August 2018 - ghc-tickets

[GHC] #15511: GHCi internal error with runQ [| it |] and _
by GHC 13 Aug '18

13 Aug '18

#15511: GHCi internal error with runQ [| it |] and _ -------------------------------------+------------------------------------- Reporter: ChaiTRex | 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: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHCi gives a GHC internal error with the following input: {{{ :set -XTemplateHaskell :m + Language.Haskell.TH.Syntax runQ [| it |] runQ [| it |] _ }}} Session: {{{ $ ghci GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> :set -XTemplateHaskell Prelude> :m + Language.Haskell.TH.Syntax Prelude Language.Haskell.TH.Syntax> runQ [| it |] UnboundVarE it Prelude Language.Haskell.TH.Syntax> runQ [| it |] VarE Ghci1.it Prelude Language.Haskell.TH.Syntax> _ <interactive>:1:1: error: GHC internal error: ‘Ghci1.it’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [] Prelude Language.Haskell.TH.Syntax> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15511> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15507: Deriving with QuantifiedConstraints is unable to penetrate type families
by GHC 12 Aug '18

12 Aug '18

#15507: Deriving with QuantifiedConstraints is unable to penetrate type families -------------------------------------+------------------------------------- Reporter: isovector | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple QuantifiedConstraints | Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'd expect the following code to successfully derive a usable `Eq` instance for `Foo`. {{{#!hs {-# LANGUAGE QuantifiedConstraints #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} module QuantifiedConstraints where import Data.Functor.Identity type family HKD f a where HKD Identity a = a HKD f a = f a data Foo f = Foo { zoo :: HKD f Int , zum :: HKD f Bool } deriving instance (forall a. Eq (HKD f a)) => Eq (Foo f) }}} However, it complains: {{{ • Could not deduce (Eq (HKD f a)) from the context: forall a. Eq (HKD f a) bound by an instance declaration: forall (f :: * -> *). (forall a. Eq (HKD f a)) => Eq (Foo f) at /home/sandy/prj/book-of- types/code/QuantifiedConstraints.hs:20:19-56 • In the ambiguity check for an instance declaration To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the stand-alone deriving instance for ‘(forall a. Eq (HKD f a)) => Eq (Foo f)’ }}} Adding -XAllowAmbiguousTypes doesn't fix the situation: {{{ • Could not deduce (Eq (HKD f a)) arising from a use of ‘GHC.Classes.$dm/=’ from the context: forall a. Eq (HKD f a) bound by the instance declaration at /home/sandy/prj/book-of- types/code/QuantifiedConstraints.hs:21:1-56 • In the expression: GHC.Classes.$dm/= @(Foo f) In an equation for ‘/=’: (/=) = GHC.Classes.$dm/= @(Foo f) When typechecking the code for ‘/=’ in a derived instance for ‘Eq (Foo f)’: To see the code I am typechecking, use -ddump-deriv In the instance declaration for ‘Eq (Foo f)’ }}} and the result of -ddump-deriv: {{{ ==================== Derived instances ==================== Derived class instances: instance (forall a. GHC.Classes.Eq (QuantifiedConstraints.HKD f a)) => GHC.Classes.Eq (QuantifiedConstraints.Foo f) where (GHC.Classes.==) (QuantifiedConstraints.Foo a1_a6MW a2_a6MX) (QuantifiedConstraints.Foo b1_a6MY b2_a6MZ) = (((a1_a6MW GHC.Classes.== b1_a6MY)) GHC.Classes.&& ((a2_a6MX GHC.Classes.== b2_a6MZ))) Derived type family instances: ==================== Filling in method body ==================== GHC.Classes.Eq [QuantifiedConstraints.Foo f_a6N0[ssk:1]] GHC.Classes./= = GHC.Classes.$dm/= @(QuantifiedConstraints.Foo f_a6N0[ssk:1]) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15507> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4879: Deprecate exports
by GHC 12 Aug '18

