Tab-completing in a directory with Unicode heiroglyph crashes ghci

With a file called 𓅖.hs in C:\Users\acfoltzer, the following in cmd.exe:

C:\Users\acfoltzer>chcp 65001
Active code page: 65001
C:\Users\acfoltzer>ghci
GHCi, version 7.10.1: http://www.haskell.org/ghc/  :? for help
Prelude> :l C:\cygwin\home\acfoltzer\<TAB>
ghc.exe: panic! (the 'impossible' happened)
  (GHC version 7.10.1 for i386-unknown-mingw32):
        Enum.toEnum{Word16}: tag (78166) is outside of bounds (0,65535)

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Here, I'm setting the code page first according to the various bits of folk wisdom on the Internet about getting Unicode to properly display in cmd.exe. I don't get this crash with a Cygwin terminal, but rather see ??.hs.

I came across this because I was getting the same exception in the Cryptol REPL, so I suspect it's not unique to GHCi, but is rather something fishy in base.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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CC	hvr
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