🔎 Search Terms

class inference, optional class, broken inference

🕗 Version & Regression Information

This changed in PR #31116

However, this was the first time that there was even a distinction between a generic and non-generic class during inference to my knowledge. This likely means this has existed ever since the ability to infer a generic class has existed.

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAggdiAwgezgZ2AJwK4GNjKZQC8UcEA7lABQB09AhpgOZoBcUDCA2gLoCUJAHxRkAIwBWEfAG4AUHIBm2OPgCWqKACUIcACYRMAMQA2DVgFk1ADzVwAPACEGaCIjNo0UCNeC69XvBIqBg4+IRQAD5QKgaKdhB6JDH6EPHkekLUclC5UM6uAPwcBW4eaAA0coIA3gC+8nK45VAocMAMCZj2ACoi9Qo6qcZmljZ21G0dXfxyAPRzeUvLeQB6sCzYALa6wKKKUKCQUADkRxDIB1Od5JgnUGpecMh7LmhqzHAMYibQBFBgJgMHZ+IiXQ7gaAnWJpBJ6E60IA

💻 Code

type AnyConstructor = new (...args: any[]) => object;

function RenderFlagsMixin<BaseClass extends AnyConstructor | undefined = undefined>(
    Base?: BaseClass,
) {};

class Container<T> {}
//             ^ Only happens when the class is generic.

RenderFlagsMixin(Container)
//               ^ Argument of type 'typeof Container' is not assignable to parameter of type 'undefined'.

🙁 Actual behavior

BaseClass is inferred as undefined despite the call being the value Container.

🙂 Expected behavior

BaseClass should be inferred as typeof Container.

Additional information about the issue

No response