May 2018 - ghc-tickets

[GHC] #8316: GHCi debugger segfaults when trying force a certain variable
by GHC 28 Dec '18

28 Dec '18

#8316: GHCi debugger segfaults when trying force a certain variable ------------------------------------+------------------------------------- Reporter: guest | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: GHCi crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The file Test.hs has following definitions: {{{ whnf :: a -> IO () whnf a = a `seq` (return ()) foo :: [Int] foo = [1..] }}} Calling ghci as: {{{ ghci Test.hs -ignore-dot-ghci }}} and bebugging foo like this: {{{ *Main> :b foo Breakpoint 0 activated at Test.hs:5:7-11 *Main> foo Stopped at Test.hs:5:7-11 _result :: [Int] = _ [Test.hs:5:7-11] *Main> :p foo foo = (_t1::[Int]) [Test.hs:5:7-11] *Main> whnf _t1 }}} results in this segault: {{{ <interactive>: internal error: TSO object entered! (GHC version 7.6.3 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug [1] 5445 abort (core dumped) ghci Test.hs -ignore-dot-ghci }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8316> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14375: Implement with# primop
by GHC 27 Dec '18

27 Dec '18

#14375: Implement with# primop -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 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): Phab:D4110 | Wiki Page: -------------------------------------+------------------------------------- In Trac #14346 we proposed the new `with#` primop {{{ with# :: a -> (State# s -> (# State# s, b #)) -> State# s -> (# State# s, b #) }}} This ticket is to track progress. See Phab:D4110. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14375> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer
by GHC 26 Dec '18

26 Dec '18

#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1-rc2 (Type checker) | Keywords: backpack | 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 don't think this is a very harmful bug but it definitely is a bug. Consider: {{{ -- A.hs-boot module A where data T -- B.hs module B (module A) where import {-# SOURCE #-} A -- A.hs {-# LANGUAGE TemplateHaskell #-} module A where import qualified B import Language.Haskell.TH f :: B.T -> B.T f x = x $( return [] ) data T = T B.T }}} The point of the splice is to convince GHC to typecheck `f :: B.T -> B.T` before it typechecks the type declaration. But this is not going to work, because `tcLookupGlobal` is going to bail if (1) T is not in the `tcg_type_env` and (2) T comes from this module. It would be a simple matter to improve the error message but from a user's perspective, there is no good reason for this to not typecheck. On the implementation side, I am sympathetic to not letting this typecheck: if it does typecheck, then some `TyCon`s will incorrectly refer to the definition from the hs-boot file, rather than our local definition. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12034> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11627: Segmentation fault for space_leak_001 with profiling (-hc)
by GHC 24 Dec '18

24 Dec '18

#11627: Segmentation fault for space_leak_001 with profiling (-hc) -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Profiling | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: perf/space_leaks/space_leak_001 | Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `WAY=profasm` is omitted by default for this test, but the code looks like this: Test.hs: {{{ import Data.List main = print $ length $ show (foldl' (*) 1 [1..100000] :: Integer) }}} {{{ $ ghc Test.hs -prof -O $ ./Test +RTS -hc Segmentation fault (core dumped) }}} Reproducible with at least 7.10.3 and HEAD, also without `-O`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11627> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14758: Retainer profiler can overflow the C stack
by GHC 24 Dec '18

