May 2018 - ghc-tickets

Re: [GHC] #7411: Exceptions are optimized away in certain situations
by GHC 29 May '18

29 May '18

#7411: Exceptions are optimized away in certain situations -------------------------------------+------------------------------------- Reporter: SimonHengel | Owner: tdammers Type: bug | Status: new Priority: high | Milestone: 8.6.1 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: seq, deepseq, | evaluate, exceptions Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: Incorrect result | Test Case: at runtime | simplCore/should_fail/T7411 Blocked By: | Blocking: Related Tickets: #5129 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): I ran two full builds of GHC (`make clean; ./boot; ./configure; make -j2` on a dual-core i5 machine, 4 GB RAM, 7200 RPM HDD, debian stretch, stage0 = GHC 8.4.1), one with the `prof` flavour, the other with a modified `prof` flavour with `GhcLibHcOpts += -fno-state-hack`. It turns out that the `-fno-state-hack` version is slightly faster: Prof build: {{{ real 66m5.407s user 118m50.668s sys 6m7.044s }}] Prof + `-fno-state-hack` build: {{{ real 65m42.784s user 118m32.892s sys 6m5.252s }}} I haven't done any in-depth profiling yet, but it seems to me that removing the state hack would most not make things significantly worse overall. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7411#comment:32> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4806: Make error message more user friendly when module is not found because package is unusable
by GHC 28 May '18

28 May '18

#4806: Make error message more user friendly when module is not found because package is unusable -------------------------------------+------------------------------------- Reporter: mitar | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgillespie): I think the strategy should be to modify mkModuleToPkgConfAll to include all UnusablePackages in PackageState.hs. We could then add another constructor to ModuleOrigin (say, BrokenPackage) so that we could report it on lookupModuleWithSuggestions. Please correct me if this is not a reasonable approach. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
by GHC 28 May '18

28 May '18

#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -------------------------------------+------------------------------------- Reporter: ChrisKuklewicz | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 7.6.1 Component: libraries/base | Version: 7.0.2 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * status: new => closed * resolution: => fixed -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3160#comment:25> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
by GHC 28 May '18

28 May '18

#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -------------------------------------+------------------------------------- Reporter: ChrisKuklewicz | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 7.6.1 Component: libraries/base | Version: 7.0.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * owner: simonmar => (none) * status: closed => new * resolution: wontfix => -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3160#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15107: Testsuite failures on Windows
by GHC 28 May '18

