Change API to make configureDragDrop static

[gaearon]

I propose we make configureDragDrop static, and pass current component as the first argument to each method. This change is a stepping stone to fix endDrag not firing on unmounted component (#38, we'll pass null as component) and also a stepping stone to allow “resurfacing” drag sources (#53, we'll pass another component as component).

I'd like this change to be implemented in a backward-compatible way with a deprecation warning. We will make it a breaking change in 1.0 with #48.

• Support static configureDragDrop and pass component as the first argument to all methods
• Update the docs to use the new way
• Add a deprecation warning with upgrade instructions but still allow old-style configureDragDrop definitions (without component parameter)
• Make sure deprecation warning is logged once per class and includes class name (like React's own warnings)
• Prepare a separate PR that removes deprecation warning and makes it a breaking change. We will do that on 1.0 branch.

Any comments or volunteers?

@hakanderyal @nelix

[gaearon]

To clarify. Before:

var Card = React.createClass({
  mixins: [DragDropMixin],

  configureDragDrop(registerType) {
    registerType(ItemTypes.CARD, {
      dragSource: {
        beginDrag() {
          return {
            item: {
              id: this.props.id,
              children: <Card {...this.props}/>
            }
          };
        }
      },

      dropTarget: {
        over(item) {
          this.props.moveCard(item.id, this.props.id);
        }
      }
    });
  },

After:

var Card = React.createClass({
  mixins: [DragDropMixin],

  statics: {
    configureDragDrop(registerType) {
      registerType(ItemTypes.CARD, {
        dragSource: {
          beginDrag(component) {
            return {
              item: {
                id: component.props.id,
                children: <Card {...component.props}/>
              }
            };
          }
        },

        dropTarget: {
          over(component, item) {
            component.props.moveCard(item.id, component.props.id);
          }
        }
      });
    }
  }

We may want to have a less nested API later, but this is not the point. The point is using component instead of this so we can later be free to pass null or another component if we wish so.

This breaks the use case when this is accessed directly in configureDragDrop but it's a rare use case and seems only useful in contrived examples.

[gaearon]

Released in react-dnd@0.6.4.