Type Merging between extends and intersection

**TypeScript Version:** 1.8.10 **Code** ``` ts interface Foo { on(type: 'foo', listener: (event: MouseEvent) => boolean): boolean; on(type: string, listener: (event: Event) => boolean): boolean; } interface Bar { on(type: 'bar', listener: (event: MSGestureEvent) => boolean): boolean; on(type: string, listener: (event: Event) => boolean): boolean; } interface FooBarA extends Foo, Bar {} // Error: not correctly extended interface FooBarB extends Foo, Bar { on(type: 'foo', listener: (event: MouseEvent) => boolean): boolean; on(type: 'bar', listener: (event: MSGestureEvent) => boolean): boolean; on(type: string, listener: (event: Event) => boolean): boolean; } type FooBarC = Foo & Bar; let foobar: FooBarC; foobar.on('foo', (event) => { return false; }); ``` **Expected behavior:** That `FooBarA` would work instead of throwing an error. **Actual behavior:** `FooBarA` complains `Interface 'FooBarA' cannot simultaneously extend types 'Foo' and 'Bar'. Named property 'on' of types 'Foo' and 'Bar' are not identical.` While that is true in the strictest sense, the "base" override matches, which means in theory the string literal types could be merged and the error should only occur if there is a conflict between a specific string literal type. Using the intersection type works perfectly fine and the resulting type mirrors the runtime behaviour. Using the "reimplement all methods" (`FooBarB`) gets really tedious really quickly when you are trying to do something like model event listeners like the above.