June 2017 - ghc-tickets

[GHC] #11004: hsc2hs does not handle single quotes properly
by GHC 01 Feb '19

01 Feb '19

#11004: hsc2hs does not handle single quotes properly -------------------------------------+------------------------------------- Reporter: sergv | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: hsc2hs | 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 Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The tool gets confused by quotes for promoted constructors (https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/promotion.h… #promotion-syntax). Here's an example: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} data Foo = Foo | Bar data Indexed ix where Indexed :: Indexed 'Foo main :: IO () main = print $ #size int }}} gets translated into {{{#!hs {-# LINE 1 "Test.hsc" #-} {-# LANGUAGE DataKinds #-} {-# LINE 2 "Test.hsc" #-} {-# LANGUAGE GADTs #-} data Foo = Foo | Bar data Indexed ix where Indexed :: Indexed 'Foo main :: IO () main = print $ #size int }}} Then GHC complains about `#size`: {{{ Test.hsc:10:16: parse error on input ‘#’ }}} Judging from the source of utils/hsc2hs/HSCParser.hs, the tool treats single quotes the same way as double quotes. I.e. it looks for balanced, possibly multiline, strings delimited by '. At least, it seems unnecessary to expect newlines in that string-like structure, because character literals cannot contain newlines, AFAIK. It's interesting to note that this problem looks like a bit of an edge case, since highlighting in the ticket seems to be confused as well. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11004> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 11

[GHC] #13834: Error cascade with type applications
by GHC 01 Feb '19

01 Feb '19

#13834: Error cascade with type applications -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: newcomer, | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Using type applications with an out of scope identifier causes an unfortunate error cascade. {{{ foo = notInScope @Bool }}} Leads to the right out of scope error but also an error about using type application when `notInScope` is not a polytype. I think the second error should be suppressed. {{{ t.hs:4:7: error: Variable not in scope: notInScope | 4 | foo = notInScope @Bool | ^^^^^^^^^^ t.hs:4:7: error: • Cannot apply expression of type ‘t1’ to a visible type argument ‘Bool’ notInScope • In the expression: notInScope @Bool In an equation for ‘foo’: foo = notInScope @Bool | 4 | foo = notInScope @Bool | ^^^^^^^^^^^^^^^^ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13834> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 8

[GHC] #11222: Teach strictness analysis about `catch`-like operations
by GHC 31 Jan '19

31 Jan '19

#11222: Teach strictness analysis about `catch`-like operations -------------------------------------+------------------------------------- Reporter: bgamari | 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: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider the `catch#` primop, {{{#!hs catch# :: (State# RealWorld -> (# State# RealWorld, a #) ) -- ^ thing to catch exceptions from -> (b -> State# RealWorld -> (# State# RealWorld, a #) ) -- ^ exception handler -> State# RealWorld -> (# State# RealWorld, a #) }}} Semantically, this operation will always evaluate its first argument. Ideally we would indicate this in the primop's strictness signature in `primops.txt.pp`. Sadly, we can't do this at the moment due to a subtle wrinkle (discovered in #10712): Consider, {{{#!hs let r = \st -> raiseIO# blah st in catch (\st -> ...(r st)..) handler st }}} If we give the first argument of catch a strict signature, we'll get a demand `C(S)` for `r`; that is, `r` is definitely called with one argument, which indeed it is. The trouble comes when we feed `C(S)` into `r`'s RHS as the demand of the body as this will lead us to conclude that the whole `let` will diverge; clearly this isn't right. As Simon noted in ticket:10712#comment:4, > There's something very special about catch: it turns divergence into non-divergence. In order to apply a proper strictness signature to `catch`-like operations we would need to teach the strictness analyzer about this property. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11222> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 12

[GHC] #12092: Wrong error message with TypeApplications
by GHC 31 Jan '19

31 Jan '19

#12092: Wrong error message with TypeApplications -------------------------------------+------------------------------------- Reporter: kwf | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I write the following: {{{#!hs {-# language TypeApplications #-} module Bug where huh = spam @Int }}} I expect to get the error: {{{ • Variable not in scope: spam • Perhaps you meant ‘span’ (imported from Prelude) }}} But instead, I get the error: {{{ • Cannot apply expression of type ‘t0’ to a visible type argument ‘Int’ • In the expression: spam @Int In an equation for ‘huh’: huh = spam @Int }}} While it is //technically// true that I cannot apply an out-of-scope identifier to a visible type argument, this is probably the less useful error to receive. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12092> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 5

[GHC] #12758: Bring sanity to our performance testsuite
by GHC 28 Jan '19

28 Jan '19

#12758: Bring sanity to our performance testsuite -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Test Suite | 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: -------------------------------------+------------------------------------- The GHC testsuite's performance tests tends to be a constant source of busy-work as it requires that contributors manually bump performance numbers and propagate these changes across platforms. Moreover, the testsuite is poor at noticing performance regressions due to false positive failures (due to spurious environmental differences) and false negatives (due to the rather generous acceptance windows that many tests have). Joachim and I briefly discussed this at Hac Phi and came up with the following proposal: * We rip expected performance numbers out of the `.T` files * -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12758> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 20

