lua: allow using moonjit

[iii-i]

Description:
moonjit (https://github.com/moonjit/moonjit) is a continuation of
LuaJIT development, which, as of late, has, unfortunately, come to
a stall.

In comparison to LuaJIT, moonjit, among other things, supports
s390x architecture as well as some of the Lua 5.2 language
features.

With this patch, moonjit can be enabled using

--//source/extensions/filters/common/lua:moonjit=1

bazel flag.

Internally, moonjit integration is based on luajit integration.
Some of the fragments thereof (e.g. luajit.patch) were copy-pasted
with minimal modifications. While arguably ugly, this allows
updating LuaJIT and moonjit independently.

Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com

Risk Level: Low
Testing: Run tests with --//source/extensions/filters/common/lua:moonjit=1 flag
Docs Changes: None
Release Notes: None

[dio]

Thanks for this. I think we need to add an entry to docs/root/intro/version_history.rst and docs/root/configuration/http/http_filters/lua_filter.rst to let users aware of it (to try it out).

[yselkowitz]

Why not just use a more recent snapshot of luajit instead, which has support for both IBM architectures?

[dio]

@yselkowitz since this moonjit is an alternative, we can always update luajit "version".

[iii-i]

@dio done.

@yselkowitz where can I get it? I checked master and v2.1 branches of https://luajit.org/git/luajit-2.0.git, and s390x support is not there.

[yselkowitz]

The OpenResty fork of luajit2 has support for both Power LE and Z in their latest snapshot:

https://github.com/openresty/luajit2

[iii-i]

@dio done

@yselkowitz what looks interesting about OpenResty fork, is that moonjit maintainer also thinks it's the way forward for the Lua community (openresty/luajit2#80). Unfortunately, the merger discussion has somewhat stalled. What also makes it harder for us to quickly evaluate OpenResty fork, is that their test suite is much smaller than that of moonjit. So we would rather go forward with moonjit for the time being, if possible.

[dio]

Thanks!