May 2016 - ghc-tickets

[GHC] #11099: Incorrect warning about redundant constraints
by GHC 12 May '16

12 May '16

#11099: Incorrect warning about redundant constraints -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 (Type checker) | 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 following program results in an incorrect warning about a redundant constraint: {{{ {-# LANGUAGE TypeFamilies #-} type family SomeFun a f :: (SomeFun i ~ [a], Read a) => proxy i -> a f _ = read "HELLO" }}} This is the warning: {{{ Redundant constraint: SomeFun i ~ [a] In the type signature for: f :: (SomeFun i ~ [a], Read a) => proxy i -> a }}} I tried it on GHC version 7.11.20151029 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11099> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12046: AllowAmbiguousTypes doesn't work with UndecidableSuperClasses
by GHC 12 May '16

12 May '16

#12046: AllowAmbiguousTypes doesn't work with UndecidableSuperClasses -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc3 (Type checker) | 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: -------------------------------------+------------------------------------- Given the code below, `test1` and `test2` are the same except the former has an ambiguous type and the latter does not. The compiler rejects the former and accepts the latter. {{{ {-# LANGUAGE UndecidableSuperClasses #-} {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE TypeFamilies #-} class A (T a) => A a where type T a test1 :: forall a. A a => () test1 = () test2 :: A a => proxy a -> () test2 _ = () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12046> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4239: -ddump-minimal-imports vs. type operators
by GHC 11 May '16

11 May '16

#4239: -ddump-minimal-imports vs. type operators -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: T4239 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by mpickering): * keywords: => newcomer -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4239#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4239: -ddump-minimal-imports vs. type operators
by GHC 11 May '16

11 May '16

#4239: -ddump-minimal-imports vs. type operators -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: T4239 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dsf): * status: closed => new * version: 6.12.1 => 7.10.3 * resolution: fixed => * milestone: 7.4.1 => Comment: There is still at least one case where this is still happening - the operator · (char 183) comes out without parens: {{{#!hs module Test ((·), (⊃)) where (·) = undefined (⊃) = undefined }}} {{{#!hs module Test2 ((·), (⊃)) where import Test ((·), (⊃)) }}} -ddump-minimal-imports outputs this for Test2: {{{#!hs import Test ( ·, (⊃) ) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4239#comment:6> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10181: Lint check: arity invariant
by GHC 11 May '16

11 May '16

#10181: Lint check: arity invariant -------------------------------------+------------------------------------- Reporter: nomeata | Owner: nomeata Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The Arity of an ID should not exceed the arity of its type, nor the arity of its strictness signature, if it is a bottoming signatures. This should be checked by a lint check (suggested by SPJ in https://phabricator.haskell.org/D747?id=2498#inline-6058) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10181> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4012: Compilation results are not deterministic
by GHC 11 May '16

11 May '16

#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: 11362 | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, | Phab:D1268, Phab:D1360, Phab:D1373, Wiki Page: | Phab:D1396, Phab:D1457, Phab:D1468, DeterministicBuilds | Phab:D1487, Phab:D1504, Phab:D1508 -------------------------------------+------------------------------------- Comment (by Bartosz Nitka <niteria@…>): In [changeset:"0e719885f53e20f2e14a94b32d858b47b516a8fc/ghc" 0e719885/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="0e719885f53e20f2e14a94b32d858b47b516a8fc" Remove some varSetElems in dsCmdStmt varSetElems introduces unnecessary determinism and it's easy to preserve determinism here. Test Plan: ./validate Reviewers: goldfire, simonmar, austin, bgamari, simonpj Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2195 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:163> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4012: Compilation results are not deterministic
by GHC 11 May '16

