This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
if (
      Component.prototype &&
      typeof Component.prototype.render === 'function'
    ) {
      const componentName = getComponentNameFromType(Component) || 'Unknown';
      if (!didWarnAboutBadClass[componentName]) {
        console.error(
          "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
            'This is likely to cause errors. Change %s to extend React.Component instead.',
          componentName,
          componentName,
        );
        didWarnAboutBadClass[componentName] = true;
      }
    }
    if (workInProgress.mode & StrictLegacyMode) {
      ReactStrictModeWarnings.recordLegacyContextWarning(workInProgress, null);
    }
    setIsRendering(true);
    ReactCurrentOwner.current = workInProgress;
    value = renderWithHooks(
      null,
      workInProgress,
      Component,
      props,
      context,
      renderLanes,
    );
    setIsRendering(false);
  } else {