September 2016 - ghc-tickets

[GHC] #12476: Error building HList
by GHC 07 Sep '16

07 Sep '16

#12476: Error building HList -------------------------------------+------------------------------------- Reporter: | Owner: DanielWaterworth | 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: -------------------------------------+------------------------------------- {{{ [21 of 28] Compiling Data.HList.Labelable ( Data/HList/Labelable.hs, .stack-work/dist/x86_64-linux/Cabal-1.24.0.0/build/Data/HList/Labelable.o ) /home/dan/fun/HList/Data/HList/Labelable.hs:137:9: warning: [-Wredundant- constraints] • Redundant constraints: (LabeledOpticF ty f, LabeledOpticP ty p) • In the type signature for: hLens' :: (ty ~ LabelableTy LabeledR, LabeledOpticF ty f, LabeledOpticP ty p, LabeledOpticTo ty x to) => Label x -> to (p a (f b)) (p (LabeledR s) (f (LabeledR t))) In the instance declaration for ‘Labelable x LabeledR s t a b’ /home/dan/fun/HList/Data/HList/Labelable.hs:211:10: warning: [-Wredundant- constraints] • Redundant constraint: ToSym (a b c) x • In the instance declaration for ‘EnsureLabel (a b c) (Label x)’ /home/dan/fun/HList/Data/HList/Labelable.hs:277:10: warning: [-Wredundant- constraints] • Redundant constraint: HRLabelSet bs • In the instance declaration for ‘Projected Record s t a b’ /home/dan/fun/HList/Data/HList/Labelable.hs:332:10: warning: [-Wredundant- constraints] • Redundant constraint: ToSym (to p q) x • In the instance declaration for ‘HExtend (to p q) (Proxy '[])’ /home/dan/fun/HList/Data/HList/Labelable.hs:337:10: warning: [-Wredundant- constraints] • Redundant constraint: ToSym (to p q) x • In the instance declaration for ‘HExtend (to p q) (Proxy (x : xs))’ /home/dan/fun/HList/Data/HList/Labelable.hs:344:10: warning: [-Wredundant- constraints] • Redundant constraint: ToSym (to p q) x • In the instance declaration for ‘HExtend (to p q) (Proxy (Lbl n ns desc : xs))’ ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): pprIfaceCo Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This is the version I was building: https://github.com/DanielWaterworth/HList/tree/66643fb75771e71192ab380e4f2e… -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12476> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12577: The flag -xb has no effect on Windows
by GHC 07 Sep '16

07 Sep '16

#12577: The flag -xb has no effect on Windows ----------------------------------------+--------------------------------- Reporter: Phyx- | Owner: Type: bug | Status: new Priority: normal | Milestone: 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: #12576 Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- `-xb` is supposed to be used to change the base memory location for heap allocation calls. However all the calls in `rts\win32\OSMEM.c` call `VirtualAlloc` with `NULL` and not the desired start address. This makes the flag not do anything on Windows (based on quick inspection of allocated values). [[Image(http://i.imgur.com/e1O9Jlb.png, 720px)]] Allocation always starts at `0x020000` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12577> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5972: option to suppress (Monomorphic) record selector functions
by GHC 07 Sep '16

07 Sep '16

#5972: option to suppress (Monomorphic) record selector functions -------------------------------------+------------------------------------- Reporter: AntC | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: records 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 adamgundry): @AntC I think mpickering's point is that inside GHC, a(n unambiguous) field label is identified by the `Name` of its selector function when used inside curly braces. There's no real distinction between the two made by the implementation. Changing that would be possible, but tedious. In the post-DuplicateRecordFields implementation, it is possible to distinguish between fields and non-fields during name resolution. Thus it probably wouldn't be too hard to implement a variant on this whereby enabling the extension suppressed all selector functions (local or imported) //for expressions in the current module//, just as DuplicateRecordFields changes the name resolution rules within a single module. The selectors would still be generated, they just wouldn't be in scope. That wouldn't quite give the behaviour you describe on the wiki page with regard to import/export, because if you exported a field then client modules could use it as a selector (unless they enable the extension themselves). You would have the option to hide the field and export a lens of the same name though. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5972#comment:15> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5972: option to suppress (Monomorphic) record selector functions
by GHC 06 Sep '16

