[iOS][Fabric] ScrollView.scrollToEnd ignores adjustedContentInset

閱讀 RCTScrollViewComponentView::scrollToEnd，並將其目標計算與 issue 中描述的調整後 inset 行為進行比較。在 iOS 模擬器上執行必要的 reproducer，然後驗證 scrollToEnd 是否達到與手動拖曳相同的末端 offset，包括底部 safe-area inset。

Description

On iOS, ScrollView.scrollToEnd() computes its target using UIScrollView.contentInset, even when UIKit has expanded the effective scrollable area through adjustedContentInset.

This makes programmatic scrolling stop before the same end position a user can reach by dragging. The issue reproduces in the official React Native reproducer template on React Native 0.86.0 with the New Architecture. It does not require Expo, navigation, a keyboard, or an explicit contentInset.

On an iPhone 17 Pro Max simulator, stock React Native stops at offset 364 while a manual drag reaches 398. The missing 34 points exactly match the device's adjusted bottom safe-area inset.

Source-level cause

RCTScrollViewComponentView::scrollToEnd currently constructs the target with _scrollView.contentInset.bottom or .right. UIKit's safe-area and bar adjustments are represented by _scrollView.adjustedContentInset, so the command omits the system-provided part of the scrollable range.

Current source:

CGFloat offsetY = _scrollView.contentSize.height - _scrollView.bounds.size.height + _scrollView.contentInset.bottom;

Using adjustedContentInset makes the command reach the same end as a manual drag.

Relationship to #56189

This is related to, but not fixed by, #56189.

That PR moves scrollTo clamping into scrollToOffset and clamps against adjustedContentInset. I built React Native from source with that PR's effective Fabric logic:

Action with #56189 logic	Final vertical offset
scrollTo({y: 9999})	398 (fixed)
scrollToEnd()	364 (still incorrect)

scrollToEnd() constructs an already-valid target of 364 before calling scrollToOffset, so later clamping correctly leaves that target unchanged. Changing only scrollToEnd() to construct its target from adjustedContentInset makes it reach 398.

Steps to reproduce

1. Clone the mandatory reproducer, which starts from react-native-community/reproducer-react-native at React Native 0.86.0.
2. Run cd ReproducerApp && yarn install.
3. Run cd ios && pod install && cd ...
4. Run yarn ios on an iOS simulator with a bottom safe area.
5. Tap scrollToEnd.
6. Observe offset 364 / raw 364 / adjusted 398 / safe bottom 34.
7. Tap Reset, then drag the scroll view manually to its end.
8. Observe that manual scrolling reaches 398.

The reproducer uses one plain vertical ScrollView:

<ScrollView
  ref={scrollViewRef}
  contentInsetAdjustmentBehavior="always"
>
  {/* content taller than the viewport */}
</ScrollView>

and invokes:

scrollViewRef.current?.scrollToEnd({animated: false});

React Native Version

0.86.0

Affected Platforms

Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.5.1
  CPU: (12) arm64 Apple M4 Pro
  Memory: 133.78 MB / 24.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 25.5.0
    path: /opt/homebrew/bin/node
  Yarn: Not Found
  npm:
    version: 11.8.0
    path: /opt/homebrew/bin/npm
  Watchman:
    version: 2026.01.12.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.5
      - iOS 26.5
      - macOS 26.5
      - tvOS 26.5
      - visionOS 26.5
      - watchOS 26.5
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.1 AI-251.26094.121.2513.14007798
  Xcode:
    version: 26.6/17F113
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.16
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.86.0
    wanted: 0.86.0
iOS:
  New Architecture: enabled by the official reproducer template

Stacktrace or Logs

There is no crash. The deterministic runtime measurements are:

Native implementation	scrollToEnd()	scrollTo({y: 9999})	Manual end
Stock React Native 0.86.0	364	364	398
#56189 effective Fabric logic	364	398	398
#56189 logic plus the scrollToEnd fix	398	398	398

All native variants were compiled from source before testing.

MANDATORY Reproducer

https://github.com/eliotgevers/react-native-scroll-to-end-adjusted-inset-repro

Screenshots and Videos

Stock React Native 0.86.0	Patched native source
scrollToEnd() stops at 364 and cuts off the true end marker.	scrollToEnd() reaches the adjusted end at 398.