sof patch for --ghc-pkg-config-file=

[Simon Marlow]

Isaac Jones wrote:
> Duncan Coutts <duncan.coutts at worc.ox.ac.uk> writes:
> 
> 
>>On Fri, 2006-09-15 at 10:06 -0700, Isaac Jones wrote:
>>
>>>Emailing to libraries@, please followup to cabal-devel.
>>>
>>>Here's a patch from Sigbjorn which adds --ghc-pkg-config-file= to
>>>cabal.  This is an oldish patch, but I haven't stopped getting
>>>requests for this feature :)
>>>
>>>This allows you to create a "local" package config file, rather than
>>>using the --user or --global files, this is useful for in-place
>>>building, as when you're developing a set of related packages.
>>>
>>>I still have some debate about whether this patch should go in; it
>>>assumes a model of package registration where you have a config file
>>>(as opposed to a directory) which isn't the case for nhc or Hugs.  But
>>>the idea doesn't seem to bother anyone but me, and the flag is clearly
>>>marked as a ghc-related flag, so I'm thinking of letting it through.
>>>Opinions?
>>
>>Note that there is already a register --inplace flag to register a
>>package in the build tree. 
> 
> 
> And this is mostly so you can build in the build tree, register to
> --user (or global), muck around a bit, and presumably unregister the
> package later.
> 
> 
>>To allow multiple packages to be built against each other inplace
>>we'd also need some flag for configure.
> 
> 
> To specify the package file location, you mean?
> 
> I guess you could do something sloppy like:
> 
> cd my-package
> ./setup build
> ./setup register --inplace --user
> 
> cd my-other-package
> ./setup configure --user
> etc
> 
> ghc-pkg unregister my-package --user 
> 
> (which is what I just did for cabal & cabal-install.)
> 
> 
>>Would this be enough? Do we really also need the ability to specify
>>arbitrary package databases? What is the use case?
> 
> I think it's mainly for registering packages together in a build tree.

I imagine that the "local package database" idea would be what cabal-install 
uses when it builds multiple packages.  Remember our discussion a while back 
about a developer working on a multi-package system?  You want a way to build 
all the packages in dependency order, but without installing.  Some way to 
specify a local package database is the missing piece to make this doable.

We don't have to assume the package database is a file: as far as Cabal is 
concerned, the package database is just a FilePath that it passes to hc-pkg when 
it needs to modify the database in some way.  If we can assume that a database 
can always be specified by a FilePath, then this is compiler-independent (except 
that perhaps we want an 'hc-pkg init' command, which we don't currently have).

BTW, I think that this part of Sigbjorn's patch might be already addressed in 
current Cabal:

- better handling of package-specific header files during installation.
   If you use the Include-Dirs: and Includes: fields in your .cabal
   file to refer to package-local header files and directories, these
   will be created&copied during 'install'

Cheers,
	Simon