ReactPartialRendererHooks.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

import typeof {Dispatcher as DispatcherType} from 'react-reconciler/src/ReactFiberDispatcher';
import type {ThreadID} from './ReactThreadIDAllocator';
import type {ReactContext} from 'shared/ReactTypes';

import {validateContextBounds} from './ReactPartialRendererContext';

import invariant from 'shared/invariant';
import warning from 'shared/warning';
import is from 'shared/objectIs';

type BasicStateAction<S> = (S => S) | S;
type Dispatch<A> = A => void;

type Update<A> = {
  action: A,
  next: Update<A> | null,
};

type UpdateQueue<A> = {
  last: Update<A> | null,
  dispatch: any,
};

type Hook = {
  memoizedState: any,
  queue: UpdateQueue<any> | null,
  next: Hook | null,
};

let currentlyRenderingComponent: Object | null = null;
let firstWorkInProgressHook: Hook | null = null;
let workInProgressHook: Hook | null = null;
// Whether the work-in-progress hook is a re-rendered hook
let isReRender: boolean = false;
// Whether an update was scheduled during the currently executing render pass.
let didScheduleRenderPhaseUpdate: boolean = false;
// Lazily created map of render-phase updates
let renderPhaseUpdates: Map<UpdateQueue<any>, Update<any>> | null = null;
// Counter to prevent infinite loops.
let numberOfReRenders: number = 0;
const RE_RENDER_LIMIT = 25;

// In DEV, this is the name of the currently executing primitive hook
let currentHookNameInDev: ?string;

function resolveCurrentlyRenderingComponent(): Object {
  invariant(
    currentlyRenderingComponent !== null,
    'Hooks can only be called inside the body of a function component.',
  );
  return currentlyRenderingComponent;
}

function areHookInputsEqual(
  nextDeps: Array<mixed>,
  prevDeps: Array<mixed> | null,
) {
  if (prevDeps === null) {
    if (__DEV__) {
      warning(
        false,
        '%s received a final argument during this render, but not during ' +
          'the previous render. Even though the final argument is optional, ' +
          'its type cannot change between renders.',
        currentHookNameInDev,
      );
    }
    return false;
  }

  if (__DEV__) {
    // Don't bother comparing lengths in prod because these arrays should be
    // passed inline.
    if (nextDeps.length !== prevDeps.length) {
      warning(
        false,
        'The final argument passed to %s changed size between renders. The ' +
          'order and size of this array must remain constant.\n\n' +
          'Previous: %s\n' +
          'Incoming: %s',
        currentHookNameInDev,
        `[${nextDeps.join(', ')}]`,
        `[${prevDeps.join(', ')}]`,
      );
    }
  }
  for (let i = 0; i < prevDeps.length && i < nextDeps.length; i++) {
    if (is(nextDeps[i], prevDeps[i])) {
      continue;
    }
    return false;
  }
  return true;
}

function createHook(): Hook {
  return {
    memoizedState: null,
    queue: null,
    next: null,
  };
}

function createWorkInProgressHook(): Hook {
  if (workInProgressHook === null) {
    // This is the first hook in the list
    if (firstWorkInProgressHook === null) {
      isReRender = false;
      firstWorkInProgressHook = workInProgressHook = createHook();
    } else {
      // There's already a work-in-progress. Reuse it.
      isReRender = true;
      workInProgressHook = firstWorkInProgressHook;
    }
  } else {
    if (workInProgressHook.next === null) {
      isReRender = false;
      // Append to the end of the list
      workInProgressHook = workInProgressHook.next = createHook();
    } else {
      // There's already a work-in-progress. Reuse it.
      isReRender = true;
      workInProgressHook = workInProgressHook.next;
    }
  }
  return workInProgressHook;
}

export function prepareToUseHooks(componentIdentity: Object): void {
  currentlyRenderingComponent = componentIdentity;

  // The following should have already been reset
  // didScheduleRenderPhaseUpdate = false;
  // firstWorkInProgressHook = null;
  // numberOfReRenders = 0;
  // renderPhaseUpdates = null;
  // workInProgressHook = null;
}

export function finishHooks(
  Component: any,
  props: any,
  children: any,
  refOrContext: any,
): any {
  // This must be called after every function component to prevent hooks from
  // being used in classes.

