ReactFiberSuspenseContext.js — react Source File

Source Code

/**
 * Copyright (c) Meta Platforms, Inc. and 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 type {SuspenseProps} from 'shared/ReactTypes';
import type {Fiber} from './ReactInternalTypes';
import type {StackCursor} from './ReactFiberStack';
import type {SuspenseState} from './ReactFiberSuspenseComponent';

import {enableSuspenseAvoidThisFallback} from 'shared/ReactFeatureFlags';
import {createCursor, push, pop} from './ReactFiberStack';
import {isCurrentTreeHidden} from './ReactFiberHiddenContext';
import {OffscreenComponent} from './ReactWorkTags';

// The Suspense handler is the boundary that should capture if something
// suspends, i.e. it's the nearest `catch` block on the stack.
const suspenseHandlerStackCursor: StackCursor<Fiber | null> =
  createCursor(null);

// Represents the outermost boundary that is not visible in the current tree.
// Everything above this is the "shell". When this is null, it means we're
// rendering in the shell of the app. If it's non-null, it means we're rendering
// deeper than the shell, inside a new tree that wasn't already visible.
//
// The main way we use this concept is to determine whether showing a fallback
// would result in a desirable or undesirable loading state. Activing a fallback
// in the shell is considered an undersirable loading state, because it would
// mean hiding visible (albeit stale) content in the current tree — we prefer to
// show the stale content, rather than switch to a fallback. But showing a
// fallback in a new tree is fine, because there's no stale content to
// prefer instead.
let shellBoundary: Fiber | null = null;

export function getShellBoundary(): Fiber | null {
  return shellBoundary;
}

export function pushPrimaryTreeSuspenseHandler(handler: Fiber): void {
  // TODO: Pass as argument
  const current = handler.alternate;
  const props: SuspenseProps = handler.pendingProps;

  // Shallow Suspense context fields, like ForceSuspenseFallback, should only be
  // propagated a single level. For example, when ForceSuspenseFallback is set,
  // it should only force the nearest Suspense boundary into fallback mode.
  push(
    suspenseStackCursor,
    setDefaultShallowSuspenseListContext(suspenseStackCursor.current),
    handler,
  );

  // Experimental feature: Some Suspense boundaries are marked as having an
  // undesirable fallback state. These have special behavior where we only
  // activate the fallback if there's no other boundary on the stack that we can
  // use instead.
// ... (174 more lines)