March 2017 - ghc-tickets

[GHC] #9247: Document -XDatatypeContexts in flag reference
by GHC 03 Jun '18

03 Jun '18

#9247: Document -XDatatypeContexts in flag reference ------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: low | Milestone: Component: Documentation | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- It may be a deprecated feature, but it still exists and should be listed. I can do this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9247> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11066: Inacessible branch should be warning - otherwise breaks type soundness?
by GHC 03 Jun '18

03 Jun '18

#11066: Inacessible branch should be warning - otherwise breaks type soundness? -------------------------------------+------------------------------------- Reporter: rrnewton | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC 7.10.2 reports inaccessible branches as a type error, and I think this is really a bug. First, the implicit thinking seems to be "why would a user want to write inaccessible cases, they'd be crazy!". But that only applies to human-written code. Program generators can have a great deal of trouble avoiding this error, unless they replicate the GHC type checker to predict the problem and prune branches. (That's why we are hitting this error and are stuck.) Second, it seems like this is a problem for type soundness. See the attached program where "step1" typechecks but "step2" does not. And yet, the operational semantics should allow step1 to reduce to step2. Indeed, in the "GADTs meet their match" paper it seems like the intent was to warn for these inaccessible cases, not error. For example, the paper contains the language: "If we warn that a right-hand side of a non-redundant clause is inaccessible," -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11066> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12939: ghc-8.0.1.20161117 did not install ghc.1 manpage
by GHC 02 Jun '18

02 Jun '18

#12939: ghc-8.0.1.20161117 did not install ghc.1 manpage ----------------------------------------+--------------------------------- Reporter: juhpetersen | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Build System | Version: 8.0.2-rc1 Keywords: | Operating System: Linux Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- This seems to be a build regression from ghc-8.0.1. The ghc.1 manpage was not installed for the 8.0.2 RC1 build. I reported this in mail earlier and unfortunately in the meantime lost the buildlogs on Fedora Copr, but since the upstream binary tarballs for Linux also don't seem to contain ghc.1 either it should not be too hard to reproduce. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12939> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC 8.2
by GHC 01 Jun '18

