lua_objlen with Lua 5.3 using -DLUA_COMPAT_5_1

[peter-evans]

I'm trying to install lua-cjson in a Lua 5.3 environment with hererocks. While installing lua-cjson it failed with "warning: implicit declaration of function 'lua_objlen'." I found this issue suggesting it could be resolved by compiling Lua with the compatibility flag for 5.1, however, it doesn't seem to work. If someone could point me in the right direction to resolve this I would be grateful.

This is the Dockerfile that I'm building:

FROM python:3.6.5

ENV LUA_VERSION 5.3
ENV LUA_DIR “/lua_install”
ENV PATH “$PATH:$LUA_DIR/bin”

RUN apt-get -y update \
 && apt-get install -y -qq --no-install-recommends unzip \
 && pip install hererocks \
 && hererocks $LUA_DIR -r^ --lua=$LUA_VERSION --compat=all --verbose \
 && luarocks install lua-cjson

Hererocks seems to compile Lua with the -DLUA_COMPAT_5_1 flag:

Building Lua 5.3.4 (compat: all)
Skipping 4 patches, use --patch to apply them
Running gcc -std=gnu99 -O2 -Wall -Wextra -DLUA_USE_POSIX -DLUA_USE_DLOPEN -DLUA_USE_READLINE -DLUA_COMPAT_5_1 -DLUA_COMPAT_5_2 -c -o lapi.o lapi.c
...

However, the installation of lua-cjson still throws this warning and is unusable:

Installing https://luarocks.org/lua-cjson-2.1.0.6-1.src.rock
lua_cjson.c: In function ‘json_append_data’:
lua_cjson.c:743:19: warning: implicit declaration of function ‘lua_objlen’ [-Wimplicit-function-declaration]
             len = lua_objlen(l, -1);
                   ^~~~~~~~~~
gcc -O2 -fPIC -I/lua_install/include -c lua_cjson.c -o lua_cjson.o

The full Docker build log: docker-build-log.txt

[peter-evans]

Looks like this is an issue with the latest release of lua-cjson. See this issue: mpx/lua-cjson#56

Specifying the previous release fixes the problem:

luarocks install lua-cjson 2.1.0