#12785: GHC panic, `tcTyVarDetails` is missing a case -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: yes Blocked By: | Blocking: Related Tickets: #12590 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: simonpj (added) Comment: That patch did fix building the program in comment:7, FWIW. Also, I found out that Simon's commit a0899b2f66a4102a7cf21569889381446ce63833 caused the regression: {{{ From a0899b2f66a4102a7cf21569889381446ce63833 Mon Sep 17 00:00:00 2001 From: Simon Peyton Jones <simonpj@microsoft.com> Date: Tue, 1 Mar 2016 17:05:56 +0000 Subject: [PATCH] Remove unnecessary isTyVar tests in TcType These extra tests were added by Richard when he had CoVars floating around in places where previously only TyVars had been. But fortunately those days are gone, so these tests are unnecessary, and are slowing GHC down. Let's remove them. }}} It looks like Simon has [https://ghc.haskell.org/trac/ghc/changeset/f4a14d6c535bdf52b19f441fe185ea13d... done some digging] on this recently, but I'll cc him just in case. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12785#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler