noUncheckedIndexedAccess does not work correctly with Array

[SuperITMan]

Bug Report

🔎 Search Terms

noUncheckedIndexedAccess with arrays

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about noUncheckedIndexedAccess

⏯ Playground Link

Playground link with relevant code

💻 Code

// @strict: true
// @noUncheckedIndexedAccess: true

const arr: string[] = [];

const test = () => {
    if (arr.length > 1) {
        // As arr.length > 1, we expect that length >= 2. That means arr[0] should be a `string`
        const str: string = arr[arr.length - 2]; 
        console.log(str);
    }

    // Same here, we check arr.length == 1, so arr[0] should be a `string` and cannot be `undefined` according to declaration `const arr: string[] = [];`
    if (arr.length === 1 && arr[0].match(/test/)) { 
        console.log("First index matches 'test'");
    }
}

🙁 Actual behavior

Get following errors:

error TS2322: Type 'string | undefined' is not assignable to type 'string'.
  Type 'undefined' is not assignable to type 'string'.
    const str: string = this.arr[this.arr.length - 2];

error TS2532: Object is possibly 'undefined'.
    if (arr.length === 1 && arr[0].match(/test/))

🙂 Expected behavior

The code should not generate any error since the array is type string[] and not (string|undefined)[]

[RyanCavanaugh]

This was one of the outlined caveats of the flag; see #13778

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.