Listing licenses with cabal-db2014-03-29
Following discussions with fellow haskellers, regarding the need to be careful with adding packages that could depends on GPL or proprietary licenses, it turns out it's not easy to get your dependencies's licenses listed.
It would be convenient to be able to ask the hackage database those things, and this is exactly what cabal-db usually works with.
The license subcommand is mainly to get a summary of the licenses of a packages and its dependencies, but it can also display the tree of licenses. Once a package has been listed, it would not appears again in the tree even if another package depend on it.
A simple example is better than many words:
$ cabal-db license -s -t BNFC BNFC: GPL process: BSD3 unix: BSD3 time: BSD3 old-locale: BSD3 base: BSD3 deepseq: BSD3 array: BSD3 bytestring: BSD3 filepath: BSD3 directory: BSD3 pretty: BSD3 mtl: BSD3 transformers: BSD3 containers: BSD3 == license summary == BSD3: 14 GPL: 1
cabal-db is only using the license listed in the license field in cabal files, so if the field is incorrectly set, cabal-db would have no idea.