#13499: "Panic: no skolem info" with StaticPointers and typed hole -------------------------------------+------------------------------------- Reporter: Otini | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | StaticPointers, hole, skolem, panic Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): Also happens on HEAD. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13499#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13499: "Panic: no skolem info" with StaticPointers and typed hole -------------------------------------+------------------------------------- Reporter: Otini | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | StaticPointers, TypedHoles Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15035 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: StaticPointers, hole, skolem, panic => StaticPointers, TypedHoles * related: => #15035 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13499#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13499: "Panic: no skolem info" with StaticPointers and typed hole -------------------------------------+------------------------------------- Reporter: Otini | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | StaticPointers, TypedHoles Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15035 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): This bug still reproduces in HEAD, but it's impossible to debug until we solve the perf problem in #14969 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13499#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13499: "Panic: no skolem info" with StaticPointers and typed hole -------------------------------------+------------------------------------- Reporter: Otini | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: | StaticPointers, TypedHoles Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15035 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Thanks Ryan. I know what is happening here. Here's the code for typechecking `static e` {{{ tcExpr (HsStatic fvs expr) res_ty = do { res_ty <- expTypeToType res_ty ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty ; (expr', lie) <- captureConstraints $ addErrCtxt (hang (text "In the body of a static form:") 2 (ppr expr) ) $ tcPolyExprNC expr expr_ty -- Check that the free variables of the static form are closed. -- It's OK to use nonDetEltsUniqSet here as the only side effects of -- checkClosedInStaticForm are error messages. ; mapM_ checkClosedInStaticForm $ nonDetEltsUniqSet fvs -- Require the type of the argument to be Typeable. -- The evidence is not used, but asking the constraint ensures that -- the current implementation is as restrictive as future versions -- of the StaticPointers extension. ; typeableClass <- tcLookupClass typeableClassName ; _ <- emitWantedEvVar StaticOrigin $ mkTyConApp (classTyCon typeableClass) [liftedTypeKind, expr_ty] -- Insert the constraints of the static form in a global list for later -- validation. ; emitStaticConstraints lie -- Wrap the static form with the 'fromStaticPtr' call. ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty ; let wrap = mkWpTyApps [expr_ty] ; loc <- getSrcSpanM ; return $ mkHsWrapCo co $ HsApp noExt (L loc $ mkHsWrap wrap fromStaticPtr) (L loc (HsStatic fvs expr')) } }}} Notice that the constraints arising from `e` are captured as `lie`, and given to `emitStaticConstraints`, which puts them in a top-level bag of consraints. The idea is that we should not be using any local (dynamic) givens in a `static` construct. But in doing so, we also put those coustraints outside the scope of any skolems, in this case the `a`. So we end up with a constraint like {{{ wanted = WC {wc_simple = [WD] __a1hn {0}:: t_a1hm[tau:2] (CHoleCan: ExprHole(_)) wc_impl = Implic { TcLevel = 2 Skolems = a_a1hi[sk:2] No-eqs = False Status = Unsolved Given = $dTypeable_a1hk :: Typeable a_a1hi[sk:2] Wanted = WC {wc_simple = [WD] $dTypeable_a1ho {0}:: Typeable (a_a1hi[sk:2] -> a_a1hi[sk:2]) (CNonCanonical) [WD] $dIsStatic_a1hv {0}:: GHC.StaticPtr.IsStatic StaticPtr (CNonCanonical)} Binds = EvBindsVar<a1hw> Needed inner = [] Needed outer = [] the type signature for: f :: forall a. Typeable a => StaticPtr (a -> a) }} }}} Notice that `CHoleCan` outside the scope of the implication. This all smells wrong, but I don't immediately know how to fix it. We want the constraints from `e` to be inside an implication shorn of any givens, and that's not very easy to do. The story for `static` and constraints, or even polymorphism, is is not well worked out. Even top-level values with type `forall a. Static (a->a)` is suspiciuos, although useful. So rather than trying some kluge to fix it I think I'll leave the embarrassing crash as an inceniive to work out what the Right Thing might be. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13499#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler