November 2017 - ghc-tickets

[GHC] #14230: Gruesome kind mismatch errors for associated data family instances
by GHC 30 Nov '18

30 Nov '18

#14230: Gruesome kind mismatch errors for associated data family instances -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 (Type checker) | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: #14175 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Spun off from https://ghc.haskell.org/trac/ghc/ticket/14175#comment:9. This program, which can only really be compiled on GHC HEAD at the moment: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} module Bug where class C k where data CD :: k -> k -> * instance C (Maybe a) where data CD :: (k -> *) -> (k -> *) -> * }}} Gives a heinous error message: {{{ Bug.hs:11:3: error: • Expected kind ‘(k -> *) -> (k -> *) -> *’, but ‘CD :: (k -> *) -> (k -> *) -> *’ has kind ‘Maybe a -> Maybe a -> *’ • In the data instance declaration for ‘CD’ In the instance declaration for ‘C (Maybe a)’ | 11 | data CD :: (k -> *) -> (k -> *) -> * | ^^^^^^^ }}} * We shouldn't be expecting kind `(k -> *) -> (k -> *) -> *`, but rather kind `Maybe a -> Maybe a -> *`, due to the instance head itself. * The phrase `‘CD :: (k -> *) -> (k -> *) -> *’ has kind ‘Maybe -> Maybe a -> *’` is similarly confusing. This doesn't point out that the real issue is the use of `(k -> *)`. Another program in a similar vein: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind class C a where data CD k (a :: k) :: k -> * instance C (Maybe a) where data CD k (a :: k -> *) :: (k -> *) -> * }}} {{{ Bug.hs:13:3: error: • Expected kind ‘(k -> *) -> *’, but ‘CD k (a :: k -> *) :: (k -> *) -> *’ has kind ‘k -> *’ • In the data instance declaration for ‘CD’ In the instance declaration for ‘C (Maybe a)’ | 13 | data CD k (a :: k -> *) :: (k -> *) -> * | ^^^^^^^^^^^^^^^^^^^^^^^ }}} This error message is further muddled by the incorrect use of `k` as the first type pattern (instead of `k -> *`, as subsequent kind signatures would suggest). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14230> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13492: -p option report much less time than actual on high intensity of FFI calls application
by GHC 30 Nov '18

30 Nov '18

#13492: -p option report much less time than actual on high intensity of FFI calls application -------------------------------------+------------------------------------- Reporter: varosi | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | Version: 8.0.2 Keywords: | Operating System: Windows Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Proprietary application is ran on 44 cores (88 with HT) machine (same problem on 12 core). It is Haskell between wxHaskell (wxWidgets for UI) and C API. It is doing FFI calls most of the time. Calls are not so many, but possibly not so fast. I'm trying to profile where is the problem, in which calls. But very strange behaviour is there. "total time" of application that is running 30secs to 1min is showing 0.33secs. Even MAIN function is not 100%. Please, see first part of .prof file: Tue Mar 28 15:38 2017 Time and Allocation Profiling Report (Final) app.exe +RTS -N -A40m -qb0 -p -RTS total time = 0.33 secs (325 ticks @ 1000 us, 1 processor) total alloc = 86,317,264 bytes (excludes profiling overheads) COST CENTRE MODULE SRC %time %alloc MAIN MAIN <built- in> 12.6 2.2 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13492> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8177: Roles for type families
by GHC 29 Nov '18

29 Nov '18

#8177: Roles for type families ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | 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: | ------------------------------------+------------------------------------- Now that we have [wiki:Roles roles], it might be helpful to be able to give a role signature for a data/type family. At the moment, data/type family constructors have all parameters conservatively assigned to be role `N`. Thus {{{ data family D a -- Parameter conservatively assumed to be N class C a where op :: D a -> a instance C Int where .... newtype N a = MkN a deriving( C ) -- Rejected }}} The generalised-newtype-deriving clause `deriving( C )` is rejected because `D` might use its parameter at role `N` thus: {{{ data instance D [b] = MkD (F b) -- F is a type function }}} It would be strictly more expressive if we could * '''Declare''' the roles of D's arguments (as we can declare their kinds). E.g. {{{ data family D a@R }}} * '''Check''' that each family instance obeys that role signature. E.g. given the preceding role signature, reject this instance: {{{ data instance D [b] = MkD (F b) -- F is a type function }}} I think there is no technical difficulty here. Just a question of doing it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8177> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14506: Configure Harbormaster to trigger CircleCI commits
by GHC 28 Nov '18

28 Nov '18

#14506: Configure Harbormaster to trigger CircleCI commits -------------------------------------+------------------------------------- Reporter: bgamari | Owner: bgamari Type: bug | Status: new Priority: normal | Milestone: Component: Continuous | Version: 8.2.1 Integration | 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: -------------------------------------+------------------------------------- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14506> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12965: String merging broken on Windows
by GHC 26 Nov '18

26 Nov '18

#12965: String merging broken on Windows ----------------------------------------+--------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- #9577 introduced string literal merging via the linker. Unfortunately I haven't been able to get this to function on Windows, resulting in testsuite failures of #9577. Even `gcc` appears to do the wrong thing here, {{{ $ cat hi.c #include <stdio.h> const char *hi = "hello world"; extern const char *hi2; void main() { printf("%p %p", hi, hi2); } $ cat hi2.c const char *hi2 = "hello world"; $ gcc -c hi.c; gcc -c hi2.c; gcc -fmerge-all-constants hi2.o hi.o $ ./a.exe 0x100403040 0x100403030 $ gcc -s hi2.c $ cat hi2.s .file "hi2.c" .globl hi .section .rdata,"dr" .LC0: .ascii "hello world\0" .data .align 8 hi: .quad .LC0 .ident "GCC: (GNU) 5.3.0" }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12965> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14482: GHC -M mode fails to ensure that boot files are built before source files
by GHC 26 Nov '18