  while (didScheduleRenderPhaseUpdate) {
    // Updates were scheduled during the render phase. They are stored in
    // the `renderPhaseUpdates` map. Call the component again, reusing the
    // work-in-progress hooks and applying the additional updates on top. Keep
    // restarting until no more updates are scheduled.
    didScheduleRenderPhaseUpdate = false;
    numberOfReRenders += 1;

    // Start over from the beginning of the list
    workInProgressHook = null;

    children = Component(props, refOrContext);
  }
  currentlyRenderingComponent = null;
  firstWorkInProgressHook = null;
  numberOfReRenders = 0;
  renderPhaseUpdates = null;
  workInProgressHook = null;

  // These were reset above
  // currentlyRenderingComponent = null;
  // didScheduleRenderPhaseUpdate = false;
  // firstWorkInProgressHook = null;
  // numberOfReRenders = 0;
  // renderPhaseUpdates = null;
  // workInProgressHook = null;

  return children;
}

function readContext<T>(
  context: ReactContext<T>,
  observedBits: void | number | boolean,
): T {
  let threadID = currentThreadID;
  validateContextBounds(context, threadID);
  return context[threadID];
}

function useContext<T>(
  context: ReactContext<T>,
  observedBits: void | number | boolean,
): T {
  if (__DEV__) {
    currentHookNameInDev = 'useContext';
  }
  resolveCurrentlyRenderingComponent();
  let threadID = currentThreadID;
  validateContextBounds(context, threadID);
  return context[threadID];
}

function basicStateReducer<S>(state: S, action: BasicStateAction<S>): S {
  return typeof action === 'function' ? action(state) : action;
}

export function useState<S>(
  initialState: (() => S) | S,
): [S, Dispatch<BasicStateAction<S>>] {
  if (__DEV__) {
    currentHookNameInDev = 'useState';
  }
  return useReducer(
    basicStateReducer,
    // useReducer has a special case to support lazy useState initializers
    (initialState: any),
  );
}

export function useReducer<S, A>(
  reducer: (S, A) => S,
  initialState: S,
  initialAction: A | void | null,
): [S, Dispatch<A>] {
  if (__DEV__) {
    if (reducer !== basicStateReducer) {
      currentHookNameInDev = 'useReducer';
    }
  }
  let component = (currentlyRenderingComponent = resolveCurrentlyRenderingComponent());
  workInProgressHook = createWorkInProgressHook();
  if (isReRender) {
    // This is a re-render. Apply the new render phase updates to the previous
    // current hook.
    const queue: UpdateQueue<A> = (workInProgressHook.queue: any);
    const dispatch: Dispatch<A> = (queue.dispatch: any);
    if (renderPhaseUpdates !== null) {
      // Render phase updates are stored in a map of queue -> linked list
      const firstRenderPhaseUpdate = renderPhaseUpdates.get(queue);
      if (firstRenderPhaseUpdate !== undefined) {
        renderPhaseUpdates.delete(queue);
        let newState = workInProgressHook.memoizedState;
        let update = firstRenderPhaseUpdate;
        do {
          // Process this render phase update. We don't have to check the
          // priority because it will always be the same as the current
          // render's.
          const action = update.action;
          // Temporarily clear to forbid calling Hooks.
          currentlyRenderingComponent = null;
          newState = reducer(newState, action);
          currentlyRenderingComponent = component;
          update = update.next;
        } while (update !== null);

        workInProgressHook.memoizedState = newState;

        return [newState, dispatch];
      }
    }
    return [workInProgressHook.memoizedState, dispatch];
  } else {
    currentlyRenderingComponent = null;
    if (reducer === basicStateReducer) {
      // Special case for `useState`.
      if (typeof initialState === 'function') {
        initialState = initialState();
      }
    } else if (initialAction !== undefined && initialAction !== null) {
      initialState = reducer(initialState, initialAction);
    }
    currentlyRenderingComponent = component;
    workInProgressHook.memoizedState = initialState;
    const queue: UpdateQueue<A> = (workInProgressHook.queue = {
      last: null,
      dispatch: null,
    });
    const dispatch: Dispatch<A> = (queue.dispatch = (dispatchAction.bind(
      null,
      currentlyRenderingComponent,
      queue,
    ): any));
    return [workInProgressHook.memoizedState, dispatch];
  }
}

