January 2016 - ghc-tickets

[GHC] #11390: GHC does not warn about redundant equations
by GHC 11 Jan '16

11 Jan '16

#11390: GHC does not warn about redundant equations -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: warnings | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given the Phab:D1535 effort in GHC 8.0 I was curious how an example from Richard's post [https://typesandkinds.wordpress.com/2015/09/09/what-are- type-families/ What are type families?] would fare: {{{ % ghci -Wall -XTypeFamilies -ignore-dot-ghci GHCi, version 8.1.20160105: http://www.haskell.org/ghc/ :? for help Prelude> :set +m Prelude> type family F1 a where Prelude| F1 Int = Bool Prelude| Prelude> let Prelude| sillyId :: F1 Char -> F1 Char Prelude| sillyId x = x Prelude| Prelude> }}} This seems to fly, even though as the blog post noted, ”[...] sillyId can’t ever be called on a value.” Isn't the clause redundant and should be defined using `EmptyCase` (#2431) as `sillyId x = case x of {}`? It seems GHC doesn't care that the pattern match in the equation `absurd2 _ = ...` is redundant either: {{{#!hs data Void absurd1 :: Void -> a; absurd1 = \case absurd2 :: Void -> a absurd2 _ = undefined }}} Is this intended or known behaviour? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11390> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 15

[GHC] #11356: GHC panic
by GHC 11 Jan '16

11 Jan '16

#11356: GHC panic -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: | Operating System: Linux Architecture: x86 | Type of failure: Compile-time | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The attached file causes GHC (version 8.1.20160102) panic. I tried shrinking, attached code is bogus at this point. Interestingly inlining the type synonym `T = Nat` into Category's superclass context fixes the panic, and causes a regular error. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11356> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 9

Re: [GHC] #4243: Make a proper options parser for the RTS
by GHC 11 Jan '16

11 Jan '16

#4243: Make a proper options parser for the RTS -------------------------------------+------------------------------------- Reporter: igloo | Owner: Type: task | Status: new Priority: normal | Milestone: 8.0.1 Component: Runtime System | Version: 6.13 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 7535 Related Tickets: #9839 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): I'd prefer not to add a dependency on an external tool if possible. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4243#comment:21> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

[GHC] #11406: RTS gets stuck in scheduleDetectDeadlock()
by GHC 11 Jan '16

11 Jan '16

#11406: RTS gets stuck in scheduleDetectDeadlock() -------------------------------------+------------------------------------- Reporter: osa1 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 8.1 System | 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: -------------------------------------+------------------------------------- Steps to reproduce: - Compile HEAD. - Add this line to MkId.mkDataConRep: {{{#!haskell pprTrace "mkDataConRep" (text "wrap_body:" <+> ppr wrap_body) (return ()) }}} - Recompile only stage1. (stage2 will fail, see next step) - Compile any file using newly generated stage1. GHC gets stuck, not using any CPU or RAM. The stack trace: {{{ #0 0x00007fd56d570650 in __pause_nocancel () at ../sysdeps/unix/syscall- template.S:81 #1 0x0000000002174e11 in awaitUserSignals () at rts/posix/Signals.c:343 #2 0x0000000002168a6a in scheduleDetectDeadlock (pcap=<synthetic pointer>, task=<optimized out>) at rts/Schedule.c:931 #3 schedule (task=0x42fa8e0, initialCapability=<optimized out>) at rts/Schedule.c:282 #4 scheduleWaitThread (tso=<optimized out>, ret=ret@entry=0x0, pcap=pcap@entry=0x7fffb90b7778) at rts/Schedule.c:2380 #5 0x0000000002187724 in rts_evalLazyIO (cap=cap@entry=0x7fffb90b7778, p=<optimized out>, ret=ret@entry=0x0) at rts/RtsAPI.c:500 #6 0x0000000002166637 in real_main () at rts/RtsMain.c:63 #7 hs_main (argc=<optimized out>, argv=<optimized out>, main_closure=<optimized out>, rts_config=...) at rts/RtsMain.c:114 #8 0x0000000000421fe4 in main () }}} It's basically stuck in pause() syscall. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11406> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 1

Re: [GHC] #1311: newtypes of unboxed types disallowed - documentation bug and/or feature request
by GHC 11 Jan '16

11 Jan '16

#1311: newtypes of unboxed types disallowed - documentation bug and/or feature request -------------------------------------+------------------------------------- Reporter: Isaac Dupree | Owner: osa1 Type: feature request | Status: new Priority: low | Milestone: ⊥ Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): It'd be easier to help if you had a branch of the GHC repo, or a remote clone thereof, that Richard or I could use to reproduce what you have. I would really like a wiki page to describe the design, please. Maybe it's a simple page -- if so, so much the better. Simon -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1311#comment:15> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

[GHC] #10719: Malformed data type quotation accepted
by GHC 11 Jan '16

11 Jan '16

#10719: Malformed data type quotation accepted -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- This is accepted: Prelude Language.Haskell.TH> {{{$(stringE . show =<< [d| data A where C :: C |])}}} "[DataD [] A_1627402878 [] [ForallC [] [] (NormalC C_1627402879 [])] []]" In contrast this is rejected: Prelude Language.Haskell.TH> {{{$(stringE . show =<< [d| data A p where C :: C |])}}} <interactive>:29:22: Malformed constructor result type: C However it would make sense to form an equality constraint (for later kind/type checking) in these cases, something along the lines of: {{{#!hs data A p where C :: (A p ~ C) => C }}} as there could be type synonym (or family) `C`. I have tested various versions >= 7.8.3 and all seem to behave the same. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10719> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 8

