January 2017 - ghc-tickets

[GHC] #11774: Regression on GHC 8 branch (vs 7.10.3) when using the GHC API to parse code that uses TH
by GHC 17 May '18

17 May '18

#11774: Regression on GHC 8 branch (vs 7.10.3) when using the GHC API to parse code that uses TH ----------------------------------------+--------------------------------- Reporter: SimonHengel | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc2 Keywords: | Operating System: Linux Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- If you use the GHC API to parse code that uses TH, the code does not work after a {{{:reload}}} in {{{ghci}}} anymore. = Steps to reproduce Given the following three modules {{{#!hs module Extract where import Prelude hiding (mod) import Data.Generics import DynFlags import FastString import GHC import GHC.Paths import Control.Monad import Digraph (flattenSCCs) extractDocStrings :: IO [String] extractDocStrings = do concatMap (extract . pm_parsed_source . tm_parsed_module) <$> do runGhc (Just libdir) $ do _ <- getSessionDynFlags >>= setSessionDynFlags . setHaddockMode guessTarget "Foo.hs" Nothing >>= setTargets . return mods <- depanal [] False >>= enableCompilation let sortedMods = flattenSCCs (topSortModuleGraph False mods Nothing) mapM (parseModule >=> typecheckModule >=> loadModule) sortedMods where setHaddockMode :: DynFlags -> DynFlags setHaddockMode dynflags = (gopt_set dynflags Opt_Haddock) extract :: ParsedSource -> [String] extract m = [unpackFS s | HsDocString s <- everything (++) ([] `mkQ` return) m] enableCompilation :: ModuleGraph -> Ghc ModuleGraph enableCompilation modGraph = do let enableComp d = let platform = targetPlatform d in d { hscTarget = defaultObjectTarget platform } modifySessionDynFlags enableComp let upd m = m { ms_hspp_opts = enableComp (ms_hspp_opts m) } let modGraph' = map upd modGraph return modGraph' modifySessionDynFlags :: (DynFlags -> DynFlags) -> Ghc () modifySessionDynFlags f = do dflags <- getSessionDynFlags let dflags' = case lookup "GHC Dynamic" (compilerInfo dflags) of Just "YES" -> gopt_set dflags Opt_BuildDynamicToo _ -> dflags _ <- setSessionDynFlags (f dflags') return () }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Foo where import Bar -- | some documentation foo :: Int foo = $(bar) }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module Bar where bar = [|23|] }}} == Expected (GHC 7.10.2 behavior) {{{ $ ghci Extract.hs GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help *Extract> extractDocStrings [" some documentation"] *Extract> :reload *Extract> extractDocStrings [" some documentation"] }}} == Actual (GHC 8.0.0.20160329 behavior) {{{ $ ghci Extract.hs GHCi, version 8.0.0.20160329: http://www.haskell.org/ghc/ :? for help *Extract> extractDocStrings [" some documentation"] *Extract> :reload *Extract> extractDocStrings /tmp/ghc24970_1/libghc_7.so: file not recognized: File truncated collect2: error: ld returned 1 exit status *** Exception: `gcc' failed in phase `Linker'. (Exit code: 1) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11774> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13167: GC and weak reference finalizers and exceptions
by GHC 16 May '18

16 May '18

#13167: GC and weak reference finalizers and exceptions -------------------------------------+------------------------------------- Reporter: Yuras | 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: -------------------------------------+------------------------------------- When GC runs a number of finalizers in a row, and the first of them throws an exception, then other finalizers are ignored. The relevant piece of code is [https://github.com/ghc/ghc/blob/fb4092642f057f258d07cd6979925f4e2579eda6/li… here]. The following program reproduces the issue: {{{ import Data.IORef import Control.Monad import Control.Exception import System.Mem main :: IO () main = do run run run run performMajorGC performMajorGC run :: IO () run = do ref <- newIORef () void $ mkWeakIORef ref $ do putStr "." throwIO $ ErrorCall "failed" }}} I expect it to output "....", but I get only "." The issue makes it unsafe to rely on finalizer for resource cleanup because unrelated finalizer (e.g. from some other library) may prevent your finalizer from running. Actually I was sure the issue is known, but today I tried to find a reference to it, and failed. If it is by design, then it should be documented somewhere. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13167> 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] #12012: Socket operations on Windows check errno instead of calling WSAGetLastError()
by GHC 15 May '18