01 Jun '18

#13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC 8.2 -------------------------------------+------------------------------------- Reporter: hvr | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I notice that buildbots were having a hard-time building GHC 8.2 snapshots... so I investigated... One thing that jumped at me was the memory usage while compiling DynFlags which is the worst memory-offender with 4777MiB of resident size: {{{ "inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -Wall -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist-ghcconstants/header -this-unit-id ghc-8.2.0.201 70313 -hide-all-packages -i -icompiler/backpack -icompiler/basicTypes -icompiler/cmm -icompiler/codeGen -icompiler/coreSyn -icompiler/deSugar -icompiler/ghci -icompiler/hsSyn -icompiler/iface -icompiler/llvmGen - icompiler/main -icompiler/nativeGen -icompiler/parser -icompiler/prelude -icompiler/profiling -icompiler/rename -icompiler/simplCore -icompiler/simplStg -icompiler/specialise -icompiler/stgSyn -icompiler/stranal -icompiler/typecheck -icompiler/types -icompiler/utils -icompiler/vectorise -icompiler/stage2/build -Icompiler/stage2/build -icompiler/stage2/build/./autogen -Icompiler/stage2/build/./autogen -Icompiler/. -Icompi ler/parser -Icompiler/utils -Icompiler/../rts/dist/build -Icompiler/stage2 -optP-DGHCI -optP-include -optPcompiler/stage2/build/./autogen/cabal_macros.h -package-id base-4.10.0.0 -package-id deepseq-1.4.3.0 -pa ckage-id directory-1.3.0.2 -package-id process-1.4.3.0 -package-id bytestring-0.10.8.2 -package-id binary-0.8.4.1 -package-id time-1.8.0.1 -package-id containers-0.5.10.2 -package-id array-0.5.1.2 -package-id fil epath-1.4.1.1 -package-id template-haskell-2.12.0.0 -package-id hpc-0.6.0.3 -package-id transformers-0.5.2.0 -package-id ghc- boot-8.2.0.20170313 -package-id ghc-boot-th-8.2.0.20170313 -package-id ghci-8.2.0.20170 313 -package-id hoopl-3.10.2.2 -package-id unix-2.7.2.1 -package-id terminfo-0.4.0.2 -Wall -fno-warn-name-shadowing -this-unit-id ghc -XHaskell2010 -optc-DTHREADED_RTS -DGHCI_TABLES_NEXT_TO_CODE -DSTAGE=2 -Rghc-t iming -O2 -no-user-package-db -rtsopts -Wnoncanonical-monad- instances -odir compiler/stage2/build -hidir compiler/stage2/build -stubdir compiler/stage2/build -dynamic-too -c compiler/main/DynFlags.hs -o compiler/stage2/build/DynFlags.o -dyno compiler/stage2/build/DynFlags.dyn_o }}} {{{ <<ghc: 63014533832 bytes, 4032 GCs, 395131448/1973969928 avg/max bytes residency (24 samples), 4777M in use, 0.000 INIT (0.000 elapsed), 32.207 MUT (33.221 elapsed), 26.682 GC (26.685 elapsed) :ghc>> }}} Then I did two clean full builds of the `ghc-8.0` and `ghc-8.2` branch, and collected the -Rghc-timings output into simple 3-columns .csv files; Here's are the respective top-12 entries for GHC 8.0 and GHC 8.2 respectively: {{{#!bash $ sort -t, -k2n build.80.csv | tail -n12 "inplace/bin/ghc-stage1",560,compiler/stage2/build/TcRnDriver.o "inplace/bin/ghc-stage1",572,compiler/stage2/build/TcRnDriver.p_o "inplace/bin/ghc-stage1",572,compiler/stage2/build/TcSplice.o "inplace/bin/ghc-stage1",847,compiler/stage2/build/OptCoercion.p_o "/opt/ghc/bin/ghc",979,compiler/stage1/build/OptCoercion.o "/opt/ghc/bin/ghc",1036,compiler/stage1/build/DynFlags.o "/opt/ghc/bin/ghc",1040,compiler/stage1/build/X86/CodeGen.o "inplace/bin/ghc-stage1",1119,compiler/stage2/build/DynFlags.p_o "inplace/bin/ghc-stage1",1123,compiler/stage2/build/DynFlags.o "inplace/bin/ghc-stage1",1178,compiler/stage2/build/OptCoercion.o "inplace/bin/ghc-stage1",1233,compiler/stage2/build/X86/CodeGen.o "inplace/bin/ghc-stage1",1282,compiler/stage2/build/X86/CodeGen.p_o }}} {{{#!bash $ sort -t, -k2n build.82.csv | tail -n12 "inplace/bin/ghc-stage1",891,compiler/stage2/build/CmmParse.p_o "/opt/ghc/bin/ghc",1053,compiler/stage1/build/DynFlags.o "/opt/ghc/bin/ghc",1058,compiler/stage1/build/OptCoercion.o "inplace/bin/ghc-stage1",1284,compiler/stage2/build/HsExpr.p_o "inplace/bin/ghc-stage1",1313,compiler/stage2/build/HsExpr.o "/opt/ghc/bin/ghc",1394,compiler/stage1/build/X86/CodeGen.o "inplace/bin/ghc-stage1",1495,compiler/stage2/build/X86/CodeGen.o "inplace/bin/ghc-stage1",1605,compiler/stage2/build/X86/CodeGen.p_o "inplace/bin/ghc-stage1",1620,compiler/stage2/build/OptCoercion.o "inplace/bin/ghc-stage1",1733,compiler/stage2/build/OptCoercion.p_o "inplace/bin/ghc-stage1",3989,compiler/stage2/build/DynFlags.p_o "inplace/bin/ghc-stage1",4777,compiler/stage2/build/DynFlags.o }}} What's apparent from this data: - GHC stage0 (which was GHC 8.0.2) is able to build DynFlags.o for GHC 8.0 and GHC 8.2 w/ roughtly the same amount of max resident memory, i.e. 1 GiB - **GHC 8.2 stage1 however needs 4 times the amount of memory more than GHC 8.0 to build the same `DynFlags.hs` module!** -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13426> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9724: reexport IsList class from a trustworthy module
by GHC 01 Jun '18

