Samuel Susla

This commit **removes the `enableOptimizedBoxShadowParsing` feature flag**, thereby **permanently enabling the optimized box shadow parsing logic** within React Native's **StyleSheet processing**. The `processBoxShadow.js` module is **refactored** to eliminate the flag check, ensuring the performance improvement from hoisting regex patterns for box shadow parsing is always active. Concurrently, the flag definition and its getter are deleted from `ReactNativeFeatureFlags.js`. This **maintenance and cleanup** task standardizes a minor performance enhancement, providing a small but consistent benefit to all applications by making the optimized parsing the default behavior.

This commit **re-lands a critical bug fix** for **Yoga's flex basis computation** in React Native, addressing unnecessary re-measurement cascades that occur when container children with `FitContent` in the main axis are re-measured. The **refactored implementation** switches the problematic `YogaErrata` bit to a new **`YogaExperimentalFeature`** named `FIX_FLEX_BASIS_FIT_CONTENT`, ensuring the fix is individually opt-in and preventing accidental breakages in existing applications. This change primarily involves **wiring up the new feature flag** `fixYogaFlexBasisFitContentInMainAxis` across the **React Native feature flag infrastructure** (Android Java/Kotlin, C++, and JavaScript), and integrating it into **Yoga's layout calculation** to enable the experimental behavior when the flag is active. The flag defaults to `false`, providing a controlled rollout path for this **performance and stability improvement** in **Yoga layout**, with further platform-specific overrides expected in follow-up commits.

This commit **migrates** the **integration tests** for the **`SectionList`** component from the Jest testing framework to **Fantom**. It updates the test suite located in `packages/react-native/Libraries/Lists/__tests__/SectionList-itest.js` to utilize the new framework. This **testing infrastructure migration** improves the reliability and maintainability of tests for the `SectionList` component.

This commit introduces a **performance optimization** by **refactoring** the **StyleSheet processing** logic within React Native. It **hoists inline regular expression patterns to module-level constants** in `processFilter.js`, `processBackgroundImage.js`, and `processTransformOrigin.js`. This change prevents redundant regex compilation during repeated function calls, leading to **significant latency reductions** (up to 26.10% faster) when parsing `filter` and `backgroundImage` CSS strings. The **StyleSheet** module will now process these properties more efficiently, improving overall rendering performance for components utilizing these styles.

This commit **reverts** the previous addition of the `fixYogaFlexBasisFitContentInMainAxis` feature flag, effectively **removing** it from the codebase. It entails a comprehensive **refactoring** across the **React Native feature flag system**, impacting its Java, C++, and JavaScript implementations, including accessors, providers, and JNI bindings. This **maintenance** task also eliminates the conditional logic within the **Yoga layout engine** (`CalculateLayout.cpp` and `YogaLayoutableShadowNode.cpp`) that was governed by this flag. By undoing this specific flex basis adjustment, the commit simplifies the layout computation and removes an unused or problematic feature flag.

This commit significantly **expands the integration test suite** for the **`FlatList` component** within `packages/react-native/Libraries/Lists`. It introduces numerous new test cases in `FlatList-itest.js` to cover a broad array of `FlatList` props, including `ListHeaderComponent`, `ListFooterComponent`, `numColumns`, `onEndReached`, and various imperative methods. This **maintenance work** directly improves the `FlatList.js` code coverage from 44% to 62%. The expanded tests enhance the overall **reliability and stability** of this critical list component by ensuring better validation of its diverse functionalities and reducing the risk of regressions.

This commit introduces a **performance optimization** and **bug fix** within the **Yoga layout engine** to prevent unnecessary re-measurements. It implements the `fixYogaFlexBasisFitContentInMainAxis` feature flag, which, when enabled, modifies how flex basis is computed for container children in the main axis. Instead of the legacy `FitContent` behavior that caused cascading layout updates, especially in `ScrollView`s, the system now uses `MaxContent` for auto-height parents. This change significantly reduces layout thrashing and improves rendering performance by ensuring children's flex basis is independent of the parent's content-determined size, while carefully preserving correct behavior for definite-height parents and percentage-based children.

This commit **refactors** the **React Native View component** by moving prop transformations for `aria-*` to `accessibility*`, `id` to `nativeID`, and `tabIndex` to `focusable` from JavaScript to the **C++ prop parsing layer**. This change centralizes the handling of these props within `AccessibilityProps::setProp`, `Props::setProp`, and `HostPlatformViewProps::setProp`, making the **JavaScript wrapper thinner and significantly improving performance** for `View` component rendering by approximately 18%. The **core prop handling logic** is now unified in native code, enhancing consistency and efficiency across platforms. A **new feature flag**, `enableNativeViewPropTransformations`, has been introduced to gate this **performance optimization** for a safe and controlled rollout.

This commit **adds new test cases** to the `View` component's integration tests within `packages/react-native/Libraries/Components/View/__tests__/View-itest.js`. These **new tests** specifically validate that various **accessibility-related props**, including `aria-*` attributes and ID props, correctly **reset to their default values** when they are explicitly set to `undefined`. This **enhances the robustness** and reliability of the **`View` component's prop transformation logic**, ensuring consistent behavior for accessibility features in **React Native**. The added tests prevent regressions where `View` props might not properly revert, which could impact assistive technologies or component styling.

This commit introduces a **new capability** to the **Fantom API** by adding the `Fantom.getDefinedEventHandlers(element)` function. This allows developers to **introspect and retrieve the names of all event handlers** registered on any given React component. By reading `memoizedProps` directly from the React fiber, it provides a robust and unified mechanism that works for **all component types**, including component-specific events like `ScrollView`'s `onScroll`. This enhancement simplifies event handler discovery, avoiding the need for component-specific logic, and is verified by new integration tests in `FantomEventHandlers-itest.js`.

