react/packages/react-server/src/ReactFizzContext.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 {disableLegacyContext} from 'shared/ReactFeatureFlags';
import getComponentNameFromType from 'shared/getComponentNameFromType';
import invariant from 'shared/invariant';
import checkPropTypes from 'shared/checkPropTypes';

let warnedAboutMissingGetChildContext;

if (__DEV__) {
  warnedAboutMissingGetChildContext = {};
}

export const emptyContextObject = {};
if (__DEV__) {
  Object.freeze(emptyContextObject);
}

export function getMaskedContext(type: any, unmaskedContext: Object): Object {
  if (disableLegacyContext) {
    return emptyContextObject;
  } else {
    const contextTypes = type.contextTypes;
    if (!contextTypes) {
      return emptyContextObject;
    }

    const context = {};
    for (const key in contextTypes) {
      context[key] = unmaskedContext[key];
    }

    if (__DEV__) {
      const name = getComponentNameFromType(type) || 'Unknown';
      checkPropTypes(contextTypes, context, 'context', name);
    }

    return context;
  }
}

export function processChildContext(
  type: any,
  instance: any,
  parentContext: Object,
  childContextTypes: Object,
): Object {
  if (disableLegacyContext) {
    return parentContext;
  } else {
    // TODO (bvaughn) Replace this behavior with an invariant() in the future.
    // It has only been added in Fiber to match the (unintentional) behavior in Stack.
    if (typeof instance.getChildContext !== 'function') {
      if (__DEV__) {
        const componentName = getComponentNameFromType(type) || 'Unknown';

        if (!warnedAboutMissingGetChildContext[componentName]) {
          warnedAboutMissingGetChildContext[componentName] = true;
          console.error(
            '%s.childContextTypes is specified but there is no getChildContext() method ' +
              'on the instance. You can either define getChildContext() on %s or remove ' +
              'childContextTypes from it.',
            componentName,
            componentName,
          );
        }
      }
      return parentContext;
    }

    const childContext = instance.getChildContext();
    for (const contextKey in childContext) {
      invariant(
        contextKey in childContextTypes,
        '%s.getChildContext(): key "%s" is not defined in childContextTypes.',
        getComponentNameFromType(type) || 'Unknown',
        contextKey,
      );
    }
    if (__DEV__) {
      const name = getComponentNameFromType(type) || 'Unknown';
      checkPropTypes(childContextTypes, childContext, 'child context', name);
    }

    return {...parentContext, ...childContext};
  }
}