15 May '18

#12012: Socket operations on Windows check errno instead of calling WSAGetLastError() -------------------------------------+------------------------------------- Reporter: enolan | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Core | Version: Libraries | 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: -------------------------------------+------------------------------------- Winsock doesn't set errno, but it is checked in `blockingReadRawBufferPtr` and `blockingWriteRawBufferPtr` (both are in `GHC.IO.FD`). I the same thing happens in the non threaded RTS too, but that's in terms of primops and I don't understand it very well. The upshot here is that every error message originating from Winsock is wrong. Nobody noticed since any error used to just crash your program (#12010). Here's some MinGW documentation http://oldwiki.mingw.org/index.php/sockets and something from MSDN https://msdn.microsoft.com/en- us/library/windows/desktop/ms740121%28v=vs.85%29.aspx -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12012> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12463: SPECIALIZABLE pragma?
by GHC 14 May '18

14 May '18

#12463: SPECIALIZABLE pragma? -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.0.1 Keywords: Inlining | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently it is common practice for library authors to use the `INLINEABLE` pragma to make it more likely that a polymorphic function should get an unfolding in the module's interface file to ensure that GHC is able to specialize. While in practice this works reasonably well, it's not really saying what we often mean: we don't want to inline, we really just want GHC to behave like each use-site's module has a `SPECIALISE` pragma for each concrete type that the function is used at. For instance, consider, {{{#!hs module ALibrary where aLibraryFunction :: AClass a => a -> a aLibraryFunction = {- some large expression involving methods of AClass -} module SomeUser where import ALibrary aUser :: Int -> Int aUser = {- some large expression involving aLibraryFunction -} }}} Ideally, we would want GHC to take and produce one specialized version of `aLibraryFunction` for every concrete type which it is used at. However, without an `INLINEABLE` function, GHC won't even consider producing an unfolding for `aLibraryFunction` due to its size. If we include an `INLINEABLE` pragma (as most performance-aware authors would do) then we can convince GHC to produce an unfolding, but only at the expense of lowering its inlining cost as well. This is unfortunate since we never wanted GHC to inline; merely to specialize. This is issue especially prevalent in code using MTL-style effects, where we have ubiquitous overloading of very frequently-used functions (e.g. bind). Really what we want in this case is a way of indicating to GHC that a function shouldn't be inlined (use-sites replaced with the body of the function), but rather that GHC should try hard to specialize away particular type variables. This might look like, {{{#!hs aLibraryFunction :: AClass a => a -> a aLibraryFunction = {- some large expression involving methods of AClass -} {-# SPECIALIZE forall a. LibraryFunction a #-} }}} This would request that GHC would keep an inlining around and produce a specialized version of `aLibraryFunction` every time it saw a concrete instantiation of `a`. Moreover, it would try to minim -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12463> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10762: On Windows, out-of-codepage characters can cause GHC build to fail
by GHC 14 May '18

14 May '18

#10762: On Windows, out-of-codepage characters can cause GHC build to fail -----------------------------------------+--------------------------------- Reporter: snoyberg | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -----------------------------------------+--------------------------------- You can see where this hit us recently on stack with issues [https://github.com/commercialhaskell/stack/issues/738 738] and [https://github.com/commercialhaskell/stack/issues/734 734]. To demonstrate, I'm attaching a UTF-8 encoded Haskell program with some Hebrew characters, and some warnings. The contents of that file are: {{{#!hs module Main ( main , שלום ) where main :: IO () main = putStrLn שלום שלום = "shalom" }}} If I first set my codepage to 65001 (UTF-8), everything works as expected: {{{ C:\Users\Michael\Desktop>chcp 65001 Active code page: 65001 C:\Users\Michael\Desktop>ghc -fforce-recomp -Wall -ddump-hi -ddump-to-file shalom.hs [1 of 1] Compiling Main ( shalom.hs, shalom.o ) shalom.hs:9:1: Warning: Top-level binding with no type signature: שלום :: [Char] Linking shalom.exe ... }}} However, if I set my codepage to 437 (US), both the warnings sent to the console, and the .hi dump file, cause GHC to exit prematurely: {{{ C:\Users\Michael\Desktop>chcp 437 Active code page: 437 C:\Users\Michael\Desktop>ghc -fforce-recomp -Wall shalom.hs [1 of 1] Compiling Main ( shalom.hs, shalom.o ) shalom.hs:9:1: Warning: Top-level binding with no type signature: <stderr>: commitBuffer: invalid argument (invalid character) }}} {{{ C:\Users\Michael\Desktop>chcp 437 Active code page: 437 C:\Users\Michael\Desktop>ghc -fforce-recomp -ddump-hi -ddump-to-file shalom.hs [1 of 1] Compiling Main ( shalom.hs, shalom.o ) shalom.dump-hi: commitBuffer: invalid argument (invalid character) }}} At the very least, I would argue that -ddump-to-file should always dump to the output files as UTF-8, as this is the most useful for tooling. Beyond that, there are a few options here: * Have all output- including to the console- go out as UTF-8. This may not play terribly nicely with consoles without setting the output codepage. * Provide a command line option or environment variable to specify "output as UTF-8." * More radical: change the default way that all Handles work so that UTF-8 is the default, instead of paying attention to code pages and environment variables. Honestly, this is my preference, but it's a bigger discussion than this one bug. The workaround we've implemented in stack for now is setting the codepage to 65001 for the console while running stack. This is not ideal, since this is essentially a global setting for the entire console. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10762> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11389: Print a message when loading a .ghci file
by GHC 13 May '18

