The value check by index is ignored in the right-hand side of the logical conjunction

[s1owjke]

🔎 Search Terms

• is not assignable to parameter of type
• noUncheckedIndexedAccess &&
• logical conjunction

🕗 Version & Regression Information

• This occurs since 4.1 when the noUncheckedIndexedAccess option was added

⏯ Playground Link

https://www.typescriptlang.org/play?noUncheckedIndexedAccess=true&target=7&module=6&noFallthroughCasesInSwitch=true&ts=5.4.0-dev.20231202#code/MYewdgzgLgBA0gUQJoH0BKCDiCAaMC8MA9AHoC0ZAFAHQBUAlEQNwBQoksAhgE4DmEALhjRuASzC8A2gF0CMSQCIKnYFFEA3AKYKANDCVkwAVwC2AI03dd+gIwLprNuGgxxAE00APOQAZWogDNKHn5Jdy8YAGoYG1kAMjj4ZHQsXGooTWhgvggwsA9vaNj6ehgAbwBfFicOGDAvKABJfIjCcMKY-wCYbND6zyaWz3jExFQMbBx0zKhe3P7BgukS8qqalwXGjJM5EPmG5qWuns3tmASk8dSpjKzTzRMVyqA

💻 Code

const KEY_REGEX = /^--(.*)/;
const args: string[] = ["--active", "--number", "1"];

// error
const index = 0;
if(args[index + 1] && KEY_REGEX.test(args[index + 1])) {}

// error
const nextIndex = index + 1;
if (args[nextIndex] && KEY_REGEX.test(args[nextIndex])) {}

// no error - can be used as workaround
const nextItem = args[nextIndex];
if (nextItem && KEY_REGEX.test(nextItem)) {}

🙁 Actual behavior

If we do an check by index, we get the following error:

Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
  Type 'undefined' is not assignable to type 'string'. (2345)

🙂 Expected behavior

No error

Additional information about the issue

This only happens if the noUncheckedIndexedAccess option is set to true

[MartinJohns]

Duplicate of #56389.