[Nix-dev] Building Haskell Package with Tests and Data Files.

[Peter Simons]

Hi Bas,

 > I have a Haskell library that contains a test-suite. The test
 > requires a data file of the package. When building the package with
 > nix-build the test is run but fails because the path to the data file
 > is wrong.

"cabal test" executes test suites with the current working directory set
to the top-level directory of your source code, i.e. the same place
where the "myLib.cabal" file is. Therefore, your test code can refer to
the data file reliably as "data/Lenna.png".

If you ever want to release that project on Hackage, make sure to
add an attribute like

  extra-source-files: data/*

in your Cabal file, otherwise those data files will not be included in
the generated release tarball. If you're fine with those files being
*installed*, then the attribute

  data-files: data/*

is preferable, of course.

Best regards,
Peter