[GHC] #15147: Type checker plugin receives Wanteds that are not completely unflattened

[GHC]

#15147: Type checker plugin receives Wanteds that are not completely unflattened
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        Reporter:  nfrisby           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.4.1
  checker)                           |             Keywords:  type checker
      Resolution:                    |  plugins
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by adamgundry):

 Well, it rather depends on the plugin: my `uom-plugin` and other existing
 plugins were designed to work on the basis of receiving fully unflattened
 constraints, and at the time that seemed the simplest thing to get
 working. Of course it depends on what the plugin is doing as to which is
 simplest, so I can well understand nfrisby having an opposite preference
 in his case.

 As I say, I don't mind terribly if the interface changes to supply
 unflattened constraints, provided there is a way to properly flatten them
 again in the plugin monad. That seems like it would require resolving this
 issue anyway, though?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15147#comment:5>
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