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Re: Building GHC 8.4.3 Cross-Compiler Linux x86 -> Linux ARM
by Ben Gamari 28 May '19

28 May '19

Michael Dunn <michaelsdunn1(a)gmail.com> writes: > Ben, > > I saw that you responded to my question in #ghc on freenode last > weekend (mdunnio), and I missed your message. > Michael, I would be happy to help. I'm CCing ghc-devs so others may benefit from this discussion. > I'm trying to build a cross compiler using ghc 8.0.1 to build ghc > 8.4.3. You mentioned that you have experience. > > Have you tried on newer versions of GHC? I've looked at a few guides > (mostly https://gitlab.haskell.org/ghc/ghc/wikis/building/cross-compiling) > and they all are using pre-8.0. The problem I'm running into now just > seems to be that I can't build the base packages (ghc-pkg > specifically). > > My configure command is: > > ./configure --target=arm-linux-gnueabihf CC=arm-linux-gnueabihf-gcc > --enable-unregisterised > This is helpful to know but you didn't specify what your `make` invocation looks like or your mk/build.mk. It would be very helpful to know both of these things. Presumably you at least had to set `HADDOCK_DOCS=NO` since otherwise the build system fails very early on. Cheers, - Ben

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Is your MR failing CI test T9630 or haddock.base?
by David Eichmann 27 May '19

27 May '19

Try rebasing! Due to some unfortunate circumstances the performance tests (T9630 and haddock.base) became fragile. This should be fixed, but you need to rebase off of the latest master (at at least c931f2561207aa06f1750827afbb68fbee241c6f) for the tests to pass. Happy Hacking, David Eichmann -- David Eichmann, Haskell Consultant Well-Typed LLP, http://www.well-typed.com Registered in England & Wales, OC335890 118 Wymering Mansions, Wymering Road, London W9 2NF, England

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wiki page of notes for type checker plugin authors
by Nicolas Frisby 26 May '19

26 May '19

To: ghc-devs Cc: some plugin authors I'm aware of Today, I finally added a test that caused the type checker plugin I'm developing to fail because I'm ignoring the incoming Derived constraints. While investigating what exactly I should do with incoming Deriveds, I wrote up my notes in hopes they are helpful to other type checker plugin authors. https://gitlab.haskell.org/ghc/ghc/wikis/plugins/type-checker/notes It's a high-level summary of what the GHC constraint solver is doing, that dips down into the details a bit regarding Deriveds. I would really appreciate it if you'd check that page for errors andr glaring omissions. Also, is there a better location for it? It seemed too sprawling for a source `Note`. Thank you for your time. -Nick

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Overloaded names for Map/Set?
by Andreas Klebinger 24 May '19

24 May '19

Hello devs, I would appreciate feedback on the idea in https://gitlab.haskell.org/ghc/ghc/merge_requests/934 Maps/Sets in GHC for the most part offer the same basic functionality but their interfaces differ. In order to make this easier to work with I propose using overloading via IsSet/IsMap classes. The goal is to make working with these data structures simpler by having a uniform interface when it comes to names and argument orders. There are downsides, but to me they seem minor. Error messages can be more confusing when one get's the types wrong. We have to import the class to use it and the like. However overall I think making code easier by not having to remember the naming scheme + argument order for the different possible instances would make this worthwhile. But GHC isn't my project but one of the community so please voice your opinion on the matter on the merge request! Cheers Andreas

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Fwd: GHC | Hadrian: ld crashes linking HStime on macos (#16685)
by Shayne Fletcher 23 May '19

23 May '19

Hi Andrey, On Thu, May 23, 2019 at 10:04 AM Andrey Mokhov <gitlab(a)gitlab.haskell.org> wrote: > I've travelling all week, so can't look into this issue properly, but > can't we simply revert the commit that introduced the breakage? Looks like > it was committed just a week ago. > I'll have to defer to the approvers on this one - I'm just a reporter :) -- Shayne Fletcher Language Engineer c: +1 917 699 7763 e: shayne.fletcher(a)daml.com Digital Asset Holdings, LLC 4 World Trade Center 150 Greenwich Street, 47th Floor <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> New York, NY 10007, USA <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> digitalasset.com <http://www.digitalasset.com/> -- Shayne Fletcher Language Engineer c: +1 917 699 7763 e: shayne.fletcher(a)daml.com Digital Asset Holdings, LLC 4 World Trade Center 150 Greenwich Street, 47th Floor <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> New York, NY 10007, USA <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> digitalasset.com <http://www.digitalasset.com/> -- This message, and any attachments, is for the intended recipient(s) only, may contain information that is privileged, confidential and/or proprietary and subject to important terms and conditions available at http://www.digitalasset.com/emaildisclaimer.html <http://www.digitalasset.com/emaildisclaimer.html>. If you are not the intended recipient, please delete this message.

