April 2018 - ghc-tickets

[GHC] #13773: Types are not normalized in instance declarations
by GHC 25 Nov '18

25 Nov '18

#13773: Types are not normalized in instance declarations -------------------------------------+------------------------------------- Reporter: augustss | Owner: (none) 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: -------------------------------------+------------------------------------- Consider the example below. It does not compile, but replacing 5*2 by 10 makes it compile. This is quite annoying since it forces me to do the normalization that the computer is really much better at doing. {{{#!hs module NatInstance where import GHC.TypeLits type N = 5 * 2 data D (n :: Nat) = D instance Show (D N) where show _ = "" }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13773> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15085: :type-at/:all-types and :r don't mix
by GHC 25 Nov '18

25 Nov '18

#15085: :type-at/:all-types and :r don't mix -------------------------------------+------------------------------------- Reporter: dmwit | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.3 Component: Compiler | Version: 8.4.2 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: -------------------------------------+------------------------------------- Steps to reproduce: 1. Put `x = ()` in test.hs. 2. Start ghci. 3. Turn on collection with :set +c. 4. Load the file with :l test.hs. 5. Observe the following output from :all-types {{{ test.hs:(1,1)-(1,2): () test.hs:(1,5)-(1,7): () }}} 6. While ghci is still open, modify the file to say `x = True`. 7. In the same ghci session as before, reload with :r, or load the file again with :l test.hs, chef's choice. 8. Run :all-types again. After step 8, ghci prints the exact same thing as before, indicating that both sides of the equation have type `()`. It should instead update the source spans and types to match the file, reporting `Bool` instead of `()` and `(1,5)-(1,9)` for the second span. Manually exiting and restarting ghci appears to be the only way to freshen the collected type information. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15085> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15105: `typecheckModule` from GHC API crashes on MacOS for files with TH
by GHC 22 Nov '18

22 Nov '18

#15105: `typecheckModule` from GHC API crashes on MacOS for files with TH ----------------------------------------+---------------------------------- Reporter: harpocrates | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: GHC API | Version: 8.4.2 Keywords: | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: Runtime crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+---------------------------------- I believe this is the same issue that is causing manually built `haddock` and `doctest` to crash on MacOS when fed TH (originally reported https://github.com/haskell/haddock/issues/767 and https://github.com/sol/doctest/issues/199) I've attached a minimal program that uses the GHC API and exhibits the same problem. {{{ $ ghc-8.4.2 -package ghc -package containers -package ghc-paths Prog.hs [1 of 1] Compiling Main ( Prog.hs, Prog.o ) Linking Prog ... $ ./Prog Main-no-TH.hs -package template-haskell $ ./Prog Main-TH.hs -package template-haskell Prog: lookupSymbol failed in relocateSection (RELOC_GOT) /usr/local/lib/ghc-8.4.2/integer-gmp-1.0.2.0/HSinteger-gmp-1.0.2.0.o: unknown symbol `___gmp_rands' Prog: Prog: unable to load package `integer-gmp-1.0.2.0' }}} In case it isn't clear, I do not expect `Main-TH.hs` to crash `Prog`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15105> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14784: RTS header files can't be used with a C++ compiler
by GHC 22 Nov '18

22 Nov '18

#14784: RTS header files can't be used with a C++ compiler -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: System | 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: -------------------------------------+------------------------------------- If you compile `m1.cpp`: {{{ #include "Rts.h" int main(int argc, char** argv) { } }}} with: {{{ g++ -g m1.cpp -std=c++11 -I includes/ -c }}} you get: {{{ In file included from includes/Rts.h:29:0, from m1.cpp:1: includes/Stg.h:29:3: error: #error __STDC_VERSION__ does not advertise C99 or later # error __STDC_VERSION__ does not advertise C99 or later ^ }}} It's not advertised anywhere that it should work, but it used to work. https://phabricator.haskell.org/D2045 is what introduced this check. Judging by https://stackoverflow.com/questions/48045243/ghc-gcc-compiler- issue-stdc-version-w-c99-from-stg-h-fails-for-every-packa, it affects GHC 8.2 and later. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14784> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8634: Code valid in GHC 7.6 is impossible to move over GHC 7.7 (because of liberal coverage condition)
by GHC 22 Nov '18

