Implement interface should not add optional properties

From https://github.com/Microsoft/vscode/issues/46286

TypeScript Version: 2.8.0-dev.20180320

Search Terms:

• implement interface
• quick fix
• code action
• optional property

Code

interface IFoo {
    x?: number
    y: number
}

class Foo implements IFoo {

}

Trigger implement interface on Foo

Expected behavior: Only required properties required:

interface IFoo {
    x?: number
    y: number
}

class Foo implements IFoo {
    y: number;
}

Actual behavior: Both required and optional properties added:

interface IFoo {
    x?: number
    y: number
}

class Foo implements IFoo {
    x?: number;
    y: number;
}

[RyanCavanaugh]

Why is this expected? It’s much easier to delete the optional properties/methods you don’t want than to track down the entire hierarchy of the target interface looking for them. We could add a comment or something or split it out into two commands if needed, but just opting them out feels like a regression in functionality.

[DanielRosenwasser]

I like that idea - I think displaying “implement required members” first, and then “implement all members”, is probably the right direction.

Any opinions @mjbvz?