July 2014 - ghc-tickets

[GHC] #8597: Git Hook script to prevent large binary blobs being checked in
by GHC 24 Feb '18

24 Feb '18

#8597: Git Hook script to prevent large binary blobs being checked in ------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: Component: Trac & Git | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- It has already occurred in the past in `testsuite.git` repo, that executables were checked in by accident, and caused the Git history to get bloated. In order to avoid such accidents in the future a Git hook script in the style of [http://stackoverflow.com/questions/20226132/is-there-a-git-hook- which-can-prevent-binary-check-ins this] might be useful, but taking also into account the size, and/or possibly with a magic safeword to be put in the commit message, to override the check for a single commit, if the author really knows what (s)he's doing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8597> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8258: GHC accepts `data Foo where` in H2010 mode
by GHC 14 Feb '18

14 Feb '18

#8258: GHC accepts `data Foo where` in H2010 mode --------------------------+------------------------------------------------ Reporter: hvr | Owner: Type: bug | Status: new Priority: low | Milestone: 7.8.1 Component: | Version: 7.0.4 Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC accepts invalid program Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ According to the Haskell2010 report, The grammar productions relevant for `data` declarations are the following: {{{ topdecl → data [context =>] simpletype [= constrs] [deriving] }}} (from [http://www.haskell.org/onlinereport/haskell2010/haskellch4.html#x10-680004.2 4.2.1 Algebraic Datatype Declarations]) However, GHC 7.0.4/7.4.2/7.6.3/HEAD all happily compile the following Haskell module without any warning when using `-XHaskell2010 -Wall`, even though this is not valid Haskell2010 afaik: {{{#!hs module Foo where data Foo where }}} The trailing `where` in the `data` declaration is not valid Haskell2010 (without language extensions such as `GADT`). At the very least, this divergence from the Haskell Report should be mentioned in [http://www.haskell.org/ghc/docs/latest/html/users_guide /bugs-and-infelicities.html#haskell-standards-divergence 14.1.1. Divergence from Haskell 98 and Haskell 2010]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8258> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9269: Type families returning quantified types
by GHC 14 Feb '18

14 Feb '18

#9269: Type families returning quantified types ------------------------------------+------------------------------------- Reporter: pumpkin | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Is there a fundamental reason for not being able to use quantification in a type family? I'd very much like to be able to do it, obviously turning on RankNTypes if necessary. I'm looking for things like this: {{{#!haskell type family Foo (x :: Bool) where Foo True = forall a. [a] Foo False = () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9269> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8684: hWaitForInput cannot be interrupted by async exceptions on unix
by GHC 05 Feb '18

05 Feb '18

#8684: hWaitForInput cannot be interrupted by async exceptions on unix ------------------------------------+------------------------------------- Reporter: nh2 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | 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: | ------------------------------------+------------------------------------- http://hackage.haskell.org/package/base-4.6.0.1/docs/System-Timeout.html claims that {{{timeout}}} can interrupt {{{hWaitForInput}}}, but in fact that's false (e.g. mentioned in https://ghc.haskell.org/trac/ghc/ticket/7353#comment:4) {{{ -- import Control.Concurrent import System.IO import System.Timeout main = timeout (1 * 1000000) $ hWaitForInput stdin (5 * 1000) }}} will not be killed after 1 second, but instead wait for the full 5 seconds timeout passed to {{{hWaitForInput}}}. The implementation is {{{ready}}} at http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-IO- FD.html, where we have two foreign calls: {{{safe fdReady}}} and {{{unsafe unsafe_fdReady}}}. The actual C implementation is at https://github.com/haskell- suite/base/blob/master/cbits/inputReady.c#L16. It uses {{{select}}} on Unix, and does check for {{{EINTR}}}, so I believe that according to http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/ffi.html#ffi- interruptible both foreign calls can be replaced by a single {{{interruptible}}} one. Is that true? If not, it's a documentation bug in {{{timeout}}} at least. Also, does {{{interruptible}}}, apart from allowing the function to be interrupted, behave more like {{{safe}}} or {{{unsafe}}}? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8684> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8228: GHC built under Windows does not generate dyn_hi files
by GHC 04 Feb '18

04 Feb '18

#8228: GHC built under Windows does not generate dyn_hi files ------------------------------+-------------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.7 Keywords: | Operating System: Windows Architecture: | Type of failure: GHC doesn't work at all Unknown/Multiple | Test Case: cabal01 Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- I found cabal01 failing with: {{{ =====> cabal01(normal) 1 of 1 [0, 0, 0] cd . && $MAKE -s --no-print-directory cabal01 VANILLA=--enable-library- vanilla PROF=--disable-l ibrary-profiling DYN=--enable-shared </dev/null >cabal01.run.stdout 2>cabal01.run.stderr Wrong exit code (expected 0 , actual 2 ) Stdout: Stderr: Creating library file: dist\build\libHStest-1.0-ghc7.7.20130904.dll.a setup.exe: Error: Could not find module: A with any suffix: ["dyn_hi"] in the search path: ["dist\\build"] make[2]: *** [cabal01] Error 1 }}} but I bet some of the other failures are due to this. Indeed, in dist/build, there are no dyn_hi files When I look more closely at the commands being run, I see: {{{ bash.exe-3.1$ c:/Users/ezyang/Dev/ghc-validate/inplace/bin/ghc-stage2.exe --make -fbuilding-ca bal-package -O -static -dynamic-too -dynosuf dyn_o -dynhisuf dyn_hi -outputdir dist/build -odi r dist/build -hidir dist/build -stubdir dist/build -i -idist/build -i. -idist/build/autogen -I dist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -package- name test-1.0 -hide-all- packages -no-user-package-db -package-db local.db -package-db dist/pac kage.conf.inplace -package-id base-4.7.0.0-inplace -XHaskell98 -XForeignFunctionInterface A B. A -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db [1 of 2] Compiling B.A ( B\A.hs, dist\build\B\A.o ) [2 of 2] Compiling A ( A.hs, dist\build\A.o ) }}} which should result in dyn_hi files but does not. I haven't traced it any further yet. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8228> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9285: IO manager startup procedure somewhat odd
by GHC 15 Jan '18

15 Jan '18

#9285: IO manager startup procedure somewhat odd ------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Currently the RTS startup procedure for the threaded runtime with a single capability looks something like this: '''1. Capability gets initialized''' {{{ hs_main real_main hs_init_ghc initScheduler initCapabilities }}} '''2. IO Manager is started''' {{{ hs_main real_main hs_init_ghc ioManagerStart }}} '''3. ensureIOManagerIsRunning''' The IO manager of course is mostly written in Haskell, so `ioManagerStart` does {{{ cap = rts_lock(); rts_evalIO(&cap,&base_GHCziConcziIO_ensureIOManagerIsRunning_closure,NULL); rts_unlock(cap); }}} '''4. Bound task is created and we start running Haskell code''' Since this is the first call to `rts_lock`, it creates a bound task to correspond to the current OS thread. '''5. Haskell code does a safe FFI call: create worker task 1''' The first safe FFI call that the IO manager makes (ignoring `labelThread`) is to `c_setIOManagerControlFd`. At this point, the bound task gets suspended and we create a worker task. '''6. Worker task 1 starts executing `GHC.Event.Manager.loop`''' The worker tasks gets suspended due to an explicit call to `yield` in `GHC.Event.Manager.step`, at which point the bound task continues execution. It continues and finishes (`ensureIOManagerRunning` completes). The worker task takes over. '''7. Worker task 1 does a safe FFI call to `I.poll`, create new worker task 2''' (This safe call is from `GHC.Event.Manager.step`) '''8. Worker task 2 executes `GHC.Event.TimerManager.loop`, and does safe FFI call to `I.poll`; create worker task 3''' This worker task will remain spare for now. '''9. Start executing the actual main function''' The IO manager calls `rts_unlock`, which verifies if there are any spare workers available; it finds that there are and doesn't start a new one. Then when we start `main` itself of course we go through this `rts_lock, rts_evalIO, rts_unlock` sequence ''again''. This is somewhat confusing, and makes tracing the startup of the code more difficult to interpret. It seems that this could be simpler: only a single `rts_lock` should be necessary, in which we first call `ensureIOManagerIsRunning` and then `main`, followed by a single `rts_unlock`. A similar simplification should be possible in `forkProcess`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9285> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8487: Debugger confuses variables
by GHC 02 Jan '18

