January 2019 - ghc-tickets

[GHC] #14420: Data families should not instantiate to non-Type kinds
by GHC 19 Jan '19

19 Jan '19

#14420: Data families should not instantiate to non-Type kinds -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 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: -------------------------------------+------------------------------------- {{{#!hs data family Any :: k -- allowable now due to fix for #12369 type family F (a :: Bool) :: Nat where F True = 0 F False = 1 F Any = 2 }}} {{{ ghci> :kind! F True F True :: Nat = 0 ghci> :kind! F False F False :: Nat = 1 ghci> :kind! F Any F Any :: Nat = 2 }}} Oh dear. We should require that any instantiation of a data family be to a kind that ends in `Type`. Inspired by comment:31:ticket:9429 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14420> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15726: Don't include Haskeline (and others) in the global package DB
by GHC 19 Jan '19

19 Jan '19

#15726: Don't include Haskeline (and others) in the global package DB -------------------------------------+------------------------------------- Reporter: judah | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Build System | 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: -------------------------------------+------------------------------------- GHC installations include `haskeline` in their global DB, as well as its dependencies (currently: `stm` and `terminfo`). However, Haskeline isn't a dependency of the `ghc` library, so that shouldn't be necessary. Originally suggested by hvr here, in response to needing to pull `stm` into the global DB: https://github.com/judah/haskeline/pull/61#issuecomment-294878302 This change would let Haskeline add dependencies more easily. See in particular the pending PR to depend on the "exceptions" package: https://github.com/judah/haskeline/pull/97 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15726> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16182: Retainer Profiling is broken
by GHC 19 Jan '19

19 Jan '19

#16182: Retainer Profiling is broken -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: profiling | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I had a large program which I was trying to profile, and I noticed that the program always ran into a segfault when running with `+RTS -hr`. I was able to able to reliably get segfaults in both the `warp-tls` and `http- client-tls` packages, as well as a third large and independent package with essentially no overlapping dependencies. This led me to believe that the bug is in the retainer profiler itself, and is not (much) dependent on the code being profiled. To that point, I was able to reproduce the bug with the `bytestring` test suites. I've modified bytestring (attached) enough to make it compile with GHC 8.6.3*. To reproduce the segfault, run {{{ $ stack build --profile $ stack exec prop-compiled -- +RTS -hr }}} * Renamed the package to bytestring2 to avoid circular packages. * Removed a duplicate instance in tests/QuickCheckUtils.hs * Changed all test-suites to executables in the cabal file so that they could be compiled with profiling. I have confirmed the problem on Linux (Ubuntu 18.04), where prop-compiled quickly segfaults, and on Windows 10, where the program just hangs. [I observed the same behavior in all the other programs I tested: Linux sefaulted, and Windows just hung.] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16182> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14976: WebAssembly support
by GHC 19 Jan '19

19 Jan '19

#14976: WebAssembly support -------------------------------------+------------------------------------- Reporter: sven | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.2.2 Keywords: wasm, | Operating System: Unknown/Multiple webassembly | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I would like to suggest adding a wasm backend to GHC. PureScript is also offering something similar. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14976> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13452: Lock .tix file
by GHC 19 Jan '19

19 Jan '19

#13452: Lock .tix file -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Code Coverage | 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: -------------------------------------+------------------------------------- The HPC documentation [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/profiling.h… #caveats-and-shortcomings-of-haskell-program-coverage warns] that > HPC does not attempt to lock the `.tix` file, so multiple concurrently running binaries in the same directory will exhibit a race condition. This sounds like something that shouldn't be too terribly hard to fix, once we determine exactly how we want to deal with contention. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13452> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15381: Write documentation for iserv-proxy
by GHC 19 Jan '19

19 Jan '19

#15381: Write documentation for iserv-proxy -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 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: -------------------------------------+------------------------------------- We merged `iserv-proxy` but it doesn't yet have users guide documentation. We should fix this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15381> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15916: GHC doesn't build on powerpc64 architecture on systems other than GNU / Linux
by GHC 18 Jan '19

18 Jan '19

#15916: GHC doesn't build on powerpc64 architecture on systems other than GNU / Linux ---------------------------------+---------------------------------------- Reporter: pkubaj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Research needed Component: Compiler | Version: 8.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: powerpc64 | Type of failure: Building GHC failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ---------------------------------+---------------------------------------- I'd like to bootstrap GHC for FreeBSD/powerpc64, but GHC seems to be supported only on Linux for powerpc64 architecture. Relevant code: https://github.com/ghc/ghc/blob/1c2c2d3dfd4c36884b22163872feb87122b4528d/rt… https://github.com/ghc/ghc/blob/1c2c2d3dfd4c36884b22163872feb87122b4528d/rt… -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15916> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16078: Hide -Weverything warnings for GHCi internals
by GHC 18 Jan '19

18 Jan '19

#16078: Hide -Weverything warnings for GHCi internals -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider Bar.hs {{{ module Bar where }}} Main.hs {{{ import Bar main :: IO () main = print "" }}} `stack ghci Main.hs --ghc-options -Weverything` produces {{{ ... GHCi, version 8.6.2: http://www.haskell.org/ghc/ :? for help <interactive>:1:1: warning: [-Wmissing-local-signatures] Polymorphic local binding with no type signature: _compileParsedExpr :: forall a. GHC.Types.IO a -> GHC.Types.IO a <interactive>:1:1: warning: [-Wmissing-import-lists] The module `Prelude' does not have an explicit import list Loaded GHCi configuration from C:\Users\ericcro\Desktop\VPC-Key- Distribution\src\.ghci <no location info>: warning: [-Wmissing-home-modules] Modules are not listed in command line but needed for compilation: Bar [1 of 2] Compiling Bar ( Bar.hs, interpreted ) ... }}} Those three errors have nothing to do with my code, and seem to be related to the internals of how GHCi works. It would be nice to hide all three. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16078> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16194: deriving, wrong code: newtype T cat a = MkT ((forall xx. cat xx xx) -> a) deriving stock Functor
by GHC 18 Jan '19

