Extracted from https://github.com/facebook/react/issues/12643.

We're currently diff a host node in the complete phase even if it has bailed out in the begin phase. By itself, this just means we're doing a little bit more work than necessary. But it also has some observable effects. In particular, https://github.com/facebook/react/issues/13424 (which by itself would be very rare and probably not worth fixing) is made worse because we end up committing update to inputs from another component.

I have a fix for this in https://github.com/facebook/react/pull/13423. Filing this for posterity.
static contextTypes = {
        foo: PropTypes.string.isRequired,
      };
      render() {
        return <div>{this.context.foo}</div>;
      }
    }
    class Parent extends React.Component {
      static childContextTypes = {
        foo: PropTypes.string.isRequired,
      };
      getChildContext() {
        return {
          foo: 'bar',
        };
      }
      render() {
        return ReactDOM.createPortal(<Component />, portalContainer);
      }
    }
    ReactDOM.render(<Parent />, container);
    expect(container.innerHTML).toBe('');
    expect(portalContainer.innerHTML).toBe('<div>bar</div>');
  });
  it('should update portal context if it changes due to setState', () => {
    const portalContainer = document.createElement('div');
    class Component extends React.Component {