fix(ios): center typed text and caret in single-line TextInput when lineHeight > fontSize

UITextField's placeholder path (UILabel-based) honors
NSBaselineOffsetAttributeName, but the UIFieldEditor path that draws
typed text does not. So the Fabric baseline-offset fix centers
multi-line typed text (UITextView respects the offset) but leaves
single-line typed text pinned at the bottom of the
paragraphStyle-sized line box.

Override setDefaultTextAttributes: and setAttributedText: on
RCTUITextField to forward a stripped copy of the paragraph style to
super when paragraphStyle.maximumLineHeight > font.lineHeight —
minimumLineHeight and maximumLineHeight are zeroed out. UITextField
then renders the text at its natural font line height and its built-in
vertical centering positions it correctly in the bounds. Also drop
NSBaselineOffsetAttributeName on those ranges: the offset is wasted on
UITextField's typed-text draw path and a non-zero value inflates the
caret rect without moving the glyph.

The local _defaultTextAttributes ivar keeps the original paragraph
style so _placeholderTextAttributes and the caretRectForPosition:
override continue to see the real lineHeight.

For the caret itself: when lineHeight > font.lineHeight, UIKit sizes
the caret to the full line-box height, making it visually taller than
the surrounding glyph. Override caretRectForPosition: to match the
caret height to the font's intrinsic line height and center it within
the expanded line-box so it sits alongside the glyph.

Author: janicduplessis

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

@@ -91,12 +91,71 @@ - (void)setDefaultTextAttributes:(NSDictionary<NSAttributedStringKey, id> *)defa
   if ([_defaultTextAttributes isEqualToDictionary:defaultTextAttributes]) {
     return;
   }
-
   _defaultTextAttributes = defaultTextAttributes;
-  [super setDefaultTextAttributes:defaultTextAttributes];
+  [super setDefaultTextAttributes:[self _attributesStrippedForRendering:defaultTextAttributes]];
   [self _updatePlaceholder];
 }
 
+- (void)setAttributedText:(NSAttributedString *)attributedText
+{
+  [super setAttributedText:[self _attributedTextStrippedForRendering:attributedText]];
+}
+
+// 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 (contentVerticalAlignment)
+// centers the text in the bounds. `_defaultTextAttributes` (local) keeps the unmodified
+// paragraphStyle so the placeholder path (`_placeholderTextAttributes`) and caret override
+// (`caretRectForPosition:`) still see the real lineHeight.
+- (NSDictionary<NSAttributedStringKey, id> *)_attributesStrippedForRendering:
+    (NSDictionary<NSAttributedStringKey, id> *)attributes
+{
+  NSParagraphStyle *paragraphStyle = attributes[NSParagraphStyleAttributeName];
+  UIFont *font = attributes[NSFontAttributeName];
+  if (!paragraphStyle || !font || paragraphStyle.maximumLineHeight <= font.lineHeight) {
+    return attributes;
+  }
+  NSMutableDictionary<NSAttributedStringKey, id> *copy = [attributes mutableCopy];
+  NSMutableParagraphStyle *stripped = [paragraphStyle mutableCopy];
+  stripped.minimumLineHeight = 0;
+  stripped.maximumLineHeight = 0;
+  copy[NSParagraphStyleAttributeName] = stripped;
+  return copy;
+}
+
+- (NSAttributedString *)_attributedTextStrippedForRendering:(NSAttributedString *)attributedText
+{
+  if (attributedText.length == 0) {
+    return attributedText;
+  }
+  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];
+                      }];
+  return mutableStr;
+}
+
 - (NSDictionary<NSAttributedStringKey, id> *)defaultTextAttributes
 {
   return _defaultTextAttributes;
@@ -223,7 +282,20 @@ - (CGRect)caretRectForPosition:(UITextPosition *)position
     return CGRectZero;
   }
 
-  return [super caretRectForPosition:position];
+  CGRect rect = [super caretRectForPosition:position];
+
+  // When `lineHeight > font.lineHeight`, UIKit sizes the caret to the full
+  // line-box height, making it visually taller than the surrounding glyph.
+  // Match the caret height to the font's intrinsic line height and center it
+  // so it sits alongside the glyph rather than the whole expanded line-box.
+  NSParagraphStyle *paragraphStyle = _defaultTextAttributes[NSParagraphStyleAttributeName];
+  UIFont *font = _defaultTextAttributes[NSFontAttributeName];
+  if (paragraphStyle && font && paragraphStyle.maximumLineHeight > font.lineHeight) {
+    rect.origin.y += (rect.size.height - font.lineHeight) / 2.0;
+    rect.size.height = font.lineHeight;
+  }
+
+  return rect;
 }
 
 #pragma mark - Positioning Overrides