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, because UIKit's typingAttributes
  drops the paragraph style between keystrokes and _updateState round-trips
  the stripped attributedText through TextInputState — without the re-seed
  the helper sees maximumLineHeight == 0 and bails for typed content.

Placeholder on both UITextField.attributedPlaceholder (UILabel draw) and
RCTUITextView._placeholderView — both honor NSBaselineOffsetAttributeName.
  Add the offset computation to _placeholderTextAttributes on both backing
  views. The fix applies to both Paper and Fabric because the backing views
  are shared.

UITextField (single-line) typed text — the UIFieldEditor draw path does
NOT honor NSBaselineOffsetAttributeName, and it sizes the caret to the
paragraph-style line box height. Override setAttributedText: to forward a
copy with paragraphStyle's minimumLineHeight/maximumLineHeight zeroed out
(and NSBaselineOffsetAttributeName removed) to super. UITextField then
renders the line at the font's natural height and its built-in vertical
centering positions it correctly in the bounds; the caret rect likewise
shrinks to the natural font height. _defaultTextAttributes (the local
ivar) keeps the unmodified paragraph style so the placeholder path still
sees the real lineHeight. Yoga's frame-height measurement is unaffected.

Author: janicduplessis

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

@@ -364,6 +364,12 @@ - (void)_updatePlaceholder
     [textAttributes setValue:defaultPlaceholderFont() forKey:NSFontAttributeName];
   }
 
+  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

@@ -97,6 +97,45 @@ - (void)setDefaultTextAttributes:(NSDictionary<NSAttributedStringKey, id> *)defa
   [self _updatePlaceholder];
 }
 
+// UITextField / UIFieldEditor does not honor NSBaselineOffsetAttributeName when drawing typed
+// text, and it draws at the baseline of a paragraphStyle-sized line box — so when
+// `lineHeight > font.lineHeight` the glyphs sit at the bottom of that line box. Strip the
+// paragraphStyle line-height for the super-class rendering path so UITextField uses its
+// default intrinsic line height and its built-in vertical centering positions the glyph in the
+// bounds. `_defaultTextAttributes` (local) keeps the unmodified paragraphStyle so the
+// placeholder path (`_placeholderTextAttributes`) still sees the real lineHeight.
+- (void)setAttributedText:(NSAttributedString *)attributedText
+{
+  if (attributedText.length == 0) {
+    [super setAttributedText:attributedText];
+    return;
+  }
+  NSMutableAttributedString *mutableStr = [attributedText mutableCopy];
+  [mutableStr enumerateAttribute:NSParagraphStyleAttributeName
+                         inRange:NSMakeRange(0, mutableStr.length)
+                         options:0
+                      usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                        if (!style || style.maximumLineHeight == 0) {
+                          return;
+                        }
+                        UIFont *font = [mutableStr attribute:NSFontAttributeName
+                                                     atIndex:range.location
+                                              effectiveRange:NULL];
+                        if (!font || style.maximumLineHeight <= font.lineHeight) {
+                          return;
+                        }
+                        NSMutableParagraphStyle *stripped = [style mutableCopy];
+                        stripped.minimumLineHeight = 0;
+                        stripped.maximumLineHeight = 0;
+                        [mutableStr addAttribute:NSParagraphStyleAttributeName value:stripped range:range];
+                        // Drop any NSBaselineOffsetAttributeName applied by the Fabric baseline-offset
+                        // helper in the same range: UITextField does not honor it for typed text
+                        // rendering, but a non-zero value still inflates the caret rect.
+                        [mutableStr removeAttribute:NSBaselineOffsetAttributeName range:range];
+                      }];
+  [super setAttributedText:mutableStr];
+}
+
 - (NSDictionary<NSAttributedStringKey, id> *)defaultTextAttributes
 {
   return _defaultTextAttributes;
@@ -169,6 +208,12 @@ - (void)setDisableKeyboardShortcuts:(BOOL)disableKeyboardShortcuts
     [textAttributes removeObjectForKey:NSForegroundColorAttributeName];
   }
 
+  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

@@ -768,6 +768,30 @@ - (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
 
 - (void)_setAttributedString:(NSAttributedString *)attributedString
 {
+  // When the user types, UIKit's typingAttributes drop NSParagraphStyleAttributeName, so the
+  // attributedText round-tripping back through state lacks the paragraph style that
+  // RCTApplyBaselineOffset needs. Re-seed paragraph style from defaultTextAttributes on ranges
+  // that are missing it or carry a zero-lineHeight stub, so the helper can compute the offset.
+  NSMutableAttributedString *mutableString = [attributedString mutableCopy];
+  NSParagraphStyle *defaultParagraphStyle =
+      _backedTextInputView.defaultTextAttributes[NSParagraphStyleAttributeName];
+  if (defaultParagraphStyle && mutableString.length > 0) {
+    [mutableString
+        enumerateAttribute:NSParagraphStyleAttributeName
+                   inRange:NSMakeRange(0, mutableString.length)
+                   options:0
+                usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                  if (!style || style.maximumLineHeight == 0) {
+                    [mutableString addAttribute:NSParagraphStyleAttributeName
+                                          value:defaultParagraphStyle
+                                          range:range];
+                  }
+                }];
+  }
+
+  RCTApplyBaselineOffset(mutableString);
+  attributedString = mutableString;
+
   if ([self _textOf:attributedString equals:_backedTextInputView.attributedText]) {
     return;
   }