Sebastian Markbåge

This commit introduces a **new feature** to **Next.js client-side rendering** by assigning a descriptive name to the **hydration stream**, significantly improving its visibility and debugging experience within **React DevTools**. It also **corrects timing metrics** by preventing the `startTime` from being set for client resume fetches in `app-index.tsx`, ensuring these are accurately represented as client-side waterfall events rather than server-initiated navigations. This enhancement provides developers with more precise performance insights into application hydration and data loading processes, making it easier to diagnose related issues.

This commit **refactors** the **Next.js server-side rendering** logic within `packages/next/src/server/app-render/app-render.tsx` to resolve an issue with promise display names. It specifically removes the explicit assignment of `displayName` for internal promises, such as those for `params` and `searchParams`, when called by `createAsyncApiPromisesInDev` in development mode. This **bug fix** ensures that the intended, more meaningful display names are correctly prioritized, thereby improving the **debugging and profiling experience** for developers. The change prevents internal implementation details from inadvertently overriding more relevant information in development tools.

This commit implements a **new feature** to enhance debugging within **React DevTools** by explicitly **naming the return stream 'use cache'** for cache-related operations. Specifically, the `generateCacheEntryImpl` function in the **`next/server/use-cache` subsystem** now labels its output stream within `packages/next/src/server/use-cache/use-cache-wrapper.ts`. This allows developers to more easily identify "rsc stream" chunks originating from the cache when inspecting application behavior in **development mode**.

This commit introduces a **bug fix** within the **Next.js server request handling** to improve how `params` and `searchParams` are resolved and displayed. It **wraps existing promises for `params` and `searchParams`** in new Promises within `packages/next/src/server/request/params.ts` and `packages/next/src/server/request/search-params.ts`. This change ensures **proper tracking and accurate display of these parameters** in asynchronous contexts, particularly when third-party code is involved in `await` operations. By doing so, it prevents the system from showing misleading `internal params` and instead reveals the actual values, enhancing debugging and clarity for developers.

This commit **adds crucial documentation comments** to the `bindSnapshot` function within Next.js's server-side rendering context and async local storage modules. The comments clarify a specific, non-obvious constraint: the function passed to `bindSnapshot` **must be anonymous**. This **maintenance and documentation update** explains that using a named function would cause it to be incorrectly identified as an I/O operation by `AsyncResource`, potentially leading to misleading performance monitoring. The change helps developers avoid this pitfall and correctly utilize the server-side utility in `packages/next/src/server/after/after-context.ts` and `packages/next/src/server/app-render/async-local-storage.ts`.

This commit **updates the `lightningcss` dependency** to a newer version, primarily to incorporate a **fix for View Transitions within CSS modules**. This **dependency update** affects the **CSS compilation process**, specifically altering the output for **media queries**. Consequently, the `test/integration/css/test/css-compilation.test.js` **integration tests** were updated to reflect these changes in the `lightningcss` output. This ensures correct behavior and compilation for CSS features, especially those related to View Transitions, while maintaining test accuracy.

This commit delivers a **bug fix** to the **React Fiber reconciler**, specifically within the `packages/react-reconciler/src/ReactFiberTreeReflection.js` module. It **refactors the logic** of the `getNearestMountedFiber` function to correctly identify and return the nearest mounted fiber, even when that fiber has an alternate. This ensures that fibers with alternates are properly considered mounted, preventing incorrect state identification and improving the **robustness of React's internal tree reflection and reconciliation processes**.

This commit **fixes an animation cleanup issue** by ensuring that animations associated with **custom Timelines** are explicitly cancelled during component unmount. Previously, the cleanup function for these timelines only handled internal state, potentially leaving animations running. The change modifies `fixtures/view-transition/src/components/Page.js` to add explicit animation cancellation and updates `packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js` to track created animations via `viewTransitionAnimations` for proper disposal. This is a crucial **bug fix** for **Firefox**, which relies on a `ScrollTimeline` polyfill, preventing animations from persisting unexpectedly after a component unmounts.

This commit refines the **developer warnings** related to **gesture transitions** within **React DOM bindings**. It **removes a general warning** that previously fired when the root element was cloned during a gesture, as this warning was not actionable without an unimplemented optimization for subtree isolation. Instead, the commit **introduces new development-mode warnings** specifically for problematic elements like `VIDEO` and `IFRAME` when they are cloned via `cloneMutableInstance` during a gesture transition. This **maintenance and developer experience improvement** provides more targeted feedback, highlighting cases in `packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js` where cloning might lead to performance issues and encouraging consideration of alternative rendering strategies.

This commit **enhances the React reconciler's gesture application** by **temporarily mounting `useInsertionEffect` hooks** during the computation of a gesture snapshot. This ensures that styles inserted via `useInsertionEffect`, which are crucial for **precomputing layout before mounting**, are present in the snapshot, preventing **missing styles** during **view transitions**. The changes in `packages/react-reconciler/src/ReactFiberApplyGesture.js` implement this temporary mounting and unmounting for new effects, guaranteeing accurate styling for dynamic UI changes. This is a **feature enhancement** to improve the reliability of visual transitions.

This commit introduces a **new capability** for **React's View Transition API**, allowing developers to return cleanup functions from `onViewTransition` and `onGestureTransition` event handlers. These cleanup functions are now properly registered and invoked when a view transition is forced to stop, addressing previous issues where manual animations or custom timers could leak resources. The **React reconciler** (`ReactFiberWorkLoop.js`) has been updated to schedule and flush these cleanup callbacks, and **DOM bindings** (`ReactFiberConfigDOM.js`) along with various other renderers now support the `addViewTransitionFinishedListener` mechanism. This enhancement ensures more robust resource management and prevents memory leaks during interrupted view transitions.

