Incorrect type narrowing on generic type above 4.9.5

[zheeeng]

Bug Report

🔎 Search Terms

Generic type narrowing

🕗 Version & Regression Information

• This changed between versions 4.8.4 and 4.9.5

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.0.4#code/GYVwdgxgLglg9mABFApgZygHgCqJQD1TABM1EBDMATwG0BdRAH0QCUUI4AnYzDTmMAHMANBWoA+cQAo4AIwBWALkTYAlIgDeAWABQifYhjBEUgIKdO5KgDoYac5aoyF6xswDkAGxRCoAC3dDJDl5dW09A30QgG5dfQB6eMQAPQB+OIMAXzxPNBRNDMiYjMSU9Ij9TN0qnV1QSFgEZHQoACYcPEIfUjFaBmY2Dm5eKH4hUUoqSWclFTDCw2MzCytbexWnENV5ioNiiNK0heyUXPzwyKiFWIOko92amqA

💻 Code

function test<T extends any[] | Record<string, any>>(obj: T) {
    if (Array.isArray(obj) || 'length' in obj) {
      obj;
  // ^? (parameter) obj: T extends any[] | Record<string, any>
    } else {
      obj;
  // ^? (parameter) obj: never
    }
}

function test2<T extends any[] | Record<string, any>>(obj: T) {
    if (Array.isArray(obj)) {
      obj;
  // ^? (parameter) obj: T & any[]
    } else {
      obj;
  // ^? (parameter) obj: T extends any[] | Record<string, any>
    }
}

🙁 Actual behavior

In the else branch of the test function, obj is inferred as never type.

🙂 Expected behavior

In the else branch of the test function, obj should be inferred as T extends any[] | Record<string, any> type.