August 2018 - ghc-tickets

Re: [GHC] #4022: GHC Bindist is Broken on FreeBSD/amd64
by GHC 24 Aug '18

24 Aug '18

#4022: GHC Bindist is Broken on FreeBSD/amd64 -------------------------------------+------------------------------------- Reporter: pgj | Owner: pgj Type: bug | Status: new Priority: lowest | Milestone: Component: Core Libraries | Version: 6.13 Resolution: | Keywords: GMP,integer- | gmp, sharedlibs Operating System: FreeBSD | Architecture: x86_64 Type of failure: Building GHC | (amd64) failed | Test Case: Blocked By: | Blocking: Related Tickets: #8156 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): The FreeBSD bindists went on a bit of a hiatus while (a) we fixed GHC's FreeBSD support (the `unix` library had compatibility issues previously) and (b) we enable support in GHC's continuous integration infrastructure. However, (a) is now done and while (b) isn't quite there yet I will build a bindist manually for 8.6.1. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4022#comment:35> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7670: StablePtrs should be organized by generation for efficient minor collections
by GHC 24 Aug '18

24 Aug '18

#7670: StablePtrs should be organized by generation for efficient minor collections -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | 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 dfeuer): Ah, now I think I understand what you mean about per-capability tables. One hash table for the nursery associated with each capability. Assuming it's cheap to determine which nursery the underlying object pointer is in (if it is in one), we can perform the lookup/insertion in the matching hash table. Since it's rare to create a stable name for an object in another thread's nursery, there will be very little contention for the nursery table locks. Side note: if we do implement the generational scheme, we'll want to edit the users' guide to note that it's somewhat more efficient to create a stable name for an object very soon after the object is created than to do so later. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7670#comment:19> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #855: Improvements to SpecConstr
by GHC 24 Aug '18

24 Aug '18

#855: Improvements to SpecConstr -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.4.2 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: N/A Blocked By: | Blocking: 915 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by maoe): * cc: maoe (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/855#comment:21> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #849: Offer control over branch prediction
by GHC 23 Aug '18

23 Aug '18

#849: Offer control over branch prediction -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonmar Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 6.4.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: N/A Blocked By: | Blocking: Related Tickets: #14672 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by maoe): * cc: maoe (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/849#comment:31> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #605: Optimisation: strict enumerations
by GHC 23 Aug '18

23 Aug '18

#605: Optimisation: strict enumerations -------------------------------------+------------------------------------- Reporter: simonmar | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: None Resolution: None | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: N/A Blocked By: | Blocking: Related Tickets: #6135 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by maoe): * cc: maoe (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/605#comment:28> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15535: Expose the StableName constructor
by GHC 23 Aug '18

23 Aug '18

#15535: Expose the StableName constructor -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.8.1 Component: Core | Version: 8.4.3 Libraries | 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: -------------------------------------+------------------------------------- A `StableName` is just a wrapper around `StableName#`, but we don't reveal that anywhere. That means that user code needs to use `unsafeCoerce` to convert between `StableName` and `StableName#`, which seems terrible. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15535> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15518: -ddump-splices pretty-prints LambdaCase nonsensically
by GHC 23 Aug '18

23 Aug '18

#15518: -ddump-splices pretty-prints LambdaCase nonsensically -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE LambdaCase #-} {-# LANGUAGE TemplateHaskell #-} {-# OPTIONS_GHC -ddump-splices #-} module Bug where $([d| f :: Bool -> () f = \case True -> () False -> () |]) }}} {{{ $ /opt/ghc/8.4.3/bin/ghci Bug.hs GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/ryanglscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:(6,3)-(9,6): Splicing declarations [d| f_a1xr :: Bool -> () f_a1xr = \case True -> () False -> () |] ======> f_a48E :: Bool -> () f_a48E = \case \ True -> GHC.Tuple.() \ False -> GHC.Tuple.() Ok, one module loaded. }}} Notice the use of `\ True` and `\ False`. Those patterns should not be preceded with backslashes. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15518> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15361: Error message displays redundant equality constraint
by GHC 23 Aug '18

