# Cabal

The cabal source uses the `ghc-pkg` command to enumerate dependencies and provide metadata.  It is un-opinionated on GHC packagedb locations and requires some configuration to ensure that all packages are properly found.

The rubygem source will detect dependencies when the source is enabled and a `.cabal` file is found at an apps `source_path`.

### Specifying GHC packagedb locations through environment
You can configure the `cabal` source to use specific packagedb locations by setting the `GHC_PACKAGE_PATH` environment variable before running `licensed`.

For example, the following is a useful configuration for use with `cabal new-build`.
```bash
ghc_version="$(ghc --numeric-version)"
CABAL_STORE_PACKAGE_DB="$(cd ~/.cabal/store/ghc-$ghc_version/package.db && pwd)"
LOCAL_PACKAGE_DB="$ROOT/dist-newstyle/packagedb/ghc-$ghc_version"
GLOBAL_PACKAGE_DB="$(ghc-pkg list --global | head -n 1)"
export GHC_PACKAGE_PATH="$LOCAL_PACKAGE_DB:$CABAL_STORE_PACKAGE_DB:$GLOBAL_PACKAGE_DB:$GHC_PACKAGE_PATH"

bundle exec licensed <args>
```

### Specifying GHC packagedb locations through configuration
Alternatively, the `cabal` source can use packagedb locations set in the app configuration.  The following is an example configuration identical to the above environment configuration.

```yml
cabal:
  ghc_package_db:
    - ~/.cabal/store/ghc-<ghc_version>/package.db
    - dist-newstyle/packagedb/ghc-<ghc_version>
    - global
```

Ordering is preserved when evaluating the configuration values.  Paths are expanded from the root of the `git` repository and used as values for CLI `--package-db="<path>"` arguments.  Additionally, in all specified paths, `<ghc_version>` will be replaced with the result of `ghc --numeric-version`.

The `global` and `user` keywords are supported and will expand to the `--global` and `--user` CLI arguments, respectively.

Like most other settings, the `cabal` configuration can be specified for the root configuration, or per-app.  If specified at root, it will be inherited by all apps unless explicitly overridden.

### Stack sandboxes
The current recommended way to use `licensed` with stack is to run the `licensed` command with `stack exec`: `stack exec -- bundle exec licensed <args>`.  This will allow stack to control the GHC packagedb locations.