Edgelord von Hresvelg@vantablack the PKGBUILD just downloads the jar from the website so assuming you trust the website it's safe. Nothing shady looking in the AUR at least
Jonkman Microblog is a social network, courtesy of SOBAC Microcomputer Services. It runs on GNU social, version 1.2.0-beta5, available under the GNU Affero General Public License.
All Jonkman Microblog content and data are available under the Creative Commons Attribution 3.0 license.