fix(ios): ignore the event emitter attribute when comparing TextInput text

packages/react-native/React/Tests/Text/RCTAttributedTextUtilsTest.mm

@@ -14,6 +14,7 @@
 #import <react/renderer/textlayoutmanager/RCTFontUtils.h>
 
 #include <react/renderer/attributedstring/conversions.h>
+#include <react/renderer/core/EventEmitter.h>
 #include <react/renderer/core/RawValue.h>
 
 #include <array>
@@ -245,6 +246,76 @@ - (void)testSamenessOfMissingInsensitiveAttributes
       attributedString2, attributedString1, insensitiveAttributes, TextAttributes{}));
 }
 
+- (void)testSamenessOfDifferentEventEmitters
+{
+  // The emitter is metadata a TextInput never dispatches through, so even a different one is not a difference.
+  auto eventEmitter1 = std::make_shared<const EventEmitter>(nullptr, EventDispatcher::Weak{});
+  auto eventEmitter2 = std::make_shared<const EventEmitter>(nullptr, EventDispatcher::Weak{});
+
+  NSMutableAttributedString *attributedString1 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString1 addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 5)];
+  [attributedString1 addAttribute:RCTAttributedStringEventEmitterKey
+                            value:RCTWrapEventEmitter(eventEmitter1)
+                            range:NSMakeRange(0, 12)];
+
+  NSMutableAttributedString *attributedString2 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString2 addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 5)];
+  [attributedString2 addAttribute:RCTAttributedStringEventEmitterKey
+                            value:RCTWrapEventEmitter(eventEmitter2)
+                            range:NSMakeRange(0, 12)];
+
+  NSDictionary<NSAttributedStringKey, id> *insensitiveAttributes = @{};
+
+  XCTAssertTrue(RCTIsAttributedStringEffectivelySame(
+      attributedString1, attributedString2, insensitiveAttributes, TextAttributes{}));
+  XCTAssertTrue(RCTIsAttributedStringEffectivelySame(
+      attributedString2, attributedString1, insensitiveAttributes, TextAttributes{}));
+}
+
+- (void)testSamenessOfMissingEventEmitter
+{
+  // Text typed into a field carries no event emitter; the state echoing it does.
+  auto eventEmitter = std::make_shared<const EventEmitter>(nullptr, EventDispatcher::Weak{});
+
+  NSMutableAttributedString *attributedString1 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString1 addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 5)];
+  [attributedString1 addAttribute:RCTAttributedStringEventEmitterKey
+                            value:RCTWrapEventEmitter(eventEmitter)
+                            range:NSMakeRange(0, 12)];
+
+  NSMutableAttributedString *attributedString2 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString2 addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 5)];
+
+  NSDictionary<NSAttributedStringKey, id> *insensitiveAttributes = @{};
+
+  XCTAssertTrue(RCTIsAttributedStringEffectivelySame(
+      attributedString1, attributedString2, insensitiveAttributes, TextAttributes{}));
+  XCTAssertTrue(RCTIsAttributedStringEffectivelySame(
+      attributedString2, attributedString1, insensitiveAttributes, TextAttributes{}));
+}
+
+- (void)testDifferenceOfOtherAttributesNextToEventEmitter
+{
+  // Ignoring the event emitter must not hide a real difference in the same run.
+  auto eventEmitter = std::make_shared<const EventEmitter>(nullptr, EventDispatcher::Weak{});
+
+  NSMutableAttributedString *attributedString1 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString1 addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 12)];
+  [attributedString1 addAttribute:RCTAttributedStringEventEmitterKey
+                            value:RCTWrapEventEmitter(eventEmitter)
+                            range:NSMakeRange(0, 12)];
+
+  NSMutableAttributedString *attributedString2 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];
+  [attributedString2 addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(0, 12)];
+
+  NSDictionary<NSAttributedStringKey, id> *insensitiveAttributes = @{};
+
+  XCTAssertFalse(RCTIsAttributedStringEffectivelySame(
+      attributedString1, attributedString2, insensitiveAttributes, TextAttributes{}));
+  XCTAssertFalse(RCTIsAttributedStringEffectivelySame(
+      attributedString2, attributedString1, insensitiveAttributes, TextAttributes{}));
+}
+
 - (void)testSamenessOfResolvedParagraphStyleLtr
 {
   NSMutableAttributedString *attributedString1 = [[NSMutableAttributedString alloc] initWithString:@"Hello world!"];

packages/react-native/ReactCommon/react/renderer/textlayoutmanager/platform/ios/react/renderer/textlayoutmanager/RCTAttributedTextUtils.mm

@@ -568,6 +568,13 @@ static BOOL RCTIsAttributeEffectivelySame(
     NSDictionary<NSAttributedStringKey, id> *insensitiveAttributes,
     const TextAttributes &baseTextAttributes)
 {
+  // The event emitter is React-internal metadata, not something UIKit shows, and a TextInput dispatches its events
+  // through its own emitter rather than through this attribute. Text typed into the field often carries no
+  // emitter while the state echoing it does, so comparing it reports a difference for identical text.
+  if ([attributeKey isEqualToString:RCTAttributedStringEventEmitterKey]) {
+    return YES;
+  }
+
   id attribute1 = attributes1[attributeKey] ?: insensitiveAttributes[attributeKey];
   id attribute2 = attributes2[attributeKey] ?: insensitiveAttributes[attributeKey];