It's not really valid but enough to make ghc-mod happy, without it
findCradle doesn't work properly and without the empty `library`
sections it crashes even.
- cradle now stores a list of active package databases instead of only
the user store (if present).
- rename `cradlePackageDb` -> `cradlePkgDbStack` as that`s what the ghc
documentaion calls this kind of thing
- `getPackageDbPackages` now returns names of all visible packages in
the given directory. Also the implementation now uses `ghc-pkg`
instead of manually looking at the package database
This commit add a failing test to check extracting package id. The test will
fail with the following output for now:
1) Cradle.getPackageDbPackages find a config file and extracts packages with their ids
expected: [("template-haskell",Just "template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c")]
but got: []
Daniel Gröber