24 Dec '18

#14758: Retainer profiler can overflow the C stack -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Profiling | Version: 8.4.1-alpha1 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 not entirely sure what conditions trigger this, but I am observing a reliable segmentation fault with a program with large heap compiled with 8.4.1-alpha3 and run with retainer profiling enabled. Judging by the fact that the crashing instruction is a `mov _, ($rsp)`, I'm reasonable certain that the issue is a C stack overflow. The top of the stack looks like, {{{ #0 0x000000000249212c in retainClosure (c0=0x42af3459b8, cp0=cp0@entry=0x42af347000, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1488 #1 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af347000, bitmap=<optimized out>, size=<optimized out>, p=0x42af347260) at rts/RetainerProfile.c:1209 #2 retainStack (c=c@entry=0x42af347000, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af347370) at rts/RetainerProfile.c:1350 #3 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af345b28, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #4 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3473e0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #5 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af3473e0, bitmap=<optimized out>, size=<optimized out>, p=0x42af347690) at rts/RetainerProfile.c:1209 #6 retainStack (c=c@entry=0x42af3473e0, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af347750) at rts/RetainerProfile.c:1350 #7 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af345d88, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #8 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3477c0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #9 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af3477c0, bitmap=<optimized out>, size=<optimized out>, p=0x42af347a70) at rts/RetainerProfile.c:1209 #10 retainStack (c=c@entry=0x42af3477c0, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af347b30) at rts/RetainerProfile.c:1350 #11 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3481a8, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #12 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af347ba0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #13 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af347ba0, bitmap=<optimized out>, size=<optimized out>, p=0x42af347e50) at rts/RetainerProfile.c:1209 #14 retainStack (c=c@entry=0x42af347ba0, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af347f10) at rts/RetainerProfile.c:1350 #15 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af348408, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #16 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af349000, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #17 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af349000, bitmap=<optimized out>, size=<optimized out>, p=0x42af3492b0) at rts/RetainerProfile.c:1209 #18 retainStack (c=c@entry=0x42af349000, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af349370) at rts/RetainerProfile.c:1350 #19 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af348668, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #20 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3493e0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #21 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af3493e0, bitmap=<optimized out>, size=<optimized out>, p=0x42af349690) at rts/RetainerProfile.c:1209 #22 retainStack (c=c@entry=0x42af3493e0, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af349750) at rts/RetainerProfile.c:1350 #23 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3488c8, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #24 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af3497c0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 #25 0x00000000024932b0 in retain_small_bitmap (c_child_r=0x42bc4fd1a0, c=0x42af3497c0, bitmap=<optimized out>, size=<optimized out>, p=0x42af349a70) at rts/RetainerProfile.c:1209 #26 retainStack (c=c@entry=0x42af3497c0, c_child_r=c_child_r@entry=0x42bc4fd1a0, stackStart=<optimized out>, stackEnd=0x42af349b30) at rts/RetainerProfile.c:1350 #27 0x0000000002492870 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af348b28, r0=r0@entry=0x2a5ac20 <CCS_SYSTEM>) at rts/RetainerProfile.c:1686 #28 0x0000000002492887 in retainClosure (c0=<optimized out>, cp0=cp0@entry=0x42af349ba0, r0=r0@entry=0x42bc4fd1a0) at rts/RetainerProfile.c:1695 ... }}} and this goes on for at least 30000 frames. It looks very much like this is a bug in the retainer profiler. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14758> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9627: Type error with functional dependencies
by GHC 24 Dec '18

24 Dec '18

#9627: Type error with functional dependencies -------------------------------------+------------------------------------- Reporter: augustss | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The attached file should compile. The types T1, T2, and T3 are all equivalent types (T1 and T2 normalize to T3), but with foo::T1 and bar::T2 there is a type error. Rewriting the example using type families instead of FD makes it work. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9627> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13322: Pattern synonyms in hs-boot files
by GHC 24 Dec '18

24 Dec '18

#13322: Pattern synonyms in hs-boot files -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: hs-boot | Operating System: Unknown/Multiple backpack | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Pattern synonyms are not permitted in hs-boot files: {{{ ezyang@sabre:~/bun$ ghc-head -c A.hs-boot A.hs-boot:3:5: error: Misplaced pattern synonym signature: pattern X :: Bool | 3 | pattern X :: Bool | ^^^^^^^^^^^^^^^^^ A.hs-boot:3:13: error: The pattern synonym signature for ‘X’ lacks an accompanying binding | 3 | pattern X :: Bool | }}} There isn't really any reason why they shouldn't be supported. One thing to check closely: if we bundle a pattern synonym declared in an hs-boot file with another type, in an hs-boot file, what happens? In particular, does an hs file which doesn't bundle the pattern synonym and the type valid? If we add support for them, make sure that Backpack signatures handle it properly. In particular, suppose we have: {{{ signature A(T(X)) where data T pattern X :: T }}} Then, when we instantiate A, we must be careful to NOT blindly reuse the implementing module of T for X (as we do today in `uAvailInfo` in `NameShape`), since T and X may be defined in different modules. I'm not likely to implement this unless someone asks. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13322> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11534: Allow class associated types to reference functional dependencies
by GHC 22 Dec '18