22 Nov '18

#8634: Code valid in GHC 7.6 is impossible to move over GHC 7.7 (because of liberal coverage condition) ------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: high | 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: | ------------------------------------+------------------------------------- == Abstract == Hi! I'm writing a compiler, which produces Haskell code. I've discovered it is impossible to keep currently used features / logic using GHC 7.7 instead of 7.6 Below is more detailed description of the problem: == The idea == I'm writing a [DSL][1], which compiles to Haskell. Users of this language can define own immutable data structures and associated functions. By associated function I mean a function, which belongs to a data structure. For example, user can write (in "pythonic" pseudocode): {{{#!python data Vector a: x,y,z :: a def method1(self, x): return x }}} (which is equivalent to the following code, but shows also, that associated functions beheva like type classes with open world assumption): {{{#!python data Vector a: x,y,z :: a def Vector.method1(self, x): return x }}} In this example, `method1` is a function associated with `Vector` data type, and can be used like `v.testid(5)` (where `v` is instance of `Vector` data type). I'm translating such code to Haskell code, but I'm facing a problem, which I'm trying to solve for a long time. == The problem == I'm trying to move the code from GHC 7.6 over GHC 7.7. The code works perfectly under GHC 7.6, but does not under GHC 7.7. I want to ask you how can I fix it to make it working in the new version of the compiler? == Example code == Lets see a simplified version of generated (by my compiler) Haskell code: {{{#!haskell {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE FunctionalDependencies #-} import Data.Tuple.OneTuple ------------------------------ -- data types ------------------------------ data Vector a = Vector {x :: a, y :: a, z :: a} deriving (Show) -- the Vector_testid is used as wrapper over a function "testid". newtype Vector_testid a = Vector_testid a ------------------------------ -- sample function, which is associated to data type Vector ------------------------------ testid (v :: Vector a) x = x ------------------------------ -- problematic function (described later) ------------------------------ testx x = call (method1 x) $ OneTuple "test" ------------------------------ -- type classes ------------------------------ -- type class used to access "method1" associated function class Method1 cls m func | cls -> m, cls -> func where method1 :: cls -> m func -- simplified version of type class used to "evaluate" functions based on -- their input. For example: passing empty tuple as first argument of `call` -- indicates evaluating function with default arguments (in this example -- the mechanism of getting default arguments is not available) class Call a b where call :: a -> b ------------------------------ -- type classes instances ------------------------------ instance (out ~ (t1->t1)) => Method1 (Vector a) Vector_testid out where method1 = (Vector_testid . testid) instance (base ~ (OneTuple t1 -> t2)) => Call (Vector_testid base) (OneTuple t1 -> t2) where call (Vector_testid val) = val ------------------------------ -- example usage ------------------------------ main = do let v = Vector (1::Int) (2::Int) (3::Int) -- following lines equals to a pseudocode of ` v.method1 "test" ` -- OneTuple is used to indicate, that we are passing single element. -- In case of more or less elements, ordinary tuples would be used. print $ call (method1 v) $ OneTuple "test" print $ testx v }}} The code compiles and works fine with GHC 7.6. When I'm trying to compile it with GHC 7.7, I'm getting following error: {{{ debug.hs:61:10: Illegal instance declaration for ‛Method1 (Vector a) Vector_testid out’ The liberal coverage condition fails in class ‛Method1’ for functional dependency: ‛cls -> func’ Reason: lhs type ‛Vector a’ does not determine rhs type ‛out’ In the instance declaration for ‛Method1 (Vector a) Vector_testid out’ }}} The error is caused by new rules of checking what functional dependencies can do, namely `liberal coverage condition` (as far as I know, this is `coverage condition` relaxed by using `-XUndecidableInstances`) == Some attemps to fix the problem == I was trying to overcome this problem by changing the definition of `Method1` to: {{{#!haskell class Method1 cls m func | cls -> m where method1 :: cls -> m func }}} Which resolves the problem with functional dependencies, but then the line: {{{#!haskell testx x = call (method1 x) $ OneTuple "test" }}} is not allowed anymore, causing a compile error (in both 7.6 and 7.7 versions): {{{ Could not deduce (Method1 cls m func0) arising from the ambiguity check for ‛testx’ from the context (Method1 cls m func, Call (m func) (OneTuple [Char] -> s)) bound by the inferred type for ‛testx’: (Method1 cls m func, Call (m func) (OneTuple [Char] -> s)) => cls -> s at debug.hs:50:1-44 The type variable ‛func0’ is ambiguous When checking that ‛testx’ has the inferred type ‛forall cls (m :: * -> *) func s. (Method1 cls m func, Call (m func) (OneTuple [Char] -> s)) => cls -> s’ Probable cause: the inferred type is ambiguous }}} It is also impossible to solve this issue using type families (as far as I know). If we replace `Method1` type class and instances with following code (or simmilar): {{{#!haskell class Method1 cls m | cls -> m where type Func cls method1 :: cls -> m (Func cls) instance Method1 (Vector a) Vector_testid where type Func (Vector a) = (t1->t1) method1 = (Vector_testid . testid) }}} We would get obvious error `Not in scope: type variable ‛t1’`, because type families does not allow to use types, which does not appear on LHS of type expression. == The final question == How can I make this idea work under GHC 7.7? I know the new `liberal coverage condition` allows GHC devs make some progress with type checking, but it should somehow be doable to port idea working in GHC 7.6 over never compiler version. (without forcing user of my DSL to introduce any further types - everything so far, like type class instances, I'm genarating using Template Haskell) Maybe is there a way to indroduce an extension, which will disable liberal coverage condition in such situations? There is also a StackOverflow discussion available, here: http://stackoverflow.com/questions/20778588/liberal-coverage-condition- introduced-in-ghc-7-7-breaks-code-valid-in-ghc-7-6 [1]: http://en.wikipedia.org/wiki/Domain-specific_language -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8634> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10445: Wrong stack space size when using -Ksize
by GHC 19 Nov '18

