Building and linking lua from source via makefile - lua

Question

I've tried to compile and link lua with my application. This is my makefile:
app.o: app.cpp
g++ -c app.cpp
PATH_LUA=../lua-5.4.3/src
LUA= \
$(PATH_LUA)/lapi.c \
$(PATH_LUA)/lauxlib.c \
$(PATH_LUA)/lbaselib.c \
$(PATH_LUA)/lcode.c \
$(PATH_LUA)/lcorolib.c \
$(PATH_LUA)/lctype.c \
$(PATH_LUA)/ldblib.c \
$(PATH_LUA)/ldebug.c \
$(PATH_LUA)/ldo.c \
$(PATH_LUA)/ldump.c \
$(PATH_LUA)/lfunc.c \
$(PATH_LUA)/lgc.c \
$(PATH_LUA)/linit.c \
$(PATH_LUA)/liolib.c \
$(PATH_LUA)/llex.c \
$(PATH_LUA)/lmathlib.c \
$(PATH_LUA)/lmem.c \
$(PATH_LUA)/loadlib.c \
$(PATH_LUA)/lobject.c \
$(PATH_LUA)/lopcodes.c \
$(PATH_LUA)/loslib.c \
$(PATH_LUA)/lparser.c \
$(PATH_LUA)/lstate.c \
$(PATH_LUA)/lstring.c \
$(PATH_LUA)/lstrlib.c \
$(PATH_LUA)/ltable.c \
$(PATH_LUA)/ltablib.c \
$(PATH_LUA)/ltm.c \
$(PATH_LUA)/lundump.c \
$(PATH_LUA)/lutf8lib.c \
$(PATH_LUA)/lvm.c \
$(PATH_LUA)/lzio.c
libLua.so:
g++ -shared $(LUA) -fPIC -o lua/libLua.so
all: libLua.so app.o
g++ -o app app.o -I$(PATH_LUA) -lLua -Llua -ldl
The compilation works fine, but something is wrong with the linkage, because I get tons of undefined references to "lua_XYZ-function". The undefined reference to lua_tointegerx for example makes no sense, since its implementation is located in lapi.c which is in the file-list above.
(INB4: "This is a duplicate question!" … I've tried my best to check them all.)
What am I missing?

Answer 1

You are putting the libLua.so (by the way, personally I think it's a really bad idea to name your library the same name as the standard library, just uppercase... there's no way that can't bite you or someone in the rear at some point) in the lua subdirectory but you don't tell the linker where to find it.
Then, you list liblua.a as the prerequisite, but you have no actual rule to build liblua.a, which means make will come up with one based on its internal rules... whatever rule it uses will certainly not include all your source files (how could it know?).
If you show us the actual output of running make (before all the error messages) it should be pretty clear this has gone wrong from the beginning.
Speaking from a strictly makefile perspective, it's virtually always wrong to have the name of the file your recipe builds be different than the name of the target in the makefile.

Answer 2

You have to compile lua as c++-code explicitly.
You do this by including
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
instead of
#include <lua.hpp> which includes that extern "C" {...} statement.