[GHC] #15346: Core Lint error in GHC 8.6.1: From-type of Cast differs from type of enclosed expression

[GHC]

#15346: Core Lint error in GHC 8.6.1: From-type of Cast differs from type of
enclosed expression
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15419            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Richard Eisenberg <rae@…>):

 In [changeset:"af624071fa063158d6e963e171280676f9c0a0b0/ghc"
 af624071/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="af624071fa063158d6e963e171280676f9c0a0b0"
 Fix some casts.

 This fixes #15346, and is a team effort between Ryan Scott and
 myself (mostly Ryan). We discovered two errors related to FC's
 "push" rules, one in the TPush rule (as implemented in pushCoTyArg)
 and one in KPush rule (it shows up in liftCoSubstVarBndr).

 The solution: do what the paper says, instead of whatever random
 thoughts popped into my head as I was actually implementing.

 Also fixes #15419, which is actually the same underlying problem.

 Test case: dependent/should_compile/T{15346,15419}.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15346#comment:11>
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