[GHC] #11371: Bogus in-scope set in substitutions

[GHC]

#11371: Bogus in-scope set in substitutions
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                Owner:  niteria
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11360            |  Differential Rev(s):  phab:D1792,
       Wiki Page:                    |  phab:D1801, phab:D1802
-------------------------------------+-------------------------------------

Comment (by niteria):

 Changing it to:
 {{{
 empty_subst = mkEmptyTCvSubst $! mkInScopeSet $! tyCoVarsOfTypes (ty:args)
 }}}
 gives me:
 {{{
 $ ("/data/users/bnitka/ghc-perf/ghc-after/inplace/test   spaces/ghc-
 stage2" -c T5030.hs -fforce-recomp -no-user-package-db -rtsopts -fno-warn-
 tabs -fno-warn-missed-specialisations -fno-ghci-history  -freduction-
 depth=300 +RTS -V0 -tT5030.comp.stats --machine-readable -P -RTS)
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.1.20160216 for x86_64-unknown-linux):
         exprToType
 CallStack (from -prof):
   GHC.withCleanupSession (compiler/main/GHC.hs:(464,1)-(473,27))
   GHC.runGhc (compiler/main/GHC.hs:(437,1)-(442,26))
   GHC.defaultErrorHandler (compiler/main/GHC.hs:(377,1)-(409,7))
   CoreSyn.CAF (<entire-module>)

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 Is it worth looking at?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11371#comment:37>
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