12 Aug '18

#4879: Deprecate exports -------------------------------------+------------------------------------- Reporter: basvandijk | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.0.1 Resolution: | Keywords: deprecate | warning Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #10071 #2119 | Differential Rev(s): Phab:D638 Wiki Page: | -------------------------------------+------------------------------------- Comment (by thomie): [https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0028 -deprecating-exports-proposal.rst GHC proposal] accepted. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4879#comment:31> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15506: CI setup should build and run nofib
by GHC 11 Aug '18

11 Aug '18

#15506: CI setup should build and run nofib -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Build System | Version: 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: -------------------------------------+------------------------------------- Every now and then, a commit breaks nofib; recently changeset:aab8656ba0561e56048a1222c396d2d117aca5a7. This should be avoidable if we compile and run `nofib` as part of the CI setup (and if CI would be usually green, but that’s a different story…) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15506> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14373: Introduce PTR-tagging for big constructor families
by GHC 11 Aug '18

11 Aug '18

#14373: Introduce PTR-tagging for big constructor families -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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 only ''small'' constructor families come into the benefit of pointer tagging. In big fams, 1 is the tag that says "I am evaluated". I suggest to do best-effort pointer tagging on big families too by this scheme: Ptr-tag 1..6 for the first 6 constructors, 7 would signify "look into the info table and branch on that tag". In the info table the tags will then be 6..(familySize - 1). I have an implementation which I'll submit to fabricator soon. TODOs: update wiki pages. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14373> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9214: UNPACK support for sum types
by GHC 11 Aug '18

11 Aug '18

#9214: UNPACK support for sum types ------------------------------------+------------------------------------- Reporter: mojojojo | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | 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: | ------------------------------------+------------------------------------- Currently the pragma only supports single-constructor types. So in the following example it will simply be ignored: {{{ data A = A1 Char | A2 {-# UNPACK #-} !B data B = B1 Int | B2 Bool }}} However the problem seems to be easily solvable by denormalizing the type {{{A}}} to something like the following during unpacking: {{{ data A = A1 Char | A2_1 Int | -- from B1 A2_2 Bool -- from B2 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9214> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #11445: Turn on SplitSections by default
by GHC 11 Aug '18

11 Aug '18

#11445: Turn on SplitSections by default -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: task | Status: closed Priority: normal | Milestone: 8.8.1 Component: Build System | Version: 8.0.1-rc1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1800 Wiki Page: | -------------------------------------+------------------------------------- Changes (by thomie): * status: new => closed * resolution: => fixed Comment: The build system now uses `-split-sections` to build GHC and the core libraries on supported platforms, see comment:21. See #12913 for remaining work to be done for Windows. Closing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11445#comment:26> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12065: there is a way to override the .tix path with HPCTIXFILE
by GHC 11 Aug '18

11 Aug '18

#12065: there is a way to override the .tix path with HPCTIXFILE -------------------------------------+------------------------------------- Reporter: kostmo | 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: -------------------------------------+------------------------------------- Under the [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/hpc.html#id… "Caveats and Shortcomings of Haskell Program Coverage" section], it says: > There is no way to change the name of the .tix file generated, apart from renaming the binary. However, specifying `HPCTIXFILE` as an environment variable when running the executable program does change the output path of the `.tix` file. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12065> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14294: IndexError: pop from empty list
by GHC 10 Aug '18

