swc/crates/swc_ecma_parser/tests/tsc/controlFlowAssignmentExpression.ts

let x: string | boolean | number;
let obj: any;

x = "";
x = x.length;
x; // number

x = true;
(x = "", obj).foo = (x = x.length);
x; // number

// https://github.com/microsoft/TypeScript/issues/35484
type D = { done: true, value: 1 } | { done: false, value: 2 };
declare function fn(): D;
let o: D;
if ((o = fn()).done) {
    const y: 1 = o.value;
}