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

[GHC]

#11371: Bogus in-scope set in substitutions
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        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
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Comment (by goldfire):

 Replying to [comment:16 simonpj]:

 > Richard, can you see anything wrong with that?

 Not at all. I very nearly did that myself a while ago, but it meant some
 code duplication around `instSkolTyCoVarX` (and perhaps one other place,
 if memory serves -- I'm sure you'll find it by looking at use sites of
 `extendTCvSubst`).

 Yes -- go for it. This is an improvement.

 The comment about `tcCoercionToCoercion` is historical and should be
 removed, along with that case, which should indeed never be triggered now.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11371#comment:18>
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