02 Jan '18

#8487: Debugger confuses variables ------------------------------------+------------------------------------- Reporter: edsko | 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: | ------------------------------------+------------------------------------- Consider the following example: {{{ import Control.Exception f = do ma <- try $ evaluate a case ma of Right str -> return a Left err -> return $ show (err :: SomeException) where a :: String a = error "hi" }}} Load into ghci, set a breakpoint on the 5th line, then run f: {{{ :break 5 f }}} You will get {{{ Stopped at Ex.hs:(5,3)-(7,53) _result :: IO String = _ a :: Either SomeException String = Left _ }}} This doesn't make sense. `a` has type `String`; it is `ma` that has type `Either SomeException String`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8487> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8642: Allow GHCi to print non-pretty forms of things.
by GHC 29 Dec '17

29 Dec '17

#8642: Allow GHCi to print non-pretty forms of things. ------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: GHCi | 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: | ------------------------------------+------------------------------------- Currently when we ask GHCi for :info or :type of something, it will do things like splitting over multiple lines and all that eye candy that people like to see. This however makes it more difficult for people to write text editor plugins &c that rely on GHCi output. Currently one has to write parsers to stitch the GHCi output back together which is fairly error prone and not really future-proof. Is there any chance for a more machine-friendly output? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8642> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9291: Don't reconstruct sum types if the type subtly changes
by GHC 28 Dec '17

28 Dec '17

#9291: Don't reconstruct sum types if the type subtly changes ----------------------------------------------+---------------------------- Reporter: schyler | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 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: ----------------------------------------------+---------------------------- Consider this test case: {{{ module Main (main) where fun :: Either Int String -> Either String String fun x = case x of Left int -> Left (show int) Right str -> Right str {-# NOINLINE fun #-} main :: IO () main = do l <- getLine print $ fun (Right l) }}} The core we get for fun looks like: {{{ Main.fun [InlPrag=NOINLINE] :: Data.Either.Either GHC.Types.Int GHC.Base.String -> Data.Either.Either GHC.Base.String GHC.Base.String [GblId, Arity=1, Caf=NoCafRefs, Str=DmdType <S,1*U>] Main.fun = \ (x_aur :: Data.Either.Either GHC.Types.Int GHC.Base.String) -> case x_aur of _ [Occ=Dead] { Data.Either.Left int_aus -> Data.Either.Left @ GHC.Base.String @ GHC.Base.String (GHC.Show.$fShowInt_$cshow int_aus); Data.Either.Right str_aCG -> Data.Either.Right @ GHC.Base.String @ GHC.Base.String str_aCG } }}} There would be less allocations and probably perform better if we just coerced `x` into the new type. Because the coercion is common code, this also means that if hypothetically some other sum type which had 15 constructors, and only 3 had subtle type changes, 12 of the case branches could be CSE'd into the single coerce greatly reducing code generated and also hinting the inliner better. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9291> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9244: Compiler could warn about type variable shadowing, and hint about ScopedTypeVariables
by GHC 18 Dec '17

18 Dec '17

#9244: Compiler could warn about type variable shadowing, and hint about ScopedTypeVariables -------------------------+------------------------------------------------- Reporter: | Owner: stusmith | 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: | -------------------------+------------------------------------------------- GHC already warns about variable shadowing: {{{ timesTwoPlusOne x = timesTwo x + 1 where timesTwo x = x * 2 Warning: This binding for `x' shadows the existing binding bound at <location> }}} However the similar warning doesn't happen for type variables. {{{ tryMaybe :: IO a -> IO (Maybe a) tryMaybe action = do result <- (try action) :: IO (Either SomeException a) return $ case result of Left _ -> Nothing Right v -> Just v Couldn't match type `a' with `a1' `a' is a rigid type variable bound by the type signature for tryMaybe :: IO a -> IO (Maybe a) at types.hs:<line>:13 `a1' is a rigid type variable bound by an expression type signature: IO (Either SomeException a1) at types.hs:<line>:15 Expected type: IO a1 Actual type: IO a ... }}} Here, I thought that the 'a' in the function's type declaration was the same 'a' in the expression type declaration. However in Haskell 98, they are completely different variables. Suggestion: if a type variable is renamed by the compiler due to a clash with another type variable, issue a warning that the second shadows the first, and give a hint about using -XScopedTypeVariables and forall. Alternative suggestion: if an error is displayed, where the error contains a renamed type variable, issue a hint that the second shadows the first, and give a hint about using -XScopedTypeVariables and forall. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9244> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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