GHC panics with dsImpSpecs on SPECIALISE pragma with -fhpc enabled

Minimal example code: https://github.com/nh2/ghc-omit-interface-pragmas-dsImpSpecs-bug/

I'm encountering a problem that prevents me from using Haskell program coverage on a code base, getting a GHC panic referring to dsImpSpecs.

This looks pretty much like this old bug: #4870 (closed)

I checked that it happens on GHC 7.8.4 and GHC 7.10.1.

---

The problem happens when I run cabal build --ghc-options "-fhpc", giving me

Package has never been configured. Configuring with default flags. If this
fails, please run configure manually.
Resolving dependencies...
Configuring ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0...
Building ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0...
Preprocessing library ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0...
[1 of 2] Compiling A                ( src/A.hs, dist/build/A.o )
[2 of 2] Compiling B                ( src/B.hs, dist/build/B.o )

src/B.hs:5:1: Warning:
    SPECIALISE pragma for non-overloaded function ‘myfun’
ghc: panic! (the 'impossible' happened)
  (GHC version 7.8.4 for x86_64-unknown-linux):
    dsImpSpecs
    ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0:A.myfun{v rpu} [gid]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.4
$ cabal --version
cabal-install version 1.18.0.8
using version 1.18.1.5 of the Cabal library

This doesn't happen when I compile directly with ghc --make:

$ cd src && ghc --make -fhpc -fomit-interface-pragmas B.hs -Wall
[1 of 2] Compiling A                ( A.hs, A.o )
[2 of 2] Compiling B                ( B.hs, B.o )

So running cabal with -v, I see that the problem happens in:

/home/niklas/opt/ghc-7.8/bin/ghc --make -fbuilding-cabal-package -O -static -dynamic-too -dynosuf dyn_o -dynhisuf dyn_hi -outputdir dist/build -odir dist/build -hidir dist/build -stubdir dist/build -i -idist/build -isrc -idist/build/autogen -Idist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -package-name ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0 -hide-all-packages -package-db dist/package.conf.inplace -package-id base-4.7.0.2-bfd89587617e381ae01b8dd7b6c7f1c1 -XHaskell98 B A -Wall -fhpc
[1 of 2] Compiling A                ( src/A.hs, dist/build/A.o )
[2 of 2] Compiling B                ( src/B.hs, dist/build/B.o )

src/B.hs:5:1: Warning:
    SPECIALISE pragma for non-overloaded function ‘myfun’
ghc: panic! (the 'impossible' happened)
  (GHC version 7.8.4 for x86_64-unknown-linux):
	dsImpSpecs
    ghc-omit-interface-pragmas-dsImpSpecs-bug-0.1.0.0:A.myfun{v rpu} [gid]

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

So there it be some flag that cabal passes to GHC that makes this GHC crash appear.

Nevertheless, it's a panic, so I guess it's a bug in GHC.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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