What Cabal stuff is permanent?

[John Goerzen]

I have been using the info at
http://www.haskell.org/ghc/docs/latest/html/Cabal/authors.html as my
guide to Cabal.

I recently added an include-dirs line to my .cabal file, only to find
that ghc-pkg would fail to register this package.  It appears that
include-dirs was placed into the ghc-pkg file, and of course, the
relative path doesn't exist at install time and isn't even relevant
there.

The problem is: the Cabal docs don't say which fields are "permanent"
and registered in the package and which aren't.  There are many cases
where it is not desirable to have fields be "permanent", and this is one
such case.

I'm not sure how to specify "just search for .h files here at build time
of this library" through Cabal.

Ideas?

-- John