function useMemo<T>(nextCreate: () => T, deps: Array<mixed> | void | null): T {
  let component = (currentlyRenderingComponent = resolveCurrentlyRenderingComponent());
  workInProgressHook = createWorkInProgressHook();

  const nextDeps = deps === undefined ? null : deps;

  if (workInProgressHook !== null) {
    const prevState = workInProgressHook.memoizedState;
    if (prevState !== null) {
      if (nextDeps !== null) {
        const prevDeps = prevState[1];
        if (areHookInputsEqual(nextDeps, prevDeps)) {
          return prevState[0];
        }
      }
    }
  }

  // Temporarily clear to forbid calling Hooks.
  currentlyRenderingComponent = null;
  const nextValue = nextCreate();
  currentlyRenderingComponent = component;
  workInProgressHook.memoizedState = [nextValue, nextDeps];
  return nextValue;
}

function useRef<T>(initialValue: T): {current: T} {
  currentlyRenderingComponent = resolveCurrentlyRenderingComponent();
  workInProgressHook = createWorkInProgressHook();
  const previousRef = workInProgressHook.memoizedState;
  if (previousRef === null) {
    const ref = {current: initialValue};
    if (__DEV__) {
      Object.seal(ref);
    }
    workInProgressHook.memoizedState = ref;
    return ref;
  } else {
    return previousRef;
  }
}

export function useLayoutEffect(
  create: () => mixed,
  deps: Array<mixed> | void | null,
) {
  if (__DEV__) {
    currentHookNameInDev = 'useLayoutEffect';
  }
  warning(
    false,
    'useLayoutEffect does nothing on the server, because its effect cannot ' +
      "be encoded into the server renderer's output format. This will lead " +
      'to a mismatch between the initial, non-hydrated UI and the intended ' +
      'UI. To avoid this, useLayoutEffect should only be used in ' +
      'components that render exclusively on the client.',
  );
}

function dispatchAction<A>(
  componentIdentity: Object,
  queue: UpdateQueue<A>,
  action: A,
) {
  invariant(
    numberOfReRenders < RE_RENDER_LIMIT,
    'Too many re-renders. React limits the number of renders to prevent ' +
      'an infinite loop.',
  );

  if (componentIdentity === currentlyRenderingComponent) {
    // This is a render phase update. Stash it in a lazily-created map of
    // queue -> linked list of updates. After this render pass, we'll restart
    // and apply the stashed updates on top of the work-in-progress hook.
    didScheduleRenderPhaseUpdate = true;
    const update: Update<A> = {
      action,
      next: null,
    };
    if (renderPhaseUpdates === null) {
      renderPhaseUpdates = new Map();
    }
    const firstRenderPhaseUpdate = renderPhaseUpdates.get(queue);
    if (firstRenderPhaseUpdate === undefined) {
      renderPhaseUpdates.set(queue, update);
    } else {
      // Append the update to the end of the list.
      let lastRenderPhaseUpdate = firstRenderPhaseUpdate;
      while (lastRenderPhaseUpdate.next !== null) {
        lastRenderPhaseUpdate = lastRenderPhaseUpdate.next;
      }
      lastRenderPhaseUpdate.next = update;
    }
  } else {
    // This means an update has happened after the function component has
    // returned. On the server this is a no-op. In React Fiber, the update
    // would be scheduled for a future render.
  }
}

export function useCallback<T>(
  callback: T,
  deps: Array<mixed> | void | null,
): T {
  // Callbacks are passed as they are in the server environment.
  return callback;
}

function noop(): void {}

export let currentThreadID: ThreadID = 0;

export function setCurrentThreadID(threadID: ThreadID) {
  currentThreadID = threadID;
}

export const Dispatcher: DispatcherType = {
  readContext,
  useContext,
  useMemo,
  useReducer,
  useRef,
  useState,
  useLayoutEffect,
  useCallback,
  // useImperativeHandle is not run in the server environment
  useImperativeHandle: noop,
  // Effects are not run in the server environment.
  useEffect: noop,
  // Debugging effect
  useDebugValue: noop,
};
export const DispatcherWithoutHooks = {
  readContext,
};