How to define type hints for user callback functions

[ChillerDragon]

I am working on a lua api for a C++ game. And users creating these plugins can implement global function that will be called by C++. I tried putting a few type hints into my meta file like these but it did not properly let me autocomplete function on_<tab>

---@meta

---@type fun(client_id: integer)
on_player_connect = nil

functions.mp4

[ChillerDragon]

Hmm I had a look at how it is done for love2d and I could not get that to work either :/

I installed this https://github.com/LuaCATS/love2d/tree/main

And I get type hints for the functions the user can call just fine

But no type hints for the callbacks the user can define

Even tho they seem to be defined here

https://github.com/LuaCATS/love2d/blob/765abafe49775ba52937430e2546dfc330381d6b/library/love.lua#L319-L322

[tomlau10]

AFAIK, the callback types are expected to be used like this

---@type love.update
function love.update(dt)
    -- your callback logic
    print(dt) --> dt: number
end

• i.e. meta file using @alias to define a function type
• then user need to write the type annotation above the callback function definition 😅

[ChillerDragon]

@tomlau10 oof :/ thanks for sharing that c:

I also figured out this works. But that requires my users to be deep into the type annotation game. That is not realistic. Or do love2d users for example actually actively do that in the wild?

Also it does not even autocomplete function love.up<tab> right? So users would have to know the full callback name and type name. If they match that is of course easier. But this means that users have to read the documentation or manually find the meta file somehow to be able to use a library. Because the language server is not giving support here.

I mean the project is really cool already and I take what I get I just assumed it could do that smoothly somehow.

[tomlau10]

But that requires my users to be deep into the type annotation game. That is not realistic.

Yes, and I agree with you.

Also it does not even autocomplete function love.up right?

Yep, because @alias only defines a type, not the global function.
You will only get the autocompletion when completing a type, eg ---@type love.up<tab> => it should show up

---

Because the language server is not giving support here.

I am just a user and contributor (fixed a few bugs) not maintainer. So I am not able to help further 🙈

[ChillerDragon]

I am just a user and contributor (fixed a few bugs) not maintainer. So I am not able to help further 🙈

You did good. Thanks for responding. I wanted to make sure I am not missing something and it looks like I did not. The issue was more of a question than a feature request. While I would love this feature I understand it might be tricky to realize. So if any maintainer sees this feel free to close the issue. I will leave it open for now with the hope of someone chipping in some other workaround.

[CppCXY]

[ChillerDragon]

Interesting how did t get the type?

UPDATE:

Ah wait I see it now :D
Okay let me test this real quick thanks.

[ChillerDragon]

@CppCXY so doing naked global functions does not work but members of a table do? I can change my api just to make that work :D just wanted to double check.

[ChillerDragon]

Okay I tested this it works really well. Amazing thanks @CppCXY !!!

Even the function name completes here function t.on_player_co<tab> sadly it does not complete the parameters with it :(
And I also wonder how to then give the parameters detailed descriptions but thats for another issue #3372.

Does that mean the LuaCATS/love2d annotations are wrong?

[CppCXY]

that maybe mean a function param type:

[ChillerDragon]

Ah yes I see. The alias can be useful if the user wants to annotate callbacks. But as far as I understand it love.update is mostly implemented by the user and rarely passed around as callback by the user. So my assumption stays that the LuaCATS/love2d annotations are wrong. Or at least not as good as they can be. Or not vibing with this language server 🤷

I kinda assumed that the love annotations were the gold standard.

Anyways this comment is exactly what I opened the issue for and it works great for me. Thanks!