#12562: GHC panic on rebuild (idInfo r_XsTP) -------------------------------------+------------------------------------- Reporter: cocreature | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"692c8df03969ee6a0de5158f05907b16689945d0/ghc" 692c8df0/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="692c8df03969ee6a0de5158f05907b16689945d0" Fix shadowing in mkWwBodies This bug, exposed by Trac #12562 was very obscure, and has been lurking for a long time. What happened was that, in the worker/wrapper split a tyvar binder for a worker function accidentally shadowed an in-scope term variable that was mentioned in the body of the function It's jolly hard to provoke, so I have not even attempted to make a test case. There's a Note [Freshen WW arguments] to explain. Interestingly, fixing the bug (which meant fresher type variables) revealed a second lurking bug: I'd failed to apply the substitution to the coercion in the second last case of mkWWArgs, which introduces a Cast. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler