Function getMaskedContext

packages/react-reconciler/src/ReactFiberLegacyContext.js:73–110

(
  workInProgress: Fiber,
  unmaskedContext: Object,
)

}

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

    // Avoid recreating masked context unless unmasked context has changed.
    // Failing to do this will result in unnecessary calls to componentWillReceiveProps.
    // This may trigger infinite loops if componentWillReceiveProps calls setState.
    const instance = workInProgress.stateNode;
    if (
      instance &&
      instance.__reactInternalMemoizedUnmaskedChildContext === unmaskedContext
    ) {
      return instance.__reactInternalMemoizedMaskedChildContext;
    }

    const context: {[string]: $FlowFixMe} = {};
    for (const key in contextTypes) {
      context[key] = unmaskedContext[key];
    }

    // Cache unmasked context so we can avoid recreating masked context unless necessary.
    // Context is created before the class component is instantiated so check for instance.
    if (instance) {
      cacheContext(workInProgress, unmaskedContext, context);
    }

    return context;
  }
}

function hasContextChanged(): boolean {
  if (disableLegacyContext) {