[GHC] #12918: Make DefaultSignatures more particular about their types on the RHS of a context

[GHC]

#12918: Make DefaultSignatures more particular about their types on the RHS of a
context
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        Reporter:  RyanGlScott       |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.0.2-rc1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12784            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 1.  In `TcClassDcl.tcClassSigs`.

 2.  Yes, I agree it should be insensitive to alpha renaming of any
 locally-quantified variables. (It would be ok for it to be sensitive to
 order, I guess.  There's a little wiggle room there.)

 3. Yes I think it should be rejected.  I think the alternative version you
 give is actually clearer!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12918#comment:4>
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