I have run into another issue with cabal packaging, which seems
related to the issues discussed above. (see attached tar file for
complete example of failure scenario)
If I have a cabal package that depends on two other packages
-- package xml-parsec requires HaXml == 1.19.4 (the latest)
-- package HAppS-Server requires HaXml == 1.13.3 (the default)
ghc --make testDepConflict.hs
works fine.
But I can't install via cabal without, I guess, breaking out the
conflict into a separate cabal package.
Build-Depends: HAppS-Server, xml-parsec, HaXml
-- (Uses HaXml 1.13.3, the default HaXml if no version number is specified)
-- Cabal says:
---- Could not find module `Text.XML.HaXml.Posn':
---- it is a member of package HaXml-1.19.4, which is hidden
-- I say:
---- Ok, I understand why this doesn't work.
Build-Depends: HAppS-Server xml-parsec, HaXml == 1.19.4
-- Cabal says:
---- cabal: dependencies conflict: HAppS-Server requires HaXml ==1.13.3 however
---- HaXml-1.13.3 was excluded because CabalDepConflict-0.1 requires
HaXml ==1.19.4
-- I say:
---- Since HAppS-Server is its own separate package, why is this a conflict?
---- Shouldn't this work?
The workaround is to put the bits of the current package that depend
on HaXml 1.19.4 into their own separate package,
which doesn't require HAppS-Server.
But shouldn't it be possible for cabal to figure out how to install
the package without doing this?
2008/11/15 Duncan Coutts
On Sat, 2008-11-15 at 13:31 +0100, Thomas Hartman wrote:
This is all news to me, and un-googleable to boot:
(no results)
It finds something for me (with the right spelling of preferred), eg this thread from the libraries list:
http://archive.netbsd.se/?ml=haskell-libraries&a=2008-10&t=8748731
So yes, I think this referred-versions machinery should at least be made more transparent for situations when it does the wrong thing, like with xml-parsec.
Sure, though it is worth remembering that doing the right thing for xml-parsec is completely a guessing game since the package does not say which version it needs and yet works with some versions and not others. That is the root of this problem. We should be thinking about ways to persuade package authors (or others) to supply the correct information.
That's where the package versioning policy comes in.
I think your last suggestion is good
cabal install haxml Downloading HaXml-1.13.3... Note: the recommended version is HaXml-1.13.3 but latest version is HaXml-1.19, use cabal install haxml-1.19 if you want that version.
I would have this message pop up for both cabal install and cabal upgrade -- especiallly since with cabal upgrade the result was for me completely bafflling.
Ok, so that we do not forget this, would you mind filing a ticket to explain the confusion and the suggested solution. Linking to this thread would also help.
http://hackage.haskell.org/trac/hackage/
Duncan