06 Sep '16

#5972: option to suppress (Monomorphic) record selector functions -------------------------------------+------------------------------------- Reporter: AntC | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: records 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 AntC): Hi Matthew, I guess this whole ticket has been overtaken by the DuplicateRecordFields extension in GHC 8.0. This ticket was written way before SPJ and Adam arrived at that approach. There might still be some lensaholics who hanker after the namespace. For the record ... > A field label and record selector are currently the same thing. You might think that because they are spelt the same, and one always comes with the other under H98, but actually as at H98 they're not. And that's the point: * a record selector is a function, first-class. If the language didn't create one automatically, you could do it yourself. * a field label can only appear in specific record access contexts {inside curly braces}. It is not first-class; only syntax sugar for positional access to the fields of the constructor. I agree there are namespace concerns if a user creates their own function with the same name (which is indeed the purpose). This chiefly affects module export/import. See the link in the OP for more detail. > It would seem that a correct solution would place field labels in a separate namespace ... I believe the pre-DuplicateRecordFields implementation unsugarred the field labels so they didn't occupy a namespace atall. Perhaps the situation is now different with Overloaded labels. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5972#comment:14> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12569: TypeApplications doesn't allow unticked list constructors.
by GHC 06 Sep '16

06 Sep '16

#12569: TypeApplications doesn't allow unticked list constructors. -------------------------------------+------------------------------------- Reporter: vagarenko | 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: -------------------------------------+------------------------------------- TypeApplications doesn't allow unticked list constructor even when it is unambiguous: {{{ GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help > :set -XDataKinds > :set -XTypeApplications > :set -XScopedTypeVariables > :set -XKindSignatures > let foo :: forall (xs :: [Nat]). (); foo = () > foo @'[0] () > foo @[0] <interactive>:17:6: error: * Expected kind `[Nat]', but `[0]' has kind `*' * In the type `[0]' In the expression: foo @[0] In an equation for `it': it = foo @[0] <interactive>:17:7: error: * Expected a type, but `0' has kind `Nat' * In the type `[0]' In the expression: foo @[0] In an equation for `it': it = foo @[0] }}} why `[0]` has kind `*` here? However this is legal: {{{ > let foo :: forall (x :: Bool). (); foo = () > foo @True () > foo @'True () }}} and this is wierd: {{{ > :set -XPolyKinds > let foo :: forall (x :: k). (); foo = () > foo @'True <interactive>:12:6: error: * Expected a type, but 'True has kind `Bool' * In the type `True' In the expression: foo @True In an equation for `it': it = foo @True > foo @True <interactive>:13:6: error: * Expected a type, but 'True has kind `Bool' * In the type `True' In the expression: foo @True In an equation for `it': it = foo @True }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12569> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12560: ‘:info TYPE’ mentions any instance that includes ‘Type’
by GHC 06 Sep '16

06 Sep '16

#12560: ‘:info TYPE’ mentions any instance that includes ‘Type’ -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- Unexpected behaviour {{{ $ ghci -ignore-dot-ghci GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> import GHC.Types Prelude GHC.Types> :i TYPE type role TYPE nominal data TYPE (t1 :: RuntimeRep) -- Defined in ‘GHC.Prim’ }}} Importing `Data.Proxy` gives me some of its instances, {{{ Prelude GHC.Types> import Data.Proxy Prelude GHC.Types Data.Proxy> :i TYPE type role TYPE nominal data TYPE (t1 :: RuntimeRep) -- Defined in ‘GHC.Prim’ instance Monad Proxy -- Defined in ‘Data.Proxy’ instance Functor Proxy -- Defined in ‘Data.Proxy’ instance Applicative Proxy -- Defined in ‘Data.Proxy’ instance Foldable Proxy -- Defined in ‘Data.Foldable’ instance Traversable Proxy -- Defined in ‘Data.Traversable’ Prelude GHC.Types Data.Proxy> }}} because they mention `*` {{{ Prelude GHC.Types Data.Proxy> :set -fprint-explicit-kinds Prelude GHC.Types Data.Proxy> :i TYPE type role TYPE nominal data TYPE (t1 :: RuntimeRep) -- Defined in ‘GHC.Prim’ instance Monad (Proxy *) -- Defined in ‘Data.Proxy’ instance Functor (Proxy *) -- Defined in ‘Data.Proxy’ instance Applicative (Proxy *) -- Defined in ‘Data.Proxy’ instance Foldable (Proxy *) -- Defined in ‘Data.Foldable’ instance Traversable (Proxy *) -- Defined in ‘Data.Traversable’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12560> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12443: DEFAULT_TMPDIR is documented, but doesn't exist
by GHC 06 Sep '16

