[GHC] #14723: GHC 8.4.1-alpha loops infinitely when typechecking

[GHC]

#14723: GHC 8.4.1-alpha loops infinitely when typechecking
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.4.1-alpha1
  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:"efba054640d3418d7477316ae0c1e992d0aa0f22/ghc"
 efba0546/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="efba054640d3418d7477316ae0c1e992d0aa0f22"
 Prioritise equalities when solving, incl deriveds

 We already prioritise equalities when solving, but
 Trac #14723 showed that we were not doing so consistently
 enough, and as a result the type checker could go into a loop.
 Yikes.

 See Note [Prioritise equalities] in TcSMonad.

 Fixng this bug changed the solve order enough to demonstrate
 a problem with fundeps: Trac #14745.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14723#comment:6>
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