Function resetWorkInProgress

packages/react-reconciler/src/ReactFiber.js:439–519

(
  workInProgress: Fiber,
  renderLanes: Lanes,
)

// Used to reuse a Fiber for a second pass.
export function resetWorkInProgress(
  workInProgress: Fiber,
  renderLanes: Lanes,
): Fiber {
  // This resets the Fiber to what createFiber or createWorkInProgress would
  // have set the values to before during the first pass. Ideally this wouldn't
  // be necessary but unfortunately many code paths reads from the workInProgress
  // when they should be reading from current and writing to workInProgress.

  // We assume pendingProps, index, key, ref, return are still untouched to
  // avoid doing another reconciliation.

  // Reset the effect flags but keep any Placement tags, since that's something
  // that child fiber is setting, not the reconciliation.
  workInProgress.flags &= StaticMask | Placement;

  // The effects are no longer valid.

  const current = workInProgress.alternate;
  if (current === null) {
    // Reset to createFiber's initial values.
    workInProgress.childLanes = NoLanes;
    workInProgress.lanes = renderLanes;

    workInProgress.child = null;
    workInProgress.subtreeFlags = NoFlags;
    workInProgress.memoizedProps = null;
    workInProgress.memoizedState = null;
    workInProgress.updateQueue = null;

    workInProgress.dependencies = null;

    workInProgress.stateNode = null;

    if (enableProfilerTimer) {
      // Note: We don't reset the actualTime counts. It's useful to accumulate
      // actual time across multiple render passes.
      workInProgress.selfBaseDuration = 0;
      workInProgress.treeBaseDuration = 0;
    }
  } else {
    // Reset to the cloned values that createWorkInProgress would've.
    workInProgress.childLanes = current.childLanes;
    workInProgress.lanes = current.lanes;

    workInProgress.child = current.child;
    workInProgress.subtreeFlags = NoFlags;
    workInProgress.deletions = null;
    workInProgress.memoizedProps = current.memoizedProps;
    workInProgress.memoizedState = current.memoizedState;
    workInProgress.updateQueue = current.updateQueue;
    // Needed because Blocks store data on type.
    workInProgress.type = current.type;

    // Clone the dependencies object. This is mutated during the render phase, so
    // it cannot be shared with the current fiber.
    const currentDependencies = current.dependencies;
    workInProgress.dependencies =