Generic parameters are sometimes not optional when their type resolves to void

[bave8672]

Bug Report

🔎 Search Terms

Generic function method static constructor void optional required

🕗 Version & Regression Information

• Tested up to 4.3.0-beta
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about generics and function signatures.

⏯ Playground Link

https://www.typescriptlang.org/play?ts=4.2.3#code/PQKhAIGUBcEMDsAmsBOjwDcD2BLdAjAUwAtYMcsVwRgAoAMwFd4BjaC+cegHgBUA+ABQAPAFyZciAJTgA3gF8Gg5okL0c8QtIDc4YMHAB5ANJKpu-UdO1QEAGqTwRUuSyMqAd2KFOjAM4aAObgAAaEwtA+iH4h4H4AnvBwwtR0TKzsWJyBfEJi4Lzg4ZFIfuAI8eAA-BJ44OLYeDIKtIHKSGoaWjKWJq2C5noGAKLCAA6EbFrgAIzlKIGMALY+0H4ANE6M0OCBWDsADAB0rdx+0ChBQoOWoxNT6HOoiytJG1s7e4cnOfDLRChrhYRuNJpFHvMXqt3vhtrt9uBjrQbGBwABhAA2sD8ZXCsCWYwxhHAAFpwPB9sToKQditqVhouUxhNUOBoFgnCQyMTsUVQQ9UrQWFiceAAIK5OS0cAy8AsLLnFCMNiUETiQrFKJlP5LAHVWroBqSZqKWVxODsFhcXJqgp8kqMnV6mqNQ0Gk3S2X0W0aiJa8n-QhUF2OI1NOSKRSaDzis4XK4DYHgYYoFCUcR3MHTJ4LZbQzawz4IpFio48RUJm4jVPp5P88GzSF5t4FuFfRG0aOxivwQJCFSdTTSMuJoZWWhAA

💻 Code

/** Standard void behavior */
function f<T>(x: void) {}
f(undefined); // OK
f(); // OK

/** Void behavior when using `extends` syntax */
function g<T>(x: T extends any ? void : void) {}
g(undefined) // OK
g(); // Expected 1 arguments, but got 0.
g<string>(); // Expected 1 arguments, but got 0.
g<number>(); // Expected 1 arguments, but got 0.

/** Class example - note that methods appear to behave as expected */
class A<T> {
    constructor(x: T extends number ? void : void) {}
    static f<T>(x: T extends number ? void : void) {}
    f(x: T extends number ? void : void) {}
}
new A<string>(); // Error: Expected 1 arguments, but got 0.
A.f<string>(); // Error: Expected 1 arguments, but got 0
new A<string>(undefined).f(); // OK

🙁 Actual behavior

For functions, static methods, constructors, that use the extends syntax, typescript treats void arguments as required.

🙂 Expected behavior

Arguments that are known to be void are always treated as optional.

[jcalz]

Duplicate of #29131?

[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.