Bug: Class extending & incompatible methods

[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.

[alexcorvi]

Adding the Details interface as a declaration for the return type in the class B method does solve the issue.

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

class A {
 method(): Details { 
 return {
 name: "Alex",
 age:30
 }
 }
}

class B extends A {
 method(): Details {
 return {
 name: "Alex",
 age:50
 }
 }
}

However, I don't have to add a declaration for the method() in class B since the class B is extending another class (B) where the method has a return declaration.

[mhegazy]

Duplicate of #1373

Related discussion in #6118 and #10570

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.