Union table|class doesn't accept a generic table and only accepts a class instance (causing false missing-fields diagnostic)

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, Diagnostics/Syntax Checking

Expected Behaviour

When a function is declared as accepting both table and a custom class type, it should accept getting passed a generic table.

Actual Behaviour

LLS insists on a table matching the class being passed (with all the fields set) and reports the missing-fields diagnostic when passing a generic table.

Reproduction steps

LLS definition file contains the following:

---@meta

---@class TestClass
---@field TestField number A test field in test class
TestClass = {}

-- TestFunction1
---@param generic_table_or_testclass_instance table|TestClass
function TestFunction1(generic_table_or_testclass_instance) end

-- TestFunction2
---@param generic_table table
---@param testclass_instance TestClass
---@overload fun(generic_table: table)
---@overload fun(testclass_instance: TestClass)
function TestFunction2(generic_table, testclass_instance) end

-- TestFunction3
---@param generic_table table
function TestFunction3(generic_table) end

-- TestFunction3
---@param testclass_instance TestClass
function TestFunction3(testclass_instance) end

And then a lua code file contains a call to either test function like

TestFunction1({1,2,3})
TestFunction2({1,2,3})
TestFunction3({1,2,3})

LLS reports Missing required fields in type ``TestClass``: ``TestField`` Lua Diagnostics.(missing-fields) for all 3 calls. Instead it should accept the table as input parameter for the 3 functions.

Additional Notes

No response

Log File

No response

Start with the Lua and type annotations in the reproduction, then trace the type-checking path that produces the missing-fields diagnostic for union and overload parameters. Done means generic tables are accepted for all three calls without reporting TestClass.TestField as missing; no source files or tests are named in the issue.