fix(ios): center TextInput text, placeholder, and caret when lineHeight > fontSize

On iOS, when a TextInput's lineHeight exceeds its font's line height, UIKit
anchors glyphs to the bottom of the attributed-string line box instead of
centering them within it. The same misalignment affects the placeholder.
On single-line UITextField the caret is also sized to the full line box.

This patch fixes all three surfaces. The approach varies by UIKit
rendering path:

UITextView (multi-line) typed text — honors NSBaselineOffsetAttributeName.
  Call RCTApplyBaselineOffset in RCTTextInputComponentView._setAttributedString:
  to inject the offset. Re-seed NSParagraphStyleAttributeName from
  defaultTextAttributes on ranges missing it (or carrying a zero-line-height
  stub), because UIKit's typingAttributes drops the paragraph style between
  keystrokes — without the re-seed the helper sees maximumLineHeight == 0 and
  bails for typed content.

UITextField (single-line) typed text — does NOT honor NSBaselineOffsetAttributeName.
  Per-range zero out paragraphStyle.minimumLineHeight / maximumLineHeight on
  the displayed attributedText so UITextField uses the font's natural line
  height; its built-in vertical centering then positions the glyph in the
  bounds, and the caret rect (sized from the same line box) shrinks to match.
  Other paragraph-style fields (alignment, indent) are preserved so nested
  <Text> styling survives. The shadow node measures from state, so undo the
  strip in _updateState before pushing — restore stripped line heights from
  defaultTextAttributes so the cell height stays at the configured lineHeight
  across edits.

Placeholder on both UITextField.attributedPlaceholder (UILabel draw) and
RCTUITextView._placeholderView — both honor NSBaselineOffsetAttributeName.
  Add the offset computation to _placeholderTextAttributes on both backing
  views so the placeholder is centered to match (single string, single set
  of attributes — a direct computation is equivalent to RCTApplyBaselineOffset).

Bug only manifests on Fabric. Paper has had a similar baseline-offset fix in
RCTUITextView.attributedText since 0.66 (see RCTUITextView setAttributedText:),
which never made it into the Fabric component view.

Author: janicduplessis

packages/react-native/Libraries/Text/TextInput/Multiline/RCTUITextView.mm

@@ -364,6 +364,15 @@ - (void)_updatePlaceholder
     [textAttributes setValue:defaultPlaceholderFont() forKey:NSFontAttributeName];
   }
 
+  // The placeholder UILabel honors NSBaselineOffsetAttributeName. Center the placeholder
+  // glyph in the line box when `lineHeight > font.lineHeight` (placeholder is a single
+  // string with one set of attributes, so a direct computation is equivalent to RCTApplyBaselineOffset).
+  NSParagraphStyle *paragraphStyle = textAttributes[NSParagraphStyleAttributeName];
+  UIFont *font = textAttributes[NSFontAttributeName];
+  if (paragraphStyle && font && paragraphStyle.maximumLineHeight > font.lineHeight) {
+    textAttributes[NSBaselineOffsetAttributeName] = @((paragraphStyle.maximumLineHeight - font.lineHeight) / 2.0);
+  }
+
   return textAttributes;
 }
 

packages/react-native/Libraries/Text/TextInput/Singleline/RCTUITextField.mm

@@ -169,6 +169,14 @@ - (void)setDisableKeyboardShortcuts:(BOOL)disableKeyboardShortcuts
     [textAttributes removeObjectForKey:NSForegroundColorAttributeName];
   }
 
+  // The UILabel-based draw path used by `attributedPlaceholder` honors
+  // NSBaselineOffsetAttributeName (unlike the typed-text path).
+  NSParagraphStyle *paragraphStyle = textAttributes[NSParagraphStyleAttributeName];
+  UIFont *font = textAttributes[NSFontAttributeName];
+  if (paragraphStyle && font && paragraphStyle.maximumLineHeight > font.lineHeight) {
+    textAttributes[NSBaselineOffsetAttributeName] = @((paragraphStyle.maximumLineHeight - font.lineHeight) / 2.0);
+  }
+
   return textAttributes;
 }
 

packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm

@@ -712,10 +712,10 @@ - (void)handleInputAccessoryDoneButton
   return {
       .text = RCTStringFromNSString(_backedTextInputView.attributedText.string),
       .selectionRange = [self _selectionRange],
-      .eventCount = static_cast<int>(_mostRecentEventCount),
+      .contentSize = RCTSizeFromCGSize(_backedTextInputView.contentSize),
       .contentOffset = RCTPointFromCGPoint(_backedTextInputView.contentOffset),
       .contentInset = RCTEdgeInsetsFromUIEdgeInsets(_backedTextInputView.contentInset),
-      .contentSize = RCTSizeFromCGSize(_backedTextInputView.contentSize),
+      .eventCount = static_cast<int>(_mostRecentEventCount),
       .layoutMeasurement = RCTSizeFromCGSize(_backedTextInputView.bounds.size),
       .zoomScale = _backedTextInputView.zoomScale,
   };
@@ -729,12 +729,47 @@ - (void)_updateState
   NSAttributedString *attributedString = _backedTextInputView.attributedText;
   auto data = _state->getData();
   _lastStringStateWasUpdatedWith = attributedString;
-  data.attributedStringBox = RCTAttributedStringBoxFromNSAttributedString(attributedString);
+  data.attributedStringBox = RCTAttributedStringBoxFromNSAttributedString([self _stateAttributedString:attributedString]);
   _mostRecentEventCount += _comingFromJS ? 0 : 1;
   data.mostRecentEventCount = _mostRecentEventCount;
   _state->updateState(std::move(data));
 }
 
