February 2017 - ghc-tickets

[GHC] #12619: Allow users guide to be built independently from GHC
by GHC 20 Mar '18

20 Mar '18

#12619: Allow users guide to be built independently from GHC -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | 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: -------------------------------------+------------------------------------- At HIW 2016 it was suggested that this would greatly reduce the friction to contributing users guide fixes. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12619> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12389: Limit duplicate export warnings for datatypes
by GHC 20 Mar '18

20 Mar '18

#12389: Limit duplicate export warnings for datatypes -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: #11959 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `containers` sometimes exports data constructors/patterns conditionally (depending on GHC version and whether `TESTING` is defined). Presently, to avoid a duplicate export warning, it's necessary to write a separate export line for each combination of exported constructors, which is horrible: {{{#!hs module Foo ( #ifdef TESTING #ifdef USE_PATTERN_SYNONYMS Foo (Foo, Pat1, Pat2) #else Foo (Foo) #endif #elif USE_PATTERN_SYNONYMS Foo (Pat1, Pat2) #else Foo #endif }}} or to break up the lines with CPP, which is so horrible I can't even bring myself to write it. I'd much rather be able to write {{{#!hs module Foo ( Foo #ifdef TESTING ,Foo(Foo) #endif #ifdef USE_PATTERN_SYNONYMS ,Foo(Pat1, Pat2) #endif ) }}} The trouble here is that GHC warns about duplicate export of the type `Foo`. I think there's a pretty simple partial solution: only warn about a type export that is *completely* redundant, adding neither type constructor nor pattern. And offer a way to turn off the redundant export warning entirely for types and classes without turning it off for bindings. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12389> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10774: Use `Natural` rather than `Integer` in `GHC.TypeLits`
by GHC 19 Mar '18

19 Mar '18

#10774: Use `Natural` rather than `Integer` in `GHC.TypeLits` -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: | Version: 7.10.2 libraries/base | Keywords: TypeLits | Operating System: Unknown/Multiple Natural | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- When the numeric type-literals were implement via `GHC.TypeLits` there was no `Natural` type in `base` yet. But since GHC 7.10 we finally have `Natural` available in base! Specifically, the following 3 type-signatures in `GHC.TypeLits` cpmtaom `Integer` that ought rather be `Natural`s: {{{#!hs someNatVal :: Integer -> Maybe SomeNat natVal :: forall n proxy. KnownNat n => proxy n -> Integer natVal' :: forall n. KnownNat n => Proxy# n -> Integer }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10774> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9671: Allow expressions in patterns
by GHC 17 Mar '18

17 Mar '18

#9671: Allow expressions in patterns -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: Keywords: patterns, pattern | Operating System: synonyms | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I've outlined a proposal for extending pattern synonyms to depend on terms (PatternFamilies), the name is less than ideal but I'll keep the page under that name for now. The proposal's introduction has been rewritten. The simplest use case are patterns that matches only when a set contains an element (`IsMember`) or when a set does not contain an element (`NotMember`): [[Image(wiki:PatternFamilies:member.png)]] {{{#!hs hasKeys :: Set Item -> IO () hasKeys (IsMember "keys") = leaveHouse hasKeys (NotMember "keys") = findKeys >> leaveHouse }}} or a pattern that matches a map if the key exists: [[Image(wiki:PatternFamilies:lookup.png)]] used like this: {{{#!hs age :: Map Person Age -> String age (Lookup "Alice" 60) = "Alice is 60 years old!" age (Lookup "Alice" age) = "Alice is " ++ show age ++ "." age (Lookup "Bob" _) = "No info on Alice but we know how old Bob is." age _ = "..." }}} Further details and examples can be found here: PatternFamilies, I discussed it with several people ICFP 2014. This would not require a new extension but would extend PatternSynonyms. This feature can be quite useful, especially when working with deeply nested structures (ASTs, JSON, XML, ...). If people are fine with it I will implement it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9671> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11312: GHC inlining primitive string literals can affect program output
by GHC 14 Mar '18

14 Mar '18

#11312: GHC inlining primitive string literals can affect program output -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: #11292 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- First noted in #11292, this program, when compiled with `-O1` or higher: {{{#!hs {-# LANGUAGE MagicHash #-} module Main (main) where import GHC.Exts (Addr#, isTrue#) import GHC.Prim (eqAddr#) data A = A { runA :: Addr# } a :: A a = A "a"# main :: IO () main = print (isTrue# (eqAddr# (runA a) (runA a))) }}} will result in the following after inlining: {{{ Main.main2 = case GHC.Prim.tagToEnum# @ GHC.Types.Bool (GHC.Prim.eqAddr# "a"# "a"#) of _ [Occ=Dead] { GHC.Types.False -> GHC.Show.shows26; GHC.Types.True -> GHC.Show.shows24 } }}} As a result, there are two of the same string constant with different addresses, which causes `eqAddr#` to return `False`. If compiled without optimizations, `"a"#` is not inlined, and as a result, `eqAddr#` returns `True`. Two questions: 1. Is this okay semantics-wise? Or is this a necessary risk when working with primitive string literals, and should programmers judiciously use `{-# NOINLINE #-}` with them? 2. Is this okay from a code duplication standpoint? As Reid Barton noted in #11292, `"a"#` is duplicated due to inlining. In this example, not much is duplicated, but if it were a longer string constant, that could result in a noticeable increase in the object file size. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11312> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8542: Suggest NegativeLiterals
by GHC 14 Mar '18

