June 2016 - ghc-tickets

[GHC] #12170: Add flag to control whether out of scope variables should be deferred with -fdefer-typed-holes
by GHC 01 Sep '16

01 Sep '16

#12170: Add flag to control whether out of scope variables should be deferred with -fdefer-typed-holes -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: newcomer | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #10569 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As a result of #10569, out of scope variables are turned into special type holes so that type information of the variable can be attached to the error message. However, this causes problems when used with `-fdefer-typed-holes` as scope errors have been turned into type errors and are now deferred when using this flag. Richard sums up the situation, "Even if someone is deferring type errors, I imagine most people don't want to defer scope errors". It would be good to add a flag which controls whether out of scope variables are also deferrable when used with existing deferral flags. Goal: Add a flag ` -fdefer-out-of-scope-variables` which controls whether out of scope variables are deferred when using `-fdefer-typed-holes`. It should be turned off by default. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12170> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12040: Code that builds on 7.8.4 and 7.10.3 but fails with requiring UndecidableInstances on 8.0.1-rc4
by GHC 31 Aug '16

31 Aug '16

#12040: Code that builds on 7.8.4 and 7.10.3 but fails with requiring UndecidableInstances on 8.0.1-rc4 -------------------------------------+------------------------------------- Reporter: dmcclean | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (I am not sure if this is an issue with the release candidate or with my code. I'm sorry, I've tried hard to investigate that but not come to a firm conclusion. I'm reporting it on the chance that it might be an issue with the release candidate.) The code at https://github.com/bjornbm/dimensional/tree/c5b41bbcecb710d566f8af6e561dcaf… builds and passes tests on 7.8.4 and 7.10.3. The same code fails under 8.0.1-rc4 with the following message: {{{ src/Numeric/Units/Dimensional/Dynamic.hs:79:10: error: • The constraint ‘KnownDimension d’ is no smaller than the instance head (Use UndecidableInstances to permit this) • In the instance declaration for ‘Demotable (Quantity d)’ }}} I'm not sure if the relationship here between `Demotable`, `KnownDimension`, `HasDimension`, and `HasDynamicDimension` in fact requires undecidable instances (in which case 7.8.4 and 7.10.3 are either allowing it in error? or helpfully allowing it even though they aren't obligated to?) or if it does not in fact require undecidable instances (in which case 8.0.1-rc4 is disallowing it in error). Making things even more interesting, a new feature branch of the same project doesn't appear to change any of the things that should be relevant to this error message, but compiles and tests without the error on 8.0.1-rc4 as well as the earlier compiler versions. That one's at https://github.com/dmcclean/dimensional/tree/9f3b0a207258851964defd90ce497e…. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12040> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12177: Relevant bindings includes shadowed bindings
by GHC 30 Aug '16

30 Aug '16

#12177: Relevant bindings includes shadowed bindings -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | 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: -------------------------------------+------------------------------------- {{{ ezyang@sabre:~$ ghc-8.0 --interactive GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> \x -> \x -> _ <interactive>:1:13: error: • Found hole: _ :: t2 Where: ‘t2’ is a rigid type variable bound by the inferred type of it :: t -> t1 -> t2 at <interactive>:1:1 • In the expression: _ In the expression: \ x -> _ In the expression: \ x -> \ x -> _ • Relevant bindings include x :: t1 (bound at <interactive>:1:8) x :: t (bound at <interactive>:1:2) it :: t -> t1 -> t2 (bound at <interactive>:1:1) }}} GHC should not report bindings which are shadowed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12177> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12198: Stack fails to compile using GHC 8.0.1 on MacOS 10.12
by GHC 29 Aug '16

29 Aug '16

#12198: Stack fails to compile using GHC 8.0.1 on MacOS 10.12 -------------------------------------+------------------------------------- Reporter: mistydemeo | 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: -------------------------------------+------------------------------------- GHC failed when trying to build stack from source on MacOS 10.12 using GHC 8.0.1. The relevant part of the error is here: {{{ [ 1 of 87] Compiling Stack.FileWatch ( src/Stack/FileWatch.hs, dist/dist- sandbox-68bf8d9c/build/Stack/FileWatch.o ) [ 2 of 87] Compiling System.Process.PagerEditor ( src/System/Process/PagerEditor.hs, dist/dist-sandbox- 68bf8d9c/build/System/Process/PagerEditor.o ) [ 3 of 87] Compiling System.Process.Log ( src/System/Process/Log.hs, dist /dist-sandbox-68bf8d9c/build/System/Process/Log.o ) [ 4 of 87] Compiling System.Process.Read ( src/System/Process/Read.hs, dist/dist-sandbox-68bf8d9c/build/System/Process/Read.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/4d/rttdp_9d2s7f36zplgwnqrgr0000gn/T/ghc94633_0/libghc_44.dylib, 5): no suitable image found. Did find: /var/folders/4d/rttdp_9d2s7f36zplgwnqrgr0000gn/T/ghc94633_0/libghc_44.dylib: malformed mach-o: load commands size (40192) > 32768 }}} Full build logs (includes dependency installation via cabal-install): https://gist.github.com/8e005710eab17139c02267bac3029e33 This occurred when installing stack, but reporting here because of the "Please report this as a GHC bug" message in the failed build output. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12198> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12349: Parallel make should interleave output if it means we can report an error earlier
by GHC 29 Aug '16

