[GHC] #15646: ghci takes super long time to find the type of large fractional number

[GHC]

#15646: ghci takes super long time to find the type of large fractional number
-------------------------------------+-------------------------------------
        Reporter:  Johannkokos       |                Owner:
                                     |  JulianLeviston
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.4.3
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5692             |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by JulianLeviston):

 I can't seem to successfully build my ghc any more...

 {{{
 GHC error in desugarer lookup in GHC.Real:
   Can't find interface-file declaration for type constructor or class
 mkRational
     Probable cause: bug in .hi-boot file, or inconsistent .hi file
     Use -ddump-if-trace to get an idea of which file caused the error
 ghc-stage1: panic! (the 'impossible' happened)
   (GHC version 8.7.20181012 for x86_64-apple-darwin):
         initDs
 }}}

 after I attempted to do the profiler build... that's from attempting a
 `BuildFlavour = devel2` build without `stage=2` specified. I might follow
 the build instructions from the ground up again without my code in place
 then put it back and see if that works.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15646#comment:55>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler