readPackageDescription >>= writeGenericPackageDescription adds strange duplicate stanza

[peti]

I used the following test program

import Distribution.PackageDescription.Parse ( readPackageDescription )
import Distribution.PackageDescription.PrettyPrint ( writeGenericPackageDescription )
import Distribution.Verbosity

test :: FilePath -> IO ()
test cabalFile = readPackageDescription deafening cabalFile >>= writeGenericPackageDescription (cabalFile++"-new")

to read, parse, and write the Cabal file of arithmoi, and I found that the output has a duplicated build-depends stanza I don't understand. The original file (cut down to the relevant part) says:

library
    build-depends       : base >= 4 && < 5, array >= 0.3 && < 0.6, ghc-prim,
                          integer-gmp < 1, containers >= 0.3 && < 0.6, random >= 1.0 && < 1.1,
                          mtl >= 2.0 && < 2.3
    exposed-modules     : ...
    extensions          : BangPatterns
    ghc-options         : -O2 -Wall
    if flag(llvm)
        ghc-options     : -fllvm
    ghc-prof-options    : -O2 -auto

The re-generated expression, however, says:

library
    build-depends:
        base >=4 && <5,
        array >=0.3 && <0.6,
        ghc-prim -any,
        integer-gmp <1,
        containers >=0.3 && <0.6,
        random >=1.0 && <1.1,
        mtl >=2.0 && <2.3

    if flag(llvm)
        ghc-options: -fllvm
    exposed-modules:
        ...
    build-depends:
        base >=4 && <5,
        array >=0.3 && <0.6,
        ghc-prim -any,
        integer-gmp <1,
        containers >=0.3 && <0.6,
        random >=1.0 && <1.1,
        mtl >=2.0 && <2.3
    extensions: BangPatterns
    other-modules:
        ...

Why is that dependency information duplicated in the generated output?

[phadej]

Tried with current master. Seems to be fixed.

[BardurArantsson]

Thanks @phadej . Perhaps we should just close?