This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
let nextChildren;
  prepareToReadContext(workInProgress, renderLanes);
  if (__DEV__) {
    ReactCurrentOwner.current = workInProgress;
    setIsRendering(true);
    nextChildren = renderWithHooks(
      current,
      workInProgress,
      render,
      nextProps,
      ref,
      renderLanes,
    );
    if (
      debugRenderPhaseSideEffectsForStrictMode &&
      workInProgress.mode & StrictLegacyMode
    ) {
      disableLogs();
      try {
        nextChildren = renderWithHooks(
          current,
          workInProgress,
          render,
          nextProps,
          ref,
          renderLanes,
        );
      } finally {
        reenableLogs();