October 2015 - ghc-tickets

[GHC] #10635: -fwarn-redundant-constraints should not be part of -Wall
by GHC 07 Feb '17

07 Feb '17

#10635: -fwarn-redundant-constraints should not be part of -Wall -------------------------------------+------------------------------------- Reporter: Lemming | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.11 Component: Compiler | Operating System: Unknown/Multiple (Type checker) | Type of failure: Incorrect Keywords: | warning at compile-time Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- When I compile existing code with GHC-7.11.20150707 I get lot of "redundant constraints" warnings. Generally I think that this warning can be very useful for minimizing constraints, nonetheless there are good reasons not choose minimal constraints for a type signature. E.g. if I have to implement `Data.Map.singleton` I do not need the `Ord k` constraint for the key type. However, I might add it anyway in order to be able to change the implementation in future such that it uses `Ord k` dictionary. Thus I suggest to exclude `-fwarn-redundant-constraints` from `-Wall`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10635> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10823: Expose keepAlive to Template Haskell
by GHC 04 Feb '17

04 Feb '17

#10823: Expose keepAlive to Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | 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 Revisions: | -------------------------------------+------------------------------------- {{{keepAlive}}} is a [https://github.com/ghc/ghc/blob/efa7b3a474bc373201ab145c129262a73c86f959/co… function in TcRnMonad] that adds a {{{Name}}} to the set of {{{Name}}}s to keep when pruning out dead code. A concrete use case for exposing this to Template Haskell is in LiquidHaskell, which will soon function as a Core plugin. In LiquidHaskell, a subset of Haskell functions can be "lifted" to the logic level and used in types. For example: {{{ module Test (ok) where [lq| inline gt |] gt x y = x > y [lq| ok :: x:Int -> { v:Int | gt x v } |] ok x = x + 1 }}} LiquidHaskell runs a transformation from the {{{CoreBind}}} for {{{gt}}} to its internal representation of decidable logic. Since Core plugins are run after "dead" code is removed at the end of desugaring, and since {{{gt}}} is not exported, the {{{CoreBind}}} for {{{gt}}} would not reach the {{{CoreBinds}}} LH receives as a Core plugin. The solution for this is to be able to mark names with {{{keepAlive}}} from Template Haskell. Proposed specification: {{{ keepAlive :: Name -> Q () }}} where {{{Name}}} is a Template Haskell {{{Name}}}. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10823> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10746: No non-exhaustive pattern match warning given for empty case analysis
by GHC 03 Feb '17

03 Feb '17

#10746: No non-exhaustive pattern match warning given for empty case analysis -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- I would expect GHC to warn of a non-exhaustive pattern match at compile- time when faced with this, {{{#!hs {-# LANGUAGE EmptyCase #-} module Test where test :: Bool -> Int test a = case a of }}} Yet it happily accepts this without complaint. If one attempts to evaluate, e.g., `test True` the expected "Non-exhaustive patterns in case" error is thrown at runtime. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10746> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10052: Panic (something to do with floatExpr?)
by GHC 01 Feb '17

01 Feb '17

#10052: Panic (something to do with floatExpr?) -------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1-rc2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Loading {{{ main = let (x :: String) = "hello" in putStrLn x }}} using a very simple driver for the GHC API (see T145.hs) causes a ghc panic: {{{ [1 of 1] Compiling Main ( T145-input.hs, interpreted ) T145: T145: panic! (the 'impossible' happened) (GHC version 7.10.0.20150128 for x86_64-apple-darwin): floatExpr tick <<details unavailable>> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This panic is arising in our test case for #8333, so it may be related to that bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10052> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10420: "Care with plugin imports" is wrong / orphan RULE visibility
by GHC 29 Jan '17

