February 2014 - ghc-tickets

[GHC] #8489: clean up dependency and usages handling in interface files
by GHC 02 Jul '18

02 Jul '18

#8489: clean up dependency and usages handling in interface files ----------------------------------------------+---------------------------- Reporter: errge | Owner: errge Type: task | Status: new Priority: normal | Milestone: 7.10.1 Component: Template Haskell | Version: 7.7 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less than a day) | Type of failure: Blocked By: 1480 | None/Unknown Related Tickets: | Test Case: | Blocking: ----------------------------------------------+---------------------------- While reviewing #1480, it was found that there are corner cases that are not easy to handle. This task is about fixing TH module reification to reify direct import list, not usages. For this we may need to extend the current `ModIface`. This task also includes cleaning up the comments and code in related areas, to quote simonpj: "we need more precise commentary on the fields of `HscTypes.Dependencies`, `TcRnTypes.ImportAvails`, and `mi_usages` of `ModIface`. For example, I wonder whether the `mi_usages` field could be part of the `Dependencies`". -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8489> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8695: Arithmetic overflow from (minBound :: Int) `quot` (-1)
by GHC 30 Jun '18

30 Jun '18

#8695: Arithmetic overflow from (minBound :: Int) `quot` (-1) -------------------------------------+------------------------------------- Reporter: rleslie | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.6.3 libraries/haskell2010 | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result Architecture: Unknown/Multiple | at runtime Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- According to the documentation for Data.Int, “All arithmetic is performed modulo 2!^n, where n is the number of bits in the type.” However, this promise is broken by the following exception: {{{ Prelude> (minBound :: Int) `quot` (-1) *** Exception: arithmetic overflow }}} (This also occurs with Int8, Int16, Int32, and Int64, and likewise for `div`.) If all arithmetic is performed modulo 2!^n, I would rather expect the above to evaluate to `minBound`, since after all `minBound * (-1) == minBound`. The fact that an exception is raised adds an unnecessary burden in pure code to ensure `quot` (or `div`) is never called with these specific arguments. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8695> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8619: Support anonymous string literals in C-- (OR) give better ASSERT failure messages in C--
by GHC 17 Jun '18

17 Jun '18

#8619: Support anonymous string literals in C-- (OR) give better ASSERT failure messages in C-- ------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- So if I say "foobar" in C--, it turns into: {{{ section "rodata" { fresh_name : bits8[] "foobar\0"; } }}} This would let us fix the ASSERT macro in Cmm.h to also get the filename. Requires parser changes. Alternatively, we can redefine the ASSERT macro per C-- file to have a hardcoded filename with some preprocessor trickery. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8619> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8516: Add (->) representation and the Invariant class to GHC.Generics
by GHC 04 Jun '18

04 Jun '18

#8516: Add (->) representation and the Invariant class to GHC.Generics ----------------------------------------------+---------------------------- Reporter: nfrisby | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type checker) | Version: 7.7 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less than a day) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: ----------------------------------------------+---------------------------- We currently disallow any use of the parameter in the domain of (->). {{{ newtype F a = F ((a -> Int) -> Int) deriving Generic1 <interactive>:4:38: Can't make a derived instance of `Generic1 (F g)': Constructor `F' must use the last type parameter only as the last argument of a data type, newtype, or (->) In the data declaration for `F' }}} !DeriveFunctor succeeds for this F. I'd like to add this representation type to GHC.Generics and !DeriveGeneric. {{{ newtype (f :->: g) a = FArrow1 (f a -> g a) }}} We could then represent the first example above. We could also derive the more interesting Generic1 (F g). {{{ newtype F g a = F (g a -> Int) deriving Generic1 type instance Rep1 (F g) = Rec1 g :->: Rec0 Int instance Generic1 (F g) where to x = F $ unRec0 . unArrow1 x . Rec1 from (F x) = FArrow1 $ Rec0 . x . unRec1 }}} Admittedly, there's not many generic definitions impeded by not having (:->:). Contra- and in-variant types are uncommon. I'm suggesting this feature without strong motivating examples because I think this would streamline the implementation of -XDeriveGenerics in some ways while also making it more general — assuming that we added the Invariant class to base or ghc-prim. {{{ class Invariant t where invmap :: (a -> b) -> (b -> a) -> t a -> t b invmap_covariant :: Functor t => (a -> b) -> (b -> a) -> t a -> t b invmap_covariant f _ = fmap f instance (Invariant f,Invariant g) => Invariant (FArrow f g) where invmap co contra (FArrow h) = FArrow $ invmap co contra . h . invmap contra co }}} (Of course, Invariant should be a super class of Functor. :/ ) Now we can handle quite involved examples: {{{ newtype F g h a = F (g (h a)) deriving Generic1 instance Invariant g => Generic1 (F g h) where to x = invmap unRec1 Rec1 $ unComp1 x from (F x) = Comp1 $ invmap Rec1 unRec1 }}} All of that said, I'm mostly opening this ticket so I can get feedback on difficulties I might not be anticipating and have a place to reference from the compiler source code comments. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8516> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8089: Implementation of GHC.Event.Poll.poll is broken due to bad coercion
by GHC 16 May '18

