[GHC] #15170: GHC HEAD panic (dischargeFmv)

[GHC]

#15170: GHC HEAD panic (dischargeFmv)
-------------------------------------+-------------------------------------
        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:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"57858fc8b519078ae89a4859ce7588adb39f6e96/ghc" 57858fc/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="57858fc8b519078ae89a4859ce7588adb39f6e96"
 Make dischargeFmv handle Deriveds

 A Derived CFunEqCan does not "own" its FlatMetaTv (fmv), and should not
 update it.  But one caller (canCFunEqCan) was failing to satisfy the
 precondition to dischargeFmv, which led to a crash (Trac #15170).

 I fixed this by making dischargeFmv handle Deriveds (to avoid forcing
 each caller to do so separately).

 NB: this does not completely fix the original #15170 bug, but I'll
 explain that on the ticket.  The test case for this patch is actually
 the program in comment:1.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15170#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler