No error thrown when calling concat with T[] and T[][]

[thomasschafer]

🔎 Search Terms

"concat", "concat wrong type", "concat no error"

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play?ts=3.3.3#code/MYewdgzgLgBAhgJwQRhgXhgbU8gurgKFElkQQCZ14lkA6Y4OKACk3NwEojwIQAbAKa0+IAObMy5LtxLUEAZirYARHGX4Z0OQBYqZefXCMWmZQCN1XYr0HCxEpNo5A

💻 Code

const arr1 = [[1]]
const arr2 = arr1.concat([2]) // No error

const arr3 = [["a"]]
const arr4 = arr3.concat(["b"]) // No error

🙁 Actual behavior

No error is shown, and type of the result is incorrectly inferred as T[]

🙂 Expected behavior

Either an error should be shown, or the result of concat should be (T | T[])[]

Additional information about the issue

No response

[MartinJohns]

Duplicate of #36554 (comment).

[typescript-bot]

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