[GHC] #15577: TypeApplications-related infinite loop (GHC 8.6+ only)

[GHC]

#15577: TypeApplications-related infinite loop (GHC 8.6+ only)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |             Keywords:
      Resolution:                    |  TypeApplications, TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"2e226a46c422c12f78dc3d3f62fe5a15e22bd986/ghc"
 2e226a46/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2e226a46c422c12f78dc3d3f62fe5a15e22bd986"
 canCFunEqCan: use isTcReflexiveCo (not isTcReflCo)

 As Trac #15577 showed, it was possible for a /homo-kinded/
 constraint to trigger the /hetero-kinded/ branch of canCFunEqCan,
 and that triggered an infinite loop.

 The fix is easier, but there remains a deeper questions: why is
 the flattener producing giant refexive coercions?
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15577#comment:4>
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