Function processChildContext

packages/react-server/src/ReactFizzLegacyContext.js:42–83

(
  instance: any,
  type: any,
  parentContext: Object,
  childContextTypes: Object,
)

}

export function processChildContext(
  instance: any,
  type: 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) {
      if (!(contextKey in childContextTypes)) {
        throw new Error(
          `${
            getComponentNameFromType(type) || 'Unknown'
          }.getChildContext(): key "${contextKey}" is not defined in childContextTypes.`,
        );
      }
    }
    return {...parentContext, ...childContext};
  }
}