01 Jun '18

#9724: reexport IsList class from a trustworthy module -------------------------------------+------------------------------------- Reporter: int-e | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | 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: -------------------------------------+------------------------------------- ==== Motivation GHC's Safe Haskell extension relies to a large extent on inferring safety of modules automatically. As a concrete example, [[http://hackage.haskell.org/package/data-default|data-default]] used to be inferred safe. This is no longer the case, because [[http://hackage.haskell.org/package/dlist-0.7.1|dlist-0.7.1]] added an {{{IsList}}} instance for difference lists. The only way to do that currently is to import the relevant parts of {{{GHC.Exts}}}, and that module is not safe. Of course the resulting non-safety of the {{{Data.DList}}} module can be fixed by adding a {{{TrustWorthy}}} pragma to the module and trusting the {{{dlist}}} package. But that is unsatisfactory, because there is nothing unsafe about providing an instance for the {{{IsList}}} class. This issue is bound to pop up in other packages as well. ==== Proposed Solution (this is one of many possibilities) Add a {{{GHC.Exts.Safe}}} module that is marked {{{TrustWorthy}}} and reexports the {{{IsList}}} class, and possibly other things from {{{GHC.Exts}}} that are safe to use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9724> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9479: Report required constraints when reporting the type of a hole
by GHC 31 May '18

31 May '18

#9479: Report required constraints when reporting the type of a hole -------------------------------------+------------------------------------- Reporter: dominiquedevriese | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 7.8.3 checker) | Operating System: Keywords: holes | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- For the following code {{{ module Test where test :: String test = show _h }}} GHC currently reports: {{{ Found hole ‘_h’ with type: a0 Where: ‘a0’ is an ambiguous type variable Relevant bindings include test :: String (bound at /tmp/Test.hs:4:1) In the first argument of ‘show’, namely ‘_h’ In the expression: show _h In an equation for ‘test’: test = show _h }}} It correctly does not report the lack of a `Show _a` instance as a separate type error. However, it would be useful if the report containing the type of the hole would also contain the constraints that apply to its type. Something like: {{{ Found hole ‘_h’ with type: a0 Where: ‘a0’ is an ambiguous type variable Applicable constraints: Show a0 Relevant bindings include test :: String (bound at /tmp/Test.hs:4:1) In the first argument of ‘show’, namely ‘_h’ In the expression: show _h In an equation for ‘test’: test = show _h }}} I am explicitly *not* suggesting to report a type like `Show a0 => a0` for the hole, because that might mistakenly suggest that we are looking for a value of type `forall a0. Show a0 => a0`, which we are not. A possible alternative is to use an imaginary exists type like `exists a0. Show a0 => a0` but that's probably just even more confusing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9479> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12567: `ghc --make` recompiles unchanged files when using `-fplugin` OPTIONS
by GHC 30 May '18