28 May '18

#15107: Testsuite failures on Windows -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 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: -------------------------------------+------------------------------------- For some time now there have been quite a few testsuite failures on Windows, but that number seems to have increaded recently. Here are the failures from {{{ sh validate --fast }}} with today's HEAD {{{ SUMMARY for test run started at Mon Apr 30 16:41:18 2018 GMTST 5:46:04 spent to go through 6321 total tests, which gave rise to 18197 test cases, of which 11980 were skipped 46 had missing libraries 5963 expected passes 171 expected failures 6 caused framework failures 1 caused framework warnings 0 unexpected passes 31 unexpected failures 6 unexpected stat failures Unexpected failures: backpack/cabal/bkpcabal07/bkpcabal07.run bkpcabal07 [bad exit code] (normal) backpack/cabal/bkpcabal06/bkpcabal06.run bkpcabal06 [bad exit code] (normal) cabal/ghcpkg05.run ghcpkg05 [bad stderr] (normal) ghci/linking/ghcilink001.run ghcilink001 [bad exit code] (normal) ghci/linking/ghcilink004.run ghcilink004 [bad exit code] (normal) ghci/linking/dyn/big-obj.run big-obj [bad exit code] (normal) ghci/scripts/ghci057.run ghci057 [bad stdout] (ghci) ghci/scripts/T9293.run T9293 [bad stdout] (ghci) ghci.debugger/scripts/break006.run break006 [bad stdout] (ghci) ghci.debugger/scripts/hist001.run hist001 [bad stdout] (ghci) ghci.debugger/scripts/hist002.run hist002 [bad stdout] (ghci) perf/compiler/T14697.run T14697 [[Errno 2] No such file or directory: '/c/Users/simonpj/AppData/Local/Temp/ghctest- 4kcp39ag/test spaces/./perf/compiler/T14697.run/T14697.comp.stats'] (normal) plugins/plugins07.run plugins07 [bad exit code] (normal) plugins/T10420.run T10420 [bad exit code] (normal) plugins/T11244.run T11244 [bad stderr] (normal) rts/T11788.run T11788 [bad exit code] (normal) rts/T14695.run T14695 [bad stderr] (normal) rts/T11223/T11223_simple_link.run T11223_simple_link [bad exit code] (normal) rts/T11223/T11223_simple_link_lib.run T11223_simple_link_lib [bad exit code] (normal) rts/T11223/T11223_simple_duplicate_lib.run T11223_simple_duplicate_lib [bad exit code] (normal) rts/T11223/T11223_simple_unused_duplicate_lib.run T11223_simple_unused_duplicate_lib [bad exit code] (normal) rts/T11223/T11223_link_order_a_b_succeed.run T11223_link_order_a_b_succeed [bad exit code] (normal) rts/T11223/T11223_link_order_b_a_succeed.run T11223_link_order_b_a_succeed [bad exit code] (normal) rts/T11223/T11223_link_order_a_b_2_fail.run T11223_link_order_a_b_2_fail [bad exit code] (normal) rts/T11223/T11223_link_order_b_a_2_succeed.run T11223_link_order_b_a_2_succeed [bad exit code] (normal) rts/T12771/T12771.run T12771 [bad exit code] (normal) rts/T13082/T13082_good.run T13082_good [bad exit code] (normal) rts/T14611/T14611.run T14611 [bad exit code] (normal) /../libraries/base/tests/tempfiles.run tempfiles [bad stdout] (normal) /../libraries/process/tests/T9775/T9775_fail.run T9775_fail [bad exit code] (normal) /../libraries/process/tests/T9775/T9775_good.run T9775_good [bad exit code] (normal) Unexpected stat failures: perf/compiler/T12234.run T12234 [stat not good enough] (optasm) perf/compiler/T12425.run T12425 [stat not good enough] (optasm) perf/compiler/T12150.run T12150 [stat not good enough] (optasm) perf/should_run/T14052.run T14052 [stat not good enough] (ghci) perf/should_run/T14936.run T14936 [stat too good] (normal) perf/compiler/MultiLayerModules.run MultiLayerModules [stat not good enough] (normal) Framework failures: plugins/plugins07.run plugins07 [normal] (pre_cmd failed: 2) plugins/T10420.run T10420 [normal] (pre_cmd failed: 2) plugins/T11244.run T11244 [normal] (pre_cmd failed: 2) safeHaskell/check/pkg01/ImpSafeOnly08.run ImpSafeOnly08 [runTest] (Unhandled exception during cleanup: Unable to remove folder '/c/Users/simonpj/AppData/Local/Temp/ghctest-4kcp39ag/test spaces/./safeHaskell/check/pkg01/ImpSafeOnly08.run': [Errno 13] Permission denied: '/c/Users/simonpj/AppData/Local/Temp/ghctest-4kcp39ag/test spaces/./safeHaskell/check/pkg01/ImpSafeOnly08.run/pdb.ImpSafeOnly08/install/x86_64 -windows-ghc-8.5.20180420/safePkg01-1.0-LQOvw3iv9WM6fIcv695PaM' Unable to start current test.) ../../libraries/process/tests/T9775/T9775_fail.run T9775_fail [normal] (pre_cmd failed: 2) ../../libraries/process/tests/T9775/T9775_good.run T9775_good [normal] (pre_cmd failed: 2) Framework warnings: . T13701 [numfield-no-expected] (No expected value found for bytes allocated in num_field check) }}} That's an uncomfortably long list. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15107> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15191: Deriving via DeriveAnyClass not behaving the same as an emply instance declaration
by GHC 28 May '18

28 May '18

#15191: Deriving via DeriveAnyClass not behaving the same as an emply instance declaration -------------------------------------+------------------------------------- Reporter: Darwin226 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I've opened [https://stackoverflow.com/questions/50557019/deriving-via- deriveanyclass-not-behaving-the-same-as-an-emply-instance-declarati a question on StackOverflow] describing the issue. I'll copy it here: ---- I have the following code {{{#!hs {-# LANGUAGE PolyKinds, DefaultSignatures, FlexibleContexts, DeriveAnyClass, DeriveGeneric #-} {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, UndecidableInstances #-} module DeriveTest where import GHC.Generics class GenericClass a m where instance GenericClass f m => GenericClass (M1 i c f) m instance Condition a m => GenericClass (K1 i a) m class Condition (a :: k) (m :: * -> *) where instance (Condition a m, Condition b m) => Condition (a b) m instance {-# OVERLAPPABLE #-} Condition (a :: k) m class Class (e :: (* -> *) -> *) where classF :: e m -> () default classF :: GenericClass (Rep (e m)) m => e m -> () classF = undefined }}} It defines the class Class of types that have a higher-kinded type as a parameter. It also defines a generic way to derive an instance of that class. Now if I declare a new datatype like this, and try to derive an instance of Class {{{#!hs data T a m = T { field :: a } deriving (Generic, Class) }}} I get the following error: {{{ * Overlapping instances for Condition a m arising from the 'deriving' clause of a data type declaration Matching instances: instance [overlappable] forall k (a :: k) (m :: * -> *). Condition a m instance forall k1 k2 (a :: k1 -> k2) (m :: * -> *) (b :: k1). (Condition a m, Condition b m) => Condition (a b) m (The choice depends on the instantiation of `a, m' To pick the first instance above, use IncoherentInstances when compiling the other instance declarations) * When deriving the instance for (Class (T a)) | 22 | deriving (Generic, Class) | ^^^^^ }}} The error sort of makes sense because I guess. The instance really does depend on the instantiation of a. However, if I just write an empty instance like this: {{{#!hs data T a m = T { field :: a } deriving (Generic) instance Class (T a) -- works }}} It works. Why? And how can I make it behave the same with the deriving statement? ---- Ryan Scott suggested I open a ticket and that the issue probably isn't with the deriving mechanisms. Still, I chose to keep the title because that's what the original problem was and I've seen [https://github.com/GetShopTV/swagger2/issues/144 similar issues] before -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15191> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12540: RFC: Allow not quantifying every top-level quantifiee
by GHC 27 May '18

27 May '18

#12540: RFC: Allow not quantifying every top-level quantifiee -------------------------------------+------------------------------------- Reporter: Iceland_jack | 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: -------------------------------------+------------------------------------- Minor nuisance, does this happen to anyone else? Currently Haskell has an all-nothing policy on quantified type variables, either you quantify none or all (fine, let's ignore non-prenex quantification `foo :: a -> forall b. b -> a`). Can we have a top-level quantification of only a subset of the free variables? Say I'm working on a function {{{#!hs reflected :: forall s m a. (Applicative m, Reifies s a) => TaggedT s m a }}} and I need to make ''s'' a scoped type variable, I always accidentally write {{{#!hs reflected :: forall s. (Applicative m, Reifies s a) => TaggedT s m a reflected = TagT . pure . reflect $ (Proxy :: Proxy s) }}} This causes GHC to complain that the other types — ''m'', ''a'' — are not in scope so and I have to add the remaining quantifiees I don't really care about (may have long names as well). It could be worse (''dramatization'') {{{#!hs ipartsOf :: forall i p f s t a. (Indexable [i] p, Functor f) => Traversing (Indexed i) f s t a a -> Over p f s t [a] [a] ipartsOf l = conjoined (\f s -> let b = inline l sell s in outs b <$> f (wins b)) (\f s -> let b = inline l sell s; (is, as) = unzip (pins b) in outs b <$> indexed f (is :: [i]) as) appendAssocAxiom :: forall p q r as bs cs. p as -> q bs -> r cs -> Dict ((as ++ (bs ++ cs)) ~ ((as ++ bs) ++ cs)) appendAssocAxiom _ _ _ = unsafeCoerce (Dict :: Dict (as ~ as)) }}} It would be nice to be nice to only have to specify the type one is interested in: {{{#!hs ipartsOf :: forall i. (Indexable [i] p, Functor f) => Traversing (Indexed i) f s t a a -> Over p f s t [a] [a] appendAssocAxiom :: forall as. p as -> q bs -> r cs -> Dict ((as ++ (bs ++ cs)) ~ ((as ++ bs) ++ cs)) }}} and have the others chosen in some way. This is not just useful for writing, but it makes it easier to read: If I see a type `forall i p f s t a. ...` any of them may appear in the function body, if I see a type `forall i. ...` I know only one is. Thoughts? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12540> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9427: Do finer-grained dependency analysis to infer more general kinds on type/class declarations
by GHC 27 May '18

