Function updateFunctionComponent

packages/react-reconciler/src/ReactFiberBeginWork.js:1423–1532

(
  current: null | Fiber,
  workInProgress: Fiber,
  Component: any,
  nextProps: any,
  renderLanes: Lanes,
)

}

function updateFunctionComponent(
  current: null | Fiber,
  workInProgress: Fiber,
  Component: any,
  nextProps: any,
  renderLanes: Lanes,
) {
  if (__DEV__) {
    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);
    }

    if (current === null) {
      // Some validations were previously done in mountIndeterminateComponent however and are now run
      // in updateFuntionComponent but only on mount
      validateFunctionComponentInDev(workInProgress, workInProgress.type);

      if (Component.contextTypes) {
        const componentName = getComponentNameFromType(Component) || 'Unknown';

        if (!didWarnAboutContextTypes[componentName]) {
          didWarnAboutContextTypes[componentName] = true;
          if (disableLegacyContext) {
            console.error(
              '%s uses the legacy contextTypes API which was removed in React 19. ' +
                'Use React.createContext() with React.useContext() instead. ' +
                '(https://react.dev/link/legacy-context)',
              componentName,
            );
          } else {
            console.error(
              '%s uses the legacy contextTypes API which will be removed soon. ' +
                'Use React.createContext() with React.useContext() instead. ' +
                '(https://react.dev/link/legacy-context)',
              componentName,
            );
          }
        }
      }
    }
  }