February 2018 - ghc-tickets

[GHC] #14764: Make $! representation-polymorphic
by GHC 04 Apr '18

04 Apr '18

#14764: Make $! representation-polymorphic -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Core | Version: 8.2.2 Libraries | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): Phab:D4382 | Wiki Page: -------------------------------------+------------------------------------- Currently, {{{#!hs ($) :: forall r a (b :: TYPE r). (a -> b) -> a -> b }}} but {{{#!hs ($!) :: (a -> b) -> a -> b }}} It seems fairly obvious that we should generalize `($!)`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14764> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14795: Data type return kinds don't obey the forall-or-nothing rule
by GHC 04 Apr '18

04 Apr '18

#14795: Data type return kinds don't obey the forall-or-nothing rule -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Originally noticed [https://github.com/ghc-proposals/ghc- proposals/pull/103#issuecomment-364562974 here]. GHC accepts this: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeInType #-} import Data.Kind data Foo :: forall a. a -> b -> Type where MkFoo :: a -> Foo a b }}} Despite the fact that `Foo`'s return kind is headed by an explicit `forall` which does not quantify `b`. The users' guide doesn't explicitly indicate that the `forall`-or-nothing rule should apply to data type return kinds, but goldfirere believes that not doing so is an [https://github.com/ghc-proposals/ghc- proposals/pull/103#issuecomment-364670215 inconsistent design], so I'm opening this ticket to track this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14795> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13845: Runtime linker too eagerly checks for symbol names
by GHC 04 Apr '18

04 Apr '18

#13845: Runtime linker too eagerly checks for symbol names -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 8.0.1 System (Linker) | 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: -------------------------------------+------------------------------------- I discovered this bug in https://github.com/haskell- foundation/foundation/issues/326. Take this file: {{{#!hs module Main (main) where foreign import ccall "notAThing" notAThing :: IO () main :: IO () main = putStrLn "Hello, World!" }}} Compiling and running this file works without issue. But if you try to use the runtime linker, things go haywire: {{{ $ C:\Users\RyanGlScott\Software\ghc\inplace\bin\runghc Bug.hs ghc-stage2.exe: ^^ Could not load 'notAThing', dependency unresolved. See top entry above. Bug.hs: ByteCodeLink: can't find label During interactive linking, GHCi couldn't find the following symbol: notAThing This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org }}} This isn't just limited to Windows, since the same thing happens on Linux. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13845> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13330: forkIO has inconsistent behavior under optimization
by GHC 04 Apr '18

04 Apr '18

#13330: forkIO has inconsistent behavior under optimization -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Core | Version: 8.1 Libraries | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Troubleshooting the T4030 failure in SimonPJ's early-inline branch, Reid and I discovered that the problem showed up when the argument to `forkIO` was obviously bottom. He came up with a tiny test case that fails without Simon's changes: {{{#!hs main = forkIO undefined >> threadDelay 1000000 }}} It looks like the trouble is in the definition of `forkIO`: {{{#!hs forkIO :: IO () -> IO ThreadId forkIO action = IO $ \ s -> case (fork# action_plus s) of (# s1, tid #) -> (# s1, ThreadId tid #) where action_plus = catchException action childHandler }}} This seems to run into the trouble with `catchException` and strictness explained in `GHC.IO`. It would appear that the conservative fix would be to replace `catchException` with `catch`. Personally, I find it a bit surprising that `forkIO` doesn't force its `IO` argument before forking, but changing that behavior could break working code. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13330> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10016: UNPACK support for existentials
by GHC 03 Apr '18

03 Apr '18

#10016: UNPACK support for existentials -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.4 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Consider {{{ data Foo = forall a. Show a => Foo !a !a data Bar = Bar {-# UNPACK #-} !Foo }}} The UNPACK pragma should really be able to unpack the `Foo` field, so that (implementation-wise) it would be as if you'd declared `Bar` thus: {{{ data Bar = forall a. Show a => Bar !a !a }}} But currently we get {{{ Ignoring unusable UNPACK pragma on the first argument of ‘Bar’ }}} Suggested by Nicholas Clarke [https://www.haskell.org/pipermail/glasgow- haskell-users/2015-January/025590.html here]. Vaguely related tickets: #7647, #9214. But unlike those ones, this one looks quite feasible to me. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10016> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14766: Hole-y partial type signatures greatly slow down compile times
by GHC 03 Apr '18

03 Apr '18

#14766: Hole-y partial type signatures greatly slow down compile times -------------------------------------+------------------------------------- Reporter: harpocrates | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This time, I actually mean it. :) Originally reported [https://github.com/simonmar/happy/issues/109 here], I distilled the example from [https://github.com/simonmar/happy/issues/109#issuecomment-362957245 this comment] into a one file test case. `Sigs.hs` is exactly like `NoSigs.hs`, except for the fact that it has a bunch of extra type signatures that have a lot of holes. On my machine, this is what compilation times are (I gave up timing after 15 minutes): || GHC version || 8.0.2 || 8.2.1 || 8.4.1 (445554b6d9a2263f969e25bb9f532dd0c3a9dc8c) || || `NoSigs.hs` || 24.13s || 22.93s || 34.05s || || `Sigs.hs` || >15m || >15m || >15m || -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14766> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14643: Partial type signatures in spliced TH declarations behave unexpectedly
by GHC 03 Apr '18

