[GHC] #10087: DefaultSignatures: error message mentions internal name

[GHC]

#10087: DefaultSignatures: error message mentions internal name
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        Reporter:  andreas.abel      |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.8.4
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  Other             |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by simonpj):

 Replying to [comment:3 dreixel]:
 > Simon, is there a good reason for `tc_default` in `TcInstDcls` to treat
 `DefMeth` so differently from `GenDefMeth`?

 No there isn't.  See `tc_default` in `tcMethods` in `TcInstDcls`.

  * For polymorphic default methods, `DefMeth`, we generate ''typechecked''
 `HsSyn Id`; see `Note [Default methods in instances]`.

  * For generic default methods, `GenDefMeth`, we currently generate
 ''renamed'' `HsSyn Name`, and then feed it to the type checker.

  * For user-written methods, `NoDefMeth`, we obviously just typecheck what
 the user wrote.

 I think it'd be pretty simple to instead treat `GenDefMeth` more like
 `DefMeth`.  It might be a bit more code, but we'd get decent error
 messages.

 Do you think you could do that?  I can advise.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10087#comment:4>
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