Function declarations break inheritance of ambient class declarations

[zOadT]

Bug Report

🔎 Search Terms

• Inheritance
• Function declaration
• Ambient class declaration

🕗 Version & Regression Information

• This seems to be the behaviour since Typescript 3.6 (the version that introduced merging ambient function and class declarations)
• I tried my best to find this issue, I hope this is no duplicate

⏯ Playground Link

Playground link with relevant code

💻 Code

declare class A {
    a: number;
}

declare function B(): B; // (a)
declare class B extends A {
    constructor();
    b: number;
}

let b = new B("Hey")
console.log(b.a) // Property 'a' does not exist on type 'B'.

🙁 Actual behavior

Line (a) breaks inheritance of class B.

🙂 Expected behavior

B should inherit all properties of A as it does when you remove line (a).

[DanielRosenwasser]

Thank you @Zzzen!