30 May '18

#12567: `ghc --make` recompiles unchanged files when using `-fplugin` OPTIONS -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- Consider this bare-bones module {{{#!hs {-# OPTIONS -fplugin GHC.TypeLits.Normalise #-} module A where }}} compiling it will always say {{{ $ ghc --make A.hs [1 of 1] Compiling A ( A.hs, A.o ) [GHC.TypeLits.Normalise changed] }}} even when the module was compiled before. {{{ $ ghc A.hs -c -ddump-if-trace -ddump-hi-diffs }}} will give the reason: {{{ imported module ‘GHC.TypeLits.Normalise’ is from package ‘ghc-typelits- natnormalise-0.5’, which is not among previous dependencies }}} Which is the probable cause: when writing the `.hi` file, the used plugins' package dependencies should be also written out. AFAICS they are extracted fron the `DynFlags` but for this comparison in {{{ checkDependencies :: HscEnv -> ModSummary -> ModIface -> IfG RecompileRequired }}} but not found in the `ModSummary` that was originally written to disk. This is pretty nasty for `clash` compilations and the suspected bug is documented here: https://github.com/clash-lang/ghc-typelits- natnormalise/issues/2 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12567> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9438: panic: loading archives not supported
by GHC 29 May '18

29 May '18

#9438: panic: loading archives not supported ----------------------------------+---------------------------------- Reporter: egl | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: MacOS X Architecture: x86_64 (amd64) | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: ----------------------------------+---------------------------------- Running {{{ ghci -L/opt/local/lib -latlas }}} eventually leads to {{{ Loading object (static archive) /opt/local/lib/libatlas.a ... ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Loading archives not supported Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This looks similar to 8164 and 4828, which are marked closed. Mac OSX 10.9.4 Xcode 5.1.1 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9438> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13126: Support for hexadecimal floats
by GHC 29 May '18

29 May '18

#13126: Support for hexadecimal floats -------------------------------------+------------------------------------- Reporter: lerkok | 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: -------------------------------------+------------------------------------- Currently, Haskell only allows writing floating-point numbers in the decimal format. Unfortunately, writing floats in decimal/scientific format is not always the best option, due to loss of precision. As an alternative, there's the so called "hexadecimal floating point" format, described in p57-58 of: http://www.open- std.org/jtc1/sc22/wg14/www/docs/n1256.pdf The format is rather simple, unambiguous, and relatively easy to implement. And it's been around for about 10 years by now. It would be nice if the Haskell standard was changed to include such literals. But in the meantime, perhaps GHC can support such literals via a pragma, such as `LANGUAGE HexadecimalFloats` or similar. A corresponding pretty printer (similar to C's %a specifier) is also needed; which should go into the standard `Numerics` module. Such a function can be called `showHFloat` to accompany the similarly named functions for rendering float values. A reference implementation can be given by template-Haskell splicing, and indeed the hackage package FloatingHex (http://hackage.haskell.org/package/FloatingHex) provides both a quasi- quoter for such literals, and the pretty printer `showHFloat.` Unfortunately, this solution is less than satisfactory as it relies on the rather heavy mechanism for quasi-quotes, requires an extra library dependency, a pragma (`QuasiQuotes`), and the import and dependency of a hackage package, which sounds a lot for just being able to write floats precisely! Furthermore, Tempate Haskell has an issue with the storage of floats (https://ghc.haskell.org/trac/ghc/ticket/13124) which makes the library solution less than ideal in overflow cases. (Long story short: Template- Haskell stores floating literals as rationals, and thus has no reliable way of representing floats such as NaN, Infinity, and especially negative- zero.) Numeric programming is important, especially in this new era of HPC, and many-core architectures tuned for crunching floating-point data seamlessly. While this is admittedly a minor step, I think it'll be a positive addition to GHC from a maturity perspective, and that of matching/leading other languages out there. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13126> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10843: Allow do blocks without dollar signs as arguments
by GHC 29 May '18

29 May '18

#10843: Allow do blocks without dollar signs as arguments -------------------------------------+------------------------------------- Reporter: agibiansky | Owner: agibiansky Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (Parser) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- I would like the following to be valid Haskell code: {{{#!hs main = when True do putStrLn "Hello!" }}} Instead of requiring a dollar sign before the "do". This would parse as {{{#!hs main = when True (do putStrLn "Hello!") }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10843> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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