06 Sep '16

#12443: DEFAULT_TMPDIR is documented, but doesn't exist -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Documentation | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Documentation Unknown/Multiple | bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The user's guide claims {{{ Even better idea: Set the :envvar:`DEFAULT_TMPDIR` :command:`make` variable when building GHC, and never worry about :envvar:`TMPDIR` again. (see the build documentation). }}} But only vestiges of this functionality remain in `mk/config.mk.in` and in `nofib`, and it doesn't appear to actually do anything. I suggest removing it from the documentation. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12443> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5972: option to suppress (Monomorphic) record selector functions
by GHC 06 Sep '16

06 Sep '16

#5972: option to suppress (Monomorphic) record selector functions -------------------------------------+------------------------------------- Reporter: AntC | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: records 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 mpickering): This sounds good in theory but there are some namespacing problems. Say that we just want to suppress the record selectors, that is easy enough to achieve, but the intention is clearly that users can then define their own selectors with whatever semantics they want with the same names as the field labels. A field label and record selector are currently the same thing. In order to resolve record updates, the current implementation looks up the record selector with the right name. It would seem that a correct solution would place field labels in a separate namespace to variables so they would become truly distinct and properly distinguish the record selector and the field label. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5972#comment:13> 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 06 Sep '16

06 Sep '16

#4806: Make error message more user friendly when module is not found because package is unusable -------------------------------------+------------------------------------- Reporter: mitar | Owner: bollu 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 Phyx-): Aha, no you're right, sandboxes would be ideal it sounds like. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:21> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10062: Codegen on sequential FFI calls is not very good
by GHC 05 Sep '16

05 Sep '16

#10062: Codegen on sequential FFI calls is not very good -------------------------------------+------------------------------------- Reporter: chadaustin | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 (CodeGen) | Operating System: Unknown/Multiple Keywords: | Type of failure: Runtime Architecture: | performance bug Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I'm writing a library for efficiently building up a byte buffer. The fastest approach I've found is via FFI, with restricted effects like ST. It's over twice as fast as ByteString Builder. Consider this example API usage: https://github.com/chadaustin/buffer- builder/blob/6bd0a39c56f63ab751faf29f9784ac87d52638be/bench/Bench.hs#L46 It compiles into an instruction sequence containing direct, sequenced FFI calls. For example, the last three calls work out to: addq $8,%rsp movq %rbx,%rdi movq 72(%rsp),%rax movq %rax,%rsi subq $8,%rsp movl $0,%eax call bw_append_bsz addq $8,%rsp movq %rbx,%rdi movl $35,%esi subq $8,%rsp movl $0,%eax call bw_append_byte addq $8,%rsp movq %rbx,%rdi movq 64(%rsp),%rax movq %rax,%rsi subq $8,%rsp movl $0,%eax call bw_append_bsz I don't know why rsp is being changed so much. I also can't explain the assignment to eax before the call. (It should also be xorl eax,eax, I would think.) To my reading, the above instruction sequence could be reduced to: movq %rbx,%rdi movq 64(%rsp),%rsi call bw_append_bsz movq %rbx,%rdi movl $35,%esi call bw_append_byte movq %rbx,%rdi movq 56(%rsp),%rsi call bw_append_bsz To reproduce, check out git@github.com:chadaustin/buffer-builder.git at revision 6bd0a39c56f63ab751faf29f9784ac87d52638be cabal configure --enable-benchmarks cabal bench And then look at the ./dist/build/bench/bench-tmp/bench/Bench.dump-asm file. This is specifically on OS X 64-bit with GHC 7.8.3, but I saw similar code generation on GHC 7.6 on Linux 64-bit. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10062> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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