Re: [GHC] #15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar"

#15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar" -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: | QuantifiedConstraints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: quantified- | constraints/T15290, T15290a Blocked By: | Blocking: 9123 Related Tickets: | Differential Rev(s): Phab:D4895 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): OK, this commit fixes the problem reported in comment:22, and adds the code there as a regression test. This is the ''third'' separate bug exposed by the original bug report. Wow. {{{ commit 261dd83cacec71edd551e9c581d05285c9ea3226 Author: Simon Peyton Jones Date: Mon Jun 25 17:42:57 2018 +0100 Fix TcLevel manipulation in TcDerivInfer.simplifyDeriv The level numbers we were getting simply didn't obey the invariant (ImplicInv) in TcType Note [TcLevel and untouchable type variables] That leads to chaos. Easy to fix. I improved the documentation. I also added an assertion in TcSimplify that checks that level numbers go up by 1 as we dive inside implications, so that we catch the problem at source rather than than through its obscure consequences. That in turn showed up that TcRules was also generating constraints that didn't obey (ImplicInv), so I fixed that too. I have no idea what consequences were lurking behing that bug, but anyway now it's fixed. Hooray. }}} Are we done now? (Once Ryan has committed the stuff in comment:31.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15290#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler