[GHC] #15473: GHC 8.6+ loops infinitely on an UndecidableInstances error message

[GHC]

#15473: GHC 8.6+ loops infinitely on an UndecidableInstances error message
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:
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:"db6f1d9cfc74690798645a7cc5b25040c36bb35d/ghc" db6f1d9/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="db6f1d9cfc74690798645a7cc5b25040c36bb35d"
 Turn infinite loop into a panic

 In these two functions
   * TcIface.toIfaceAppTyArgsX
   * Type.piResultTys
 we take a type application (f t1 .. tn) and try to find
 its kind. It turned out that, if (f t1 .. tn) was ill-kinded
 the function would go into an infinite loop.

 That's not good: it caused the loop in Trac #15473.

 This patch doesn't fix the bug in #15473, but it does turn the
 loop into a decent panic, which is a step forward.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15473#comment:3>
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