[Nix-dev] Using Nix for installing local projects

[Alexander Foremny]

Hello list,

today I ran into a problem which I don't know how to solve. I needed
the Haskell library hoauth [1] which was not available in Nixpkgs.
Using cabal2nix and my local Nixpkgs repository creating a Nix
expression and installing it via

> $ nix-env -f ~/code/nixpkgs/default.nix -i haskell-hoauth-ghc7.4.1

was no problem. However, I realized I need to perform some
modifications to the hoauth package. So I grabbed the source from
hoauth and modified it according to my needs.

Now I need to install this modified version in order to test the
changes. I'd like to use Nix instead of cabal to keep my system clean.
However, placing those changes into ~/code/nixpkgs is cumbersome
because I don't want to distribute those changes just yet.
Of course I could create a diff and apply this in ~/code/nixpkgs, but
it would be much easier if I could just create a Nix expression within
the modified hoauth directory and somehow tell Nix to install this.

Is this possible? How do you handle such cases?

Another option would be to specify a file path as src in
cabal.mkDerivation. Is this possible?

Regards,
Alexander Foremny

[1] http://hackage.haskell.org/package/hoauth