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Bug: Class extending & incompatible methods #14288

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@alexcorvi

Description

@alexcorvi

TypeScript Version: 2.1.1

Code (playground link)

interface Details { 
    name: "Alex" | "Dan",
    age:number
}

class A {
    method(): Details { 
        return {
            name: "Alex", // this doesn't fire any error
            age:30
        }
    }
}

class B extends A {
    method() {
        return {
            name: "Alex", // this fires an error
            age:50
        }
    }
}

Expected behavior:

No compilation errors

Actual behavior:

An error that says:

Class 'B' incorrectly extends base class 'A'.
Types of property 'method' are incompatible.
Type '() => { name: string; age: number; }' is not assignable to type '() => Details'.
Type '{ name: string; age: number; }' is not assignable to type 'Details'.
Types of property 'name' are incompatible.
Type 'string' is not assignable to type '"Alex" | "Dan"'.

But method in class B is returning an object that is compatible with the declared interface an the error doesn't show up on class A method.

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