I've been investigating ways to incorporate third-party repositories and
libraries into my Git projects. Subversion's
svn:externals capabilities are one compelling feature for that particular
VCS, and few, if any, other VCS systems, particularly the DVCS systems, have a
truly viable equivalent. Git
submodules aren't terrible, but they assume you
want the entire repository — whereas SVN allows you to cherry-pick
subdirectories if desired.
Why might I want to link only a subdirectory? Consider a project with this structure:
docs/ api/ manual/ html/ module_specs/ library/ Foo/ ComponentA/ ComponentB/ tests/ Foo/ ComponentA/ ComponentB/
On another project, I want to use ComponentB. With
svn:externals, this is easy:
and now the directory is added and tracked.
With Git, it's a different story. One solution I've found is using
git-subtree, an extension to Git. It
takes a bit more effort to setup than
svn:externals, but offers the benefits
of easily freezing on a specific commit, and squashing all changes into a
Jon Whitcraft recently had some questions about how to use it, and I answered him via email. Evidently what I gave him worked for him, as he then requested if he could post my guide — which you can find here.