[GHC] #13947: GHC 8.2 gives misleading error message for out-of-scope infix type constructor

[GHC]

#13947: GHC 8.2 gives misleading error message for out-of-scope infix type
constructor
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        Reporter:  RyanGlScott       |                Owner:  RyanGlScott
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:  ORF
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * owner:  (none) => RyanGlScott


Comment:

 After skimming the commitdiff, I'm reasonably confident I know what is
 happening, and how fix it. I'll post a Phab Diff after I've validated.

 Also, I just realized that there's another problem with the error message
 in GHC 8.2: it claims that a constructor `:~:` is in scope, but that's
 untrue. I'll submit a separate ticket for this later.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13947#comment:3>
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