[GHC] #8984: Improve output of failed GeneralizedNewtypeDeriving coercion due to type roles

[GHC]

#8984: Improve output of failed GeneralizedNewtypeDeriving coercion due to type
roles
-------------------------------------+-------------------------------------
              Reporter:  haasn       |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.1
             Component:  Compiler    |         Keywords:
  (Type checker)                     |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 The patch above does not implement the proposal in comment:6 and agreed to
 in comment:7. I'll implement this proposal soon, but it will likely miss
 the 7.10 branch. This is OK -- it won't hurt anyone to have this unfixed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8984#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler