I realized that the refactor to use ReactDebugCurrentFrame as a decoupled stack frame for error messages is not reentrant: https://github.com/facebook/react/pull/10105/files#r127573520

Fiber is not reentrant but other renderers might be. The synchronous server renderer is atm.

We should add tests for warnings between renderers, such as calling a server-render from within a client render, and update the set/reset callsites to use push/pop instead to account for that.

this.stack.push(frame);
          return '';
        }
        // eslint-disable-next-line-no-fallthrough
        default:
          break;
      }
      if (typeof elementType === 'object' && elementType !== null) {
        switch (elementType.$$typeof) {
          case REACT_FORWARD_REF_TYPE: {
            const element: ReactElement = ((nextChild: any): ReactElement);
            const nextChildren = toArray(
              elementType.render(element.props, element.ref),
            );
            const frame: Frame = {
              type: null,
              domNamespace: parentNamespace,
              children: nextChildren,
              childIndex: 0,
              context: context,
              footer: '',
            };
            if (__DEV__) {
              ((frame: any): FrameDev).debugElementStack = [];
            }
            this.stack.push(frame);
            return '';
          }
          case REACT_PROVIDER_TYPE: {
            const provider: ReactProvider<any> = (nextChild: any);