[Haskell-cafe] build-depends contraints in a .cabal file

[Duncan Coutts]

On Mon, 2008-02-18 at 20:05 -0600, Antoine Latter wrote:
> Can I specify an equality constraint in the build-depends field of a
> .cabal file?  This would say that I want one specific version (because
> all the rest of my packages are compiled against that version and I'm
> getting type-checking errors trying to install the new package).
> 
> neither
> > build-depends: foobar = 3.0.1
> 
> or
> > build-depends: foobar-3.0.1
> 
> seem to work.

> Do I have any choices other than re-compiling everything?

As Wolfgang says, use ==.

I should note that I'm also just about to add detection for this kind of
problem where we end up getting inconsistent versions of installed
packages. In future you'll get a warning like:

Configuring Foo-1.0...
Warning: This package indirectly depends on multiple versions of the
same package. This is highly likely to cause a compile failure.
package rss-3000.0.1 requires HaXml-1.13.3
package Foo-1.0 requires HaXml-1.19.2

http://hackage.haskell.org/trac/hackage/ticket/220

Separately we're also trying to add a:
cabal configure --constraint "HaXml < 1.19"
construct to let users add additional constraints on the configure
command line.

http://hackage.haskell.org/trac/hackage/ticket/224

This should be useful in the above situation until we have something
more automatic, though the real purpose is to make it easier for people
to test with various versions of deps and to allow cabal-install to
specify exact dependencies after it has constructed its install plan.

BTW, if you have a suggestion for a better command line flag name then
do say.

Duncan