+// For single-line inputs, `_setAttributedString:` zeros the paragraph-style line
+// heights on the displayed text so UITextField centers the glyph correctly when
+// `lineHeight > font.lineHeight`. The shadow node measures from state, so undo
+// that strip here — restore stripped line heights from the default paragraph
+// style so layout sizing reflects the configured `lineHeight`, not the render-
+// time strip.
+- (NSAttributedString *)_stateAttributedString:(NSAttributedString *)attributedString
+{
+  if ([_backedTextInputView isKindOfClass:[RCTUITextView class]] || attributedString.length == 0) {
+    return attributedString;
+  }
+  NSDictionary<NSAttributedStringKey, id> *defaults = _backedTextInputView.defaultTextAttributes;
+  NSParagraphStyle *defaultParagraphStyle = defaults[NSParagraphStyleAttributeName];
+  UIFont *defaultFont = defaults[NSFontAttributeName];
+  if (!defaultParagraphStyle || !defaultFont ||
+      defaultParagraphStyle.maximumLineHeight <= defaultFont.lineHeight) {
+    return attributedString;
+  }
+  NSMutableAttributedString *mutableString = [attributedString mutableCopy];
+  [mutableString enumerateAttribute:NSParagraphStyleAttributeName
+                            inRange:NSMakeRange(0, mutableString.length)
+                            options:0
+                         usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                           if (style && style.maximumLineHeight == 0 && style.minimumLineHeight == 0) {
+                             NSMutableParagraphStyle *restored = [style mutableCopy];
+                             restored.minimumLineHeight = defaultParagraphStyle.minimumLineHeight;
+                             restored.maximumLineHeight = defaultParagraphStyle.maximumLineHeight;
+                             [mutableString addAttribute:NSParagraphStyleAttributeName
+                                                   value:restored
+                                                   range:range];
+                           }
+                         }];
+  return mutableString;
+}
+
 - (AttributedString::Range)_selectionRange
 {
   UITextRange *selectedTextRange = _backedTextInputView.selectedTextRange;
@@ -768,6 +803,56 @@ - (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
 
 - (void)_setAttributedString:(NSAttributedString *)attributedString
 {
+  // When `lineHeight > font.lineHeight`, UIKit's draw paths anchor glyphs to the bottom of the
+  // paragraph line box. UITextView honors NSBaselineOffsetAttributeName to re-center; UITextField
+  // does not, so for single-line we instead zero the paragraph-style line height (UITextField
+  // then renders at the font's natural line height and its built-in vertical centering positions
+  // the glyph in the bounds; the caret rect, sized from the same line box, shrinks to match).
+  NSDictionary<NSAttributedStringKey, id> *defaults = _backedTextInputView.defaultTextAttributes;
+  NSParagraphStyle *defaultParagraphStyle = defaults[NSParagraphStyleAttributeName];
+  UIFont *defaultFont = defaults[NSFontAttributeName];
+  if (attributedString.length > 0 && defaultParagraphStyle && defaultFont &&
+      defaultParagraphStyle.maximumLineHeight > defaultFont.lineHeight) {
+    NSMutableAttributedString *mutableString = [attributedString mutableCopy];
+    NSRange fullRange = NSMakeRange(0, mutableString.length);
+    if ([_backedTextInputView isKindOfClass:[RCTUITextView class]]) {
+      // UIKit's typingAttributes drop NSParagraphStyle on the round-trip, so chars typed
+      // since the last state push arrive without a paragraph style. Re-seed those ranges
+      // (and ranges with a zero-line-height stub) from the default so UITextView resolves a
+      // consistent line-box height across the whole string. RCTApplyBaselineOffset then
+      // computes the centering offset using the max font.lineHeight present on each line —
+      // correct for mixed-font input from nested <Text> children.
+      [mutableString enumerateAttribute:NSParagraphStyleAttributeName
+                                inRange:fullRange
+                                options:0
+                             usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                               if (!style || style.maximumLineHeight == 0) {
+                                 [mutableString addAttribute:NSParagraphStyleAttributeName
+                                                       value:defaultParagraphStyle
+                                                       range:range];
+                               }
+                             }];
+      RCTApplyBaselineOffset(mutableString);
+    } else {
+      // Single-line: per-range zero out the paragraph-style line height while preserving any
+      // other paragraph-style fields (alignment, indent) the user set on nested <Text>.
+      [mutableString enumerateAttribute:NSParagraphStyleAttributeName
+                                inRange:fullRange
+                                options:0
+                             usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                               NSParagraphStyle *source = style ?: defaultParagraphStyle;
+                               if (source.maximumLineHeight == 0 && source.minimumLineHeight == 0) {
+                                 return;
+                               }
+                               NSMutableParagraphStyle *stripped = [source mutableCopy];
+                               stripped.minimumLineHeight = 0;
+                               stripped.maximumLineHeight = 0;
+                               [mutableString addAttribute:NSParagraphStyleAttributeName value:stripped range:range];
+                             }];
+    }
+    attributedString = mutableString;
+  }
+
   if ([self _textOf:attributedString equals:_backedTextInputView.attributedText]) {
     return;
   }