[GHC] #14873: GHC HEAD regression (piResultTy)

[GHC]

#14873: GHC HEAD regression (piResultTy)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"3d252037234ce48f9bdada7d5c9b1d8eba470829/ghc"
 3d252037/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3d252037234ce48f9bdada7d5c9b1d8eba470829"
 Respect Note [The tcType invariant]

 I tried to do this with

     commit 0a12d92a8f65d374f9317af2759af2b46267ad5c
     Author: Simon Peyton Jones <simonpj at microsoft.com>
     Date:   Wed Dec 13 12:53:26 2017 +0000

     Further improvements to well-kinded types

     The typechecker has the invariant that every type should be well-
 kinded
     as it stands, without zonking.  See Note [The well-kinded type
 invariant]
     in TcType.

     That invariant was not being upheld, which led to Trac #14174.  I
 fixed
     part of it, but T14174a showed that there was more.  This patch
 finishes
     the job.

 But I didn't get it quite right as Trac #14873 showed.

 This patch fixes the problem; although I am still a bit unhappy.
 (See "A worry" in the HsApp case of tc_infer_hs_type.)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14873#comment:3>
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