>_N :: ('[Int] :: [*]) GHC.Prim.~# ('[Int] :: [*])) x_aZg) } }}} So the rule never fires, and `vinr` is still there, even though it is directly applied to `LZ :: Length '[]`. My dilettante analysis is that, for some reason, GHC keeps the `Remove 'Z '[Int]` as-is, not evaluating it to `'[]`, and, since the types don't match //syntactically//, doesn't apply the rule. In particular, if I replace type families with classes with functional dependencies, the rule fires as expected. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14279> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14222: Simple text fusion example results in rather duplicative code
by GHC 05 Oct '17

05 Oct '17

#14222: Simple text fusion example results in rather duplicative code -------------------------------------+------------------------------------- Reporter: bgamari | 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: -------------------------------------+------------------------------------- Consider this program, {{{#!hs module T14221 where import Data.Text as T isNumeric :: Text -> Bool isNumeric t = T.all isNumeric' t && T.any isNumber t where isNumber c = '0' <= c && c <= '9' isNumeric' c = isNumber c || c == 'e' || c == 'E' || c == '.' || c == '-' || c == '+' }}} Compiling with `-O` results in over 1 kilobyte of assembler. After looking at the simplified Core the issue becomes apparent: the case analysis of `isNumeric'` is duplicated six times, {{{#!hs case ww4_X2zB of { __DEFAULT -> GHC.Types.False; '+'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#); '-'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#); '.'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#); 'E'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#); 'e'# -> jump $wloop_all_s2z2 (GHC.Prim.+# ww3_s2z0 2#) }; }}} It seems to me that we would ideally try to share this bit. Of course, this may be quite tricky to do in practice. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14222> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14316: Precedence of type-level operators
by GHC 04 Oct '17

04 Oct '17

#14316: Precedence of type-level operators -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: precedence | Operating System: Unknown/Multiple TypeOperators DataKinds | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `a ': b ~ c ': d` seems to be parsed as `a ': (b ~ (c ': d))`. This is kind of unfortunate; It seems to me that (~) having a lower precedence would make more sense, i.e. have it parse as `(a ': b) ~ (c ': d)`. What //are// the precedences of (~) and XDataKind-lifted operators? The userguide mentions precedences when discussing TypeOperators, but not in combination with DataKinds, or the type-equality-constraint. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14316> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14322: Simplifying an instance context makes a rewrite rule no longer typecheck
by GHC 04 Oct '17

04 Oct '17

#14322: Simplifying an instance context makes a rewrite rule no longer typecheck -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 (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: -------------------------------------+------------------------------------- This code (taken from the `reducers` package) compiles: {{{#!hs {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} import Prelude (Applicative(..), Functor(..), (.)) class Semigroup m where (<>) :: m -> m -> m class Semigroup m => Reducer c m where snoc :: m -> c -> m newtype Traversal f = Traversal { getTraversal :: f () } instance Applicative f => Semigroup (Traversal f) where Traversal a <> Traversal b = Traversal (a *> b) instance Applicative f => Reducer (f a) (Traversal f) where Traversal a `snoc` b = Traversal (() <$ (a *> b)) snocTraversal :: Reducer (f ()) (Traversal f) => Traversal f -> f () -> Traversal f snocTraversal a = (<>) a . Traversal {-# RULES "snocTraversal" snoc = snocTraversal #-} }}} But on GHC 8.2.1 and later, it gives this warning: {{{ GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:21:18: warning: [-Wsimplifiable-class-constraints] • The constraint ‘Reducer (f ()) (Traversal f)’ matches an instance declaration instance Applicative f => Reducer (f a) (Traversal f) -- Defined at Bug.hs:18:10 This makes type inference for inner bindings fragile; either use MonoLocalBinds, or simplify it using the instance • In the type signature: snocTraversal :: Reducer (f ()) (Traversal f) => Traversal f -> f () -> Traversal f | 21 | snocTraversal :: Reducer (f ()) (Traversal f) => Traversal f -> f () -> Traversal f | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ }}} I decided to follow GHC's orders and reduce the `Reducer (f ()) (Traversal f)` context to just `Applicative f`: {{{#!hs {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} import Prelude (Applicative(..), Functor(..), (.)) class Semigroup m where (<>) :: m -> m -> m class Semigroup m => Reducer c m where snoc :: m -> c -> m newtype Traversal f = Traversal { getTraversal :: f () } instance Applicative f => Semigroup (Traversal f) where Traversal a <> Traversal b = Traversal (a *> b) instance Applicative f => Reducer (f a) (Traversal f) where Traversal a `snoc` b = Traversal (() <$ (a *> b)) snocTraversal :: Applicative f => Traversal f -> f () -> Traversal f snocTraversal a = (<>) a . Traversal {-# RULES "snocTraversal" snoc = snocTraversal #-} }}} But after doing so, the file no longer typechecks! {{{ GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:23:34: error: • Could not deduce (Applicative f) arising from a use of ‘snocTraversal’ from the context: Reducer (f ()) (Traversal f) bound by the RULE "snocTraversal" at Bug.hs:23:11-46 Possible fix: add (Applicative f) to the context of the RULE "snocTraversal" • In the expression: snocTraversal When checking the transformation rule "snocTraversal" | 23 | {-# RULES "snocTraversal" snoc = snocTraversal #-} | ^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14322> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14321: -fsolve-constant-dicts is not very robust when dealing with GADTs
by GHC 04 Oct '17