23 Aug '18

#15361: Error message displays redundant equality constraint -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: #14394 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When compiling this program: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeOperators #-} module Bug where import Data.Kind import Data.Type.Equality foo :: forall (a :: Type) (b :: Type) (c :: Type). a :~~: b -> a :~~: c foo HRefl = HRefl }}} GHC complains thus: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:12:13: error: • Could not deduce: a ~ c from the context: (* ~ *, b ~ a) bound by a pattern with constructor: HRefl :: forall k1 (a :: k1). a :~~: a, in an equation for ‘foo’ at Bug.hs:12:5-9 ‘a’ is a rigid type variable bound by the type signature for: foo :: forall a b c. (a :~~: b) -> a :~~: c at Bug.hs:(10,1)-(11,27) ‘c’ is a rigid type variable bound by the type signature for: foo :: forall a b c. (a :~~: b) -> a :~~: c at Bug.hs:(10,1)-(11,27) Expected type: a :~~: c Actual type: a :~~: a • In the expression: HRefl In an equation for ‘foo’: foo HRefl = HRefl • Relevant bindings include foo :: (a :~~: b) -> a :~~: c (bound at Bug.hs:12:1) | 12 | foo HRefl = HRefl | ^^^^^ }}} That `* ~ *` constraint is entirely redundant. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15361> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15269: Qualified Names in --show-iface output
by GHC 23 Aug '18

23 Aug '18

#15269: Qualified Names in --show-iface output -------------------------------------+------------------------------------- Reporter: sjakobi | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 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: -------------------------------------+------------------------------------- == Motivation In the Hi Haddock project we use tests based on the `--show-iface` mode. In the `.hi`-files we dump, we list the `Name`s that may correspond to an identifier found in a docstring. In the case of ambiguous identifiers, it would be nice to see the module names of the corresponding `Name`s, so we can tell them apart. == Possible solutions * In Phab:D4806, I proposed to hardcode qualification for `--show-iface`. But this may create unwanted noise in different usecases. * If I could use `-dppr-debug` with `--show-iface` I would do that. Currently I get the following error if try: {{{ Warning: the following files would be used as linker inputs, but linking is not being done: NoExportList.hi -dppr-debug: openBinaryFile: does not exist (No such file or directory) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15269> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11474: incorrect redundant-constraints warning
by GHC 23 Aug '18

23 Aug '18

#11474: incorrect redundant-constraints warning -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code when compiled with GHC 8 {{{#!hs {-# LANGUAGE Haskell2010, FunctionalDependencies, KindSignatures, ScopedTypeVariables, TypeOperators, UndecidableInstances #-} import GHC.Generics data Options data Value newtype Tagged s b = Tagged {unTagged :: b} class GToJSON f where gToJSON :: Options -> f a -> Value class SumToJSON f allNullary where sumToJSON :: Options -> f a -> Tagged allNullary Value class AllNullary (f :: * -> *) allNullary | f -> allNullary instance ( AllNullary (a :+: b) allNullary, -- <- removing this line causes a compile error SumToJSON (a :+: b) allNullary ) => GToJSON (a :+: b) where gToJSON opts = (unTagged :: Tagged allNullary Value -> Value) . sumToJSON opts }}} emits a warning {{{ bug.hs:19:10: warning: • Redundant constraint: AllNullary (a :+: b) allNullary • In the instance declaration for ‘GToJSON (a :+: b)’ }}} when commenting out the `AllNullary` constraint, this however results the compile error {{{ bug.hs:19:10: error: • Could not deduce (SumToJSON (a :+: b) allNullary0) from the context: SumToJSON (a :+: b) allNullary bound by an instance declaration: SumToJSON (a :+: b) allNullary => GToJSON (a :+: b) at redconstr.hs:(19,10)-(22,24) The type variable ‘allNullary0’ is ambiguous • In the ambiguity check for an instance declaration To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the instance declaration for ‘GToJSON (a :+: b)’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11474> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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