Unexpected generic behaviour

[Frityet]

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

MacOS

What is the issue affecting?

Annotations

Expected Behaviour

local ffi = require("ffi")

---@generic T
---@param ct `T`
---@return fun(x: T): `T`*
local function ref(ct)
    return function (init)
        return ffi.new(ct.."[1]", {init})
    end
end

ffi.cdef [[
    typedef struct MyStruct {
        int a, b;
    } MyStruct;
]]

---@class MyStruct
---@field a integer
---@field b integer

---@class MyStruct* : { [integer] : MyStruct }, ffi.cdata*

local x = ffi.ref "MyStruct" {
    a = 4,
    b = 2
}

--type of `x` expected to be `MyStruct*`

Actual Behaviour

type of x is MyStruct

Reproduction steps

Run the code and check types

Additional Notes

No response

Log File

No response

[tomlau10]

I think your annotation is incorrect.
The backtick capture syntax is used in @param only, not in @return.
It is for capturing the literal string input and convert it as type name, and optionally modify the name by appending other string.

I just tested a bit and you have to write it like this:

local ffi = {}

---@generic T1, T2
---@param ct `T1`|`T2`*
---@return fun(x: T1): T2
function ffi.ref(ct) end

---@class MyStruct
---@field a integer
---@field b integer

---@class MyStruct* : { [integer] : MyStruct }, ffi.cdata*

local x = ffi.ref "MyStruct" { --> x: MyStruct*
    a = 4,
    b = 2,
}

local y = ffi.ref "MyStruct" { --> y: MyStruct*
    a = 4,
    --> error: Missing required fields in type `MyStruct`: `b`
}

• capture ct literal string input into 2 captured generic names T1 and T2
• T1 is just the original literal string type name
• T2 we append a * at the back
• then use these 2 types in the @return function