[GHC] #11364: Possible type-checker regression in GHC 8.0
by GHC 11 Jan '16

11 Jan '16

#11364: Possible type-checker regression in GHC 8.0 -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.10.3 (Type checker) | 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 code fragment works with GHCs prior to GHC 8.0 but not with GHC 8.0: {{{#!hs {-# LANGUAGE RoleAnnotations #-} {-# LANGUAGE IncoherentInstances #-} {-# LANGUAGE RankNTypes #-} module Issue where import Data.Coerce (coerce) data Proxy a = Proxy newtype Catch a = Catch a class Throws e type role Throws representational instance Throws (Catch e) newtype Wrap e a = Wrap { unWrap :: Throws e => a } coerceWrap :: Wrap e a -> Wrap (Catch e) a coerceWrap = coerce unthrow :: proxy e -> (Throws e => a) -> a unthrow _ = unWrap . coerceWrap . Wrap {- this works in GHC 7.10.3, but fails in GHC 8.0 with GHCi, version 8.0.0.20160105: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Issue ( Issue.hs, interpreted ) Issue.hs:25:13: error: • Could not deduce (Throws e) from the context: Throws e0 bound by a type expected by the context: Throws e0 => a at Issue.hs:26:13-38 Possible fix: add (Throws e) to the context of the type signature for: unthrow :: proxy e -> (Throws e => a) -> a • In the expression: unWrap . coerceWrap . Wrap In an equation for ‘unthrow’: unthrow _ = unWrap . coerceWrap . Wrap Failed, modules loaded: none. -} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11364> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 7

[GHC] #11363: Parser groups "::" and "*" together in kind signature (a::*)
by GHC 11 Jan '16

11 Jan '16

#11363: Parser groups "::" and "*" together in kind signature (a::*) -----------------------------------------+--------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler (Parser) | Version: 8.1 Keywords: | Operating System: Linux Architecture: x86 | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -----------------------------------------+--------------------------------- Compare a session in 7.10 {{{ GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help Prelude> data A (a :: *) = B <interactive>:2:14: Illegal kind signature: ‘*’ Perhaps you intended to use KindSignatures In the data type declaration for ‘A’ Prelude> data A (a::*) = B <interactive>:3:13: parse error on input ‘)’ }}} to a session in 8.1 {{{ GHCi, version 8.1.20160105: http://www.haskell.org/ghc/ :? for help Prelude> data A (a :: *) = B <interactive>:1:14: error: Illegal kind signature: ‘*’ Perhaps you intended to use KindSignatures In the data type declaration for ‘A’ Prelude> data A (a::*) = B <interactive>:2:9: error: Unexpected type ‘a ::*’ In the data declaration for ‘A’ A data declaration should have form data A a = ... }}} GHC seems to group "::" and "*" together. Same with (★) from Data.Kind with TypeInType enabled. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11363> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 4

[GHC] #11393: Ability to define INLINE pragma for all instances of a given typeclass
by GHC 11 Jan '16

11 Jan '16

#11393: Ability to define INLINE pragma for all instances of a given typeclass -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- Hello! I would like to request a feature that would allow me to define the `INLINE` pragma for all instances of a given type class. Currently when we are creating high-performance libraries, that strongly depend on type- level computations we are using a lot of typeclasses that we want to be cut-out during the compilation time. We can use the `INLINE` pragma to be sure that after type-class resolution the code will be inlined and hopefully strongly optimized, but we have to put the pragme in every single type class instance, which makes the code look ugly and is just impractival. So I would like to transform code like (this is just example, not a real-world problem solving code): {{{ class Foo a b where foo :: a -> b instance Foo Int String where foo = show {-# INLINE foo #-} instance Foo Int Int where foo = id {-# INLINE foo #-} instance Foo Int Float where foo = fromIntegral {-# INLINE foo #-} }}} into: {{{ class Foo a b where foo :: a -> b {-# INLINE foo #-} instance Foo Int String where foo = show instance Foo Int Int where foo = id instance Foo Int Float where foo = fromIntegral }}} I think it would be pretty easy to support such syntax and a lot of libraries would benefit from the design. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11393> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 3

[GHC] #11253: Duplicate warnings for pattern guards and relevant features (e.g. View Patterns)
by GHC 11 Jan '16

11 Jan '16

#11253: Duplicate warnings for pattern guards and relevant features (e.g. View Patterns) -------------------------------------+------------------------------------- Reporter: gkaracha | Owner: gkaracha Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: pattern | Operating System: Unknown/Multiple matching, exhaustiveness | Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: #595 Differential Rev(s): | Wiki Page: | PatternMatchCheck, | PatternMatchCheckImplementation -------------------------------------+------------------------------------- There are some cases where the new exhaustiveness checker emits duplicate warnings. E.g. for `f`: {{{#!hs f :: Bool -> Bool -> () f (not -> True) (not -> False) = () }}} we get: {{{ DuplicateWarn.hs:6:1: warning: Pattern match(es) are non-exhaustive In an equation for ‘f’: Patterns not matched: _ _ -- represents (not -> False) _ _ _ -- represents (not -> True) (not -> True) }}} As indicated in the comments, the two comments represent different missing cases, but since we do not print the additional information, they look alike. It would be better to either: * Give additional information to the user to distinguish between the two or * Print a single warning `(_ _)` I cannot think of a nice solution to this yet but I will keep thinking about it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11253> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 4