10 Aug '18

#14294: IndexError: pop from empty list -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- ==== How to Reproduce ==== While doing a GET operation on `/attachment/ticket/14293/`, Trac issued an internal error. ''(please provide additional details here)'' Request parameters: {{{ {u'action': u'new', 'path': u'14293/', 'realm': u'ticket'} }}} User agent: `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/603.3.8 (KHTML, like Gecko) Version/10.1.2 Safari/603.3.8` ==== System Information ==== ''Systeminformation nicht verfügbar'' ==== Enabled Plugins ==== ''Plugininformation nicht verfügbar'' ==== Interface Customization ==== ''Interface customization information not available'' ==== Python Traceback ==== {{{ Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/trac/web/main.py", line 623, in _dispatch_request dispatcher.dispatch(req) File "/usr/local/lib/python2.7/dist-packages/trac/web/main.py", line 259, in dispatch iterable=chrome.use_chunked_encoding) File "/usr/local/lib/python2.7/dist-packages/trac/web/chrome.py", line 1165, in render_template encoding='utf-8') File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 184, in render return encode(generator, method=method, encoding=encoding, out=out) File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 58, in encode for chunk in iterator: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 350, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 829, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 669, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 774, in __call__ for kind, data, pos in chain(stream, [(None, None, None)]): File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 594, in __call__ for ev in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/trac/web/chrome.py", line 1432, in _strip_accesskeys for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/trac/web/chrome.py", line 1421, in _generate for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 706, in _unmark for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 1101, in __call__ for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 118, in __iter__ event = self.stream.next() File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 734, in __call__ for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 702, in _mark for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 378, in _match ctxt, start=idx + 1, **vars): File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 378, in _match ctxt, start=idx + 1, **vars): File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 362, in _match content = list(content) File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 326, in _match for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/path.py", line 588, in _generate subevent = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/path.py", line 588, in _generate subevent = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/filters/i18n.py", line 178, in _generate for event in msgbuf.translate(gettext(msgbuf.format())): File "/usr/local/lib/python2.7/dist-packages/genshi/filters/i18n.py", line 1051, in translate events = self.events[order].pop(0) IndexError: pop from empty list }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14294> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15153: GHC uses O_NONBLOCK on regular files, which has no effect, and blocks the runtime
by GHC 10 Aug '18

10 Aug '18

#15153: GHC uses O_NONBLOCK on regular files, which has no effect, and blocks the runtime -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Runtime | Version: 8.2.2 System | Keywords: | Operating System: Linux Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is the outcome of https://mail.haskell.org/pipermail/ghc- devs/2018-May/015749.html Reading through the code of [http://hackage.haskell.org/package/base-4.11.1.0/docs/src/GHC.IO.FD.html#re… readRawBufferPtr] the first line jumped to my eye: {{{ | isNonBlocking fd = unsafe_read -- unsafe is ok, it can't block }}} This looks suspicious. On Linux, if `fd` is a a descriptor to a regular file (on disk, a networked filesystem, or a block device), then `O_NONBLOCK` will have no effect, yet `unsafe_read` is used which will block the running OS thread. You can read more about `O_NONBLOCK` not working on regular files on Linux here: * https://www.nginx.com/blog/thread-pools-boost-performance-9x/ * https://stackoverflow.com/questions/8057892/epoll-on-regular-files * https://jvns.ca/blog/2017/06/03/async-io-on-linux--select--poll--and- epoll/ * https://groups.google.com/forum/#!topic/comp.os.linux.development.system/K -fC-G6P4EA And indeed, the following program does NOT keep printing things in the printing thread, and instead blocks for 30 seconds: {{{ module Main where import Control.Concurrent import Control.Monad import qualified Data.ByteString as BS import System.Environment main :: IO () main = do args <- getArgs case args of [file] -> do forkIO $ forever $ do putStrLn "still running" threadDelay 100000 -- 0.1 s bs <- BS.readFile file putStrLn $ "Read " ++ show (BS.length bs) ++ " bytes" _ -> error "Pass 1 argument (a file)" }}} when compiled with {{{ ~/.stack/programs/x86_64-linux/ghc-8.2.2/bin/ghc --make -O -threaded blocking-regular-file-read-test.hs }}} on my Ubuntu 16.04 and on a 2GB file like {{{ ./blocking-regular-file-read-test /mnt/images/ubuntu-18.04-desktop- amd64.iso }}} And `strace -f -e open,read` on it shows: {{{ open("/mnt/images/ubuntu-18.04-desktop-amd64.iso", O_RDONLY|O_NOCTTY|O_NONBLOCK) = 11 read(11, <unfinished ...> }}} So GHC is trying to use `O_NONBLOCK` on regular files, which cannot work and will block when used through unsafe foreign calls like that. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15153> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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