May 2016 - ghc-tickets

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: | -------------------------------------+------------------------------------- Changes (by osa1): * owner: osa1 => @@ -1,10 +1,34 @@ - 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 - }}} + 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. New description: 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. -- Comment: 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. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7401#comment:46> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

Re: [GHC] #4806: Make error message more user friendly when module is not found because package is unusable
by GHC 10 May '16

10 May '16

#4806: Make error message more user friendly when module is not found because package is unusable -------------------------------------+------------------------------------- Reporter: mitar | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by mpickering): * owner: lstrano => Comment: Please reassign if you still plan to work on this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

Re: [GHC] #4012: Compilation results are not deterministic
by GHC 10 May '16

10 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:"7e28e47ca36e849ed104f5a13e0c08253b135fae/ghc" 7e28e47/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="7e28e47ca36e849ed104f5a13e0c08253b135fae" Get rid of Traversable UniqFM and Foldable UniqFM Both Traversable and Foldable can introduce non-determinism and because of typeclass overloading it's implicit and not obvious at the call site. This removes the instances, so that they can't accidentally be used. Test Plan: ./validate Reviewers: austin, goldfire, bgamari, simonmar, simonpj Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2190 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:161> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

[GHC] #9478: Partial type signatures
by GHC 10 May '16

10 May '16

#9478: Partial type signatures -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | 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: Phab:D168 -------------------------------------+------------------------------------- This ticket tracks progress on '''partial type signatures'''. * Wiki page [wiki:PartialTypeSignatures] * Phabricator link: Phab:D168 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9478> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 10

Re: [GHC] #4012: Compilation results are not deterministic
by GHC 10 May '16

10 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:"b58b0e18a568bbf6381a85eea7adc72679355671/ghc" b58b0e1/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="b58b0e18a568bbf6381a85eea7adc72679355671" Make simplifyInstanceContexts deterministic simplifyInstanceContexts used cmpType which is nondeterministic for canonicalising typeclass constraints in derived instances. Following changes make it deterministic as explained by the Note [Deterministic simplifyInstanceContexts]. Test Plan: ./validate Reviewers: simonmar, goldfire, simonpj, austin, bgamari Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2173 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:160> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

Re: [GHC] #4012: Compilation results are not deterministic
by GHC 10 May '16

10 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:"4ac0e815739f6362c2815dd3ae531055a095d6a9/ghc" 4ac0e81/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="4ac0e815739f6362c2815dd3ae531055a095d6a9" Kill unnecessary cmpType in lhs_cmp_type This is the only call site of `lhs_cmp_type` and we only care about equality. `cmpType` is nondeterministic (because `TyCon`s are compared with Uniques in `cmpTc`), so if we don't have to use it, it's better not to. Test Plan: ./validate Reviewers: simonmar, goldfire, bgamari, austin, simonpj Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2172 GHC Trac Issues: #4012 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:159> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

[GHC] #11432: Cannot export operator newtype
by GHC 10 May '16

10 May '16

#11432: Cannot export operator newtype -------------------------------------+------------------------------------- Reporter: phadej | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc1 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: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE TypeOperators #-} module Main (main, (-.->)(..)) where main :: IO () main = return () newtype (f -.-> g) a = Fn { apFn :: f a -> g a } }}} Fails to compile with {{{ [1 of 1] Compiling Main ( fn.hs, interpreted ) fn.hs:2:20: error: Not in scope: ‘-.->’ fn.hs:2:20: error: The export item ‘(-.->)(..)’ attempts to export constructors or class methods that are not visible here }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11432> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 34

[GHC] #11961: PatBind test suite failure with `-DDEBUG`
by GHC 10 May '16

10 May '16

#11961: PatBind test suite failure with `-DDEBUG` -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: high | 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: -------------------------------------+------------------------------------- I get {{{ Compile failed (status 256) errors were: ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160420 for x86_64-unknown-linux): ASSERT failed! CallStack (from HasCallStack): assertPprPanic, called at compiler/types/TyCoRep.hs:2082:56 in ghc:TyCoRep checkValidSubst, called at compiler/types/TyCoRep.hs:2118:17 in ghc:TyCoRep substTy, called at compiler/types/TyCoRep.hs:2060:3 in ghc:TyCoRep in_scope InScope {a_apN t_apW a_apX} tenv [apC :-> t_apW[tau:3], apN :-> a_apX[tau:3]] tenvFVs [apD :-> t_apD[tau:3], apW :-> t_apW[tau:3], apX :-> a_apX[tau:3]] cenv [] cenvFVs [] tys [a_apN[sk] -> a_apN[sk]] cos [] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for PatBind(normal) }}} with a `-DDEBUG` build, e.g. on travis: https://s3.amazonaws.com/archive .travis-ci.org/jobs/124426776/log.txt -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11961> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 2

Re: [GHC] #6118: Kind variable falls out of scope in instance declaration
by GHC 09 May '16

09 May '16

#6118: Kind variable falls out of scope in instance declaration -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.5 Resolution: fixed | Keywords: PolyKinds Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | polykinds/T6118 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): 8.1.20160503: {{{#!hs -- twgv.hs:32:3-43: error: … -- The RHS of an associated type declaration mentions ‘k’ -- All such variables must be bound on the LHS -- Compilation failed. instance SingE (a :: Maybe k) where type Demote a = Maybe (Demote (Any :: k)) }}} Still fails, kind annotation needed: {{{#!hs instance SingE (a :: Maybe k) where type Demote (a ::Maybe k) = Maybe (Demote (Any :: k)) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6118#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0

Re: [GHC] #7100: Loosen requirement for free variables in constraint in class declaration
by GHC 09 May '16

09 May '16

#7100: Loosen requirement for free variables in constraint in class declaration -------------------------------------+------------------------------------- Reporter: selinger | Owner: Type: feature request | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.4.2 Resolution: wontfix | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by Iceland_jack): * cc: Iceland_jack (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7100#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 0