ArraySchema: CLEAR + PUSH results in onAdd called twice

[endel]

Due to how new connections receive the full state through .encodeAll(), and incoming patches through .encode() right after, it is a known issue that onAdd is going to be called twice when a client joins a room on this scenario:

state.points.clear();
state.points.push(new Point().assign({ x: 2, y: 2 }));
state.points.push(new Point().assign({ x: 3, y: 3 }));

• When the client joins a room, he's going to receive the FULL STATE through state.encodeAll(). This includes the OPERATION.CLEAR on the array.
• The next patch (via state.encode()) is also going to include the OPERATION.CLEAR - thus causing the array items to be included again.

Related issue: colyseus/colyseus#249

Here's a test-case reproducing this problem:

schema/test/ArraySchemaTest.ts

Lines 1293 to 1311 in 448870a

	xit("should trigger onAdd callback only once after clearing and adding one item", () => {
	const state = new State();
	const decodedState = new State();
	// state.points.push(new Point().assign({ x: 0, y: 0 }));
	// state.points.push(new Point().assign({ x: 1, y: 1 }));
	state.points.clear();
	state.points.push(new Point().assign({ x: 2, y: 2 }));
	state.points.push(new Point().assign({ x: 3, y: 3 }));
	decodedState.points.onAdd = (point, key) => console.log(point.toJSON(), key);
	const onAddSpy = sinon.spy(decodedState.points, 'onAdd');
	decodedState.decode(state.encodeAll());
	decodedState.decode(state.encode());
	sinon.assert.callCount(onAddSpy, 2);
	});