#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | PolyKinds Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * priority: normal => high * failure: None/Unknown => Compile-time performance bug * milestone: => 8.4.1 Comment: This is a regression from GHC 8.0.2, which simply gives an error message: {{{ $ /opt/ghc/8.0.2/bin/ghci Bug3.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug3.hs, interpreted ) Bug3.hs:31:12: error: • Expected kind ‘k ~> k’, but ‘IddSym0’ has kind ‘Type ~> Type’ • In the first argument of ‘Dom’, namely ‘(IddSym0 :: Type ~> Type)’ In the type instance declaration for ‘Dom’ In the instance declaration for ‘Varpi (IddSym0 :: k ~> k)’ }}} This bug first appeared in commit b207b536ded40156f9adb168565ca78e1eef2c74 (`Generalize kind of the (->) tycon`). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | PolyKinds Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Alright, with `master` `-ddump-tc-trace` is a bit more useful. While looping it appears to dump {{{ Start solver pipeline { work item = [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) inerts = {Equalities: [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (TYPE q_a20F[tau:1] :: *) (CTyEqCan) [W] hole{a20K} {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) [W] hole{a20M} {1}:: (k_aWv :: *) GHC.Prim.~# (TYPE q_a20F[tau:1] :: *) (CTyEqCan) Unsolved goals = 2} rest of worklist = WL {Eqs = [WD] hole{a20I} {0}:: (TYPE r_a20G[tau:1] :: *) GHC.Prim.~# (k_aWv :: *) (CNonCanonical)} runStage canonicalization { workitem = [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) can_eq_nc False [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) nominal equality k_aWv k_aWv * * can_eq_nc False [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) nominal equality k_aWv k_aWv * * flatten { FM_FlattenAll k_aWv flatten } k_aWv flatten { FM_FlattenAll * flatten } * can_eq_nc True [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) nominal equality k_aWv k_aWv * * end stage canonicalization } runStage interact with inerts { workitem = [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) Can't solve tyvar equality LHS: k_aWv :: * RHS: * :: * addInertEq { Adding new inert equality: [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) Kick out, tv = k_aWv n-kicked = 1 kicked_out = WL {Eqs = [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (TYPE q_a20F[tau:1] :: *) (CTyEqCan)} Residual inerts = {Equalities: [W] hole{a20K} {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) (CTyEqCan) [W] hole{a20M} {1}:: (k_aWv :: *) GHC.Prim.~# (TYPE q_a20F[tau:1] :: *) (CTyEqCan) Unsolved goals = 2} addInertEq } end stage interact with inerts } Step 3424[l:1,d:1] Kept as inert: [D] _ {1}:: (k_aWv :: *) GHC.Prim.~# (* :: *) End solver pipeline (discharged) } ----------------------------- }}} In particular, unless I've misunderstood something, this strikes me as quite odd, {{{ Can't solve tyvar equality LHS: k_aWv :: * RHS: * :: * }}} There's no sign that `k_aWv` is a skolem so why is the solver not simply instantiating it at `*`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | PolyKinds Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): OK -- I'll take a look in due course. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | PolyKinds Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"0a85190312a1de3d300912051309b94589c08683/ghc" 0a851903/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="0a85190312a1de3d300912051309b94589c08683" Fix a TyVar bug in the flattener A year ago I gave up on trying to rigorously separate TyVars from TcTyVars, and instead allowed TyVars to appear rather more freely in types examined by the constraint solver: commit 18d0bdd3848201882bae167e3b15fd797d217e93 Author: Simon Peyton Jones Date: Wed Nov 23 16:00:00 2016 +0000 Allow TyVars in TcTypes See Note [TcTyVars in the typechecker] in TcType. However, TcFlatten.flatten_tyvar1 turned out to treat a TyVar specially, and implicitly assumed that it could not have an equality constraint in the inert set. Wrong! This caused Trac #14450. Fortunately it is easily fixed, by deleting code. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: closed Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: fixed | Keywords: TypeInType, | PolyKinds Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: performance bug | polykinds/T14450 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Is this an instance of the same bug? Loops on 8.3.20170920 and 8.2 {{{#!hs {-# Language KindSignatures, TypeOperators, PolyKinds, DataKinds, TypeInType, TypeFamilies, AllowAmbiguousTypes #-} import Data.Kind type a-->b = (a, b) -> Type type Cat k = k -> k -> Type class F (f::k-->k') where type D f :: Cat k type C f :: Cat k' f :: D f a a' -> C d (App f a) (App f a') data DupSym0 :: a --> (a, a) type family App (f::a-->b) (x::a) :: b where App DupSym0 a = '(a, a) instance F DupSym0 where type D DupSym0 = (->) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler