Keep placeholder attributes sync with text input text's attributes (#23738)

Summary:
We need to keep placeholder attributes sync with text input's text attributes, like `font`,`kern` ....., to keep style the same.

Also fixes #19002 .

[iOS] [Fixed] - Keep placeholder attributes sync with text input text's attributes
Pull Request resolved: #23738

Differential Revision: D14298482

Pulled By: cpojer

fbshipit-source-id: 3555091bf3bc01e4b026d5a4cdbe93b4122106e8

Author: zhongwuzw

Libraries/Text/TextInput/Multiline/RCTUITextView.m

@@ -82,7 +82,7 @@ - (NSString *)accessibilityLabel
 - (void)setPlaceholder:(NSString *)placeholder
 {
   _placeholder = placeholder;
-  _placeholderView.text = _placeholder;
+  _placeholderView.attributedText = [[NSAttributedString alloc] initWithString:_placeholder ?: @"" attributes:[self placeholderEffectiveTextAttributes]];
 }
 
 - (void)setPlaceholderColor:(UIColor *)placeholderColor
@@ -98,7 +98,8 @@ - (void)setReactTextAttributes:(RCTTextAttributes *)reactTextAttributes
   }
   self.typingAttributes = reactTextAttributes.effectiveTextAttributes;
   _reactTextAttributes = reactTextAttributes;
-  _placeholderView.font = self.font ?: defaultPlaceholderFont();
+  // Update placeholder text attributes
+  [self setPlaceholder:_placeholder];
 }
 
 - (RCTTextAttributes *)reactTextAttributes
@@ -249,6 +250,17 @@ - (void)invalidatePlaceholderVisibility
   _placeholderView.hidden = !isVisible;
 }
 
+- (NSDictionary<NSAttributedStringKey, id> *)placeholderEffectiveTextAttributes
+{
+  NSDictionary<NSAttributedStringKey, id> *effectiveTextAttributes = @{
+                                                                       NSFontAttributeName: _reactTextAttributes.effectiveFont ?: defaultPlaceholderFont(),
+                                                                       NSForegroundColorAttributeName: self.placeholderColor ?: defaultPlaceholderColor(),
+                                                                       NSKernAttributeName:isnan(_reactTextAttributes.letterSpacing) ? @0 : @(_reactTextAttributes.letterSpacing)
+                                                                       };
+  
+  return effectiveTextAttributes;
+}
+
 #pragma mark - Utility Methods
 
 - (void)copyTextAttributesFrom:(NSAttributedString *)sourceString

Libraries/Text/TextInput/Singleline/RCTUITextField.m

@@ -70,6 +70,7 @@ - (void)setReactTextAttributes:(RCTTextAttributes *)reactTextAttributes
   }
   self.defaultTextAttributes = reactTextAttributes.effectiveTextAttributes;
   _reactTextAttributes = reactTextAttributes;
+  [self _updatePlaceholder];
 }
 
 - (RCTTextAttributes *)reactTextAttributes
@@ -87,6 +88,10 @@ - (void)_updatePlaceholder
   if (_placeholderColor) {
     [attributes setObject:_placeholderColor forKey:NSForegroundColorAttributeName];
   }
+  // Kerning
+  if (!isnan(_reactTextAttributes.letterSpacing)) {
+    attributes[NSKernAttributeName] = @(_reactTextAttributes.letterSpacing);
+  }
 
   self.attributedPlaceholder = [[NSAttributedString alloc] initWithString:self.placeholder
                                                                attributes:attributes];