Reset contentInset in scroll view prepareForRecycle (#55733)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55733

React Native's Fabric view recycling pools UIScrollView instances by component type, meaning vertical and horizontal scroll views share the same pool. When a scroll view is recycled via prepareForRecycle, contentInset is not reset. This causes stale bottom insets set at runtime (e.g., by the floating tab bar's content inset adjustment) to leak into recycled scroll views.

This manifests as horizontal FlatLists allowing vertical/diagonal scrolling because they inherit a non-zero bottom contentInset from a previously vertical scroll view.

Fix: Reset contentInset to UIEdgeInsetsZero in prepareForRecycle, consistent with how contentOffset, zoomScale, and contentInsetAdjustmentBehavior are already reset.

Changelog: Internal

More Context: https://fb.workplace.com/groups/rn.support/posts/30810820418539846/?comment_id=30811286738493214&reply_comment_id=30821628410792380

Reviewed By: cipolleschi

Differential Revision: D93342311

fbshipit-source-id: 84c4597596e36a535f9a10840b1ddf280f6402df

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -684,6 +684,8 @@ static inline UIViewAnimationOptions animationOptionsWithCurve(UIViewAnimationCu
   _scrollView.contentOffset = RCTCGPointFromPoint(props.contentOffset);
   // Reset zoom scale to default
   _scrollView.zoomScale = 1.0;
+  // Reset contentInset to prevent stale insets leaking into recycled scroll views.
+  _scrollView.contentInset = UIEdgeInsetsZero;
   // We set the default behavior to "never" so that iOS
   // doesn't do weird things to UIScrollView insets automatically
   // and keeps it as an opt-in behavior.

packages/react-native/ReactCommon/react/renderer/components/scrollview/ScrollViewState.h

@@ -28,7 +28,7 @@ class ScrollViewState final {
 
   Point contentOffset;
   Rect contentBoundingRect;
-  int scrollAwayPaddingTop;
+  int scrollAwayPaddingTop{0};
 
   /*
    * View Culling has to be disabled when accessibility features are used.

packages/react-native/ReactCommon/react/renderer/components/scrollview/tests/ScrollViewTest.cpp

@@ -5,10 +5,90 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-#include <memory>
+#include <react/renderer/components/scrollview/ScrollViewState.h>
 
 #include <gtest/gtest.h>
 
-TEST(ScrollViewTest, testSomething) {
-  // TODO
+namespace facebook::react {
+
+TEST(ScrollViewStateTest, defaultConstructor) {
+  ScrollViewState state;
+
+  EXPECT_EQ(state.contentOffset.x, 0);
+  EXPECT_EQ(state.contentOffset.y, 0);
+  EXPECT_EQ(state.scrollAwayPaddingTop, 0);
+  EXPECT_FALSE(state.disableViewCulling);
 }
+
+TEST(ScrollViewStateTest, parameterizedConstructor) {
+  Point contentOffset{.x = 10.0f, .y = 20.0f};
+  Rect contentBoundingRect{
+      .origin = {.x = 0.0f, .y = 0.0f},
+      .size = {.width = 100.0f, .height = 200.0f}};
+  int scrollAwayPaddingTop = 5;
+
+  ScrollViewState state(
+      contentOffset, contentBoundingRect, scrollAwayPaddingTop);
+
+  EXPECT_EQ(state.contentOffset.x, 10.0f);
+  EXPECT_EQ(state.contentOffset.y, 20.0f);
+  EXPECT_EQ(state.scrollAwayPaddingTop, 5);
+  EXPECT_FALSE(state.disableViewCulling);
+}
+
+TEST(ScrollViewStateTest, getContentSize) {
+  Point contentOffset{.x = 0.0f, .y = 0.0f};
+  Rect contentBoundingRect{
+      .origin = {.x = 0.0f, .y = 0.0f},
+      .size = {.width = 150.0f, .height = 300.0f}};
+  int scrollAwayPaddingTop = 0;
+
+  ScrollViewState state(
+      contentOffset, contentBoundingRect, scrollAwayPaddingTop);
+
+  Size contentSize = state.getContentSize();
+  EXPECT_EQ(contentSize.width, 150.0f);
+  EXPECT_EQ(contentSize.height, 300.0f);
+}
+
+TEST(ScrollViewStateTest, disableViewCulling) {
+  ScrollViewState state;
+
+  // Default should be false
+  EXPECT_FALSE(state.disableViewCulling);
+
+  // Can be set to true
+  state.disableViewCulling = true;
+  EXPECT_TRUE(state.disableViewCulling);
+}
+
+TEST(ScrollViewStateTest, contentOffsetWithNegativeValues) {
+  Point contentOffset{.x = -10.0f, .y = -20.0f};
+  Rect contentBoundingRect{
+      .origin = {.x = 0.0f, .y = 0.0f},
+      .size = {.width = 100.0f, .height = 200.0f}};
+  int scrollAwayPaddingTop = 0;
+
+  ScrollViewState state(
+      contentOffset, contentBoundingRect, scrollAwayPaddingTop);
+
+  EXPECT_EQ(state.contentOffset.x, -10.0f);
+  EXPECT_EQ(state.contentOffset.y, -20.0f);
+}
+
+TEST(ScrollViewStateTest, zeroSizeContentBoundingRect) {
+  Point contentOffset{.x = 0.0f, .y = 0.0f};
+  Rect contentBoundingRect{
+      .origin = {.x = 0.0f, .y = 0.0f},
+      .size = {.width = 0.0f, .height = 0.0f}};
+  int scrollAwayPaddingTop = 0;
+
+  ScrollViewState state(
+      contentOffset, contentBoundingRect, scrollAwayPaddingTop);
+
+  Size contentSize = state.getContentSize();
+  EXPECT_EQ(contentSize.width, 0.0f);
+  EXPECT_EQ(contentSize.height, 0.0f);
+}
+
+} // namespace facebook::react