Ipairs with generic

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?

Annotations

Expected Behaviour

Should have got a correct type inference in a generic function.

Actual Behaviour

1. could not specify a V-related type for result in the generic function
2. ipairs will be inferred as unknown
3. returns of the generic function will be inferred as a strange type

Reproduction steps

---@class Test
---@field name string

---@type Test[]
local tests = {
    { name = "test1" },
    { name = "test2" },
    { name = "test3" },
}

--[[
CORRECT:
    function group_by(rows: <V>[], key: string)
    -> table<string, <V>[]>
]]
---@generic V
---@param rows V[]
---@param key string
---@return table<string, V[]>
local function group_by(rows, key)
    --[[
        ---@type table<string, V[]>
        GOT: Undefined type or alias `V`.
    ]]
    local result = {}
    -- WRONG: local v: unknown
    for i, v in ipairs(rows) do
        local k = v[key]
        if not result[k] then
            result[k] = {}
        end
        table.insert(result[k], v)
    end
    return result
end

--[[
WRONG:
    local groups: table<string, <V>[]> | { [<K>]: Test }
EXPECTED:
    local groups: table<string, Test[]>
]]
local groups = group_by(tests, "name")

Additional Notes

No response

Log File

No response

まず issue の Lua スニペットを再現し、language server のジェネリックアノテーション、インデックスアクセス、ipairs の型推論の各経路を調査します。V がローカルの結果アノテーションで受け入れられ、ipairs がジェネリックな要素型を返し、group_by(tests, "name") が table<string, Test[]> として推論されれば完了です。