[Haskell-cafe] SoC / Cabal project proposal: specify Setup.hs dependencies

[Edward Kmett]

On Tue, Mar 29, 2011 at 1:26 PM, Rogan Creswick <creswick at gmail.com> wrote:

> I've been wanting to share code between cabal projects for some time,
> and I finally had a chance to write up the rough idea as a simple
> proposal.  Here's the description, with links to the SoC trac and
> reddit haskell_proposals pages.
>
> SoC ticket:
>   http://hackage.haskell.org/trac/summer-of-code/ticket/1602
>
> Reddit:
>
> http://www.reddit.com/r/haskell_proposals/comments/ge1zp/cabal_dependency_specifications_for_setuphs/
>
> Non-standard builds often need to implement specific build steps in
> Setup.hs, specifying a build-type: Custom in the project cabal file.
> The user hook system works reasonably well for modifying or replacing
> the specific sub steps of a build, but *implementing* anything more
> than the simplest logic in Setup.hs is very difficult.
>
> A great deal of this difficulty stems from the lack of library support
> for code in Setup.hs. Adding a cabal section that specifies a
> build-depends: for Custom (and possibly other) build types would allow
> developers to reuse build code between projects, to share build system
> modifications on hackage more easily, and to prototype new additions
> to cabal.
>
> Setup.hs *can* allow arbitrarily complex build system manipulations;
> however, it is not practical to do so because the infrastructure
> surrounding Setup.hs doesn't promote code reuse. The addition of
> dependencies that cabal-install would install prior to building
> setup.hs and issuing the build would enable developers to produce
> custom builds that perform complex operations that utilize the
> high-quality libraries available on hackage. Furthermore, this would
> provide the means to prototype (and distribute) new cabal /
> cabal-install features before integrating experimental code into the
> stable tools.
>
> I'm interested in thoughts / feedback about the idea, as well as
> hearing from anyone interested in pursuing this as a summer of code
> project :)
>

I really like the idea behind this proposal.

I've had some rather hairy Setup.hs files that would have benefited from
being able to use external packages. This could also be really nice when it
comes to writing custom test/benchmarking/etc. hooks, by letting you factor
out a lot of that common code into reusable libraries.

-Edward
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