Hide misplaced iOS 26 scroll edge effects on inverted lists (#58684)

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.h

@@ -52,6 +52,13 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, assign) BOOL snapToEnd;
 @property (nonatomic, copy) NSArray<NSNumber *> *snapToOffsets;
 
+/*
+ * Whether this scroll view is mirrored by a `scaleY(-1)` transform, as inverted virtualized lists
+ * are. UIKit does not account for that transform when it positions iOS 26 scroll edge effects, so
+ * they have to be compensated for here.
+ */
+@property (nonatomic, assign) BOOL inverted;
+
 /*
  * Makes `setContentOffset:` method no-op when given `block` is executed.
  * The block is being executed synchronously.

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

@@ -51,6 +51,26 @@ - (instancetype)initWithFrame:(CGRect)frame
   return self;
 }
 
+- (void)setInverted:(BOOL)inverted
+{
+  if (_inverted == inverted) {
+    return;
+  }
+  _inverted = inverted;
+
+  if (@available(iOS 26.0, *)) {
+    // UIKit positions the scroll edge effects in this scroll view's own coordinate space, and the
+    // `scaleY(-1)` mirror turns that space upside down, so neither effect lands where it belongs.
+    // Against a navigation bar, `topEdgeEffect` darkens the lower half of the screen rather than
+    // the content passing under the bar; against a bottom bar, `bottomEdgeEffect` dims the whole
+    // screen. Neither produces anything useful at any scroll position while mirrored, so both are
+    // hidden. The bars cannot be given correct effects from here, because UIKit has no notion of
+    // the transform.
+    self.topEdgeEffect.hidden = inverted;
+    self.bottomEdgeEffect.hidden = inverted;
+  }
+}
+
 - (void)preserveContentOffsetWithBlock:(void (^)())block
 {
   if (!block) {

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

@@ -455,6 +455,9 @@ - (void)updateProps:(const Props::Shared &)props oldProps:(const Props::Shared &
   }
 
   [super updateProps:props oldProps:oldProps];
+
+  // Must run after `super updateProps:` so it is based on the latest calculated view.
+  ((RCTEnhancedScrollView *)_scrollView).inverted = [self isInverted];
 }
 
 - (void)updateState:(const State::Shared &)state oldState:(const State::Shared &)oldState

scripts/cxx-api/api-snapshots/ReactAppleDebugCxx.api

@@ -1035,6 +1035,7 @@ interface RCTDivisionAnimatedNode : public RCTValueAnimatedNode {
 interface RCTEnhancedScrollView : public UIScrollView {
   public @property (assign) BOOL centerContent;
   public @property (assign) BOOL disableIntervalMomentum;
+  public @property (assign) BOOL inverted;
   public @property (assign) BOOL pinchGestureEnabled;
   public @property (assign) BOOL snapToEnd;
   public @property (assign) BOOL snapToStart;

scripts/cxx-api/api-snapshots/ReactAppleNewarchCxx.api

@@ -1035,6 +1035,7 @@ interface RCTDivisionAnimatedNode : public RCTValueAnimatedNode {
 interface RCTEnhancedScrollView : public UIScrollView {
   public @property (assign) BOOL centerContent;
   public @property (assign) BOOL disableIntervalMomentum;
+  public @property (assign) BOOL inverted;
   public @property (assign) BOOL pinchGestureEnabled;
   public @property (assign) BOOL snapToEnd;
   public @property (assign) BOOL snapToStart;

scripts/cxx-api/api-snapshots/ReactAppleReleaseCxx.api

@@ -1035,6 +1035,7 @@ interface RCTDivisionAnimatedNode : public RCTValueAnimatedNode {
 interface RCTEnhancedScrollView : public UIScrollView {
   public @property (assign) BOOL centerContent;
   public @property (assign) BOOL disableIntervalMomentum;
+  public @property (assign) BOOL inverted;
   public @property (assign) BOOL pinchGestureEnabled;
   public @property (assign) BOOL snapToEnd;
   public @property (assign) BOOL snapToStart;