Hmm. Yes, this is an (actually harmless) assertion failure if your build has -DDEBUG on. I think it’s just a fluke that it’s only just started failing. I’ll make a ticket for it; I don’t think it’s super-urgent. Simon From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Simon Marlow Sent: 09 November 2016 13:03 To: ghc-devs@haskell.org Subject: T12041 failing? I just saw the error below in a validate with -DDEBUG. Anyone know about this? --- /tmp/ghctest-uhJ8rt/test spaces/./indexed-types/should_fail/T12041.run/T12041.stderr.normalised 2016-11-09 12:13:38.206501840 +0000 +++ /tmp/ghctest-uhJ8rt/test spaces/./indexed-types/should_fail/T12041.run/T12041.comp.stderr.normalised 2016-11-09 12:13:38.206501840 +0000 @@ -1,7 +1,17 @@ +ghc: panic! (the 'impossible' happened) + (GHC version 8.1.20161109 for x86_64-unknown-linux): + ASSERT failed! + i_axb + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcType.hs:<line>:<column> in <package-id>:TcType + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + pprPanic, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcType.hs:<line>:<column> in <package-id>:TcType -T12041.hs:12:15: - Expected kind ‘i -> Constraint’, - but ‘(~) Int’ has kind ‘* -> Constraint’ - In the type ‘(~) Int’ - In the type instance declaration for ‘Ob’ - In the instance declaration for ‘Category I’ +Please report this as a GHC bug: http://www.haskell.org/ghc/reportabughttps://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.haskell.org%2Fghc%2Freportabug&data=02%7C01%7Csimonpj%40microsoft.com%7C8af7a5deff5f49d2ab9808d408a0bd62%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636142933860965747&sdata=BUkCjhjy1GhK9SVcws2TAYIVD5FzdsYrXKciuyD6MzM%3D&reserved=0 *** unexpected failure for T12041(normal)