26 Nov '18

#14482: GHC -M mode fails to ensure that boot files are built before source files -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- Imagine we have a module with a boot file. In general it is necessary to ensure that we compile the boot file *before* the source file to ensure that the `hi-boot` file exists when we go to typecheck the module (triggering the behavior observed in #14481). However, `ghc -M` doesn't guarantee this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14482> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14534: Split T12971 into its own Makefile
by GHC 26 Nov '18

26 Nov '18

#14534: Split T12971 into its own Makefile -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: task | Status: new Priority: low | Milestone: 8.6.1 Component: Test Suite | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `testsuite/tests/driver/Makefile` includes the `T12971` target. This (intentionally) has non-ASCII characters in it. As a result, any change to that makefile will trigger a lint error. We should give that test its own makefile to isolate it a bit. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14534> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14190: Typeable imposes seemingly redundant constraints on polykinded instances
by GHC 26 Nov '18

26 Nov '18

#14190: Typeable imposes seemingly redundant constraints on polykinded instances -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeableReflection | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- To derive `Data` for `Const`, we need {{{#!hs deriving instance (Typeable k, Data a, Typeable (b :: k)) => Data (Const a b) }}} Where's that `Typeable k` constraint come from? It turns out that for reasons I haven't looked into, we can only obtain `Typeable (Const a (b :: k))` if we have `Typeable k`; `(Typeable a, Typeable b)` is insufficient. Is there a reason for that? Annoyingly, we can actually ''get'' that: {{{#!hs weGotThat :: forall k (a :: k). Typeable a :- Typeable k weGotThat = Sub $ withTypeable (typeRepKind (typeRep :: TypeRep a)) Dict }}} But of course that doesn't help us. Could we use `UndecidableSuperClasses` to work around this problem? I think we likely can, although I'm concerned about the performance implications: {{{#!hs class (Typeable a, Typeable' k) => Typeable' (a :: k) instance (Typeable a, Typeable' k) => Typeable' (a :: k) withTypeable' :: forall k (a :: k) r. TypeRep a -> (Typeable' a => r) -> r withTypeable' tr f = withTypeable tr $ withTypeable (typeRepKind (typeRep @a)) f }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14190> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13573: Add Foldable1 / Traversable1 to base
by GHC 26 Nov '18

26 Nov '18

#13573: Add Foldable1 / Traversable1 to base -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) 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: #10365 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `NonEmpty` and `Semigroup` are in ''base'' and are on our way to add `Semigroup` as a superclass of `Monoid` (#10365), this is a fine time to ask if we should include [https://hackage.haskell.org/package/semigroupoids-5.1/docs/Data- Semigroup-Foldable.html Foldable1], [https://hackage.haskell.org/package/semigroupoids-5.1/docs/Data- Semigroup-Traversable.html Traversable1] in ''base'' as well. `Foldable` has partial functions already, functions that only make sense for non-empty structures such as `foldr1`, `foldl1`, `minimum` and `maximum`. There are also functions which ''could'' be defined in terms of `Foldable` like `head` / `tail` (for definition of `unimprove` and `Diff` see [https://github.com/ekmett/semigroupoids/issues/49 semigroupoids issue #49] and this [https://github.com/arkeet/difference/blob/0f0e14f51cf1ecd7ebf2d8c52204bd91a… github] page) {{{#!hs minimum1 :: (Ord a, Foldable1 f) => f a -> a minimum1 = S.getMin . foldMap1 S.Min maximum1 :: (Ord a, Foldable1 f) => f a -> a maximum1 = S.getMax . foldMap1 S.Max head1 :: Foldable1 f => f a -> a head1 = S.getFirst . foldMap1 S.First last1 :: Foldable1 f => f a -> a last1 = S.getLast . foldMap1 S.Last foldr1 :: Foldable1 t => (a -> a -> a) -> (t a -> a) foldr1 f = unimprove . foldMap1 (\a -> Diff (f a) a) foldl1 :: Foldable1 t => (a -> a -> a) -> (t a -> a) foldl1 f = unimprove . getDual . foldMap1 (\a -> Dual $ Diff (flip f a) a) }}} There is also the possibility of adding further functions such as `foldM`, `foldM_`, `foldrM` and `foldlM` for non-empty structures. As usual I don't have more concrete ideas, but let's start by testing the waters before submitting a ghc-proposal. I understand this may be controversial -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13573> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13362: GHC first generation of GC to be as large as largest cache size by default
by GHC 26 Nov '18

26 Nov '18

#13362: GHC first generation of GC to be as large as largest cache size by default -------------------------------------+------------------------------------- Reporter: varosi | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Runtime | Version: 8.0.2 System | Keywords: numa cache gc | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This will improve performance a lot by default. If anyone needs different size - there is "-A" RTS option. Machines are very different. Currently this size is 512k by default for all different architectures and hardware no matter what. In most cases machines with larger caches have more RAM as well and vice versa. So this will affect positively both small and larger machines. It will be most efficient in most cases to keep short lived objects in caches. Most modern workstation and server machines have L3 cache as well, that is why I'm asking for "largest cache size". Second idea will be if there are two short lived generations on machines with second and third level caches with sizes that match both. For NUMA machines with non-unified caches (like [http://www.hardkernel.com/main/products/prdt_info.php?g_code=G143452239825 this strange and non-common ARM]) the common solution could be to set first generation to be with size of the largest cache of smallest core. Which will not be the optimal, but close to. [https://www.reddit.com/r/haskell/comments/5rf1r5/ghc_first_generation_of_gc… Related Reddit discussion] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13362> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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