stack haddock ignores the dependencies of test suites and executables

General summary/comments (optional)

stack haddock generates the documentation for the dependencies of the library component, but not of the executable or test components.

Steps to reproduce

1. Create a cabal package where some packages are required by the executable or test but not the library
2. Run stack haddock

Expected

If I go to the doc index (.stack-work/install/x86_64-linux/lts-7.0/8.0.1/doc/all/index.html), I expect to see the executables and test suite dependencies docs.

Actual

They're not there.

Stack version

$ stack --version
Version 1.2.1, Git revision f28002bdea51468566fd9370f7f9e801c2b51bc5 (4141 commits) x86_64 hpack-0.14.1

Method of installation

Built from git.