04 Oct '17

#14321: -fsolve-constant-dicts is not very robust when dealing with GADTs -------------------------------------+------------------------------------- Reporter: mpickering | 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: #9701 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I expected `-fsolve-constant-dicts` to nail #9701, it didn't fire at all but a slightly modified version does. {{{ {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeApplications #-} module Foo where data Silly a where Silly :: Ord a => a -> Silly a isItSilly :: a -> Silly a -> Bool isItSilly a (Silly x) = a < x isItSillyIntTA :: Int -> Silly Int -> Bool isItSillyIntTA = isItSilly @Int isItSillyInt :: Int -> Silly Int -> Bool isItSillyInt a x = isItSilly a x isItSillyInt2 :: Int -> Silly Int -> Bool isItSillyInt2 a (Silly x) = a < x isItSillyInt3 :: Int -> Silly Int -> Bool isItSillyInt3 a (Silly x) = isItSilly a (Silly x) }}} Both versions 2 and 3 specialise nicely using the `Int` `Ord` dictionary. The first two versions don't. I'm unsure whether it *should* fire or not but I am making this ticket to record this fact. Clonable code and core dump - https://gist.github.com/mpickering/f84a5f842861211e8e731c63e82d5c01 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14321> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14315: GHC panic caused by destructuring with qualified name
by GHC 04 Oct '17

04 Oct '17

#14315: GHC panic caused by destructuring with qualified name ----------------------------------------+--------------------------------- Reporter: bloxx | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Linux Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- I have a cabal project with the following files: {{{#!hs -- src/Alt.hs module Alt where data Pizza = Pizza { filling :: String } -- =========== -- src/Main.hs module Main where import qualified Alt as A data Pizza = Pizza { filling :: String } unpizza :: A.Pizza -> String -- to fix it, replace "filling" with "A.filling" unpizza A.Pizza { filling = filling } = filling main :: IO () main = putStrLn "Hello Haskell!" }}} Of course, this is not valid code. "filling" belongs to "Pizza" and "A.filling" belongs to "A.Pizza". But it causes a panic in GHC 8.2.1 instead of an error, so I suppose it is a bug. Can you reproduce this behavior? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14315> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14292: Coercing between constraints of newtypes
by GHC 04 Oct '17

04 Oct '17

#14292: Coercing between constraints of newtypes -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- This doesn't work {{{#!hs {-# Language ConstraintKinds #-} {-# Language GADTs #-} import Data.Coerce newtype USD = USD Int data Dict c where Dict :: c => Dict c num :: Dict (Num Int) -> Dict (Num USD) num = coerce }}} but this does {{{#!hs data NUM a = NUM (a -> a -> a) num' :: NUM Int -> NUM USD num' = coerce }}} is this a fundamental limitation? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14292> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11959: Importing doubly exported pattern synonym and associated pattern synonym panics
by GHC 04 Oct '17

04 Oct '17

#11959: Importing doubly exported pattern synonym and associated pattern synonym panics -------------------------------------+------------------------------------- Reporter: darchon | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc3 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given {{{#!hs {-# LANGUAGE PatternSynonyms, ViewPatterns #-} module Pat (Vec2(Nil,(:>)), pattern (:>)) where newtype Vec2 a = Vec2 {unvec2 :: [a]} pattern Nil :: Vec2 a pattern Nil = Vec2 [] pattern (:>) x xs <- ((\ys -> (head $ unvec2 ys,Vec2 . tail $ unvec2 ys)) -> (x,xs)) where (:>) x xs = Vec2 (x:unvec2 xs) }}} and {{{#!hs {-# LANGUAGE PatternSynonyms #-} module Main where import Pat (Vec2(..),pattern (:>)) }}} I get: {{{ $ ghci Main.hs GHCi, version 8.0.0.20160411: http://www.haskell.org/ghc/ :? for help [1 of 2] Compiling Pat ( Pat.hs, interpreted ) Pat.hs:2:29: warning: [-Wduplicate-exports] ‘:>’ is exported by ‘(:>)’ and ‘Vec2(Nil, type (:>))’ [2 of 2] Compiling Main ( Main.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.0.20160411 for x86_64-unknown-linux): filterImports/combine (:>, :>, Nothing) (:>, Vec2{Vec2, :>, Nil}, Nothing) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Now, the warning about the duplicate export is of course correct. But the panic shouldn't happen when I try to import both the associated pattern synonym and the normal pattern synonym. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11959> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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