--ipid doesn't work with cabal install?

[mpickering]

I am trying to use the --ipid flag to install a package so it ends up with pkg-0.1.conf rather than pkg-0.1-asdf.conf. It seems the --ipid flag should do this.

I invoke GHC like this:

/nix/store/iq76wsmhvmidnyjkbgiklfi4zpwxld7h-ghc-build-environment/bin/cabal install groups/ --with-compiler /nix/store/iq76wsmhvmidnyjkbgiklfi4zpwxld7h-ghc-build-environment/bin/ghc --package-db _build/stage0/lib/package.conf.d --ipid=$pkg-$version

but the package is still registered with the suffix. Is this broken or am I doing something wrong?