This commit **fixes a bug** within the **React DOM bindings** that caused gesture animations to hang. Previously, during a gesture, newly created animations were not being properly registered for cleanup, leading to subsequent gestures freezing the UI. The change modifies the `animateGesture` and `startGestureTransition` functions in `ReactFiberConfigDOM.js` to ensure these new animations are correctly added to the `viewTransitionAnimations` array. This **maintenance fix** prevents UI freezes and ensures **smooth and responsive gesture interactions** for users.

This commit introduces **new capabilities** for **gesture-driven view transitions**, allowing developers to define `onGestureEnter`, `onGestureExit`, `onGestureShare`, and `onGestureUpdate` events. It integrates `scheduleGestureTransitionEvent` within the `react-reconciler` to queue and process these events during the commit phase and view transition application logic. This enhancement provides manual control over gesture animations using a timeline, significantly expanding the interactivity of UI transitions. The `fixtures/view-transition` component `Page.js` is updated to demonstrate this new functionality, and `ReactTypes.js` defines the necessary new event handler types.

This commit **optimizes gesture handling** within React by allowing the initial work-in-progress tree to be treated as a **suspended commit**, preventing unnecessary rerenders during active gestures. It introduces a new `scheduleGestureCommit` function in `ReactFiberGestureScheduler.js` to enable immediate commitment of pending gesture trees. The **ReactFiberWorkLoop** (`ReactFiberWorkLoop.js`) is updated to integrate this new gesture commit scheduling and performance tracking, while `SwipeRecognizer.js` is refactored to ensure proper commit ordering. This **feature enhancement** significantly **improves the responsiveness and efficiency of gesture-driven UI updates** by streamlining the reconciliation process.

This commit **fixes** an issue within the **React Reconciler's lane scheduling system** where updates originating from **gestures** were not correctly prioritized. Previously, these gesture-induced updates could be deferred, causing `useDeferredValue` to display stale data and potentially blocking the render. By including `GestureLane` in the definition of `UrgentLanes` within the `includesOnlyNonUrgentLanes` function in `packages/react-reconciler/src/ReactFiberLane.js`, this change ensures that all gesture-related updates are now treated as **urgent**. This **performance optimization** guarantees that `useDeferredValue` reflects the most current state during gesture interactions, leading to a more responsive and accurate user experience.

This commit introduces a **new capability** to **entangle `Gesture` revert lanes with `Action` transition lanes**, ensuring that the revert of a `Gesture` and the result of any canceling `Action` commit as a single, atomic batch. The **`ReactFiberGestureScheduler`** module is updated to add a `revertLane` to `ScheduledGesture` and implement logic in `cancelScheduledGesture` to entangle this lane with new transition lanes. Concurrently, **`ReactFiberHooks`** ensures a consistent `revertLane` assignment within `dispatchOptimisticSetState` for gesture instances. This **feature enhancement** significantly improves the **resilience of optimistic updates** by preventing unbatching, thereby maintaining state consistency during gesture cancellations.

This commit introduces a **new capability** for **gesture-driven view transitions**, allowing the **gesture lane's state to be committed** if the gesture ends closer to its target, rather than always reverting to the original state. This **feature enhancement** in **`ReactFiberGestureScheduler.js`** and **`ReactFiberWorkLoop.js`** enables smoother animations from the gesture's final visual state to a subsequent action's state, addressing a limitation where `startGestureTransition` previously prevented such transitions. The **reconciler's work loop** is **refactored** to integrate this gesture-specific commitment logic, while **`ReactFiberHooks.js`** is updated to prevent premature cleanup of committing gestures. This change significantly improves the fluidity of user interactions involving gestures and optimistic updates.

This commit delivers a **bug fix** for **React View Transitions** within the `React Reconciler` to ensure proper cancellation behavior. Previously, when a `<ViewTransition>` component managed **multiple child host instances**, the cancellation process would incorrectly trigger an exit animation instead of immediately hiding the old state. The fix involves adding a unique suffix to the view transition name in `packages/react-reconciler/src/ReactFiberCommitViewTransitions.js` when multiple host instances are present, ensuring the correct animation is applied for cancellation. This change guarantees that cancelled view transitions consistently hide the old state as expected, improving the visual integrity of UI updates.

This commit **fixes incorrect hydration errors** and **prevents subsequent diffing failures** in **React DOM bindings** when the **Fizz runtime** applies `view-transition-name` or `view-transition-class` to `style` attributes. It introduces logic within `packages/react-dom-bindings/src/client/ReactDOMComponent.js` to **skip hydration warnings** and diffing for these specific style properties. This **bug fix** addresses a scenario where Fiber incorrectly observed these temporary styles during hydration and where the subsequent normalization of the `style` attribute prevented proper diffing. Ultimately, it improves the robustness of **server-side rendering (SSR)** when used in conjunction with **View Transitions**.

This commit introduces a **defensive programming enhancement** to the **React Flight Reply Server** by adding a cycle protection counter. It modifies the `ReactPromise.prototype.then` method within `packages/react-server/src/ReactFlightReplyServer.js` to prevent infinite loops. This **bug fix** specifically addresses potential issues during recursive thenable resolution, safeguarding against runaway processes. The change improves the **stability** and reliability of server-side rendering and data fetching within the **React Flight** ecosystem.