GHC Build System & Cabal

[Moritz Angermann]

Dear friends,

I’m currently exploring the possibility to build two versions of base
similar to how we build various ways of the rts.  The reasons for doing
this won’t add much to the discussion.

Reading https://ghc.haskell.org/trac/ghc/wiki/Building/Architecture/Idiom/Cabal
I find the following:

> For the GHC build system we need to extract that metadata and use
> it to build the package.

which leaves me wondering why that is?  Initially I expected we’d just
shell out and let cabal do the configuration and building of .cabal’ised
packages.  But it seems to be the case that we sidestep cabal for building
ghc.

Can someone shed some light on the reasoning behind this?

Cheers,
 Moritz