03 Apr '18

#14643: Partial type signatures in spliced TH declarations behave unexpectedly -------------------------------------+------------------------------------- Reporter: mnislaih | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- Minimal example: {{{#!hs {-# LANGUAGE PartialTypeSignatures #-} {-# LANGUAGE TemplateHaskell #-} module Minimal where id [d| f :: (Monad m, _) => [m a] -> m [a] f' :: (Monad m, _) => [m a] -> m [a] f = f' f' [] = return [] f' (x:xx) = f xx |] }}} {{{ [1 of 1] Compiling Minimal ( /Users/pepe/Dropbox/code/debug- hoed/test/minimal.hs, interpreted ) /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘()’ • In the type signature: f :: (Monad m_a7NN, _) => [m_a7NN a_a7NO] -> m_a7NN [a_a7NO] | 5 | id [d| | ^^^^^^... /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘()’ • In the type signature: f' :: (Monad m_a7NL, _) => [m_a7NL a_a7NM] -> m_a7NL [a_a7NM] | 5 | id [d| | ^^^^^^... Ok, one module loaded. :browse f :: (Monad m, Monad m) => [m a] -> m [a] f' :: (Monad m, Monad m) => [m a] -> m [a] }}} Notice the duplicate Monad m constraint. Things get even more weird if the type signatures are declared together: {{{#!hs id [d| f, f' :: (Monad m, _) => [m a] -> m [a] f = f' f' [] = return [] f' (x:xx) = f xx |] }}} {{{ [1 of 1] Compiling Minimal ( /Users/pepe/Dropbox/code/debug- hoed/test/minimal.hs, interpreted ) /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘()’ • In the type signature: f :: (Monad m_a88E, _) => [m_a88E a_a88F] -> m_a88E [a_a88F] | 5 | id [d| | ^^^^^^... /Users/pepe/Dropbox/code/debug-hoed/test/minimal.hs:5:1: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘()’ • In the type signature: f' :: (Monad m_a88E, _) => [m_a88E a_a88F] -> m_a88E [a_a88F] | 5 | id [d| | ^^^^^^... Ok, one module loaded. :browse f :: (Monad ghc-prim-0.5.1.1:GHC.Types.Any, Monad m) => [ghc-prim-0.5.1.1:GHC.Types.Any ghc-prim-0.5.1.1:GHC.Types.Any] -> ghc-prim-0.5.1.1:GHC.Types.Any [ghc-prim-0.5.1.1:GHC.Types.Any] f' :: (Monad ghc-prim-0.5.1.1:GHC.Types.Any, Monad m) => [m a] -> m [a] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14643> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14658: 'Fix two more bugs in partial signatures' broke T10846
by GHC 03 Apr '18

03 Apr '18

#14658: 'Fix two more bugs in partial signatures' broke T10846 -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: bug | 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: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ =====> T10846(normal) 1 of 1 [0, 0, 0] cd "./typecheck/should_run/T10846.run" && "/home/niteria/ghc-allocate- tyids/inplace/test spaces/ghc-stage2" -o T10846 T10846.hs -dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show- caret -dno-debug-output cd "./typecheck/should_run/T10846.run" && ./T10846 Actual stdout output differs from expected: diff -uw "./typecheck/should_run/T10846.run/T10846.stdout.normalised" "./typecheck/should_run/T10846.run/T10846.run.stdout.normalised" --- ./typecheck/should_run/T10846.run/T10846.stdout.normalised 2018-01-10 13:39:29.720468420 +0000 +++ ./typecheck/should_run/T10846.run/T10846.run.stdout.normalised 2018-01-10 13:39:29.720468420 +0000 @@ -1,3 +1,3 @@ [18] -[19] -[20] +[] +[] *** unexpected failure for T10846(normal) }}} Harbormaster results: https://phabricator.haskell.org/harbormaster/build/39597/ Reverting fixed it for me locally. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14658> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14119: Refactor type patterns
by GHC 03 Apr '18

03 Apr '18

#14119: Refactor type patterns -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: 12564, 14038 | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Type patterns are used in instance heads: class instances, type instances, and data/newtype instances. These type patterns differ from ordinary types in several ways: * They must never mention a `forall`. * They must never mention a context. (The context in a class instance head is a different part of the instance construct.) * They must never mention a type family. Types that appear as arguments on the LHS of a RULE should also be type patterns. Type patterns are used in GHC differently than types as well: we should match only against patterns, never ordinary types. I thus propose that a new datatype within GHC to store type patterns. I'll call it `TyPat` here, but perhaps a longer name is better. The matcher (in the `Unify` module) would then take a `TyPat` parameter, making clear which type is the template and which is the concrete instantiation. We could have a new algorithm to typecheck/desugar source syntax into patterns. This new algorithm could accommodate issues like those mentioned in comment:6:ticket:14038. It could also avoid ever putting a type family in a kind parameter, which would fix #12564. Separating out checking type patterns from proper types could also improve GADT pattern matching in types, which is currently more like "wobbly types" than OutsideIn. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14119> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11186: Give strong preference to type variable names in scope when reporting hole contexts
by GHC 02 Apr '18

02 Apr '18

#11186: Give strong preference to type variable names in scope when reporting hole contexts -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (Type checker) | Keywords: typed-holes | 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 using `ScopedTypeVariables` with typed holes, I want GHC to bend over backwards to preserve the names of type variables that the user has chosen to bring into scope. I can't immediately reproduce the situations I've run into recently where that hasn't happened, but sometimes I've had a signature like {{{#!hs foo :: forall bar . ... foo = ... _ ... }}} and yet the typed hole message shows that `bar` has been lost in unification and replaced by some unrelated name. I would very much prefer if this never happened. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11186> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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