TextField - allow to customize cursor color in error state (flutter#136121)

The color of the TextField's cursor in error state is the same as the error text color by default. However we should be allowed to customize it

Fixes flutter#135580

Author: liranzairi

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

@@ -288,6 +288,7 @@ class TextField extends StatefulWidget {
     this.cursorRadius,
     this.cursorOpacityAnimates,
     this.cursorColor,
+    this.cursorErrorColor,
     this.selectionHeightStyle = ui.BoxHeightStyle.tight,
     this.selectionWidthStyle = ui.BoxWidthStyle.tight,
     this.keyboardAppearance,
@@ -595,6 +596,13 @@ class TextField extends StatefulWidget {
   /// the value of [ColorScheme.primary] of [ThemeData.colorScheme].
   final Color? cursorColor;
 
+  /// The color of the cursor when the [InputDecorator] is showing an error.
+  ///
+  /// If this is null it will default to [TextStyle.color] of
+  /// [InputDecoration.errorStyle]. If that is null, it will use
+  /// [ColorScheme.error] of [ThemeData.colorScheme].
+  final Color? cursorErrorColor;
+
   /// Controls how tall the selection highlight boxes are computed to be.
   ///
   /// See [ui.BoxHeightStyle] for details on available styles.
@@ -893,6 +901,7 @@ class TextField extends StatefulWidget {
     properties.add(DiagnosticsProperty<Radius>('cursorRadius', cursorRadius, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('cursorOpacityAnimates', cursorOpacityAnimates, defaultValue: null));
     properties.add(ColorProperty('cursorColor', cursorColor, defaultValue: null));
+    properties.add(ColorProperty('cursorErrorColor', cursorErrorColor, defaultValue: null));
     properties.add(DiagnosticsProperty<Brightness>('keyboardAppearance', keyboardAppearance, defaultValue: null));
     properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('scrollPadding', scrollPadding, defaultValue: const EdgeInsets.all(20.0)));
     properties.add(FlagProperty('selectionEnabled', value: selectionEnabled, defaultValue: true, ifFalse: 'selection disabled'));
@@ -946,7 +955,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
 
   bool get _hasError => widget.decoration?.errorText != null || widget.decoration?.error != null || _hasIntrinsicError;
 
-  Color get _errorColor => widget.decoration?.errorStyle?.color ?? Theme.of(context).colorScheme.error;
+  Color get _errorColor => widget.cursorErrorColor ?? widget.decoration?.errorStyle?.color ?? Theme.of(context).colorScheme.error;
 
   InputDecoration _getEffectiveDecoration() {
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);

packages/flutter/lib/src/material/text_form_field.dart

@@ -144,6 +144,7 @@ class TextFormField extends FormField<String> {
     double? cursorHeight,
     Radius? cursorRadius,
     Color? cursorColor,
+    Color? cursorErrorColor,
     Brightness? keyboardAppearance,
     EdgeInsets scrollPadding = const EdgeInsets.all(20.0),
     bool? enableInteractiveSelection,
@@ -236,6 +237,7 @@ class TextFormField extends FormField<String> {
                cursorHeight: cursorHeight,
                cursorRadius: cursorRadius,
                cursorColor: cursorColor,
+               cursorErrorColor: cursorErrorColor,
                scrollPadding: scrollPadding,
                scrollPhysics: scrollPhysics,
                keyboardAppearance: keyboardAppearance,

packages/flutter/test/material/text_form_field_test.dart

@@ -1481,27 +1481,64 @@ void main() {
   });
 
   testWidgetsWithLeakTracking('Error color for cursor while validating', (WidgetTester tester) async {
-    const Color errorColor = Color(0xff123456);
-    await tester.pumpWidget(MaterialApp(
-      theme: ThemeData(
-        colorScheme: const ColorScheme.light(error: errorColor),
-      ),
-      home: Material(
-        child: Center(
-          child: TextFormField(
-            enabled: true,
-            autovalidateMode: AutovalidateMode.always,
-            validator: (String? value) {
-              return 'Please enter value';
-            },
+    const Color themeErrorColor = Color(0xff111111);
+    const Color errorStyleColor = Color(0xff777777);
+    const Color cursorErrorColor = Color(0xffbbbbbb);
+
+    Widget buildWidget({Color? errorStyleColor, Color? cursorErrorColor}) {
+      return MaterialApp(
+        theme: ThemeData(
+          colorScheme: const ColorScheme.light(error: themeErrorColor),
+        ),
+        home: Material(
+          child: Center(
+            child: TextFormField(
+              enabled: true,
+              autovalidateMode: AutovalidateMode.always,
+              decoration: InputDecoration(
+                errorStyle: TextStyle(
+                  color: errorStyleColor,
+                ),
+              ),
+              cursorErrorColor: cursorErrorColor,
+              validator: (String? value) {
+                return 'Please enter value';
+              },
+            ),
           ),
         ),
+      );
+    }
+
+    Future<void> runTest(Widget widget, {required Color expectedColor}) async {
+      await tester.pumpWidget(widget);
+      await tester.enterText(find.byType(TextField), 'a');
+      final EditableText textField = tester.widget(
+        find.byType(EditableText).first,
+      );
+      await tester.pump();
+      expect(textField.cursorColor, expectedColor);
+    }
+
+    await runTest(
+      buildWidget(),
+      expectedColor: themeErrorColor,
+    );
+    await runTest(
+      buildWidget(errorStyleColor: errorStyleColor),
+      expectedColor: errorStyleColor,
+    );
+    await runTest(
+      buildWidget(cursorErrorColor: cursorErrorColor),
+      expectedColor: cursorErrorColor,
+    );
+    await runTest(
+      buildWidget(
+        errorStyleColor: errorStyleColor,
+        cursorErrorColor: cursorErrorColor,
       ),
-    ));
-    await tester.enterText(find.byType(TextField), 'a');
-    final EditableText textField = tester.widget(find.byType(EditableText).first);
-    await tester.pump();
-    expect(textField.cursorColor, errorColor);
+      expectedColor: cursorErrorColor,
+    );
   });
 
   testWidgetsWithLeakTracking('TextFormField onChanged is called when the form is reset', (WidgetTester tester) async {