Remove Setup.hs, use Setup.lhs only

[Ross Paterson]

On Sat, Nov 25, 2006 at 09:57:50AM -0800, Isaac Jones wrote:
> So a summary of the new rules would be something like:
> 
> * Setup.lhs will be found automatically, as it is now.
> 
> * Setup.hs will be found and complained about with an error.  Maybe in
>   the interim, we can have a warning.  In the common case, the error
>   can be fixed by deleting Setup.hs and using cabal-setup :)
> 
> * Setup will become optional, and cabal-setup will do the job of
>   defaultMain (or whatever is in the new field).
> 
> * A new field will be introduced to indicate what kind of build system
>   cabal-setup should use, in the absense of a Setup.lhs file.

I'd suggest putting the last two slightly differently.  As I understood
it, the idea of cabal-setup is that you have it pre-compiled on your
system, and you always run it, because it's smart enough to find a
compiler and suitable Cabal version to execute Setup.lhs.  If this field
is set to something other than Custom, cabal-setup can ignore Setup.lhs,
and just do the appropriate thing itself (making Setup.lhs optional).

For backward compatibility, you'd probably want the default value of
the new field to be Custom, though this would mean you couldn't omit
Setup.lhs unless this field was set.

> Ross, how do you see the fields panning out?  Want to implement it? :)

Something like

	Build-Type: (Simple|Configure|Make|Custom)

I'd be happy to implement it, if/when we get agreement.