function resumeMountClassInstance()

in packages/react-reconciler/src/ReactFiberClassComponent.new.js [926:1090]
137 lines of code
37 McCabe index (conditional complexity)

function resumeMountClassInstance(
  workInProgress: Fiber,
  ctor: any,
  newProps: any,
  renderLanes: Lanes,
): boolean {
  const instance = workInProgress.stateNode;

  const oldProps = workInProgress.memoizedProps;
  instance.props = oldProps;

  const oldContext = instance.context;
  const contextType = ctor.contextType;
  let nextContext = emptyContextObject;
  if (typeof contextType === 'object' && contextType !== null) {
    nextContext = readContext(contextType);
  } else if (!disableLegacyContext) {
    const nextLegacyUnmaskedContext = getUnmaskedContext(
      workInProgress,
      ctor,
      true,
    );
    nextContext = getMaskedContext(workInProgress, nextLegacyUnmaskedContext);
  }

  const getDerivedStateFromProps = ctor.getDerivedStateFromProps;
  const hasNewLifecycles =
    typeof getDerivedStateFromProps === 'function' ||
    typeof instance.getSnapshotBeforeUpdate === 'function';

  // Note: During these life-cycles, instance.props/instance.state are what
  // ever the previously attempted to render - not the "current". However,
  // during componentDidUpdate we pass the "current" props.

  // In order to support react-lifecycles-compat polyfilled components,
  // Unsafe lifecycles should not be invoked for components using the new APIs.
  if (
    !hasNewLifecycles &&
    (typeof instance.UNSAFE_componentWillReceiveProps === 'function' ||
      typeof instance.componentWillReceiveProps === 'function')
  ) {
    if (oldProps !== newProps || oldContext !== nextContext) {
      callComponentWillReceiveProps(
        workInProgress,
        instance,
        newProps,
        nextContext,
      );
    }
  }

  resetHasForceUpdateBeforeProcessing();

  const oldState = workInProgress.memoizedState;
  let newState = (instance.state = oldState);
  processUpdateQueue(workInProgress, newProps, instance, renderLanes);
  newState = workInProgress.memoizedState;
  if (
    oldProps === newProps &&
    oldState === newState &&
    !hasContextChanged() &&
    !checkHasForceUpdateAfterProcessing()
  ) {
    // If an update was already in progress, we should schedule an Update
    // effect even though we're bailing out, so that cWU/cDU are called.
    if (typeof instance.componentDidMount === 'function') {
      let fiberFlags: Flags = Update;
      if (enableSuspenseLayoutEffectSemantics) {
        fiberFlags |= LayoutStatic;
      }
      if (
        __DEV__ &&
        enableStrictEffects &&
        (workInProgress.mode & StrictEffectsMode) !== NoMode
      ) {
        fiberFlags |= MountLayoutDev;
      }
      workInProgress.flags |= fiberFlags;
    }
    return false;
  }

  if (typeof getDerivedStateFromProps === 'function') {
    applyDerivedStateFromProps(
      workInProgress,
      ctor,
      getDerivedStateFromProps,
      newProps,
    );
    newState = workInProgress.memoizedState;
  }

  const shouldUpdate =
    checkHasForceUpdateAfterProcessing() ||
    checkShouldComponentUpdate(
      workInProgress,
      ctor,
      oldProps,
      newProps,
      oldState,
      newState,
      nextContext,
    );

  if (shouldUpdate) {
    // In order to support react-lifecycles-compat polyfilled components,
    // Unsafe lifecycles should not be invoked for components using the new APIs.
    if (
      !hasNewLifecycles &&
      (typeof instance.UNSAFE_componentWillMount === 'function' ||
        typeof instance.componentWillMount === 'function')
    ) {
      if (typeof instance.componentWillMount === 'function') {
        instance.componentWillMount();
      }
      if (typeof instance.UNSAFE_componentWillMount === 'function') {
        instance.UNSAFE_componentWillMount();
      }
    }
    if (typeof instance.componentDidMount === 'function') {
      let fiberFlags: Flags = Update;
      if (enableSuspenseLayoutEffectSemantics) {
        fiberFlags |= LayoutStatic;
      }
      if (
        __DEV__ &&
        enableStrictEffects &&
        (workInProgress.mode & StrictEffectsMode) !== NoMode
      ) {
        fiberFlags |= MountLayoutDev;
      }
      workInProgress.flags |= fiberFlags;
    }
  } else {
    // If an update was already in progress, we should schedule an Update
    // effect even though we're bailing out, so that cWU/cDU are called.
    if (typeof instance.componentDidMount === 'function') {
      let fiberFlags: Flags = Update;
      if (enableSuspenseLayoutEffectSemantics) {
        fiberFlags |= LayoutStatic;
      }
      if (
        __DEV__ &&
        enableStrictEffects &&
        (workInProgress.mode & StrictEffectsMode) !== NoMode
      ) {
        fiberFlags |= MountLayoutDev;
      }
      workInProgress.flags |= fiberFlags;
    }

    // If shouldComponentUpdate returned false, we should still update the
    // memoized state to indicate that this work can be reused.
    workInProgress.memoizedProps = newProps;
    workInProgress.memoizedState = newState;
  }

  // Update the existing instance's state, props, and context pointers even
  // if shouldComponentUpdate returns false.
  instance.props = newProps;
  instance.state = newState;
  instance.context = nextContext;

  return shouldUpdate;
}