libpng transition?

Vincent Lefevre vincent-opdarw at
Thu Jan 27 04:44:00 PST 2011

On 2011-01-22 09:43:20 +0100, Emmanuel Hainry wrote:
> Citando Jack Howarth :
> > 
> > On Fri, Jan 21, 2011 at 05:25:46PM -0800, Bradley Giesbrecht wrote:
> > >
> > > Putting your local repository ahead of rsync in sources.conf provides a 
> > > valuable method of preventing software from being upgraded.
> > 
> > That would be a valuable method if MacPorts had the version dependency
> > checking at the package level to prevent breakage like I witnessed with
> > pymol vs libpng. Currently it is more of a high risk strategy as it leaves
> > you open to soversion mismatches.

I agree.

> According to Ryan's first answer to your question, 
> "When a port changes its library version number, all ports that use
> that library need to be rebuilt. This is handled by increasing the
> revision of those ports. For a central library like libpng, this means
> many many ports receive a revision bump."
> It means that maitainers are supposed to act. If you have a local
> Portfile, you maintain your own version of pymol. Hence you are
> supposed to revbump your Portfile. Yes being a maintainer is
> sometimes fastidious, and can be risky if you don't do it properly.

End users may also want to have a local repository to block upgrades
on purpose (using the -n option is similar), e.g. because the current
version fails to build. Time-based dependency logic is fragile and
shouldn't be used (I think that people should have already learned
that with "make").

> Also, note that pymol does not require libpng to be 1.4 or 1.2, it
> builds very well with either version, so version dependency would not
> change anything to your problem.

There can be two kinds of dependencies: static and dynamic
dependencies (some port or port-version dependencies would be
recorded at build time).

Vincent Lefèvre <vincent at> - Web: <>
100% accessible validated (X)HTML - Blog: <>
Work: CR INRIA - computer arithmetic / Arénaire project (LIP, ENS-Lyon)

More information about the macports-dev mailing list