29 Jan '17

#10420: "Care with plugin imports" is wrong / orphan RULE visibility -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- A module loaded by a plugin poisons the module cache, so we never load an orphan RULE or instance even if we legitimately should do so. The way to test this is a bit convoluted, but it goes something like this: plugins07.hs {{{ module Main where import Plugins07a import RuleDefiningPlugin {-# NOINLINE x #-} x = "foo" main = putStrLn (show x) }}} Plugins07a.hs {{{ --{-# OPTIONS_GHC -fplugin RuleDefiningPlugin #-} module Plugins07a where }}} RuleDefiningPlugin.hs, in ANOTHER PACKAGE (otherwise, EPT rules don't apply) {{{ module RuleDefiningPlugin where import GhcPlugins {-# RULES "unsound" forall x. show x = "SHOWED" #-} plugin :: Plugin plugin = defaultPlugin }}} I'll commit the full test. Here's what happens: * Building `Plugins07a` results in `loadPluginInterface` on `RuleDefiningPlugin`. We load the `ModIface` but only add its types to the environment because of the "Care with plugin imports" special case. * Building `plugins07.hs` results in a normal source level import for `RuleDefiningPlugin`, but `ModIface` is already in the cache so we don't load anything. RULE is not loaded, disaster! Admittedly, actually triggering this bug requires a convoluted chain of events. But really this problem arose because the "Care with plugin imports" fix is just completely nonsense. Here's what we should do: * We should apply the same fix from #2182 on orphan instances to orphan rules too. This way, we can safely load RULEs into the EPS without accidentally bringing them into scope when they shouldn't be. * Loading an interface should unconditionally suck in the instances and rules. The result is more correct and simpler, so it seems worth fixing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10420> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9351: add ability to version symbols .c for packages with C code
by GHC 27 Jan '17

27 Jan '17

#9351: add ability to version symbols .c for packages with C code -------------------------------------+------------------------------------- Reporter: slyfox | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: backpack | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Let's consider an example: We have a haskell package with some C code imported in haskell: {{{ // a.h file int get_something(void); // a.c file #include "a.h" int get_something(void) { return 42; } // M.hs file module M where foreign import ccall "a.h get_something" :: IO Int }}} The problem here is we can't mix that package with other packages having global 'get_something' symbol. Sometimes it happens when a package copies part of implementation from another package with .c bits under different haskell namespace. Haskell parts would coexist freely, but not C symbols. Would be great if ghc would export some unique package identifier in a way C code could attach it to all exported symbols making linking possible. Something like that: {{{ // a.h file #include "HsFFI.h" /* #define FOR_HASKELL(__sym) package_id_##__sym */ int FOR_HASKELL(get_something)(void); // a.c file #include "a.h" int FOR_HASKELL(get_something)(void) { return 42; } // M.hs file module M where foreign import ccall-for-haskell "a.h get_something" :: IO Int }}} That way we explicitly mark symbol as inaccessible to external plain C code. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9351> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8901: (very) bad inline heuristics
by GHC 25 Jan '17

25 Jan '17

#8901: (very) bad inline heuristics ------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I observe a bad case for inlining blowup for the time library. Observed for 7.7, just checked in 7.9. The problem is so bad that the PowerPC32 assembler cannot resolve cross- routine references. (I have no error message at hand, but could try to get one.) Instead here are the stats for x86, with inlining and certain inlining suppressed. The architecture seems irrelevant. {{{ $ file ./libraries/time/dist-install/build/Data/Time/Format.o ./libraries/time/dist-install/build/Data/Time/Format.o: Mach-O object i386 $ ls -l ./libraries/time/dist-install/build/Data/Time/Format.* -rw-r--r-- 1 ggreif staff 61875 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.dyn_hi -rw-r--r-- 1 ggreif staff 450864 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.dyn_o -rw-r--r-- 1 ggreif staff 61863 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.hi -rw-r--r-- 1 ggreif staff 332216 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.o }}} With following patch applied: <https://github.com/ggreif/packages- time/commit/83f08b8896b950707a910fed4e30bddb7ee7f52f> I get: {{{ $ ls -l ./libraries/time/dist-install/build/Data/Time/Format.* -rw-r--r-- 1 ggreif staff 10554 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.dyn_hi -rw-r--r-- 1 ggreif staff 106832 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.dyn_o -rw-r--r-- 1 ggreif staff 10542 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.hi -rw-r--r-- 1 ggreif staff 78864 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.o }}} The factor is 4.2 for Format.o, Format.dyn_o and 5.8 for the .hi files. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8901> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8156: amd64 + in-tree gmp build broken
by GHC 23 Jan '17

