Duplicate identifier error when merged interface is declared before class

Bug Report

🔎 Search Terms

interface accessors getters declaration merge

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about interfaces, merging, and getters

⏯ Playground Link

Playground link

💻 Code

class Foo {
    get x(): number { return 0; } // ok
}
interface Foo {
    x: number; // ok
}

interface Bar {
    x: number; // not ok
}
class Bar {
    get x(): number { return 0; } // not ok
}

🙁 Actual behavior

Bar throws an error but not Foo

🙂 Expected behavior

Neither or both throw an error (probably both).

While exploring whether an interface can merge with a class in order to narrow the type of a class's inherited getter (there is no documentation, but the answer seems to be that accessor properties are not properly representable in interfaces as of 4.2.2), I came across seemingly unpredictable conditions for what tsc would accept. Eventually, it became apparent that the order of the interface and class declarations has bearing on whether an error is thrown.