I think that 'CONFLICTS_BUILD=spidermonkey17-1.7' should be removed. I don't think it is correct. If I remove that CONFLICTS_BUILD line, install spidermonkey17 and build (and install) cjs, the build does not fail. And I don't detect any problem with either installed port.
Note that the CONFLICTS_BUILD line has been there from the beginning, so the commit log offers no hints about why it was added.
Created attachment 206347 [details]
Reset Maintainer. Two years without reaction.
A commit references this bug:
Date: Tue Oct 27 08:11:24 UTC 2020
New revision: 553424
GC outdated conflicts: lang/njs was removed on 2011-06-09 and
CONFLICTS_BUILD=spidermonkey17 does not reflect reality these
days, if it ever did.
I also couldn't see how it's useful and GC'ed it as part of ports r553424.