Garbage collection, tag, metatable questions

[mihaly-sisak]

Hi all! I am working trough porting some lua libs for luau and I have some questions I cant really find an answer for. Is there some documentation detailing every function in lua.h and lualib.h?

Garbage collection

LUA_API void* lua_newuserdatadtor(lua_State* L, size_t sz, void (*dtor)(void*));
typedef void (*lua_Destructor)(lua_State* L, void* userdata);
LUA_API void lua_setuserdatadtor(lua_State* L, int tag, lua_Destructor dtor);
LUA_API lua_Destructor lua_getuserdatadtor(lua_State* L, int tag);

Why is there difference in the function signatures for tagged and untagged data? Are there performance differences between the two? Can I access the full lua state without restrictions if I use the tag one?

Tags
Can I check what tags are in use? If I want to use 2-3 libraries, do I need to coordinate between them to do not use the same tag twice?

LUA_API void lua_setlightuserdataname(lua_State* L, int tag, const char* name);
LUA_API const char* lua_getlightuserdataname(lua_State* L, int tag);

What are these functions good for? Does it tag the top of the stack? If I set a destructor for the tag will it get called for the lightuserdata pointer created with lua_pushlightuserdatatagged?

Metatables
What does LUALIB_API int luaL_newmetatable(lua_State* L, const char* tname); do? How it is different than just lua_newtable? How does Lua know what it will be a metatable for if I do not need to provide a tag?
Where does LUA_API void lua_setuserdatametatable(lua_State* L, int tag); get the metatable from? Top of the stack?
Am I supposed to luaL_newmetatable then lua_setuserdatametatable? How do I fill it? Just like a normal lua table on top of the stack?
If I do not create an object with lua_newuserdatataggedwithmetatable but with lua_newuserdatatagged but that tag has a metatable set, what happens? Will the object get the metatable?

[mihaly-sisak]

Pls respond 😢