Incorrect typing when calling splice() on a tuple

[bbrk24]

Bug Report

🔎 Search Terms

tuple splice

🕗 Version & Regression Information

• This is the behavior in every version I tried. I reviewed the FAQ for entries about tuples, but didn't find anything.

⏯ Playground Link

Playground link with relevant code

💻 Code

declare let arr: [string, number];

arr.splice(1); // mutates arr, making it only [string]
let arr2 = arr; // incorrectly inferred as [string, number]
let arr3 = arr as [string]; // incorrect conversion error

🙁 Actual behavior

See the comments in code above. What the TypeScript compiler infers is different from the actual runtime behavior.
It's worth noting that the return value of the call to splice() is correctly inferred as (string | number)[].

🙂 Expected behavior

Either calling arr.splice(1) should be an error (due to calling splice on a tuple), or the type of arr should be different after calling arr.splice(1).

[MartinJohns]

Related, or perhaps even a duplicate of #40316. It refers to a different method, but the issue is the same.

[bbrk24]

That's true, I didn't see that. The same problem exists with shift() as well.

[typescript-bot]

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