Wrong type when function signature changes

[NilsIrl]

🔎 Search Terms

• function signature
• wrong type
• changed
• re-assigned
• re-declared
• type inference

🕗 Version & Regression Information

• This is the behavior in every version (3.3.3333 and 5.2.2) I tried, and I reviewed the FAQ for entries about bugs that aren't bugs.

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2#code/DYUwLgBAzg9gtiAYgVwHYGMIF4IAoCGAXBAPIBGAViOmAJTYB8E+A3AFDoypST7bTwkadLgDeAX1rtYCFBn656WJgFZ2nbpDL8ZQjIpZA

💻 Code

let someFunc = (a: Object) => a;
const a = someFunc({});
someFunc = () => 5;
const b = someFunc();

🙁 Actual behavior

It doesn't compile and there is an error on the second call to someFunc saying that an argument is not supplied.

🙂 Expected behavior

Because someFunc was redefined it doesn't actually expect an argument and the code is correct.

Additional information about the issue

When using the function keyword, the inferred type is correct (although it doesn't compile either but this time because there is a duplicate function implementation):

https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABAZzgWwKYDFwQBQCGAXIgPIBGAVhtAJSIDeiAThlCM0gQNyIC+AKAgJkURAUQBeFOmy48DPrW4DQkWAhmYckPPSat2nRn16DhYUYnJStc3cqA

[MartinJohns]

Possibly a duplicate of #27706, although there's no narrowing happening in this case.

Point 2 and 3 of this comment sound relevant: #36579 (comment)

Variables initialized with some expression always assume the widened form of the initializer's type
Assignment will only create a narrowing to a more-specific type if the declared type of the assigned variable is a union

So it sounds like it's working as intended.

[typescript-bot]

This issue has been marked as "Not a Defect" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[NilsIrl]

Even with a union type it doesn't work: https://www.typescriptlang.org/play?ts=5.2.2#code/DYUwLgBAzg9gtiAYgVwHYGMBcEAUBDbAeQCMArEdMASggF4A+CE8yiAH1xxoabIurq4CvFgJ54A3ACh0MVFEh5BsBCgw4A3gF8q0lUjTpBXOowCs02fMjFl8A+t1A