How Lake finds Lua

The predefined need 'lua' is for programs and shared libraries that need to link against Lua.

If luarocks is installed on your machine, then it will query luarocks' LUA_INCDIR and LUA_LIBDIR.

The 'canonical' Lua install on Unix machines is for lua.h to be on the usual include path. On Debian/Ubuntu, this isn't so because multiple versions of Lua are supported - there the path will be /usr/local/lua5.1 and the headers are provided by the liblua5.1-0-dev package. If none of these apply, then set the global LUA_INCLUDE_DIR.

Windows is always ... different. If the environment variable LUA_DEV is defined then this is Lua for Windows. This results in linking against the old MSVC 2005 runtime if using mingw (fortunately, LfW is due for replacement with a much more sensible mingw distribution based on LuaDist). From the location of the Lua executable, Lake uses a heuristic search for the include directory as a subfolder or parallel folder of this location. When using mingw it will link directly against the lua5.1.dll that will be in the executable directory, otherwise it needs to find the lib directory in the same way.