December 2016 - ghc-tickets

[GHC] #11216: RebindableSyntax with pattern guards needs `fail`
by GHC 26 Dec '16

26 Dec '16

#11216: RebindableSyntax with pattern guards needs `fail` -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 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: -------------------------------------+------------------------------------- If I say {{{ {-# LANGUAGE RebindableSyntax #-} module Bug where foo :: (a, b) -> () foo x | (_,_) <- x = () }}} I get {{{ Bug.hs:6:9: error: Not in scope: ‘fail’ }}} Yet even if I bring `fail` into scope, it's not mentioned in the Core produced by my program. And it really shouldn't: there's not a monad in sight! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11216> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #229: Integer overflow in array allocation
by GHC 26 Dec '16

26 Dec '16

#229: Integer overflow in array allocation -------------------------------------+------------------------------------- Reporter: josefs | Owner: bgamari Type: bug | Status: closed Priority: high | Milestone: 8.2.1 Component: Core Libraries | Version: 7.9 Resolution: fixed | 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: | -------------------------------------+------------------------------------- Changes (by akio): * cc: akio (added) Comment: Sorry if I'm missing something, but the overflow check looks like it may be incorrect. For example, if `Int` is 32 bits wide, `0x58000000 * 4 :: Int` is greater than `0x58000000`, so it passes the test, but the multiplication is still overflowing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/229#comment:31> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13021: Inaccessible RHS warning is confusing for users
by GHC 23 Dec '16

23 Dec '16

#13021: Inaccessible RHS warning is confusing for users -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple PatternMatchWarnings | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The pattern match checker makes the distinction between redundant matches and matches with an inaccessible right hand side. A pattern with an inaccessible RHS, is a redundant pattern which forces the argument so affects strictness. I think this is confusing for users as most of the time you write programs assuming totality but the error message doesn't make it clear why the two warnings are different. I think that instead they should both be called redundant but a note added to the inaccessible case explaining that removing it could affect strictness. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13021> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13029: Dead code in DsCCall?
by GHC 23 Dec '16

23 Dec '16

#13029: Dead code in DsCCall? -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- Simon and I were poring over `DsCCall.mk_alt`, and we seem to think that the first case (for unboxed tuples) is dead code. If it's live, it's utterly broken because it ignores the `RuntimeRep` args to an unboxed tuple. This ticket is to remind us to continue investigating. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13029> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13031: Bogus calculation of bottoming arity
by GHC 23 Dec '16

23 Dec '16

#13031: Bogus calculation of bottoming arity -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- In `CoreArity` we see {{{ andArityType (ABot n1) (ABot n2) = ABot (n1 `min` n2) }}} If you look at the documentation for `ABot` (which is about functions that are ''guaranteed'' to diverge) this is obviously bogus. The `min` should be `max`! Here's a test case: {{{ {-# LANGUAGE MagicHash #-} module Foo( f ) where import GHC.Prim f True = raise# True f False = \p q -> raise# False }}} If you compile (with GHC 8.0) `-ddump-simpl` you'll see {{{ f :: forall a p1 p2. Bool -> p2 -> p1 -> a [GblId, Arity=1, Caf=NoCafRefs, Str=<L,U>x] }}} That `Str=<L,U>x` is totally bogus; it claims that `f` will always diverge given one argument. The fix is easy. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13031> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13004: Timeout no longer kills processes on timeout
by GHC 23 Dec '16

23 Dec '16

#13004: Timeout no longer kills processes on timeout -------------------------------------+------------------------------------- Reporter: Phyx- | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Test Suite | Version: 8.1 Keywords: | Operating System: Windows Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- There's a bug in timeout where processes aren't being killed on a timeout. e.g. `~/ghc/testsuite/timeout/install-inplace/bin/timeout.exe 10 "sleep 10000s"` never ends -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13004> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12981: SMP never enabled on ARMv7
by GHC 22 Dec '16

