Generic type inference breaks for class-style tables with indexed fields (---@class list<T>: { [integer]: T })

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Type Checking

Expected Behaviour

---@type string[]
local testA = { }
local testB = { 1, 2, 3 }

local testAA = List(testA)
local testBB = List(testB)

local vAA1 = testAA[1]  -- expected: string
local vBB1 = testBB[1]  -- expected: integer

local vAA2 = testAA:at(1)  -- expected: string
local vBB2 = testBB:at(1)  -- expected: integer

 ---@type list<number>
local testCC = List {}

-- newList -> expected: list<number>
local newList = testCC:whereList(function(a) return a == 0 end)

-- front   -> expected: number
local front = newList:front()

Actual Behaviour

---@type string[]
local testA = { }
local testB = { 1, 2, 3 }

local testAA = List(testA)
local testBB = List(testB)

local vAA1 = testAA[1]  -- actual: string|<T>
local vBB1 = testBB[1]  -- actual: string|<T>

local vAA2 = testAA:at(1)  -- actual: unknown
local vBB2 = testBB:at(1)  -- actual: unknown

 ---@type list<number>
local testCC = List {}

-- newList -> actual: list<<T>>
local newList = testCC:whereList(function(a) return a == 0 end)

-- front   -> actual: unknown
local front = newList:front()

Reproduction steps

---@meta

---@generic T
---@param t T[]
---@return list<T>
function List(t)
    return listlib:new(t);
end

---@class list<T>: { [integer] : T }
listlib = {}

---@generic T
---@param t T[]
---@return list<T>
function listlib:new(t) end

---@generic T
---@param self list<T>
---@param index integer
---@return T
function listlib:at(index) end

---@generic T
---@param self list<T>
---@return T
function listlib:front() end

---@generic T
---@param self list<T>
---@param predicate fun(a: T): boolean
---@return list<T>
function listlib:whereList(predicate) end

---@type string[]
local testA = { }
local testB = { 1, 2, 3 }

local testAA = List(testA)
local testBB = List(testB)

local vAA1 = testAA[1]  -- expected: string, actual: string|<T>
local vBB1 = testBB[1]  -- expected: integer, actual: string|<T>

local vAA2 = testAA:at(1)  -- expected: string, actual: unknown
local vBB2 = testBB:at(1)  -- expected: integer, actual: unknown

 ---@type list<number>
local testCC = List {}

-- newList -> expected: list<number>, actual: list<<T>>
-- front   -> expected: number ,actual: unknown
local newList = testCC:whereList(function(a) return a == 0 end)
local front = newList:front()

Additional Notes

No response

Log File

No response

Visual Studio Code extension で最小限の Lua 例を再現し、汎用的な List/listlib 宣言とクラス形式のリストアノテーションから始めます。indexed access、at、whereList、front の型推論を追跡します。完了条件は、推論された型が unknown や未解決のジェネリック型ではなく、期待される string、integer、number の結果と一致することです。