A union type should not merge class fields

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

---@class (exact) TypeA
---@field type 'A'
---@field commonField number
---@field specificFieldA number

---@class (exact) TypeB
---@field type 'B'
---@field commonField string
---@field specificFieldB string

---@alias Type_Either_A_Or_B_But_Not_Both TypeA|TypeB

---@type Type_Either_A_Or_B_But_Not_Both
local testA = {
    type = 'A', --- Indicates that this should be of TypeA
    commonField = 'test', --- Should be an error. TypeA.commonField should be a number
    specificFieldA = 123, --- OK
    specificFieldB = 'Hello' --- Should be an error. TypeA.specificFieldB doesn't exist
}

---@type Type_Either_A_Or_B_But_Not_Both
local testB = {
    type = 'B', --- Indicates that this should be of TypeB
    commonField = 'test', --- OK
    specificFieldA = 123, --- Should be an error. TypeB.specificFieldA doesn't exist
    specificFieldB = 'Hello' --- OK
}

Actual Behaviour

TypeA|TypeB is merged, so none of the mismatched fields/types are reported as errors.

local testA: TypeA|TypeB {
    commonField: string|number,
    specificFieldA: number,
    specificFieldB: string,
    type: 'A'|'B',
}

Reproduction steps

Paste the code into vscode

Additional Notes

No response

Log File

No response

Reproduce the annotated TypeA|TypeB example in the Visual Studio Code extension, then trace how the language server merges union class fields. Done means the discriminator selects the correct class and reports the mismatched commonField and member-specific fields shown in the example.