Implicit Symbol.iterator call does not check additional arguments

[rotu]

🔎 Search Terms

Symbol.iterator, for-of, iterable protocol

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYewdgzgLgBAtgTwJJQKYCcCGAjANqmAXhgG8AoGSmAKgG0BlBObEXAOgEs0soR0BdABSoAHlCwBBdAHMAXDDABXZhgCUpClS0IOqXABNSMTPNHjMU6TAC+myrdtkA9E+NgYGdHxgALTAAd-VEhfDFQ2GABxEBB9NjIAM29BUEhYERgQBPhkbhx8BiYWdi4MTF4BQVVVci0RNkwyRxcFEA90L3RQ9HCYACFMQ1kAWkFE5NToGAysnJQyvFQau2mGprIgA

💻 Code

const myIterable = {
 *[Symbol.iterator](extraArg: number) {
 yield { a: extraArg }
 }
}

// an error happens here. Good.
for (const x of myIterable[Symbol.iterator]()){
 x.a
}

// no error here. Bad :-(
for (const x of myIterable){
 x.a
}

🙁 Actual behavior

When using a for-of loop, there is no type error.

🙂 Expected behavior

I expect an error to be reported, as if explicitly calling the [Symbol.iterator] method.

Additional information about the issue

Related to #38388, which points out that resolution does not infer this generic type parameter.