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Processing MRs very slow?
by Iavor Diatchki 22 May '19

22 May '19

Hello, I made a gitlab MR that adds two NOINLINE pragmas and some comments. It's been about a week since my last push to the MR, and nothing has happened since. Is there a way to check on what is its status: - Is it stuck because I need to do something? - Is it stuck because someone else needs to do something? - Or is it just in the queue to be merged, in which case it would be nice to know where in line it is, so I can see that there is progress, and it is not just stuck. Given that this is such a simple MR, I am not too worried about conflicts but a week long lag seems less than ideal for anything even mildly complex. -Iavor PS: I just clicked on all the little check boxes from the template---perhaps that's why things weren't progressing?

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[hadrian/macos] build broken
by Shayne Fletcher 22 May '19

22 May '19

I'm trying to isolate the commit that's causing this, but the deal is on MacOS I'm seeing stage1 `ld` crashes linking `HStime`: ``` 0 0x1052e2748 __assert_rtn + 129 1 0x1052be30f ld::Fixup::Fixup(unsigned int, ld::Fixup::Cluster, ld::Fixup::Kind, bool, char const*) + 95 2 0x1052e8736 mach_o::relocatable::Parser<x86_64>::addFixup(mach_o::relocatable::Parser<x86_64>::SourceLocation const&, ld::Fixup::Cluster, ld::Fixup::Kind, bool, char const*) + 34 3 0x1052eaa9c mach_o::relocatable::Section<x86_64>::addRelocFixup(mach_o::relocatable::Parser<x86_64>&, macho_relocation_info<Pointer64<LittleEndian> > const*) + 1722 4 0x1052ff61b mach_o::relocatable::Section<x86_64>::makeFixups(mach_o::relocatable::Parser<x86_64>&, mach_o::relocatable::Parser<x86_64>::CFI_CU_InfoArrays const&) + 105 5 0x1052faa66 mach_o::relocatable::Parser<x86_64>::parse(mach_o::relocatable::ParserOptions const&) + 2120 6 0x1052f1250 mach_o::relocatable::Parser<x86_64>::parse(unsigned char const*, unsigned long long, char const*, long, ld::File::Ordinal, mach_o::relocatable::ParserOptions const&) + 282 7 0x10534352a ld::tool::InputFiles::makeFile(Options::FileInfo const&, bool) + 808 8 0x105345f22 ld::tool::InputFiles::parseWorkerThread() + 530 9 0x7fff70a6b2eb _pthread_body + 126 10 0x7fff70a6e249 _pthread_start + 66 A linker snapshot was created at: /tmp/HStime-1.9.2.o-2019-04-22-132113.ld-snapshot ld: Assertion failed: (name != NULL), function Fixup, file /Library/Caches/com.apple.xbs/Sources/ld64/ld64-450.3/src/ld/ld.hpp, line 724. ``` I can replicate this on multiple machines and different versions of xcode command line tools. Any ideas? -- Shayne Fletcher Language Engineer c: +1 917 699 7763 e: shayne.fletcher(a)daml.com Digital Asset Holdings, LLC 4 World Trade Center 150 Greenwich Street, 47th Floor <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> New York, NY 10007, USA <https://maps.google.com/?q=150+Greenwich+Street,+47th+Floor%C2%A0+%C2%A0+%C…> digitalasset.com <http://www.digitalasset.com/> -- This message, and any attachments, is for the intended recipient(s) only, may contain information that is privileged, confidential and/or proprietary and subject to important terms and conditions available at http://www.digitalasset.com/emaildisclaimer.html <http://www.digitalasset.com/emaildisclaimer.html>. If you are not the intended recipient, please delete this message.

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RE: Bug or feature?
by Simon Peyton Jones 22 May '19

22 May '19

We have to be careful in how we define "equality" in the above sentence, including class constraints that (may) have superclass equality constraints. Indeed. That’s what happens now. I do think this would work. Cool. Nick or Iavor: would you like to turn this conversation into a ticket? (Although it is technically user-facing, it is a very small corner and I’m not sure it would need a GHC proposal – others may want to comment.) Simon From: Richard Eisenberg <rae(a)cs.brynmawr.edu> Sent: 21 May 2019 09:43 To: Simon Peyton Jones <simonpj(a)microsoft.com> Cc: Nicolas Frisby <nicolas.frisby(a)gmail.com>; Iavor Diatchki <iavor.diatchki(a)gmail.com>; ghc-devs(a)haskell.org; Ryan Scott <ryan.gl.scott(a)gmail.com> Subject: Re: Bug or feature? On May 21, 2019, at 10:23 AM, Simon Peyton Jones via ghc-devs <ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org>> wrote: But (A) looks sound to me. I like (A). (B) makes me nervous, too. > A. An implication is considered to “bind local equalities” iff it has at least one given equality whose free variables are not all bound by the same implication. We have to be careful in how we define "equality" in the above sentence, including class constraints that (may) have superclass equality constraints. I do think this would work. Richard

