#12630: Assertion failed with BuildFlavour = devel2 -------------------------------------+------------------------------------- Reporter: pacak | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I tried to reproduce random ghc panic we have in our codebase with ghc8 so I decided to compile ghc with debug enabled. Source file: ghc-8.0.1-src.tar.xz build.mk changes: {{{ BuildFlavour = devel2 GhcStage1HcOpts = -DDEBUG GhcStage2HcOpts = -DDEBUG }}} source: {{{#!hs {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE PolyKinds #-} module A where import GHC.Generics class B f where b :: [f a] toEnumDefault :: (B (Rep a)) => Int -> a toEnumDefault i = let l = b in to }}} result: {{{ [1 of 1] Compiling A ( a.hs, a.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): ASSERT failed! CallStack (from HasCallStack): assertPprPanic, called at compiler/types/TyCoRep.hs:1974:56 in ghc:TyCoRep checkValidSubst, called at compiler/types/TyCoRep.hs:2010:17 in ghc:TyCoRep substTy, called at compiler/types/TyCoRep.hs:1952:3 in ghc:TyCoRep in_scope InScope [a1BD :-> a_a1BD[sk], a1BI :-> k_a1BI[tau:3], a1BJ :-> f_a1BJ[tau:3], a1BL :-> a_a1BL[sk]] tenv [a1BD :-> a_a1BL[sk]] tenvFVs [a1Bz :-> k_a1Bz[tau:5], a1BL :-> a_a1BL[sk]] cenv [] cenvFVs [] tys [[f_a1BJ[tau:3] a_a1BD[sk]]] cos [] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12630 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler