Hello,
One of the blockers for the effort to package HHVM for Debian is the licensing of the JSON extension. This is the same problem that has afflicted PHP (see https://bugs.php.net/bug.php?id=63520: "JSON extension includes a problematic license statement") and that we have discussed in the context of bug 47413 (< https://bugzilla.wikimedia.org/show_bug.cgi?id=47431%3E: "JSON extension dependency has a non-free component".
There is a drop-in replacement which is not encumbered with licensing issues: Remi Collet's pecl-json-c, available at < https://github.com/remicollet/pecl-json-c%3E. Paul Tarjan replied on the packaging thread (see < https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg1208263.ht...), saying that the HHVM team would be interested in swapping out the JSON library and replacing it with pecl-json-c, if someone were to port it. Since both extensions provide the same API, I imagine "porting" in this context means tweaking the include paths and the build configuration.
Are any of you interested in taking this on?