[GHC] #13371: instance selection too eager

[GHC]

#13371: instance selection too eager
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        Reporter:  aavogt            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.2
  checker)                           |
      Resolution:                    |             Keywords:
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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Changes (by niteria):

 * cc: goldfire (added)


Comment:

 I think this has been broken since
 6746549772c5cc0ac66c0fce562f297f4d4b80a2.
 Running before c9bcaf3165586ac214fa694e61c55eb45eb131ab with `-dunique-
 increment=-1` reproduces the problem.

 It appears that when we `growThetaTyVarsDSet` we add some kind variables
 to the nondependent type var set, but the vars inside depend on the newly
 added kind var. We then linearize without any regard for dependencies,
 because there shouldn't be any.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13371#comment:6>
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