Install ROS dependencies from apt?

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AFAICT, using apt packages is a bit of an all-or-nothing deal— you can either:

1. install everything from apt, letting apt resolve dependencies, or

2. install everything from a rosinstall, letting rosinstall_generator resolve them.

The obvious thing for a mature package is to install the latest release from apt, and then use rosinstall to create an overlay which you can hack on. But this is not a great solution for packages which are not yet released, perhaps because they are still experimental, in early development, etc.

Am I mistaken here, or is there some ROS invocation which can scan the package.xml dependencies of a workspace, and then spit out (or execute) the necessary apt-get install command? Or is the solution to just create apt releases from the earliest possible point?

For future travellers, here are some cut and paste friendly versions of the incantation given below by @tfoote:

rosdep install --from-paths src --ignore-src --rosdistro=groovy -y
rosdep install --from-paths src --ignore-src --rosdistro=hydro -y
rosdep install --from-paths src --ignore-src --rosdistro=indigo -y
rosdep install --from-paths src --ignore-src --rosdistro=jade -y