27 May '18

#9427: Do finer-grained dependency analysis to infer more general kinds on type/class declarations -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- In the resolution to #9200, as detailed [wiki:GhcKinds/KindInference#Apossiblevariation here], we identified an area for improvement. This improvement was not implemented in the fix for #9200. This ticket will track just this improvement. (In brief: we can do better dependency analysis on mutually recursive type/class declarations to allow more kinds to generalize earlier. This would lessen the burden on programmers to put in kind annotations. See the wiki page.) A solid but unfinished attempt is [https://github.com/goldfirere/ghc/tree /re-sort-non-cusk-decls here]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9427> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10141: Kind inference regression in closed type families
by GHC 27 May '18

27 May '18

#10141: Kind inference regression in closed type families -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: highest | Milestone: 7.10.1 Component: Compiler | Version: 7.10.1-rc2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Take the following definition: {{{ type family G (a :: k) where G Int = Bool G Bool = Int G a = a }}} It compiles in 7.8.3, but not in 7.10.1 RC2. This makes me sad. I will fix. (Found by Jan Stolarek.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10141> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14662: Partial type signatures + mutual recursion = confusion
by GHC 26 May '18

26 May '18

#14662: Partial type signatures + mutual recursion = confusion -------------------------------------+------------------------------------- Reporter: goldfire | 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: -------------------------------------+------------------------------------- I'm trying to understand better how partial type signatures interact with mutual recursion. This is all in 8.4.1-alpha1. Example 1: {{{#!hs f :: forall a. _ -> a -> a f _ x = g True x g :: forall b. _ -> b -> b g _ x = f 'x' x }}} This works -- no problem. Example 2: {{{#!hs f :: forall a. _ -> a -> a f _ x = snd (g True 'a', x) g :: forall b. _ -> b -> b g _ x = f 'x' x }}} This fails, explaining that GHC inferred `g :: Bool -> a -> a` and that `a` doesn't match `Char` (in the second argument of the call site in the body of `f`). This is unsatisfactory because clearly `g` should be ''instantiated'' at `Char`. The manual does say that polymorphic recursion isn't available with partial type signatures, and I suppose this is an example of polymorphic (mutual) recursion. Example 3: {{{#!hs f :: forall a. _ -> a -> a f _ x = snd (g True 'a', x) where g :: forall b. _ -> b -> b g _ y = f 'x' y }}} This is accepted. This is the same example as the last one, but now `g` is local. It does not capture any variables (including type variables) from `f`, so it seems to me that it should be equivalent to Example 2. But somehow GHC is clever enough to accept. Example 4: {{{#!hs thdOf3 (_, _, c) = c f :: forall a. _ -> a -> a f _ x = thdOf3 (g True 'a', g False 5, x) where g :: forall b. _ -> b -> b g _ y = f 'x' y }}} This works, too. Note that `g` is applied at several different types, so it really is being generalized. Example 5: {{{#!hs f :: Int -> forall a. _ -> a -> a f n _ x = snd (g n True 'a', x) g :: Int -> forall b. _ -> b -> b g n _ x = f n 'x' x }}} This is accepted. This is the same as Example 2, but each function now takes an `Int`, which is simply passed back and forth. Evidently, when you write the type non-prenex, polymorphic recursion is OK. Example 6: {{{#!hs f :: Int -> forall a. _ -> a -> a f n _ x = snd (f n True 'x', x) }}} This is accepted, even though it's blatantly using polymorphic recursion. Example 7: {{{#!hs f :: forall a. _ -> a -> a f _ x = snd (f True 'x', x) }}} This is rejected as polymorphically recursive. -------------------------- Something is fishy here. It's not the explicit prenex `forall`s -- leaving those out doesn't change the behavior. I guess my big question is this: * If the user quantifies a partial type signature (either by using `forall`, or just using an out-of-scope type variable and using Haskell's implicit quantification), why can't we use polymorphic recursion with that variable? I understand why we can't use polymorphic recursion with wildcards. ----------------------------------- A little background for context: I'm struggling (in my work on #14066) with GHC's use of `SigTv`s for partial type signatures. I don't have a better suggestion, but `SigTv`s never make me feel good. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14662> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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