+# Preseed the go module cache and the ruby gems, using the currently checked
+# out branch of the source tree. This avoids potential compatibility issues
+# between the version of Ruby and certain gems.
+RUN git clone git://git.arvados.org/arvados.git /tmp/arvados && \
+ cd /tmp/arvados && \
+ if [[ -n "${BRANCH}" ]]; then git checkout ${BRANCH}; fi && \