13 May '18

#11389: Print a message when loading a .ghci file -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: GHCi | Version: 7.8.4 Keywords: newcomer | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It'd be nice to have a notice displayed when ghci loads a .ghci file, something like {{{ rwbarton@morphism:~$ ghci-7.10.1 GHCi, version 7.10.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rwbarton/.ghci Prelude> }}} I want this mostly so that we can tell whether people filing ghci bugs might have anything relevant in their `.ghci` files. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11389> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12721: Implement sigINT handler for Window's timeout.exe
by GHC 12 May '18

12 May '18

#12721: Implement sigINT handler for Window's timeout.exe ----------------------------------------+---------------------------- Reporter: Phyx- | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 8.0.1 Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: Other Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+---------------------------- On linux we current register a sigINT handler and kill the child processed. On Windows we don't. This sometimes leaves dangling processes when the testsuite is interrupted. Causing future failures until the dangling processes are killed. We already specifically create a job group and assign the processors to those jobs. All we have to do is register the handler and kill the process if the handler is called. See https://msdn.microsoft.com/en- us/library/windows/desktop/ms686016(v=vs.85).aspx -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12721> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10832: Generalize injective type families
by GHC 07 May '18

07 May '18

#10832: Generalize injective type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: jstolarek Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- With injective type families we can now declare that type family result determines the arguments. But ITFs are not yet as expressive as functional dependencies. For example with FDs I can say: {{{#!hs data Nat = Zero | Succ a class Add a b r | a b -> r, r a -> b instance Add Zero b b instance (Add a b r) => Add (Succ a) b (Succ r) }}} Here we declare that the result and the first argument taken together uniquely determine the second argument. This is not currently possible with ITFs: {{{#!hs type family AddTF a b = r | r a -> b where AddTF Zero b = b AddTF (Succ a) b = Succ (AddTF a b) }}} But we want to be able to say that. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10832> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11080: Open data kinds
by GHC 07 May '18

07 May '18

#11080: Open data kinds -------------------------------------+------------------------------------- Reporter: dmcclean | Owner: Type: feature | Status: new request | Priority: low | 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: -------------------------------------+------------------------------------- When we need type level symbols, we used to only have one option, `EmptyDataDecls`. The symbolic type parameters would be given kind `*`, but the convention would be to use types that are (mostly) uninhabited and that were made for the purpose of serving as symbols. For an example of this see http://hackage.haskell.org/package/servant-0.4.4.5/docs/Servant- API-ContentTypes.html. Now we also have the `Symbol` kind which can serve a similar purpose. Neither of these options is fully satisfactory for examples like servant's type-level encoding of content types, or the `units` libraries type-level encoding of physical dimensions, for the following reasons: We would prefer to give these types a kind other than `*` both because they are uninhabited and because we wish to provide documentation of what types are acceptable in these parameter positions. But the only facility we have for creating new kinds is `DataKinds`, and the kinds it creates are all closed. This is problematic because we wish to allow client modules to declare new content types or new physical dimensions. We could provide "newkind" wrappers around `Symbol` using `DataKinds`, but that runs in to name collision issues. The `EmptyDataDecls` solution is superior here because types with the same name declared in different modules remain distinct. Instead I propose the addition of a new feature where data kinds can be open. In a discussion at https://github.com/bjornbm/dimensional-dk/issues/96 in which @goldfire participated, we arrived at the following proposal for concrete syntax, but certainly there are many possible variations one could imagine which might have equal or greater merit: {{{#!hs -- declares a new kind which initially has no inhabitants data open ContentType -- declares a new type of kind ContentType, which is distinct -- from any others that may have been declared elsewhere, -- even if they have the same non-module-qualified name data constructor JSON :: ContentType }}} (@goldfire raised the possibility of one day interpreting the same `data constructor ...` syntax at the type level to declare inhabited types for which some constructors are defined in one module but which are open to extension with new constructors by other modules, but that is a distinct issue in all other ways apart from possibly wishing to share syntax.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11080> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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