Seems like webkit-patch is generating diffs in a weird way with an svn checkout on Mojave seed 1. svn-create-patch works just fine, so the root of the problem is somewhere in webkit-patch.
Looks like there are a few other svn problems in Mojave too, revealed by running 'test-webkitpy --all'.
Created attachment 342213 [details]
Comment on attachment 342213 [details]
Clearing flags on attachment: 342213
Committed r232605: <https://trac.webkit.org/changeset/232605>
All reviewed patches have been landed. Closing bug.