22 Dec '16

#12981: SMP never enabled on ARMv7 -------------------------------------+------------------------------------- Reporter: orion | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Build System | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: arm | Type of failure: Building GHC | failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- SMP support should be enabled on ARMv7, however I have been unable to force it so. The problem lies in `mk/config.mk.in`, where double quotes have been erroneously added around the `ArchSupportsSMP` variable. This causes the `GhcWithSMP` variable to always be `NO` when building for ARM. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12981> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13030: Build error from following default nixos instructions and -Werror
by GHC 22 Dec '16

22 Dec '16

#13030: Build error from following default nixos instructions and -Werror -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- When building the RTS with the nixos instructions from the wiki (https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Linux#NixNixOS) if you enable `Werror` then the build fails with warnings from the rts. For example {{{ rts/Interpreter.c: In function ‘interpretBCO’: rts/Interpreter.c:593:41: error: warning: ‘obj’ may be used uninitialized in this function [-Wmaybe- uninitialized] debugBelch("Returning: "); printObj(obj); }}} Is this something I should worry about? Are there additional flags that I should pass to gcc in order to turn these warnings off? The workaround is compile without `-Werror` and then turn it on once the `rts` has been compiled. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13030> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13017: GHC panics during build of etkmett/free
by GHC 22 Dec '16

22 Dec '16

#13017: GHC panics during build of etkmett/free -------------------------------------+------------------------------------- Reporter: jbayardo | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- While using stack, I get the following error: {{{ -- While building package free-4.12.4 using: /home/user/.stack/setup-exe-cache/x86_64-linux/Cabal- simple_mPHDZzAJ_1.24.0.0_ghc-8.0.1 --builddir=.stack- work/dist/x86_64-linux/Cabal-1.24.0.0 build --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 Logs have been written to: /home/user/dev/haskellito/.stack- work/logs/free-4.12.4.log Configuring free-4.12.4... Building free-4.12.4... Preprocessing library free-4.12.4... [ 1 of 16] Compiling Control.Monad.Free.TH ( src/Control/Monad/Free/TH.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Control/Monad/Free/TH.o ) [ 2 of 16] Compiling Control.Monad.Free.Class ( src/Control/Monad/Free/Class.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Control/Monad/Free/Class.o ) [ 3 of 16] Compiling Control.Monad.Trans.Iter ( src/Control/Monad/Trans/Iter.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Control/Monad/Trans/Iter.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): Ix{Int}.index: Index (16777216) out of range ((0,392)) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13017> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13028: Compile-time validation of literals in IsString instances
by GHC 22 Dec '16

22 Dec '16

#13028: Compile-time validation of literals in IsString instances -------------------------------------+------------------------------------- Reporter: jml | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- I would like to be able to make `IsString` instances using the `OverloadedStrings` extension such that my instance rejects some literals as being invalid and such that that rejection happens at compile time, so that programming mistakes don't make it into the code I give to my users. I have a couple of use cases where I have a `Name` type that only admits certain strings. e.g. {{{#!hs module Name (Name(getName), makeName) where import Data.Text (Text) import qualified Data.Text as Text -- | A guaranteed non-empty name. newtype Name = Name { getName :: Text } deriving (Eq, Show, Ord) makeName :: Text -> Maybe Name makeName name | Text.null name = Nothing | otherwise = Just name }}} In a real use case, I'd check for valid characters, not starting with a digit, that sort of thing. The idea is that we don't export the `Name` constructor, which means anyone using a `Name` value can trust that it has certain properties (in this case, non-empty). My problem is that I'd like to use literal names in many places. e.g. {{{#!hs programName :: Name programName = fromJust $ makeName "the-great-and-powerful-turtle" }}} Because I do this a lot, I've defined an `unsafeMakeName` helper that does pretty much the same thing: {{{#!hs unsafeMakeName :: Text -> Name unsafeMakeName name = fromMaybe (error $ "Invalid name: " <> Text.unpack name) (makeName name) }}} The problem with this approach is that even though the cause of the mistake is a programming error, I don't find out about it until run time. What I'd like to do is write an `IsString` instance for `Name` which does that validation, e.g. {{{#!hs instance IsString Name where fromString = unsafeMakeName . Text.pack }}} ... but to get the error about invalid names in literals at compile-time. This doesn't seem logically impossible to me, since the compiler could know the values of literals with certainty. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13028> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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