September 2018 - ghc-tickets

[GHC] #15584: nonVoid is too conservative w.r.t. strict argument types
by GHC 23 Sep '18

23 Sep '18

#15584: nonVoid is too conservative w.r.t. strict argument types -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.5 Keywords: | Operating System: Unknown/Multiple PatternMatchWarnings | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: #15305 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In the implementation of the pattern-match coverage checker, the `nonVoid` function checks is some `Type` is inhabitable by at least one constructor. However, `nonVoid` currently does not recursively call itself on the strict argument types of each constructor that is considered. This means that certain exhaustive functions are mistakenly flagged as non- exhaustive, such as in the following example: {{{#!hs {-# LANGUAGE EmptyCase #-} {-# OPTIONS -Wincomplete-patterns #-} module Bug where import Data.Void data V = MkV !Void data S = MkS !V f :: S -> a f x = case x of {} }}} {{{ $ /opt/ghc/head/bin/ghci Bug.hs GHCi, version 8.7.20180827: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:11:7: warning: [-Wincomplete-patterns] Pattern match(es) are non-exhaustive In a case alternative: Patterns not matched: (MkS _) | 11 | f x = case x of {} | ^^^^^^^^^^^^ }}} The natural solution would be to call `nonVoid` recursively on strict argument types, so as to be able to tell that `S` in uninhabitable. But we can't just do this willy nilly, since we could run into infinite loops with recursive examples like this one: {{{#!hs data Abyss = MkAbyss !Abyss stareIntoTheAbyss :: Abyss -> a stareIntoTheAbyss x = case x of {} }}} Better solution: put a recursive type checker into `nonVoid`, and bail out if recursion is detected. Patch incoming. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15584> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4861: Documentation for base does not include special items
by GHC 23 Sep '18

23 Sep '18

#4861: Documentation for base does not include special items -------------------------------------+------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: patch Priority: low | Milestone: ⊥ Component: Core Libraries | Version: 7.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Documentation | Unknown/Multiple bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D5167 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: upstream => patch * differential: => Phab:D5167 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4861#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15325: Panic in getIdFromTrivialExpr with -fdefer-type-errors
by GHC 23 Sep '18

23 Sep '18

#15325: Panic in getIdFromTrivialExpr with -fdefer-type-errors -------------------------------------+------------------------------------- Reporter: dramforever | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- == Steps to reproduce: Put this in `bug.hs`: (It's a very failed attempt to make a polymorphic list maker function.) {{{#!hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeFamilies #-} module PolyvariadicFunctions where class PolyList e a where polyList :: ([e] -> [e]) -> a -- instance PolyList e [e] where -- polyList dl = dl [] instance (e ~ e2, PolyList e a) => PolyList e (e2 -> a) where polyList dl x = polyList ((x :) . dl) plh :: [Integer] plh = polyList 1 2 3 4 5 }}} Load it in GHCi with `-fdefer-type-errors` to get the following output. Note the 'panic' in the end, and also note that the last `>` line is a no- module-loaded GHCi prompt. The question marks `?` seem to be encoding related and not relevant. This panic not seem to occur with GHC the compiler. The rest of the error messages seem otherwise identical. {{{ GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> :set -fdefer-type-errors Prelude> :l bug.hs [1 of 1] Compiling PolyvariadicFunctions ( bug.hs, interpreted ) bug.hs:17:7: warning: [-Wdeferred-type-errors] ? No instance for (PolyList t0 [Integer]) arising from a use of ‘polyList’ ? In the expression: polyList 1 2 3 4 5 In an equation for ‘plh’: plh = polyList 1 2 3 4 5 | 17 | plh = polyList 1 2 3 4 5 | ^^^^^^^^^^^^^^^^^^ bug.hs:17:16: warning: [-Wdeferred-type-errors] ? No instance for (Num ([t0] -> [t0])) arising from the literal ‘1’ (maybe you haven't applied a function to enough arguments?) ? In the first argument of ‘polyList’, namely ‘1’ In the expression: polyList 1 2 3 4 5 In an equation for ‘plh’: plh = polyList 1 2 3 4 5 | 17 | plh = polyList 1 2 3 4 5 | ^ bug.hs:17:18: warning: [-Wdeferred-type-errors] ? Ambiguous type variable ‘t0’ arising from the literal ‘2’ prevents the constraint ‘(Num t0)’ from being solved. Probable fix: use a type annotation to specify what ‘t0’ should be. These potential instances exist: instance Num Integer -- Defined in ‘GHC.Num’ instance Num Double -- Defined in ‘GHC.Float’ instance Num Float -- Defined in ‘GHC.Float’ ...plus two others (use -fprint-potential-instances to see them all) ? In the second argument of ‘polyList’, namely ‘2’ In the expression: polyList 1 2 3 4 5 In an equation for ‘plh’: plh = polyList 1 2 3 4 5 | 17 | plh = polyList 1 2 3 4 5 | ^ ghc.exe: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-mingw32): getIdFromTrivialExpr case $dNum_a1Be of wild_00 { } Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler\utils\Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler\\coreSyn\\CoreUtils.hs:883:18 in ghc:CoreUtils Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15325> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15607: RebindableSyntax warns `return` is not in scope when trying to call `pure`, but does not desugar between the two
by GHC 23 Sep '18

