Subversion release source tar ball ships with C source files and per language support files produced by SWIG, and each language swig bindings ports seems to use them without reproduce them, by using BUILD_DEPENDS swig3.0. If we really want to reproduce them from SWIG source files, insert clear-swig-{py|rb|pl} before swig-{py|rb|pl}-lib in ALL_TARGET= line in ports Makefile. (Or if SWIG source file is modified by patch, make swig-{py|rb|pl} trigger to rebuild rebuild its dependent). Otherwise, we can drop build dependency on swig3.0.
A commit references this bug: Author: lev Date: Sun Nov 3 22:48:12 UTC 2019 New revision: 516612 URL: https://svnweb.freebsd.org/changeset/ports/516612 Log: Addons don't neet SWIG to be installed. PR: 241602 Submitted by: Yasuhito FUTATSUKI <freebsd-bug-report-yf@yf.bsdclub.org> Changes: head/devel/subversion/Makefile.common head/devel/subversion-lts/Makefile.common
Good catch, thnx!