14 Mar '18

#8542: Suggest NegativeLiterals ------------------------------------+------------------------------------- Reporter: monoidal | 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: | ------------------------------------+------------------------------------- If we write -128 :: Int8, we get a useful warning (#7895), but it would be even better to suggest NegativeLiterals. Patch incoming. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8542> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13257: out-of-range warnings for negative literals, without -XNegativeLiterals
by GHC 13 Mar '18

13 Mar '18

#13257: out-of-range warnings for negative literals, without -XNegativeLiterals -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- By default (without `NegativeLiterals`) a negated literal `-1` is desugared as `negate (fromInteger 1)`. Hence the existing out-of-range literal warning doesn't trigger for `-1 :: Word`. But we could also recognize the pattern `negate (fromInteger lit)`, and give a warning when `-lit` is out-of-range (for `Word`, this is whenever `lit` is positive). Actually this could apply to signed integer types too: if we recognized `negate (fromInteger lit)` in preference to `fromInteger lit`, we could correctly not warn about `-128 :: Int8`, even when `NegativeLiterals` is not enabled. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13257> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12959: GHC doesn't warn about missing implementations for class methods beginning with an underscore
by GHC 09 Mar '18

09 Mar '18

#12959: GHC doesn't warn about missing implementations for class methods beginning with an underscore -------------------------------------+------------------------------------- Reporter: RyanGlScott | 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: -------------------------------------+------------------------------------- This code compiles without any warnings! {{{#!hs {-# OPTIONS_GHC -Wmissing-methods #-} module Bug where class Foo a where _Bar :: a -> Int instance Foo Int }}} This code, however, //does// emit a warning: {{{#!hs {-# OPTIONS_GHC -Wmissing-methods #-} module Warns where class Foo a where bBar :: a -> Int instance Foo Int }}} {{{ Bug.hs:7:10: warning: [-Wmissing-methods] • No explicit implementation for ‘bBar’ • In the instance declaration for ‘Foo Int’ }}} The only difference is in the name of the class method of `Foo`. Namely, when a class method is prefixed with an underscore, GHC seems to look the other way when checking if any instances are missing an implementation of it. I'd argue that this behavior is incorrect, since I can't envision any scenario in which you'd want the compiler //not// to warn you about missing method implementations (as opposed to, say, not warning about an unused record selector). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12959> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11330: Test `dynamic-paper` fails with core lint error (hpc) and "Simplifier ticks exhausted" (optasm)
by GHC 07 Mar '18

07 Mar '18

#11330: Test `dynamic-paper` fails with core lint error (hpc) and "Simplifier ticks exhausted" (optasm) -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.11 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: -------------------------------------+------------------------------------- {{{ $ ghc-head --info | grep Project [("Project name","The Glorious Glasgow Haskell Compilation System") ,("Project version","8.1.20151231") ,("Project Git commit id","8afeaad919dc67643b4eff14efafb48b59039b2b") }}} {{{ $ make slowtest TEST=dynamic-paper VERBOSE=2 TEST_HC=ghc-head ... =====> dynamic-paper(normal) 1 of 1 [0, 0, 0] =====> dynamic-paper(hpc) 1 of 1 [0, 0, 0] ... Compile failed (status 256) errors were: *** Core Lint errors : in result of Float out(FOS {Lam = Just 0, Consts = True, OverSatApps = True}) *** <no location info>: warning: In a case alternative: (TypeRepX k_s7Ec :: *, a_s7Ed :: k_a5px, tr2_s7Ee :: TypeRep a_s7Ed) @ k_a5px is out of scope *** Offending Program *** ... <no location info>: error: Compilation had errors *** unexpected failure for dynamic-paper(hpc) =====> dynamic-paper(optasm) 1 of 1 [0, 1, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone delta1 To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 203160 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for dynamic-paper(optasm) Unexpected results from: TEST="dynamic-paper" }}} This test was added in commit 52da6bdc17bb491d6d2f462b3680eb44b9be92e5: {{{ Author: Richard Eisenberg <eir(a)cis.upenn.edu> Date: Sat Dec 26 09:11:33 2015 -0500 Have mkCastTy look more closely for reflexivity. This may have performance implications. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11330> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12506: Compile time regression in GHC 8.
by GHC 07 Mar '18

07 Mar '18

#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: 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: -------------------------------------+------------------------------------- This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs) the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which about for installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install fltkhs` - At the root of the repo do `cabal build fltkhs-fluid-tree` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12506> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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