loolwsd needs the JSON library of POCO. While Debian just finally got poco 1.7.6 in experimental it of course has it without the JSON parser[1]. Would it be possible to switch to an other parser not tainted by the license? E.g. orcus' one (which already de-facto is there due to loolwd -> LO)?[2] [1] it's licenses under the JSON license from json.org. Which is non-free given it says "use it for good not evil" and thus discriminates against fields of endavour, violating point 5 of the DSFG (and thus point 6 of the OSD ) [2] though "of course" LO misses the orcus headers, but..
See also https://wiki.debian.org/qa.debian.org/jsonevil
https://raw.githubusercontent.com/pocoproject/poco/poco-1.8.0-release/CHANGELOG: - fixed GH #1614: Problematic license for JSON component: the previously used JSON.org parser has been replaced with pdjson so with poco 1.8.0 this becomes not needed anymore. neither the libreoffice-5.4.2.2 tag nor current master build against 1.8.0 but that it an other matter.... and given that this was open so long and noone even dared to try to fix this I think we can set this WONTFIX..