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.
child: Instance | TextInstance,
    ): void {
      parentInstance.children.push(child);
    },
    finalizeInitialChildren(
      domElement: Instance,
      type: string,
      props: Props,
    ): boolean {
      return false;
    },
    prepareUpdate(
      instance: Instance,
      type: string,
      oldProps: Props,
      newProps: Props,
    ): null | {} {
      if (type === 'errorInCompletePhase') {
        throw new Error('Error in host config.');
      }
      if (oldProps === null) {
        throw new Error('Should have old props');
      }
      if (newProps === null) {
        throw new Error('Should have new props');
      }
      return UPDATE_SIGNAL;
    },
    shouldSetTextContent(type: string, props: Props): boolean {
      if (type === 'errorInBeginPhase') {