29 Aug '16

#12349: Parallel make should interleave output if it means we can report an error earlier -------------------------------------+------------------------------------- Reporter: ezyang | 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: -------------------------------------+------------------------------------- Steps to reproduce: 1. Take the example from #12347 2. Run `ghc --make` and observe what order the modules are reported in (on my box the ordering is `C`, `B`, then `A`) 3. Modify `A` to be a small, quick-to-compile module with a type error. `module A where x = True True` works grand. 4. Run `ghc --make All A B C -j4 +RTS -N4` Expected result: `ghc --make` reports the error in `A` immediately Actual result: `ghc --make` ponders for a while before reporting the error An interesting way to mix up the experiment is to put the type error in `C` rather than `A`. Then indeed the error is reported early, but GHC fails to exit until some undetermined later time (it is certainly not waiting for the other threads to finish compiling, because you don't see object files being produced.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12349> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10963: Beginner-targeted language extension
by GHC 29 Aug '16

29 Aug '16

#10963: Beginner-targeted language extension -------------------------------------+------------------------------------- Reporter: kanetw | Owner: Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- FMP significantly complicated type signatures such as `length :: Foldable t => t a -> Int`, which makes teaching Haskell more difficult. I propose a language extension `-XBeginner` which instructs GHC(i) to specialize `Foldable` and `Traversable` to `[]` when possible and in case of an ambiguous instance, default those to `[]`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10963> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12029: Notify user to import * from Data.Kind with TypeInType on
by GHC 28 Aug '16

28 Aug '16

#12029: Notify user to import * from Data.Kind with TypeInType on -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: lowest | Milestone: Component: GHCi | Version: 8.1 Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With `TypeInType` asking for the kind of `*` gives the user a warning to import it {{{ ghci> :set -XTypeInType ghci> :k * <interactive>:1:1: error: Not in scope: type constructor or class ‘*’ NB: With TypeInType, you must import * from Data.Kind <interactive>:1:1: error: Illegal operator ‘*’ in type ‘*’ Use TypeOperators to allow operators in types <interactive>:1:1: error: Operator applied to too few arguments: * }}} Should a similar warning be issued when she asks for information on it {{{ ghci> :i * class Num a where ... (*) :: a -> a -> a ... -- Defined in ‘GHC.Num’ infixl 7 * }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12029> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12116: No easy way to add cost-centre to top-levels
by GHC 27 Aug '16

27 Aug '16

#12116: No easy way to add cost-centre to top-levels -------------------------------------+------------------------------------- Reporter: osa1 | Owner: Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- As far as I can see from the user manual (I also tried placing some `SCC`s), there's no way to easily add cost-centres to top-level definitions. We can do things like: {{{ f x y z = ... => f = {-# SCC f #-} \x y z -> ... }}} but it becomes too much work once we have "equations" style definitions like {{{ head [] = {-# SCC head #-} Nothing head (x : _) = {-# SCC head #-} Just x }}} Also, `where` clauses work differently after the transformations. Example: {{{ f x y z = ... where <can use x and y here> => f = {-# SCC f #-} \x y z -> ... where <can't use x and y here> }}} So it gets annoying real quick. It'd be really great if we could just add `{-# SCC ... #-}` just like `{-# INLINE ... #-}` pragmas. Any ideas/opinions? Looking at the code, it seems like `-fprof-auto` and similar flags are adding ticks to `FunBind.fun_tick`. We could do the same with this new `SCC` pragma. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12116> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10547: feature request: expanding type synonyms in error messages
by GHC 26 Aug '16

26 Aug '16

#10547: feature request: expanding type synonyms in error messages -------------------------------------+------------------------------------- Reporter: osa1 | Owner: osa1 Type: feature | Status: new request | Milestone: 7.12.1 Priority: low | Version: Component: Compiler | Operating System: Unknown/Multiple (Type checker) | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Type errors sometimes becoming confusing because of synonyms, for example, expected type and found type sometimes use different synonyms or sometimes only one of them use a synonym etc. We discussed this in the mailing list: https://mail.haskell.org/pipermail /ghc-devs/2015-June/009247.html And also moved it to the Wiki to collect examples: https://wiki.haskell.org/Expanding_type_synonyms_in_error_messages_proposal I'm currently working on a patch, I made some progress and I'll hopefully submit something for reviews in a couple of days. This ticket is for further discussions and keep track of the progress. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10547> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12125: Field accessors unnecessarily kept alive
by GHC 26 Aug '16

26 Aug '16

#12125: Field accessors unnecessarily kept alive -------------------------------------+------------------------------------- Reporter: osa1 | Owner: osa1 Type: feature | Status: new request | 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): Phab:D2270 | Wiki Page: -------------------------------------+------------------------------------- Suppose you have a record with some non-exported field accessors, like so: {{{#!haskell module Lib (Rec) where data Rec = Rec { f1 :: Int , f2 :: Int , f3 :: Int , f4 :: Int , f5 :: Int } }}} Code for fields `f1`, `f2` ... are redundantly generated, optimized etc. and they made it to the object file, causing wasted compile times and bloated object files. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12125> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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