23 Sep '18

#15607: RebindableSyntax warns `return` is not in scope when trying to call `pure`, but does not desugar between the two -------------------------------------+------------------------------------- Reporter: isovector | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.6.1-beta1 Keywords: | Operating System: Unknown/Multiple RebindableSyntax | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following (incorrect) program fails to compile: {{{#!hs {-# LANGUAGE RebindableSyntax #-} import Prelude hiding (pure, return) t = do pure 5 }}} {{{ Not in scope: ‘return’ Perhaps you want to remove ‘return’ from the explicit hiding list in the import of ‘Prelude’ (/home/sandy/Bug.hs:3:1-40). | 6 | pure 5 | }}} Changing the import of Prelude to no longer hide `return` now gives the correct error: {{{#!hs import Prelude hiding (pure) }}} {{{ • Variable not in scope: pure :: Integer -> t • Perhaps you want to remove ‘pure’ from the explicit hiding list in the import of ‘Prelude’ (/home/sandy/Bug.hs:3:1-28). | 6 | pure 5 | ^^^^ }}} This is particularly confusing when `pure` is in scope and would typecheck but `return` is not. The error suggests that there is desugaring going on behind the scenes to turn `pure` into `return` via rebindable syntax. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15607> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15659: Wacky error message when RULE mentions out-of-scope variable
by GHC 23 Sep '18

23 Sep '18

#15659: Wacky error message when RULE mentions out-of-scope variable -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 Keywords: newcomer | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If I compile the following program with GHC 8.4 or later: {{{#!hs module Foo where {-# RULES "test" forall x. f x = x #-} }}} The error message I get is somewhat eyebrow-raising: {{{ $ /opt/ghc/8.4.3/bin/ghc Foo.hs [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) Foo.hs:3:11: error: Rule "test": Not in scope: OutOfScope(f) in left-hand side: f x LHS must be of form (f e1 .. en) where f is not forall'd | 3 | {-# RULES "test" forall x. f x = x #-} | ^^^^^^^^^^^^^^^^^^^^^^^^ }}} I'm not sure what this `OutOfScope` business is, but I doubt we want to be referring to it in error messages. The error in GHC 8.2 and earlier was much less confusing: {{{ $ /opt/ghc/8.2.2/bin/ghc Foo.hs [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) Foo.hs:3:11: error: Rule "test": Not in scope: f in left-hand side: f x LHS must be of form (f e1 .. en) where f is not forall'd | 3 | {-# RULES "test" forall x. f x = x #-} | ^^^^^^^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15659> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11155: Trivial error thunk gives "undefined reference to stg_ap_0_upd_info"
by GHC 23 Sep '18

