Feat : TextField cursor color matching M2 and M3 Spec in error state (#119225)

According to Material specs, cursor should be red in error state.

Author: hasnentai

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

@@ -917,6 +917,8 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
 
   bool get _hasError => widget.decoration?.errorText != null || _hasIntrinsicError;
 
+  Color get _errorColor => widget.decoration?.errorStyle?.color ?? Theme.of(context).colorScheme.error;
+
   InputDecoration _getEffectiveDecoration() {
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);
     final ThemeData themeData = Theme.of(context);
@@ -1247,7 +1249,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         textSelectionControls ??= cupertinoTextSelectionHandleControls;
         paintCursorAboveText = true;
         cursorOpacityAnimates = true;
-        cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? cupertinoTheme.primaryColor;
+        cursorColor = _hasError ? _errorColor : widget.cursorColor ?? selectionStyle.cursorColor ?? cupertinoTheme.primaryColor;
         selectionColor = selectionStyle.selectionColor ?? cupertinoTheme.primaryColor.withOpacity(0.40);
         cursorRadius ??= const Radius.circular(2.0);
         cursorOffset = Offset(iOSHorizontalOffset / MediaQuery.devicePixelRatioOf(context), 0);
@@ -1260,7 +1262,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         textSelectionControls ??= cupertinoDesktopTextSelectionHandleControls;
         paintCursorAboveText = true;
         cursorOpacityAnimates = false;
-        cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? cupertinoTheme.primaryColor;
+        cursorColor = _hasError ? _errorColor : widget.cursorColor ?? selectionStyle.cursorColor ?? cupertinoTheme.primaryColor;
         selectionColor = selectionStyle.selectionColor ?? cupertinoTheme.primaryColor.withOpacity(0.40);
         cursorRadius ??= const Radius.circular(2.0);
         cursorOffset = Offset(iOSHorizontalOffset / MediaQuery.devicePixelRatioOf(context), 0);
@@ -1278,7 +1280,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         textSelectionControls ??= materialTextSelectionHandleControls;
         paintCursorAboveText = false;
         cursorOpacityAnimates = false;
-        cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
+        cursorColor = _hasError ? _errorColor : widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
         selectionColor = selectionStyle.selectionColor ?? theme.colorScheme.primary.withOpacity(0.40);
         break;
 
@@ -1287,7 +1289,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         textSelectionControls ??= desktopTextSelectionHandleControls;
         paintCursorAboveText = false;
         cursorOpacityAnimates = false;
-        cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
+        cursorColor = _hasError ? _errorColor : widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
         selectionColor = selectionStyle.selectionColor ?? theme.colorScheme.primary.withOpacity(0.40);
         break;
 
@@ -1296,7 +1298,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         textSelectionControls ??= desktopTextSelectionHandleControls;
         paintCursorAboveText = false;
         cursorOpacityAnimates = false;
-        cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
+        cursorColor = _hasError ? _errorColor : widget.cursorColor ?? selectionStyle.cursorColor ?? theme.colorScheme.primary;
         selectionColor = selectionStyle.selectionColor ?? theme.colorScheme.primary.withOpacity(0.40);
         handleDidGainAccessibilityFocus = () {
           // Automatically activate the TextField when it receives accessibility focus.

packages/flutter/test/material/text_form_field_test.dart

@@ -1169,4 +1169,28 @@ void main() {
     final EditableText editableText = tester.widget(find.byType(EditableText));
     expect(editableText.magnifierConfiguration, equals(myTextMagnifierConfiguration));
   });
+
+  testWidgets('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';
+            },
+          ),
+        ),
+      ),
+    ));
+    await tester.enterText(find.byType(TextField), 'a');
+    final EditableText textField = tester.widget(find.byType(EditableText).first);
+    await tester.pump();
+    expect(textField.cursorColor, errorColor);
+  });
 }