lqc failed to run without installed ffi module

[ligurio]

README says that FFI module is optional, unfortunately lqc failed to run without it:

sergeyb@pony:~/sources/MRG/topology$ lqc 
Random seed = 1617869614
/usr/bin/lua5.1: ./.rocks/share/tarantool/checks.lua:193: module 'ffi' not found:No LuaRocks module found for ffi
        no field package.preload['ffi']
        no file '/root/.luarocks/share/lua/5.1/ffi.lua'
        no file '/root/.luarocks/share/lua/5.1/ffi/init.lua'
        no file '/usr/local/share/lua/5.1/ffi.lua'
        no file '/usr/local/share/lua/5.1/ffi/init.lua'
        no file './ffi.lua'
        no file '/usr/local/lib/lua/5.1/ffi.lua'
        no file '/usr/local/lib/lua/5.1/ffi/init.lua'
        no file '/usr/share/lua/5.1/ffi.lua'
        no file '/usr/share/lua/5.1/ffi/init.lua'
        no file '/home/sergeyb/.luarocks/share/lua/5.1/ffi.lua'
        no file '/home/sergeyb/.luarocks/share/lua/5.1/ffi/init.lua'
        no file '/root/.luarocks/lib/lua/5.1/ffi.so'
        no file '/usr/local/lib/lua/5.1/ffi.so'
        no file './ffi.so'
        no file '/usr/lib/x86_64-linux-gnu/lua/5.1/ffi.so'
        no file '/usr/lib/lua/5.1/ffi.so'
        no file '/usr/local/lib/lua/5.1/loadall.so'
        no file '/home/sergeyb/.luarocks/lib/lua/5.1/ffi.so'

lqc was successfully installed using LuaRocks: luarocks --local install lua-quickcheck

Version: https://luarocks.org/lua-quickcheck-0.2-4.src.rock

[luc-tielen]

I think it used to be optional, but README is out of date?
I guess it's fine to add it to the set of dependencies, quite a lot of other libs probably use ffi anyway.

[ligurio]

I think it would be fine.
Right now rockspec missed this dependence.

[ligurio]

BTW ffi depency is required only in case of using PUC Rio Lua, because LuaJIT has builtin ffi module [1].

1. https://luajit.org/ext_ffi.html

[luc-tielen]

Yes, that's what is configured in CI also. It only installs for non-JIT Luas.