Fix `CupertinoFormRow`dark mode text color (#100313)

Improved code

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

@@ -148,7 +148,10 @@ class CupertinoFormRow extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final TextStyle textStyle = CupertinoTheme.of(context).textTheme.textStyle;
+    final CupertinoThemeData theme = CupertinoTheme.of(context);
+    final TextStyle textStyle = theme.textTheme.textStyle.copyWith(
+      color: CupertinoDynamicColor.maybeResolve(theme.textTheme.textStyle.color, context)
+    );
 
     return Padding(
       padding: padding ?? _kDefaultPadding,

packages/flutter/test/cupertino/form_row_test.dart

@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
@@ -163,4 +165,44 @@ void main() {
 
     expect(errorTextStyle.style.color, CupertinoColors.destructiveRed);
   });
+
+  testWidgets('CupertinoFormRow adapts to MaterialApp dark mode', (WidgetTester tester) async {
+    const Widget prefix = Text('Prefix');
+    const Widget helper = Text('Helper');
+
+    Widget _buildFormRow(Brightness brightness) {
+      return MaterialApp(
+        theme: ThemeData(brightness: brightness),
+        home: const Center(
+          child: CupertinoFormRow(
+            prefix: prefix,
+            helper: helper,
+            child: CupertinoTextField(),
+          ),
+        ),
+      );
+    }
+
+    // CupertinoFormRow with light theme.
+    await tester.pumpWidget(_buildFormRow(Brightness.light));
+    RenderParagraph helperParagraph = tester.renderObject(find.text('Helper'));
+    expect(helperParagraph.text.style!.color, CupertinoColors.label);
+    // Text style should not return unresolved color.
+    expect(helperParagraph.text.style!.color.toString().contains('UNRESOLVED'), isFalse);
+    RenderParagraph prefixParagraph = tester.renderObject(find.text('Prefix'));
+    expect(prefixParagraph.text.style!.color, CupertinoColors.label);
+    // Text style should not return unresolved color.
+    expect(prefixParagraph.text.style!.color.toString().contains('UNRESOLVED'), isFalse);
+
+    // CupertinoFormRow with light theme.
+    await tester.pumpWidget(_buildFormRow(Brightness.dark));
+    helperParagraph = tester.renderObject(find.text('Helper'));
+    expect(helperParagraph.text.style!.color, CupertinoColors.label);
+    // Text style should not return unresolved color.
+    expect(helperParagraph.text.style!.color.toString().contains('UNRESOLVED'), isFalse);
+    prefixParagraph = tester.renderObject(find.text('Prefix'));
+    expect(prefixParagraph.text.style!.color, CupertinoColors.label);
+    // Text style should not return unresolved color.
+    expect(prefixParagraph.text.style!.color.toString().contains('UNRESOLVED'), isFalse);
+  });
 }