Property disappears when matching type parameter name in subclass

[molisani]

🔎 Search Terms

ts2339, "property does not exist on type", "property matches type parameter"

🕗 Version & Regression Information

• This changed between versions 5.2.2 and 5.3.2

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.2#code/MYGwhgzhAEBCkFNoG8C+BuAUJg9D6AcgPbQBGi0okEANNAC4CeADks2AE5gC2C9CHaAHcAlvQAW0CDyQA7GdAC00AOpEOAawiYEAD2br6lcFGgBhAIwAeACoA+FJmjPoNgFzRZAV26kBWF0oiWQh6Di9genUACndPHz8OAEpHQMCJEQgAOhtoAF5XAJdUTBLcfHgIJCooOiZWaHYuXn5BUQkpBXleJWgAESIECFkAciMhdQ0dfUNjanMAJlsHPX5ZABMYSqRkJxc4719-PedgYNDwyJiDhIEU3bSXCC9WDmikoseM7NyCm0-oCUSkA

💻 Code

class Base {};

// No base class, type parameter with same name - Works
export class C1<T> {
    T: number;
    constructor(T: number) {
        this.T = T;
    }
}

// Base class, type parameter with same name - Doesn't work
export class C2<T> extends Base {
    T: number;
    constructor(T: number) {
        super();
        this.T = T; // Property 'T' does not exist on type 'C2<T>'.(2339)
    }
}

🙁 Actual behavior

Property 'T' does not exist on type 'C2<T>'.(2339)

TypeScript does not recognize property T on class C2 but no issue on class C1.

🙂 Expected behavior

No type error, property should be found as expected for both C1 and C2.

Additional information about the issue

This is not an issue if the class does not extend another class, or if the type parameter does not match the property. The property is also not defined on the parent class.

[RyanCavanaugh]

I'm incredibly excited to see what commit caused this...

[RyanCavanaugh]

#55252

[RyanCavanaugh]

@molisani do you have a reasonable workaround on your end, or do you need a 5.3 patch?

[molisani]

@molisani do you have a reasonable workaround on your end, or do you need a 5.3 patch?

This only affects one of our projects and changing either the property name or the type parameter resolves it for now so I don't think an immediate patch is necessary.