We are considering a move from SVN to Mercurial, and have encountered a stumbling block.
We currently use svn:externals to automatically pull a common set of libraries into the working directory. I can't find support for anything like this in Mercurial.
Is there a way to do this automatically with Mercurial, or do I need to fake it as part of my build process?
There's no good way to do it using mercurial only. The Forest Extension mentioned elsewhere causes more problems that in fixes nowadays. Most folks just use a large repo and include all their components in the repo and then have their build scripts download and use 3rd party libraries -- using maven if they're Java-heads.
Short answer "fake it in your build process".
Update:
In Mercurial 1.3 a new sub repos feature was added. it's like the old forest extension, but started as all new code.
Subrepos are considered a "feature of last resort".