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

Reproduce the minimal Lua example in the Visual Studio Code extension, starting with the generic List/listlib declarations and the class-style list annotation. Trace type inference for indexed access, at, whereList, and front. Done means inferred types match the expected string, integer, and number results instead of unknown or unresolved generic types.