CupertinoTextField: added ability to change placeholder color (#28001)

packages/flutter/lib/src/cupertino/text_field.dart

@@ -152,6 +152,10 @@ class CupertinoTextField extends StatefulWidget {
     this.decoration = _kDefaultRoundedBorderDecoration,
     this.padding = const EdgeInsets.all(6.0),
     this.placeholder,
+    this.placeholderStyle = const TextStyle(
+      fontWeight: FontWeight.w300,
+      color: _kInactiveTextColor
+    ),
     this.prefix,
     this.prefixMode = OverlayVisibilityMode.always,
     this.suffix,
@@ -238,6 +242,17 @@ class CupertinoTextField extends StatefulWidget {
   /// main text entry except a lighter font weight and a grey font color.
   final String placeholder;
 
+  /// The style to use for the placeholder text.
+  ///
+  /// The [placeholderStyle] is merged with the [style] [TextStyle] when applied
+  /// to the [placeholder] text. To avoid merging with [style], specify
+  /// [TextStyle.inherit] as false.
+  ///
+  /// Defaults to the [style] property with w300 font weight and grey color.
+  ///
+  /// If specifically set to null, placeholder's style will be the same as [style].
+  final TextStyle placeholderStyle;
+
   /// An optional [Widget] to display before the text.
   final Widget prefix;
 
@@ -422,6 +437,7 @@ class CupertinoTextField extends StatefulWidget {
     properties.add(DiagnosticsProperty<BoxDecoration>('decoration', decoration));
     properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding));
     properties.add(StringProperty('placeholder', placeholder));
+    properties.add(DiagnosticsProperty<TextStyle>('placeholderStyle', placeholderStyle));
     properties.add(DiagnosticsProperty<OverlayVisibilityMode>('prefix', prefix == null ? null : prefixMode));
     properties.add(DiagnosticsProperty<OverlayVisibilityMode>('suffix', suffix == null ? null : suffixMode));
     properties.add(DiagnosticsProperty<OverlayVisibilityMode>('clearButtonMode', clearButtonMode));
@@ -603,9 +619,10 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
     );
   }
 
-  Widget _addTextDependentAttachments(Widget editableText, TextStyle textStyle) {
+  Widget _addTextDependentAttachments(Widget editableText, TextStyle textStyle, TextStyle placeholderStyle) {
     assert(editableText != null);
     assert(textStyle != null);
+    assert(placeholderStyle != null);
     // If there are no surrounding widgets, just return the core editable text
     // part.
     if (widget.placeholder == null &&
@@ -640,12 +657,7 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
                 widget.placeholder,
                 maxLines: 1,
                 overflow: TextOverflow.ellipsis,
-                style: textStyle.merge(
-                  const TextStyle(
-                    color: _kInactiveTextColor,
-                    fontWeight: FontWeight.w300,
-                  ),
-                ),
+                style: placeholderStyle
               ),
             ),
           );
@@ -698,6 +710,7 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
     }
     final CupertinoThemeData themeData = CupertinoTheme.of(context);
     final TextStyle textStyle = themeData.textTheme.textStyle.merge(widget.style);
+    final TextStyle placeholderStyle = textStyle.merge(widget.placeholderStyle);
     final Brightness keyboardAppearance = widget.keyboardAppearance ?? themeData.brightness;
     final Color cursorColor = widget.cursorColor ?? themeData.primaryColor;
 
@@ -773,7 +786,7 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
               onDragSelectionUpdate: _handleMouseDragSelectionUpdate,
               onDragSelectionEnd: _handleMouseDragSelectionEnd,
               behavior: HitTestBehavior.translucent,
-              child: _addTextDependentAttachments(paddedEditable, textStyle),
+              child: _addTextDependentAttachments(paddedEditable, textStyle, placeholderStyle),
             ),
           ),
         ),

packages/flutter/test/cupertino/text_field_test.dart

@@ -399,6 +399,40 @@ void main() {
     },
   );
 
+  testWidgets(
+    "placeholderStyle modifies placeholder's style and doesn't affect text's style",
+    (WidgetTester tester) async {
+      await tester.pumpWidget(
+        const CupertinoApp(
+          home: Center(
+            child: CupertinoTextField(
+              placeholder: 'placeholder',
+              style: TextStyle(
+                color: Color(0X00FFFFFF),
+                fontWeight: FontWeight.w300,
+              ),
+              placeholderStyle: TextStyle(
+                color: Color(0XAAFFFFFF),
+                fontWeight: FontWeight.w600
+              ),
+            ),
+          ),
+        ),
+      );
+
+      final Text placeholder = tester.widget(find.text('placeholder'));
+      expect(placeholder.style.color, const Color(0XAAFFFFFF));
+      expect(placeholder.style.fontWeight, FontWeight.w600);
+
+      await tester.enterText(find.byType(CupertinoTextField), 'input');
+      await tester.pump();
+
+      final EditableText inputText = tester.widget(find.text('input'));
+      expect(inputText.style.color, const Color(0X00FFFFFF));
+      expect(inputText.style.fontWeight, FontWeight.w300);
+    },
+  );
+
   testWidgets(
     'prefix widget is in front of the text',
     (WidgetTester tester) async {