[GHC] #13512: GHC incorrectly warns that a variable used in a type application is unused
by GHC 27 Jan '19

27 Jan '19

#13512: GHC incorrectly warns that a variable used in a type application is unused -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This bug is reproducible on GHC 8.0.1, 8.0.2, 8.2, and HEAD. {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeInType #-} {-# OPTIONS_GHC -Wunused-foralls #-} module Bug where import Data.Proxy proxy :: forall k (a :: k). Proxy a proxy = Proxy data SomeProxy where SomeProxy :: forall k (a :: k). Proxy a -> SomeProxy someProxy :: forall k (a :: k). SomeProxy someProxy = SomeProxy (proxy @k @a) }}} {{{ $ /opt/ghc/head/bin/ghci Bug.hs GHCi, version 8.3.20170327: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:17:23: warning: [-Wunused-foralls] Unused quantified type variable ‘(a :: k)’ In the type ‘forall k (a :: k). SomeProxy’ | 17 | someProxy :: forall k (a :: k). SomeProxy | ^^^^^^^^ Ok, modules loaded: Bug. }}} But that `a` is used in `proxy @k @a`! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13512> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 9

[GHC] #9173: Better type error messages
by GHC 27 Jan '19

27 Jan '19

#9173: Better type error messages ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | 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: | ------------------------------------+------------------------------------- Generating better type-error messages is a hoary chestnut, but Herbert brought my attention to [https://pay.reddit.com/r/haskell/comments/26tcrk/curious_with_a_bit_of_begi… this thread on reddit], which has the following idea. At the moment, from {{{ module Foo where addThree = \x -> x + 3 :: Int y = addThree $ Just 5 }}} we get this error: {{{ Foo.hs:2:20 Couldn't match expected type `Int' with actual type `Maybe a0' In the return type of a call of `Just' In the second argument of `($)', namely `Just 5' In the expression: addThree $ Just 5 }}} Maybe we could generate this instead {{{ Foo.hs:2:20 inferred: "Just 5" has type "Maybe a0" expected: second argument of "($)" must have type "Int" in the expression: addThree $ Just 5 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9173> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 37

[GHC] #12364: Demand analysis for sum types
by GHC 25 Jan '19

25 Jan '19

#12364: Demand analysis for sum types -------------------------------------+------------------------------------- Reporter: nomeata | 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: -------------------------------------+------------------------------------- While working on #10613 it crossed my mind that it might be worthwhile to expand the demand type also onto sum types. So instead of {{{ | UProd [ArgUse] -- Product }}} we would have {{{ | UData [[ArgUse]] -- Data type }}} and a function like {{{ fromMaybe :: a -> Maybe a -> b }}} would have a signature of {{{ <1*U><1*U(;1*U)> }}} which indicates that the second argument of `fromMaybe` is evaluated at most once; the first constructor of the result has no arguments, the second (separated by `;`) has one argument which is also used at most once. I could imagine that this gives a lot of useful information with parsers and other code that repeatedly retuns stuff wrapped in a `Maybe` or similar type. Now, sum types are often recursive (`[]`…), and we probably want to be smarter about recursion here. But note that this is not a new problem. If you write {{{ data Stream = Stream Int Stream Stream Stream foo (Stream 0 x y z) = 0 foo (Stream 1 x y z) = foo x foo (Stream 2 x y z) = foo y foo (Stream _ x y z) = foo z }}} you already get huge demand signatures. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12364> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 13

[GHC] #12599: Add Hadrian build artifacts to gitignore
by GHC 25 Jan '19

25 Jan '19

#12599: Add Hadrian build artifacts to gitignore -------------------------------------+------------------------------------- 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: -------------------------------------+------------------------------------- Andrey wrote requesting the following, > For top-level `.gitignore`: > {{{ > # ------------------------------------------------------------------------------------- > # Hadrian's stuff. Note, **/stageN/ folders will be relocated to _build/ after > # resolving https://github.com/snowleopard/hadrian/issues/113 > # ------------------------------------------------------------------------------------- > _build/ > hadrian/ > **/stage?/ > }}} > > For `.gitignore` in affected submodules (array, deepseq, directory, filepath, > hoopl, hpc, process, utils/hsc2hs): > > {{{ > # ------------------------------------------------------------------------------------- > # Hadrian's stuff. Note, stageN/ folders will be relocated to top-level _build/ > # after resolving https://github.com/snowleopard/hadrian/issues/113 > # ------------------------------------------------------------------------------------- > stage?/ > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12599> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 9

[GHC] #9476: Implement late lambda-lifting
by GHC 25 Jan '19

25 Jan '19

#9476: Implement late lambda-lifting -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | 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: | Differential Revisions: -------------------------------------+------------------------------------- This ticket exists to coordinate work on Nick Frisby's '''late lambda- lifting''' optimisation. * Wiki page: [wiki:LateLamLift]. All the details are here. * Branch in GHC repo: `wip/llf` * Related tickets * #9279: local closure remains in final program * #9374: static argument transformation -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9476> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 82