Incorrect type inference for generic types with 'prototype' property #55199
Description
Bug Report
🔎 Search Terms
- generic type prototype inference
🕗 Version & Regression Information
- This changed between versions 4.7.4 and 5.2.0
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about
prototype
⏯ Playground Link
Playground link with relevant code
💻 Code
interface Type<T> {
new(...args: any[]): T;
}
interface Proto<T> {
prototype: T;
}
function injectWithType<T>(a: Type<T>): T { return null as T };
{
const okUnknown = injectWithType(Set); // Set<unknown> ⚠️
const okNumber = injectWithType<Set<number>>(Set); // Set<number> ✅
const okNumber2 = injectWithType(Set<number>); // Set<number> ✅
}
function injectWithProto<T>(a: Proto<T>): T { return null as T };
{
const okAny = injectWithProto(Set); // Set<any> ⚠️
const okNumber = injectWithProto<Set<number>>(Set); // Set<number> ✅
const unexpectedAny = injectWithProto(Set<number>); // Set<any> ‼️
}The compiled version has a bug too - double parentheses (reproduced both with the injectWithType and the injectWithProto.):
const unexpectedAny = injectWithProto((Set)) // >= [email protected]
const unexpectedAny = injectWithProto(Set()) // < [email protected]🙁 Actual behavior
When using an interface or atype with the prototype property to declare class, generic type is getting wrong, especially in the ExpressionWithTypeArguments (‼️) case.
🙂 Expected behavior
(⚠️) - These lines should have the same type (Set<any> or Set<unknown>)
(‼️) - This line should correctly infer generic type (Set<number>)
const arrOfNum = injectWithProto(Set<number>) // should be Set<number>, not Set<any>