22 Dec '18

#11534: Allow class associated types to reference functional dependencies -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 (Type checker) | Keywords: TypeFamilies, | Operating System: Unknown/Multiple FunctionalDependencies | Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider: {{{#!hs class Foo i j | i -> j where type Bar i :: * type Bar i = j }}} This is rejected as `j` is not an argument to `Bar`, but when we realize any instance `j` will be a known type, determined by `i`, as told to us by the | i -> j functional dependency on the class. This would likely require some sort of extra pass over the instances with class associated types of this form to elaborate them, or a slight modification of the default signature implementation for class associated types. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11534> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15147: Type checker plugin receives Wanteds that are not completely unflattened
by GHC 21 Dec '18

21 Dec '18

#15147: Type checker plugin receives Wanteds that are not completely unflattened -------------------------------------+------------------------------------- Reporter: nfrisby | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.1 (Type checker) | Keywords: type checker | Operating System: Unknown/Multiple plugins | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With the following, a plugin will receive a wanted constraint that includes a `fsk` flattening skolem. {{{ -- "Reduced" via the plugin type family F u v where {} type family G a b where {} data D p where DC :: (p ~ F x (G () ())) => D p }}} (Please ignore the apparent ambiguity regarding `x`; the goal is for the plugin to eliminate any ambiguity.) A do-nothing plugin that merely logs its inputs gives the following for the ambiguity check on DC. {{{ given [G] $d~_a4oh {0}:: (p_a4o2[sk:2] :: *) ~ (p_a4o2[sk:2] :: *) (CDictCan) [G] $d~~_a4oi {0}:: (p_a4o2[sk:2] :: *) ~~ (p_a4o2[sk:2] :: *) (CDictCan) [G] co_a4od {0}:: (G () () :: *) ~# (fsk_a4oc[fsk:0] :: *) (CFunEqCan) [G] co_a4of {0}:: (F x_a4o3[sk:2] fsk_a4oc[fsk:0] :: *) ~# (fsk_a4oe[fsk:0] :: *) (CFunEqCan) [G] co_a4og {1}:: (fsk_a4oe[fsk:0] :: *) ~# (p_a4o2[sk:2] :: *) (CTyEqCan) derived wanted [WD] hole{co_a4or} {3}:: (F x_a4o6[tau:2] fsk_a4oc[fsk:0] :: *) ~# (p_a4o2[sk:2] :: *) (CNonCanonical) untouchables [fsk_a4oe[fsk:0], fsk_a4oc[fsk:0], x_a4o3[sk:2], p_a4o2[sk:2]] }}} Note the `fsk_a4oc[fsk:0]` tyvar in the Wanted constraint, which is why I'm opening this ticket. Its presence contradicts the "The wanteds will be unflattened and zonked" claim from https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker#Callingpluginsfro… section. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15147> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8949: switch -msse2 to be on by default
by GHC 21 Dec '18

21 Dec '18

#8949: switch -msse2 to be on by default ----------------------------------------------+---------------------------- Reporter: errge | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (CodeGen) | Version: 7.9 Keywords: | Operating System: Architecture: x86 | Unknown/Multiple Difficulty: Moderate (less than a day) | Type of failure: Other Blocked By: | Test Case: Related Tickets: | Blocking: ----------------------------------------------+---------------------------- I propose msse2 to be on by default. I guess the default was chosen way back, when Pentium III support was still relevant. Nowadays we don't really win on the CPU support, because e.g. https://github.com/tibbe/hashable/blob/master/hashable.cabal is built by default with sse2 on the injected C code level. And hashable has a lot of reverse depends, therefore on an end user system (RedHat or Debian) the user is most probably unlucky with a Pentium III CPU anyways. Flipping this default would also fix the excess precision problem for most users of GHC on the i686 platform. GHC should provide a -mno-sse2 flag for the cases when this needs to be disabled. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8949> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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