Feature Request: Expose Cabal flags and GHC options in ls dependencies json

[aherrmann]

Feature Request

I would like the output of stack ls dependencies json to contain Cabal flags and GHC options that are defined in the snapshot. E.g. Cabal flags and GHC options that are defined as follows in a custom snapshot:

flags:
  unordered-containers:
    debug: true
ghc-options:
  warp:
  - -O2

This should take flags like --static (if implemented) into account.

Motivation

stack ls dependencies json is very useful for build tools that would like to call out to stack to determine how to build Stackage dependencies. Cabal flags can influence the dependency graph and can be required to build a package correctly on a given platform, similarly GHC options can be required to build a package correctly. However, currently stack does not expose these flags or options. The user of the tool that consumes stack ls dependencies json will have to repeat this configuration in some form, which is cumbersome and error-prone.