Bug#914702: ghc: The 'impossible' happens all the time in GHCi

[Samuel Hym]

Package: ghc
Version: 8.4.3+dfsg1-4
Severity: normal

Dear Maintainer,

Since updating to ghc 8.4.3, the 'impossible' is easy to trigger in
GHCi:

$ ghci
GHCi, version 8.4.3: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/hym/c/ghci
Prelude> readFile "/tmp/test"
ghc: panic! (the 'impossible' happened)
  (GHC version 8.4.3 for x86_64-unknown-linux):
        nameModule
  system $dShow_a4My
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
        pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name

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

(I get this error whether /tmp/test exists or not).

Best regards,
Samuel


-- System Information:
Debian Release: buster/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.18.0-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages ghc depends on:
ii  dpkg                              1.19.2
ii  gcc                               4:8.2.0-2
ii  libatomic1                        8.2.0-10
ii  libbsd-dev                        0.9.1-1
ii  libc6                             2.27-8
ii  libc6-dev                         2.27-8
ii  libffi-dev                        3.2.1-8
ii  libffi6                           3.2.1-8
ii  libgmp-dev                        2:6.1.2+dfsg-3
ii  libgmp10                          2:6.1.2+dfsg-3
ii  libncurses-dev [libncurses5-dev]  6.1+20181013-1
ii  libncurses5-dev                   6.1+20181013-1
ii  libtinfo6                         6.1+20181013-1

ghc recommends no packages.

Versions of packages ghc suggests:
ii  ghc-doc      8.4.3+dfsg1-4
pn  ghc-prof     <none>
pn  haskell-doc  <none>
ii  llvm-6.0     1:6.0.1-9.2
ii  perl         5.28.0-4

-- no debconf information