Hi,

this PR adds an option to allow a single extend (option:allowSingleExtend: true|false) to the ruleno-empty-interface. Our use case for this is the following:

Use case

We are building a React application with TypeScript. In React, you typically have components which might look like this:

constProductTile<ProductTileProps>=()=>{// Component implementation}

Problem

Let's say our<ProductTile> component accepts the exact same props as the members defined in aninterface Product { ... }. We could change the definition of the<ProductTile> component as follows to support that:

constProductTile<Product>=()=>{// Component implementation}

But once we have to add an additional prop (e.g.onClick?(event: MouseEvent<HTMLButtonElement>): void), we have the issue that we would have to extendProduct (which doesn't make sense asonClick doesn't belong to aProduct) or replace the interface.

Solution

Instead, we would prefer to define the component as follows initially:

interfaceProductTilePropsextendsProduct{}constProductTile<ProductTileProps>=()=>{// Component implementation}

Now if we add an additional prop likeonClick, we could simply add it to the interfaceProductTileProps and we're done:

constProductTilePropsextendsProduct{onClick?(event:MouseEvent<HTMLButtonElement>):void}// Component stays 100% the same

This PR allows to do that while still warning if empty interfaces likeinterface Foo {} are used. It's an optional configuration property so that the default behavior is not changed.

P.S.: This is my first PR to change an ESLint-style rule. Let me know if there is anything I should do differently. Thanks a lot!