23 Sep '18

#11155: Trivial error thunk gives "undefined reference to stg_ap_0_upd_info" -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- This error popped up when Alan was coding the solution for #11028. The error is utterly unrelated to what Alan was working on. Here's a reproducer {{{ {-# OPTIONS_GHC -O -fno-full-laziness #-} module Main where foo :: Bool {-# NOINLINE foo #-} foo = error "rk" bar x = let t :: Char t = case foo of { True -> 'v'; False -> 'y' } in [t] main = print (bar ()) }}} Just compile that and you get {{{ Foo.o: In function `c1Sm_info': (.text+0x29a): undefined reference to `stg_ap_0_upd_info' }}} Why do we get that unresolved symbol? The STG code for `bar` looks like {{{ Main.bar :: forall t_aup. t_aup -> [GHC.Types.Char] [GblId, Arity=1, Str=DmdType <L,A>m2, Unf=OtherCon []] = \r srt:SRT:[rf :-> Main.foo] [x_s1RR] let { sat_s1RT [Occ=Once] :: GHC.Types.Char [LclId, Str=DmdType] = \u srt:SRT:[rf :-> Main.foo] [] Main.foo; } in : [sat_s1RT GHC.Types.[]]; }}} Look at that: an updatable thunk saying `sat_s1RT = Main.foo`! The error message is terrible, but the problem is a thunk whose only payload is a single variable. Why does that happen? The Core is {{{ bar = \ (@ t_aup) _ -> let t::Char = case foo of wild_00 { } in : @ Char t ([] @ Char) }}} The `case` is needed to change `foo`'s type from `Bool` to `Char`. The Core-to-STG pass drops the empty case alternatives as useless (rightly), but leaves a bare variable as the RHS, which confuses the code generator. We should clearly substitute `Main.foo` for `t`, either in Core-to-STG, or during code generation. Why hasn't this happened before now? It is quite hard to provoke, because floating the thunk for `t` to top level stops it happening. So it only happens if you switch off full laziness (as my test case here does), or if some very delicate inlining happens after the last float-out. The latter is very rare, but it's what happened to Alan. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11155> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4022: GHC Bindist is Broken on FreeBSD/amd64
by GHC 22 Sep '18

22 Sep '18

#4022: GHC Bindist is Broken on FreeBSD/amd64 -------------------------------------+------------------------------------- Reporter: pgj | Owner: pgj Type: bug | Status: new Priority: lowest | Milestone: Component: Core Libraries | Version: 6.13 Resolution: | Keywords: GMP,integer- | gmp, sharedlibs Operating System: FreeBSD | Architecture: x86_64 Type of failure: Building GHC | (amd64) failed | Test Case: Blocked By: | Blocking: Related Tickets: #8156 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * cc: raichoo (added) Comment: Ccing raichoo who last fixed DTrace support in FreeBSD. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4022#comment:44> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6089: Allow declaration splices inside declaration brackets
by GHC 22 Sep '18

22 Sep '18

#6089: Allow declaration splices inside declaration brackets -------------------------------------+------------------------------------- Reporter: igloo | Owner: simonpj Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #11129 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by Wizek): * cc: Wizek (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6089#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4022: GHC Bindist is Broken on FreeBSD/amd64
by GHC 22 Sep '18

22 Sep '18

#4022: GHC Bindist is Broken on FreeBSD/amd64 -------------------------------------+------------------------------------- Reporter: pgj | Owner: pgj Type: bug | Status: new Priority: lowest | Milestone: Component: Core Libraries | Version: 6.13 Resolution: | Keywords: GMP,integer- | gmp, sharedlibs Operating System: FreeBSD | Architecture: x86_64 Type of failure: Building GHC | (amd64) failed | Test Case: Blocked By: | Blocking: Related Tickets: #8156 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by arrowd): > I suppose I will also need to disable DTrace. I remember there were problems with DTrace in 8.4.3 too, so yes. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4022#comment:43> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4022: GHC Bindist is Broken on FreeBSD/amd64
by GHC 21 Sep '18

21 Sep '18

#4022: GHC Bindist is Broken on FreeBSD/amd64 -------------------------------------+------------------------------------- Reporter: pgj | Owner: pgj Type: bug | Status: new Priority: lowest | Milestone: Component: Core Libraries | Version: 6.13 Resolution: | Keywords: GMP,integer- | gmp, sharedlibs Operating System: FreeBSD | Architecture: x86_64 Type of failure: Building GHC | (amd64) failed | Test Case: Blocked By: | Blocking: Related Tickets: #8156 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Sadly using `ld.bfd` (on FreeBSD 11, just as in comment:41) fails even earlier in the build with undefined DTrace symbols: {{{ /usr/home/ben/bin- dist-8.6.1-FreeBSD/ghc/rts/dist/build/libHSrts_thr_p.a(RTS.thr_p_o): In function `traceTaskMigrate': /usr/home/ben/bin-dist-8.6.1-FreeBSD/ghc/rts/Trace.h:868:0: error: undefined reference to `__dtrace_HaskellEvent___task__migrate' | 868 | dtraceTaskMigrate(serialisableTaskId(task), (EventCapNo)cap->no, | ^ }}} I suppose I will also need to disable DTrace. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4022#comment:42> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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