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make fails with "No entry for "integer library" in .../inplace/lib/settings"
by Roland Senn 21 May '19

21 May '19

Hi, Suddenly I'm unable to build ghc with make. I get the error: "inplace/bin/ghc-cabal" check libraries/ghc-prim "inplace/bin/ghc-cabal" configure libraries/ghc-prim dist-install -- with-ghc="/home/roland/Projekte/ghc/inplace/bin/ghc-stage1" --with-ghc- pkg="/home/roland/Projekte/ghc/inplace/bin/ghc-pkg" --disable-library- for-ghci --enable-library-vanilla --enable-library-for-ghci --disable- library-profiling --enable-shared --configure-option=CFLAGS="- Wall -Werror=unused-but-set-variable -Wno-error=inline" -- configure-option=LDFLAGS=" " --configure-option=CPPFLAGS=" " --gcc- options="-Wall -Werror=unused-but-set-variable -Wno- error=inline " --with-gcc="gcc" --with-ld="ld.gold" --with-ar="ar" -- with-alex="/home/roland/Software/ghc/bin/alex" --with- happy="/home/roland/Software/ghc/bin/happy" Configuring ghc-prim-0.6.1... ghc-cabal: '/home/roland/Projekte/ghc/inplace/bin/ghc-stage1' exited with an error: No entry for "integer library" in "/home/roland/Projekte/ghc/inplace/lib/settings" libraries/ghc-prim/ghc.mk:4: die Regel für Ziel „libraries/ghc- prim/dist-install/package-data.mk“ scheiterte make[1]: *** [libraries/ghc-prim/dist-install/package-data.mk] Fehler 1 Makefile:123: die Regel für Ziel „all“ scheiterte make: *** [all] Fehler 2 Any ideas what's wrong? Any ideas how to fix? Many thanks and best wishes Roland PS: I still need the old make based build system to run validations...

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Re: Bug or feature?
by Ryan Scott 21 May '19

21 May '19

Hi Iavor, This is a feature in the sense that it is an expected outcome of the OutsideIn(X) type inference algorithm (in particular, Section 5 of the corresponding paper [1]). I'll try to explain the issue to the best of my understanding. The tricky thing about the Q3 data type: data Q3 = forall a. Q3 (forall b. (F b ~ Int) => T a b) Is that there is a rank-n type with a /local/ equality constraint. In order to ensure that the type of the Q3 data constructor is never ambiguous, GHC tries to infer that Q3's type is always a subtype of itself. As a part of this, GHC attempts to solve the following implication constraint: forall a. forall b. (F b ~ Int) => (a ~ alpha) Where `alpha` is a unification variable. GHC tries to find a unique, most-general substitution that solves this constraint but ultimately gives up and reports the "untouchable" error message you observed. This is a bit strange, however. Upon first glance, this constraint would appear to have a unique solution: namely, [alpha |-> a]. Why doesn't GHC just use this? Ultimately, it's because OutsideIn(X) is conservative: there may exist constraints that admit a unique solution which it may fail to solve. This is explained in greater depth in Section 5.2 of the paper, but the essence of this restriction is because of the open-world assumption for type families. Namely, it's possible that your Q3 data type might later be linked against code which defines the following type family: type family G i a type instance G Int a = a If that were the case, then the implication constraint above would no longer have a unique solution, since there would exist another substitution [alpha |-> G (F b) a] that is incomparable with [alpha |-> a]. OutsideIn(X) was designed to only pick unique solutions that remain unique solutions even if more axioms (i.e., type family equations) are added, so for these reasons it fails to solve the implication constraint above. See also GHC issues #10651 [2], #14921 [3], and #15649 [4], which all involve similar issues. ----- I'm far from an expert on type inference, so I can't really offer a better inference algorithm that would avoid this problem. The best you can do, as far as I can tell, is to enable AllowAmbiguousTypes and hope for the best. Even then, you'll still run into situations where untouchability rears its ugly head, as in your `q3` definition. When that happens, your only available option (again, as far as I can tell) is to make use of TypeApplications. For example, the following /does/ typecheck: q3 :: Q3 q3 = Q3 @Bool t Hope that helps, Ryan S. ----- [1] https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/jfp-out… [2] https://gitlab.haskell.org/ghc/ghc/issues/10651 [3] https://gitlab.haskell.org/ghc/ghc/issues/14921 [4] https://gitlab.haskell.org/ghc/ghc/issues/15649

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