Parenthesis break narrowing.

[JeanMeche]

🔎 Search Terms

• narrowing
• parenthesis
• union
• if condition
• switch

🕗 Version & Regression Information

Tested in 5.8, probably not a regression.

⏯ Playground Link

https://www.typescriptlang.org/play/?#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

💻 Code

type Test = TestA | TestB;
interface TestA {
    type: 'a';
    name: string;
}

interface TestB {
    type: 'b';
    value: number;
}

function _tcb1(this: { test: Test }) {
    // TS generated by Angular's Type Check block
    const _t1 = (((((this).test)).type));
    if (_t1 === "a") {
        (((((this).test)).name)); // KO
    }
}

🙁 Actual behavior

TS doesn't narrow correctly

🙂 Expected behavior

TS should narrow correctly despite the execessive parenthesis.

Additional information about the issue

This is similar to a priori issue with typeof expressions #60784