16 May '18

#8089: Implementation of GHC.Event.Poll.poll is broken due to bad coercion -------------------------------------------+------------------------------- Reporter: merijn | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.6.3 Keywords: patch | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 hour) | Type of failure: Runtime Blocked By: | crash Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- Due to an unsafe coercion in GHC.Event.Poll.poll the implementation has a bug that on some platforms (.e.g. linux) results in subtly wrong semantics and on other platforms (e.g. OS X) downright crashes the runtime. The offending line is line 95 in GHC/Event/Poll.hsc: {{{ c_poll ptr (fromIntegral len) (fromIntegral (fromTimeout tout)) }}} `fromTimeout` returns a timeout in seconds as a value of type Int. `c_poll` takes a timeout in seconds as a value of type CInt. If the max value of Int is larger than that of CInt, this coercion results in an overflow, producing a negative value. The faulty semantics are in turn caused by passing this negative value as timeout to `c_poll`. This overflow happens on many 64bit platforms where GHC's Int is 64bit, but CInt is often 32bit. The result of passing a negative value to poll() depends on the platform, but is (on all platforms I checked) different from the desired semantics! On linux any negative timeouts are treated as infinite, this means that a poll() with a timeout that should be finite results in an infinitely blocking poll on linux! On OSX any negative timeout other than -1 (which is treated as infinity) is considered an invalid parameter, returning an error and crashing the runtime. A minimal example reproducing the error (on systems where `fromIntegral (maxBound :: Int) > (fromIntegral (maxBound :: CInt) :: Integer)`): {{{ import Control.Concurrent main = threadDelay maxBound }}} Using 64bit GHC on OSX this produces an immediate runtime crash. The attached patch solves the issue by comparing the Int timeout against the max value of CInt and, if necessary, looping multiple `c_poll` calls (with a timeout equal to `maxBound :: CInt`) if they return `0` (which indicates the timeout has expired with no events occurring). See also: https://github.com/merijn/packages- base/commit/6d8ea02a3f6a2cdb82a9ad786a8c4db780b92091 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8089> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8494: Warn if a pattern guard obviates all others
by GHC 03 May '18

03 May '18

#8494: Warn if a pattern guard obviates all others -------------------------+------------------------------------------------- Reporter: | Owner: JohnWiegley | Status: new Type: | Milestone: feature request | Version: 7.6.3 Priority: | Operating System: Unknown/Multiple normal | Type of failure: Incorrect warning at Component: | compile-time Compiler | Test Case: Keywords: | Blocking: Architecture: | Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | -------------------------+------------------------------------------------- The following code, when compiled with `-Wall`, gives no warnings: {{{ module Main where main :: IO () main = print $ foo (10 :: Int) where foo x | True = (20 :: Int) | x == 10 = (30 :: Int) }}} I would expect that since the pattern guard `| True` obviates the following guards, that it would warn about unreachable code. There was a bug in my code today which I tracked down to a code transposition that would have been easily spotted with such a warning. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8494> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8406: Invalid object in isRetainer() or Segfault
by GHC 25 Apr '18

25 Apr '18

#8406: Invalid object in isRetainer() or Segfault ----------------------------------+---------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: Runtime crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+---------------------------------- When compiling with -rtsopts -threaded -prof -fprof-auto -caf-all and running with -N4 -hr I get a "Segmentation fault" every time. If I run with -N4 -qg1 -hr, I either get a segfault or internal error: Invalid object in isRetainer(): 40 When the segfault happens, it happens quickly. If the segfault doesn't happen, the program runs for about 5 seconds and I get "invalid object" error (always 40). Without -hr, I have never gotten a segfault. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8406> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8165: Use GeneralizedNewtypeDeriving to automatically create associated type families
by GHC 12 Apr '18

12 Apr '18

#8165: Use GeneralizedNewtypeDeriving to automatically create associated type families ------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Here's a simple example: {{{ class C a where type T a instance C Int where type T Int = Bool newtype NT = NT Int deriving C }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8165> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8118: <stdout>: commitAndReleaseBuffer: invalid argument (invalid character)
by GHC 10 Apr '18

10 Apr '18

#8118: <stdout>: commitAndReleaseBuffer: invalid argument (invalid character) ----------------------------------+---------------------------------- Reporter: guest | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: OpenBSD Architecture: x86_64 (amd64) | Type of failure: Runtime crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+---------------------------------- I get the following error... {{{ <stdout>: commitAndReleaseBuffer: invalid argument (invalid character) }}} When running following program: {{{#!haskell {-# LANGUAGE OverloadedStrings #-} import qualified Data.Text as T import qualified Data.Text.IO as T main = T.putStrLn "čušpajž日本語" }}} Was tested in #haskell and I have all the UTF-8 Settings set and so forth. It compiles just fine, but crashes during runtime. gcc -v: {{{ Reading specs from /usr/lib/gcc-lib/amd64-unknown-openbsd5.4/4.2.1/specs Target: amd64-unknown-openbsd5.4 Configured with: OpenBSD/amd64 system compiler Thread model: posix gcc version 4.2.1 20070719 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8118> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8542: Suggest NegativeLiterals
by GHC 13 Mar '18

13 Mar '18

#8542: Suggest NegativeLiterals ------------------------------------+------------------------------------- Reporter: monoidal | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- If we write -128 :: Int8, we get a useful warning (#7895), but it would be even better to suggest NegativeLiterals. Patch incoming. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8542> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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