April 2018 - ghc-tickets

[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] #15000: Add a linter for debug information (-g)
by GHC 04 Apr '18

04 Apr '18

#15000: Add a linter for debug information (-g) -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- There are some sanity checks we can do. For example if you see following Cmm: {{{ unwind Sp = Sp + 16 Sp = Sp + 16 unwind Sp = Sp + 64 }}} You can tell that it's wrong because it's clear how `Sp` changed between the two unwind points. I think this would fit well with the Cmm linter. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15000> 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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Re: [GHC] #1600: Optimisation: CPR the results of IO
by GHC 03 Apr '18

03 Apr '18

#1600: Optimisation: CPR the results of IO -------------------------------------+------------------------------------- Reporter: simonmar | Owner: (none) Type: task | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 6.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #8598 | Differential Rev(s): Phab:D4244 Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * differential: => Phab:D4244 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:80> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14965: GHC 8.4.1 bug: -O + separate compilation + three list fields + concatenation; core-lint fails
by GHC 03 Apr '18

03 Apr '18

#14965: GHC 8.4.1 bug: -O + separate compilation + three list fields + concatenation; core-lint fails -------------------------------------+------------------------------------- Reporter: blynn | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Keywords: | Operating System: Linux Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- A simple program that works in 8.2.1 fails in 8.4.1 when compiled with -O. (Sorry, haven't tested 8.2.2.) GHC with -dcore-lint reports an error. See attached files. In one file I declared: {{{#!hs module Sep where data Sep = Sep { bugVanishesWithoutThis :: [()] , middle :: [String] , orThis :: [()] } catSep :: Sep -> Sep -> Sep catSep (Sep a b c) (Sep x y z) = Sep (a ++ x) (b ++ y) (c ++ z) cc :: Sep -> Bool cc boost = elem "foo" $ middle boost }}} and in a second file, simple code fails when compiled with -O: {{{#!hs module Main (main) where import Sep main :: IO () main = print $ cc bb bb :: Sep bb = catSep b1 b2 b1 :: Sep b1 = Sep [] ["foo"] [] b2 :: Sep b2 = Sep [] ["bar"] [] }}} This should print "True", and does so for GHC 8.2.1, and GHC 8.4.1 without -O, but prints "False" for GHC 8.4.1 with -O. I was unable to reproduce the bug with a single file. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14965> 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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