[GHC] #14132: Report an error for a missing class instance before an error for type family instances of an associated type.

[GHC]

#14132: Report an error for a missing class instance before an error for type
family instances of an associated type.
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        Reporter:  duog              |                Owner:  duog
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      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:                    |
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Comment (by duog):

 I tried moving those three `ReporterSpec`s to report2 (keeping their
 order, just adding them after "Dicts") and T12170a gave a core lint error
 (attached). I had assumed it was due to the invariant specified in the
 comment.

 I am obviously very new to the typechecker; my presumption was that
 insoluble constraints were ones that we couldn't defer by inserting a
 coercion, so it would be very bad to suppress those errors. That was my
 untrained reading of the lint error. However this must be wrong, because
 surely there's no problem inserting a coercion from Int to Bool.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14132#comment:5>
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