11 May '16

#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: 11362 | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, | Phab:D1268, Phab:D1360, Phab:D1373, Wiki Page: | Phab:D1396, Phab:D1457, Phab:D1468, DeterministicBuilds | Phab:D1487, Phab:D1504, Phab:D1508 -------------------------------------+------------------------------------- Comment (by Bartosz Nitka <niteria@…>): In [changeset:"3edbd091341ab0ab60862ba18d3107f34c7fc876/ghc" 3edbd09/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="3edbd091341ab0ab60862ba18d3107f34c7fc876" Document SCC determinism I've documented the guarantees that stronglyConnCompFromEdgedVertices provides and commented on the call sites to explain why they are OK from determinism standpoint. I've changed the functions to nonDetUFM versions, so that it's explicit they could introduce nondeterminism. I haven't defined container (VarSet, NameSet) specific versions, so that we have less functions to worry about. Test Plan: this is mostly just documentation, it should have no runtime effect Reviewers: bgamari, simonmar, austin, simonpj Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2194 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:164> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11746: I encountered an: internal error: evacuate: strange closure type 803645000
by GHC 11 May '16

11 May '16

#11746: I encountered an: internal error: evacuate: strange closure type 803645000 --------------------------------------+------------------------------- Reporter: hkBst | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: GHCi crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+------------------------------- I encountered an: internal error: evacuate: strange closure type 803645000 after loading and running the attached code under GHCi. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11746> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4012: Compilation results are not deterministic
by GHC 11 May '16

11 May '16

#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: 11362 | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, | Phab:D1268, Phab:D1360, Phab:D1373, Wiki Page: | Phab:D1396, Phab:D1457, Phab:D1468, DeterministicBuilds | Phab:D1487, Phab:D1504, Phab:D1508 -------------------------------------+------------------------------------- Comment (by Bartosz Nitka <niteria@…>): In [changeset:"8669c48d06ca260c13740e0bda97beea52d332fb/ghc" 8669c48/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="8669c48d06ca260c13740e0bda97beea52d332fb" Document why closeOverKind is OK for determinism There's no point in converting the existing call sites to use deterministic closeOverKinds if they never linearize the set. Test Plan: it compiles, this is basically just documentation Reviewers: simonpj, goldfire, simonmar, austin, bgamari Reviewed By: bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2191 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:162> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so.
by GHC 10 May '16

10 May '16

#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving, | newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D978 Wiki Page: | -------------------------------------+------------------------------------- Description changed by osa1: @@ -1,34 +1,10 @@ - mpickering reminded me this ticket so before I leave the ownership of this - ticket let me write down the current status: - - Basically there are a couple of things we can do and we just need someone - to - decide which one. - - 1. Implement {{{==}}} as {{{_ == _ = True}}}. Pro: this is consistent with - {{{Void}}}'s {{{Eq}}} instance. Con: I think this lets some bugs to sneak - in. I think it doesn't make sense to compute things based on equality of - empty types, so at this point you've probably made a mistake and it's - better to just bail out. - - 2. Implement {{{==}}} as `x == y = case x of {}`. Pro: it fixes the - problem with (1) and in a good way - you've probably used something like - {{{error "..."}}} for the empty type terms, so you get your error message. - Con: this inconsistent with {{{Void}}}. - - 3. Leave this as is - no {{{deriving (Eq)}}}. This way we make the user - decide which behaviour to have. Pro: You can have whatever you want. Con: - Inconvenient. - - These were also discussed at some point but IIRC most people agree that - these - are bad ideas: - - 4. {{{x == y = error "(==) on empty type"}}}: If it's going to fail it's - better to fail like (2). - - 5. {{{_ == _ = False}}}: Denotationally / type-theoretically bottoms are - equal or something like that? So it's better to implement (1) instead. - - 6. Implement (2), change {{{Void}}}s instance too: Can potentially break - code. + On a "phantom datatype" D, one gets the message: + {{{ + Can't make a derived instance of `Eq D': + `D' must have at least one data constructor + }}} + However there is a trivial, correct instance of Eq D: + {{{ + instance Eq D where + (==) = undefined + }}} New description: On a "phantom datatype" D, one gets the message: {{{ Can't make a derived instance of `Eq D': `D' must have at least one data constructor }}} However there is a trivial, correct instance of Eq D: {{{ instance Eq D where (==) = undefined }}} -- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:47> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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