Currently, specifying "source-depth: 1" only does a shallow checkout of the root repository. If there are any submodules, the entire submodule history is checked out. In a repository consisting largely of submodues (e.g. https://github.com/qt/qt5) this massively impacts the build time. Proposition: if "source-depth" is specified, "--depth" should also be added to the "git submodule update" command.