[GHC] #9611: Suggest the cause of "No instance" errors involving multiple versions of a package

[GHC]

#9611: Suggest the cause of "No instance" errors involving multiple versions of a
package
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              Reporter:  rwbarton    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 I expect this would be do-able (look in `TcErrors`), but it'd mean
 implementing a variant of the instance-matching code, to look for a match
 "by name" (where `p1:A.B.T` matches `p2:A.B.T`) rather than "by identity"
 where those two types are simply different.

 I can offer guidance if someone tackles this.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9611#comment:1>
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