#12746: Assertion failed with BuildFlavour = devel2 (one more) -------------------------------------+------------------------------------- Reporter: pacak | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Affected versions: ghc 8.0.1 and ghc git master as of 21 Oct 2016 (c23dc61) It compiles fine on first time but fails to compile on second attempt. Using -fforce-recomp recompiles both files and bug is not triggered. {{{ % ls A.hs B.hs % cat A.hs }}} {{{#!hs module A where import B foo a = case a of Foo -> True _ -> False }}} {{{ % cat B.hs }}} {{{#!hs {-# LANGUAGE PatternSynonyms, ScopedTypeVariables #-} module B where pattern Foo = 0x00000001 :: Int }}} {{{ % ghc -O2 A.hs ; touch A.hs ; ghc -O2 A.hs [1 of 2] Compiling B ( B.hs, B.o ) [2 of 2] Compiling A ( A.hs, A.o ) [2 of 2] 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/iface/BuildTyCl.hs:195:404 in ghc:BuildTyCl [] ~ [] [] ~ [] Int ~ Int [] ~ [] [] ~ [] [] ~ [Void#] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12746 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler