A trivial Haskell program that hopefully makes a Haskell Stack project with poorly defined package dependencies buildable with standard tools like cabal or mafia.

For example, I wanted to build haskellnews but its cabal file had close to zero dependency bounds. With jenga at least I could install the basic dependencies:

git clone https://github.com/haskellnews/haskellnews/
cd haskellnews
jenga -i haskellnews.cabal > cabal.config
# Manually remove the dependency on `base`
cabal sandbox init
cabal install --dependencies-only

It wasn't enough to actually build the project but it got me a lot closer.

You run it in Haskell project directory that contains both the projects cabal file and the stack.yaml file. It then:

1. Reads the cabal file to extract the dependent library names.
2. Reads the stack.yaml file to extract the Stack resolver version.
3. Queries the Stackage server with the resolver version to get a JSON blob containing the packages and the versions for that resolver version and converts it into a Map from package name to package info.
4. For each of the package names read in step 1. it looks up the package name in the Map from step 3.
5. Prints the package and version info from step 4. to stdout in the form of a cabal freeze file (should be named cabal.config for cabal to recognise it).