Created attachment 216253 [details]
a patch to add a comment for FreeBSD diff in "diff" option in viewvc.conf.dist file
Revision diff view on Side-By-Side style or Full Colored diff style on ViewVC depends on GNU diff. If "diff" option in [general] section in viewvc.conf is not specified on FreeBSD 12 or later, ViewVC uses /usr/bin/diff, which is incompatible with GNU diff, Side-By-Side diff view shows usage of diff and Full Colored diff view shows no diff.
So I think it is better to add textproc/diffutils to RUN_DEPENDS, or to show some message about it.
Here is a patch against conf/viewvc.conf.dist to add comment for it.
While mentioning GNU Diff is needed, it may also worth to check what's the feature required and implement in BSD diff.
(In reply to Li-Wen Hsu from comment #1)
I didn't see detailed in the code for Full Colored diff yet, however obviously it is need a feature of --side-by-side option for Side-By-Side view.
I'll check for the Full Colored diff later.
Full color diff depends on -C|--context option with option value "-1".
With this option, GNU diff acts as if larger number than number of lines in files has been passed.