[GHC] #14094: DeriveAnyClass doesn't warn about unimplemented type families

[GHC]

#14094: DeriveAnyClass doesn't warn about unimplemented type families
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        Reporter:  RyanGlScott       |                Owner:  RyanGlScott
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3828
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"3f05e5f6becc2f7174898726b6f027105b12a780/ghc"
 3f05e5f6/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3f05e5f6becc2f7174898726b6f027105b12a780"
 Don't suppress unimplemented type family warnings with DeriveAnyClass

 Summary:
 For some asinine reason, we were suppressing warnings when
 deriving associated type family instances with `DeriveAnyClass`. That
 seems
 like a bad idea. Let's not do that.

 Along the way, I noticed that the error contexts associated with these
 newly emitted warnings were less than ideal, so I did some minor
 refactoring
 to improve the story there.

 Fixes #14094

 Test Plan: ./validate

 Reviewers: bgamari, austin

 Subscribers: rwbarton, thomie

 GHC Trac Issues: #14094

 Differential Revision: https://phabricator.haskell.org/D3828
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14094#comment:3>
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