问为什么穷举检查对联合类型的工作方式不同？

EN

type Variant1 = {
    kind: 1 | 2
}

type Variant2 = {
    kind: 1
} | {
    kind: 2
}

const x: Variant1 = { kind: 1 };


function exhaustivenessCheck1(x: Variant1) {
    switch (x.kind) {
        case 1:
        case 2:
            break;
        default:
            const _x: never = x.kind; // OK
            const _y: never = x; // Error
    }
}

function exhaustivenessCheck2(x: Variant2) {
    switch (x.kind) {
        case 1:
            break;
        case 2:
            break;
        default:
            const _x: never = x.kind; // Error
            const _y: never = x; // OK
    }
}