Adding a dependency to the build system

[Mateusz Kowalczyk]

Hi,

Today I have split Haddock up a little to allow users to use the Haddock
parser without incurring the dependency on GHC. This means the Haddock
tree looks like this now:

haddock/haddock.cabal
haddock/src/…
haddock/haddock-library/haddock-library.cabal
haddock/haddock-library/src/…
haddock/haddock-library/…
haddock/…

For details see [1].

In the haddock.cabal, we now depend on haddock-library. While this works
fine in a regular development scenario, GHC build system needs to be
made aware that it has to build haddock/haddock-library before haddock/.
I tried looking at the build system but it is far too complicated to
comprehend in a reasonable amount of time.

Can someone already familiar with it make the change (in a separate
branch or give me the diff so I can push the Haddock changes while at
the same time updating submodule + build system) or tell me what exactly
needs changing? haddock-library only uses a subset of Haddock's existing
dependencies so there should be no problem on that end.

A workaround would be to simply include haddock-library paths as
additional source locations but I don't like it this approach as it
breaks the ‘haddock-library is its own package’ abstraction. For
example, this would not work if we ever wanted to move haddock-library
to its own repository.

Thanks!

[1]: https://github.com/Fuuzetsu/haddock/tree/parser-split

-- 
Mateusz K.