19 Nov '18

#10445: Wrong stack space size when using -Ksize -------------------------------------+------------------------------------- Reporter: asr | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.2 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: | -------------------------------------+------------------------------------- After compiling the first example in https://wiki.haskell.org/Performance/Accumulating_parameter: {{{ $ cat Test.hs len :: [a] -> Int len [] = 0 len (x:xs) = len xs + 1 main :: IO () main = print $ len [1..1000000] }}} {{{ $ ghc Test.hs -rtsopts }}} and running {{{ ./Test +RTS -K10K }}} GHC 7.6.3 reports {{{ Stack space overflow: current size 10240 bytes. }}} GHC 7.8.4 reports {{{ Stack space overflow: current size 33632 bytes. }}} and GHC 7.10.1 reports {{{ Stack space overflow: current size 99136 bytes. }}} GHC 7.8.3 and 7.10.1 report an incorrect stack space size. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10445> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10347: Spurious "unused constructor" warning with Coercible
by GHC 19 Nov '18

19 Nov '18

#10347: Spurious "unused constructor" warning with Coercible -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 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: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE RoleAnnotations #-} module Bug (N, twiddle) where import Data.Coerce newtype N a = MkN Int type role N representational twiddle :: N a -> N b twiddle = coerce }}} I get {{{ Bug.hs:7:15: warning: Defined but not used: data constructor ‘MkN’ }}} But the constructor ''is'' used, in order to do the coercion. The role annotation is to force GHC to use the constructor to do the coercion -- otherwise, it might not have. This bug exists in 7.10 and in HEAD. I will fix. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10347> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9207: Detect obvious cases of infinite recursion.
by GHC 18 Nov '18

18 Nov '18

#9207: Detect obvious cases of infinite recursion. --------------------------------------+------------------------------------ Reporter: mrugiero | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: infinite recursion | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: --------------------------------------+------------------------------------ Pure functions are guaranteed to return the same value if the same arguments are used. Because of that, a compiler could be able to detect infinite recursion in the form of a function calling itself with the same arguments (case, some distracted programmer forgot to apply the function tail to a list). The way I see it, one of Haskell's main selling points is that it helps the programmer to avoid sources of bugs as much as it can, and infinite recursion is one of the few that stand unchecked. I specifically point to this example because both, I'm a newbie and made that newbie mistake, and think it shouldn't be hard to implement to the parsing stage of the compiler/interpreter. It probably should throw an error when this happens in pure functions, and maybe an opt-in warning if it happens in monads. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9207> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12906: GHC fails to typecheck Main module without main
by GHC 17 Nov '18

17 Nov '18

#12906: GHC fails to typecheck Main module without main -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given a `Main` module without a `main` value, GHC 8 reports the missing `main` and then exits, without bothering to typecheck the rest of the module. Previous versions, I believe, had the more useful behavior of reporting type errors regardless. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12906> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12525: Internal identifiers creeping into :show bindings
by GHC 17 Nov '18

17 Nov '18

#12525: Internal identifiers creeping into :show bindings -------------------------------------+------------------------------------- Reporter: mniip | Owner: Type: bug | Status: new Priority: low | Milestone: Component: GHCi | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When binding variables the "new" way, or defining typeclasses, some things that are better left unseen manage to creep into the `:show Bindings` list. {{{#!html <pre class="wiki"> GHCi, version 8.1.20160725: http://www.haskell.org/ghc/ :? for help > :show bindings > x = () > :show bindings <b>$trModule :: GHC.Types.Module = _</b> x :: () = _ > class Foo a > :show bindings x :: () = _ class Foo a <b>$tcFoo :: GHC.Types.TyCon = _ $tc'C:Foo :: GHC.Types.TyCon = _ $trModule :: GHC.Types.Module = _</b> </pre> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12525> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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