18 Jan '19

#16194: deriving, wrong code: newtype T cat a = MkT ((forall xx. cat xx xx) -> a) deriving stock Functor -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 Keywords: DeriveFunctor | Operating System: Unknown/Multiple deriving RankNTypes | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This fails (`deriving stock Functor`) (data type comes from [https://duplode.github.io/extras/applicative-archery-manuscript.pdf Applicative Archery]) {{{ $ ./ghc-stage2 --interactive -ignore-dot-ghci GHCi, version 8.7.20181230: https://www.haskell.org/ghc/ :? for help Prelude> :set prompt "> " > :set -XRankNTypes -XDeriveFunctor -ddump-deriv > :set -dsuppress-idinfo -dsuppress-coercions -dsuppress-type-applications -dsuppress-uniques -dsuppress-module-prefixes > newtype T cat a = MkT ((forall xx. cat xx xx) -> a) deriving Functor ==================== Derived instances ==================== Derived class instances: instance Functor (T cat) where fmap f (MkT a1) = MkT ((\ b2 b3 -> f (b2 ((\ b1 -> b1) b3))) a1) (<$) z (MkT a1) = MkT ((\ b3 b4 -> (\ b2 -> z) (b3 ((\ b1 -> b1) b4))) a1) Derived type family instances: <interactive>:4:62: error: • Couldn't match type ‘forall xx. cat xx xx’ with ‘cat xx0 xx0’ Expected type: cat xx0 xx0 -> a Actual type: (forall xx. cat xx xx) -> a • In the first argument of ‘\ b2 b3 -> f (b2 ((\ b1 -> b1) b3))’, namely ‘a1’ In the first argument of ‘MkT’, namely ‘((\ b2 b3 -> f (b2 ((\ b1 -> b1) b3))) a1)’ In the expression: MkT ((\ b2 b3 -> f (b2 ((\ b1 -> b1) b3))) a1) When typechecking the code for ‘fmap’ in a derived instance for ‘Functor (T cat)’: To see the code I am typechecking, use -ddump-deriv • Relevant bindings include a1 :: (forall xx. cat xx xx) -> a (bound at <interactive>:4:62) fmap :: (a -> b) -> T cat a -> T cat b (bound at <interactive>:4:62) <interactive>:4:62: error: • Couldn't match type ‘forall xx. cat xx xx’ with ‘cat xx1 xx1’ Expected type: cat xx1 xx1 -> b Actual type: (forall xx. cat xx xx) -> b • In the first argument of ‘\ b3 b4 -> (\ b2 -> z) (b3 ((\ b1 -> b1) b4))’, namely ‘a1’ In the first argument of ‘MkT’, namely ‘((\ b3 b4 -> (\ b2 -> z) (b3 ((\ b1 -> b1) b4))) a1)’ In the expression: MkT ((\ b3 b4 -> (\ b2 -> z) (b3 ((\ b1 -> b1) b4))) a1) When typechecking the code for ‘<$’ in a derived instance for ‘Functor (T cat)’: To see the code I am typechecking, use -ddump-deriv • Relevant bindings include a1 :: (forall xx. cat xx xx) -> b (bound at <interactive>:4:62) (<$) :: a -> T cat b -> T cat a (bound at <interactive>:4:62) > }}} Generates odd code {{{#!hs fmap .. = MkT ((\ b2 b3 -> f (b2 ((\ b1 -> b1) b3))) a1) }}} It works fine (in HEAD) to `deriving newtype Functor` (it didn't in 8.2 where I checked) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16194> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15717: Performance regression in for_ alternatives from GHC 8.2.2 to newer GHCs
by GHC 18 Jan '19

18 Jan '19

#15717: Performance regression in for_ alternatives from GHC 8.2.2 to newer GHCs -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- We are investigating various ways to make `for_` and `traverse_` not leak space by changing the type signature from `(a -> f b) -> t a -> f ()` to `(a -> f ()) -> t a -> f ()`. While doing so, we noticed a regression from GHC 8.2.2 to 8.4.3 and 8.6.1. The code: https://gist.github.com/nh2/b8f9f8e60443bdb30c1cd7e0acb8c8eb/bb1cc1a4987091… Run against 3 different GHC releases: {{{ # 8.2.2 stack --resolver lts-11.22 ghc -- --make -O2 -rtsopts ./TraverseMaybePerformance.hs && /usr/bin/time ./TraverseMaybePerformance 8 +RTS -sstderr 460,309,368 bytes allocated in the heap # 8.4.3 stack --resolver lts-12.11 ghc -- --make -O2 -rtsopts ./TraverseMaybePerformance.hs && /usr/bin/time ./TraverseMaybePerformance 8 +RTS -sstderr 860,301,736 bytes allocated in the heap # 8.6.1 stack --resolver nightly-2018-10-06 ghc -- --make -O2 -rtsopts ./TraverseMaybePerformance.hs && /usr/bin/time ./TraverseMaybePerformance 8 +RTS -sstderr 860,301,784 bytes allocated in the heap }}} Allocations doubled starting with 8.4. All was run on Ubuntu 16.04 64-bit. We haven't investigated in detail yet (also whether it's a GHC or libraries problem) since we're actually trying to do something else and this came out on the side, but it looks important enough to share already. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15717> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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