23 Jan '17

#8156: amd64 + in-tree gmp build broken -------------------------------------+------------------------------------- Reporter: errge | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Build System | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 (amd64) | Type of failure: Building GHC Difficulty: Easy (less than 1 | failed hour) | Test Case: Blocked By: | Blocking: Related Tickets: #4022 #4366 #4374 | -------------------------------------+------------------------------------- Currently, the GHC build system has an in-tree GMP. This GMP seems to be used only if there is no usable GMP found on the system and the user didn't provide one using configure flags. When we build GHC using an external shared version of GMP, the resulting GHC is dynamically linked against GMP and also the generated programs are linked dynamically against GMP. When the in-tree GMP is used, it is built statically, even if the GHC we are building is shared GHC on GNU/Linux. This feature is currently broken on amd64 (#4366, #4022), but is working currently very well on Linux i686. Apart from the breakage this setting is very flexible and I'd be very happy if it were possible to keep it, in spite of removeal requests like #4374. When there is a system GMP, nothing would change, this is the most typical usage, e.g. distributions are all building this way. On the other hand, if the user removes his GMP (maybe we should provide an option to explicity trigger this in ./configure, instead of having to remove GMP); she can build a GHC that is not linked dynamically against GMP and the resulting programs are not linked either. This makes it possible to generate binaries that link dynamically against libc (no -static) which is quite compatible amongst versions, but doesn't require a libgmp.so to run. For binary deployments this seems to be the best kind of setup nowadays. Now, if we were only able to fix this for amd64. See this: https://www.gentoo.org/proj/en/base/amd64/howtos/index.xml?part=1&chap=3 On amd64 we can continue to compile GMP statically and link into the binary library, we just have to compile GMP with the fPIC. I attached the patch to fix this. Previously a similar patch has been rejected in #4022 because "this shouldn't be platform specific", but this is clearly not the case, this is specific to amd64. Tadaaaam: {{{ errge@sid64:~/ghc/inplace/bin$ cat test.hs main = print (2^100) errge@sid64:~/ghc/inplace/bin$ ./ghc-stage2 test.hs [1 of 1] Compiling Main ( test.hs, test.o ) Linking test ... errge@sid64:~/ghc/inplace/bin$ ./test 1267650600228229401496703205376 errge@sid64:~/ghc/inplace/bin$ ldd ./test linux-vdso.so.1 (0x00007fff79962000) libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fe4b9a83000) librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fe4b987a000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fe4b9676000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fe4b92c6000) libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fe4b90a6000) /lib64/ld-linux-x86-64.so.2 (0x00007fe4b9d83000) }}} No GMP! I attach the build file patch to the bugreport. So, can we please apply this patch and just keep the in-tree GMP? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8156> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9223: Type equality makes type variable untouchable
by GHC 21 Jan '17

21 Jan '17

#9223: Type equality makes type variable untouchable -------------------------------------------+------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- This doesn't look right: {{{ {-# LANGUAGE RankNTypes, TypeFamilies #-} type family TF (m :: * -> *) run1 :: (forall m . Monad m => m a) -> a run1 = undefined run2 :: (forall m . (Monad m, TF m ~ ()) => m a) -> a run2 = undefined -- this works x1 = run1 (return ()) -- this fails x2 = run2 (return ()) {- Couldn't match expected type ‘a’ with actual type ‘()’ ‘a’ is untouchable inside the constraints (Monad m, TF m ~ ()) bound by a type expected by the context: (Monad m, TF m ~ ()) => m a at untouchable.hs:15:6-21 ‘a’ is a rigid type variable bound by the inferred type of x2 :: a at untouchable.hs:15:1 Relevant bindings include x2 :: a (bound at untouchable.hs:15:1) In the first argument of ‘return’, namely ‘()’ In the first argument of ‘run2’, namely ‘(return ())’ -} }}} I would expect x2 to type check just like x1 does. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9223> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10515: ghc: panic: tyThingTyCon Identifier ‘$fStencil:.a(,,,,)7’
by GHC 21 Jan '17

21 Jan '17

#10515: ghc: panic: tyThingTyCon Identifier ‘$fStencil:.a(,,,,)7’ -------------------------------------+------------------------------------- Reporter: yongqli | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Has anyone seen something like this? {{{ <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.10.1.20150519 for x86_64-unknown-linux): tyThingTyCon Identifier ‘$fStencil:.a(,,,,)7’ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10515> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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