This commit **fixes a bug** in the **Fantom rendering system** where `getRenderedOutput` failed to reflect removed props, leading to stale UI states. Previously, `RenderOutput::renderView` incorrectly merged old cached props with new debug props, and `renderedViews_.insert()` did not overwrite existing entries, preventing removed properties from being cleared. The fix involves **removing the problematic caching and prop merging logic** from `RenderOutput::renderView` and cleaning up the `render` method in `RenderOutput.cpp`. This ensures that **removed props are accurately reflected in the rendered output**, and a new test case in `View-itest.js` validates this corrected behavior for the `View` component.

This commit introduces a **performance optimization** by enabling **pre-allocation of mutation vectors** within the **`Differentiator`** component, specifically in the `calculateShadowViewMutations` function. This change aims to **reduce reallocation overhead** during UI updates, leading to significant speed improvements, such as a **45% reduction in processing time for 1000 uncollapsable views**. The new behavior is controlled by a **feature flag**, `enableDifferentiatorMutationVectorPreallocation`, which has been integrated across the `ReactNativeFeatureFlags` system to allow for dynamic enablement and A/B testing. This enhancement directly improves **React Native's rendering performance** for complex view hierarchies by optimizing a core part of the UI reconciliation process.

This commit introduces a **performance optimization** for the **`StyleSheet` module** by refactoring the `processBoxShadow` function. It hoists regex patterns to module-level constants to avoid repeated compilation, improving the efficiency of box shadow parsing. This **refactoring**, identified as a hotspot by a JS sampling profiler, results in a **6-7% improvement in rendering performance** for views with complex styles. A new feature flag, `enableOptimizedBoxShadowParsing`, has been added to the **feature flag system** to control the activation of this optimized parsing logic.

This commit **adds new integration tests** for the **`View` component** within `react-native`, specifically targeting its **accessibility features**. The tests verify the correct mapping of various **`aria-` props** (including `aria-label`, `aria-live`, `aria-busy`, `aria-disabled`, `aria-expanded`, `aria-selected`, `aria-checked`) and the `id` prop to their respective accessibility properties. This **enhances test coverage** for the `View` component's accessibility implementation, ensuring these critical props are handled as expected. The work is a **maintenance** task, improving the robustness and reliability of the **accessibility subsystem** by validating existing functionality.

This commit **refactors** the **React Native renderer's Differentiator** by replacing the custom `TinyMap` implementation with `std::unordered_map`. This change **simplifies the codebase** by leveraging a standard library container, demonstrating no performance regression and even some improvements in various view hierarchy benchmarks. A new **feature flag**, `useUnorderedMapInDifferentiator`, was introduced across the **feature flags system** (C++, Java, JS) to control this transition, allowing the `Differentiator` to conditionally use either map via a `DiffMap` facade. This **maintenance** effort streamlines core rendering logic, potentially leading to **improved performance** and easier future development within the **view reconciliation process**.

This commit **migrates** and **adds new integration tests** for the **`processBoxShadow` utility** located in `Libraries/StyleSheet`. This **testing infrastructure update** leverages **Fantom** to provide comprehensive coverage, specifically using `fantom_flags enableOptimizedBoxShadowParsing:*` to automatically test both optimized and non-optimized code paths. The new tests cover various string and object parsing scenarios, including expected failure cases, ensuring the utility's resilience. This **enhances the robustness and reliability** of the `processBoxShadow` functionality by thoroughly validating its behavior across different configurations and inputs.

This commit **optimizes C++ header includes** within the `UIManagerAnimationBackend.h` file, a core component of the **React Native renderer's UIManager animation backend**. It performs a **refactoring** by removing redundant headers such as `BaseViewProps.h` and `ShadowNodeFamily.h`, while introducing more appropriate ones like `ReactPrimitives.h`, `chrono`, `functional`, and `memory`. This effort aims to **improve build performance and reduce compilation times** by streamlining header dependencies. Ultimately, this contributes to a **more efficient and maintainable C++ codebase** within the native renderer.

This commit **adds new Fantom integration tests** for the **`ActivityIndicator` component** within the `react-native` library. These comprehensive tests significantly improve the **quality assurance** for `ActivityIndicator.js`, bringing its line coverage from 0% to 100%. The new integration suite validates various props including `size`, `color`, `animating`, `style`, `accessibilityLabel`, `testID`, and `ref` behavior. This **maintenance** effort ensures the core UI component functions reliably across different configurations, **enhancing its robustness** and preventing regressions.

This commit **refactors** the **`ShadowNodeFamily`** class to improve **const-correctness** within the **React Native Fabric renderer**. It achieves this by **removing unnecessary `const` qualifiers** from several member functions and **eliminating `mutable` keywords** from member variables in `ShadowNodeFamily.h` and `ShadowNodeFamily.cpp`. This **internal architectural improvement** affects how `ShadowNodeFamily` objects are managed across modules like the **`AnimatedModule`**, **`RootShadowNode`**, and **`FabricUIManagerBinding`**. Specifically, it updates calls to use `getFamilyShared()` instead of `getFamily()` in relevant contexts. The change simplifies the codebase by reducing the need for `mutable` and clarifies object state management.

This commit **restores** the `getUIImplementation()` method within the **`UIManagerModule`** in **React Native Android** as a deprecated stub that returns `null`. This **bug fix** addresses build failures in third-party libraries, like `react-native-safe-area-context`, which were referencing the method after its removal during the Legacy Architecture cleanup. By reintroducing the stub, the change ensures **backwards compatibility** for these external dependencies, preventing build failures and allowing them to continue functioning, albeit with the expectation that they handle the `null` return value or update their usage. This maintains the integrity of the Legacy Architecture cleanup while mitigating immediate breaking changes for the ecosystem.