Function readContext

packages/react-debug-tools/src/ReactDebugHooks.js:161–190

(context: ReactContext<T>)

}

function readContext<T>(context: ReactContext<T>): T {
  if (currentFiber === null) {
    // Hook inspection without access to the Fiber tree
    // e.g. when warming up the primitive stack cache or during `ReactDebugTools.inspectHooks()`.
    return context._currentValue;
  } else {
    if (currentContextDependency === null) {
      throw new Error(
        'Context reads do not line up with context dependencies. This is a bug in React Debug Tools.',
      );
    }

    let value: T;
    // For now we don't expose readContext usage in the hooks debugging info.
    if (hasOwnProperty.call(currentContextDependency, 'memoizedValue')) {
      // $FlowFixMe[incompatible-use] Flow thinks `hasOwnProperty` mutates `currentContextDependency`
      value = ((currentContextDependency.memoizedValue: any): T);

      // $FlowFixMe[incompatible-use] Flow thinks `hasOwnProperty` mutates `currentContextDependency`
      currentContextDependency = currentContextDependency.next;
    } else {
      // Before React 18, we did not have `memoizedValue` so we rely on `setupContexts` in those versions.
      // Multiple reads of the same context were also only tracked as a single dependency.
      // We just give up on advancing context dependencies and solely rely on `setupContexts`.
      value = context._currentValue;
    }

    return value;
  }
}

const SuspenseException: mixed = new Error(
  "Suspense Exception: This is not a real error! It's an implementation " +