[GHC] #8576: Improve deriving error messages

[GHC]

#8576: Improve deriving error messages
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        Reporter:  nomeata                  |            Owner:  nomeata
            Type:  feature request          |           Status:  new
        Priority:  low                      |        Milestone:
       Component:  Compiler (Type checker)  |          Version:
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by Joachim Breitner <mail@…>):

 In [changeset:"4025d66cc795b728f745aec23fc5c2267d1839f0/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4025d66cc795b728f745aec23fc5c2267d1839f0"
 Elaborate "deriving" error messages

 If "deriving (C)" fails, it will now, if possible, indicate which
 particular field of which constructor has caused the failure. (This
 fixes #8576)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8576#comment:2>
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