Avoid copying text fragments and re-attributing runs when building NSAttributedString

`RCTNSAttributedStringFromAttributedString` iterated the fragments by value,
copying each one (its string, its text attributes and a shadow view with
three shared pointers), and attached the event emitter to a text fragment in
a second `addAttributes:range:` pass over the string it had just created with
its attributes, which splits and re-merges the attribute runs. Iterate by
reference and put the emitter into a text fragment's initial attribute
dictionary. Attachment fragments keep the existing second pass, so the
attributes on every run are unchanged.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: hryhoriiK97

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

@@ -403,7 +403,8 @@ void RCTApplyBaselineOffset(NSMutableAttributedString *attributedText)
 
 static NSMutableAttributedString *RCTNSAttributedStringFragmentFromFragment(
     const AttributedString::Fragment &fragment,
-    UIImage *placeholderImage)
+    UIImage *placeholderImage,
+    NSData *_Nullable eventEmitterWrapper)
 {
   if (fragment.isAttachment()) {
     auto layoutMetrics = fragment.parentShadowView.layoutMetrics;
@@ -427,21 +428,32 @@ void RCTApplyBaselineOffset(NSMutableAttributedString *attributedText)
       string = RCTNSStringFromStringApplyingTextTransform(string, textTransform);
     }
 
-    return [[NSMutableAttributedString alloc]
-        initWithString:string
-            attributes:RCTNSTextAttributesFromTextAttributes(fragment.textAttributes)];
+    // The event emitter is part of the initial attributes: adding it afterwards
+    // with `addAttributes:range:` splits and re-merges the attribute runs the
+    // string was just created with.
+    NSMutableDictionary<NSAttributedStringKey, id> *attributes =
+        RCTNSTextAttributesFromTextAttributes(fragment.textAttributes);
+    if (eventEmitterWrapper != nil) {
+      attributes[RCTAttributedStringEventEmitterKey] = eventEmitterWrapper;
+    }
+
+    return [[NSMutableAttributedString alloc] initWithString:string attributes:attributes];
   }
 }
 
 static NSMutableAttributedString *RCTNSAttributedStringFragmentWithAttributesFromFragment(
     const AttributedString::Fragment &fragment,
     UIImage *placeholderImage)
 {
-  auto nsAttributedStringFragment = RCTNSAttributedStringFragmentFromFragment(fragment, placeholderImage);
+  NSData *eventEmitterWrapper =
+      fragment.parentShadowView.componentHandle ? RCTWrapEventEmitter(fragment.parentShadowView.eventEmitter) : nil;
 
-  if (fragment.parentShadowView.componentHandle) {
-    auto eventEmitterWrapper = RCTWrapEventEmitter(fragment.parentShadowView.eventEmitter);
+  auto nsAttributedStringFragment =
+      RCTNSAttributedStringFragmentFromFragment(fragment, placeholderImage, eventEmitterWrapper);
 
+  // A text fragment received the emitter with its initial attributes above;
+  // an attachment's string comes from `attributedStringWithAttachment:`.
+  if (fragment.isAttachment() && eventEmitterWrapper != nil) {
     NSDictionary<NSAttributedStringKey, id> *additionalTextAttributes =
         @{RCTAttributedStringEventEmitterKey : eventEmitterWrapper};
 
@@ -464,7 +476,7 @@ void RCTApplyBaselineOffset(NSMutableAttributedString *attributedText)
 
   [nsAttributedString beginEditing];
 
-  for (auto fragment : attributedString.getFragments()) {
+  for (const auto &fragment : attributedString.getFragments()) {
     NSMutableAttributedString *nsAttributedStringFragment =
         RCTNSAttributedStringFragmentWithAttributesFromFragment(fragment, placeholderImage);