Fix false positive validation result on form submission with AutovalidateMode.onUnfocus (flutter#159394)

Fixes flutter#159378
Resolved an issue where focused TextFormField was bypassed during form
validation
when using AutovalidateMode.onUnfocus on mobile devices. Validation is
now correctly
triggered for all fields, including those that are focused.

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Author: Mairramer

packages/flutter/lib/src/widgets/form.dart

@@ -354,9 +354,11 @@ class FormState extends State<Form> {
     final bool validateOnFocusChange = widget.autovalidateMode == AutovalidateMode.onUnfocus;
 
     for (final FormFieldState<dynamic> field in _fields) {
-      if (!validateOnFocusChange || !field._focusNode.hasFocus) {
+      final bool hasFocus = field._focusNode.hasFocus;
+
+      if (!validateOnFocusChange || !hasFocus || (validateOnFocusChange && hasFocus)) {
         final bool isFieldValid = field.validate();
-        hasError = !isFieldValid || hasError;
+        hasError |= !isFieldValid;
         // Ensure that only the first error message gets announced to the user.
         if (errorMessage.isEmpty) {
           errorMessage = field.errorText ?? '';

packages/flutter/test/widgets/form_test.dart

@@ -1505,4 +1505,53 @@ void main() {
     expect(find.text(errorText('foo')), findsOneWidget);
     expect(find.text(errorText('bar')), findsOneWidget);
   });
+
+  testWidgets('AutovalidateMode.onUnfocus should validate all fields manually with FormState', (WidgetTester tester) async {
+    final GlobalKey<FormState> formKey = GlobalKey<FormState>();
+    const Key fieldKey = Key('form field');
+    String errorText(String? value) => '$value/error';
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Center(
+          child: Form(
+            key: formKey,
+            autovalidateMode: AutovalidateMode.onUnfocus,
+            child: Material(
+              child: Column(
+                children: <Widget>[
+                  TextFormField(
+                    key: fieldKey,
+                    initialValue: 'foo',
+                    validator: errorText,
+                  ),
+                  TextFormField(
+                    initialValue: 'bar',
+                    validator: errorText,
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+
+    // Focus on the first field.
+    await tester.tap(find.byKey(fieldKey));
+    await tester.pump();
+
+    // Check no error messages are displayed initially.
+    expect(find.text('foo/error'), findsNothing);
+    expect(find.text('bar/error'), findsNothing);
+
+    // Validate all fields manually using FormState.
+    expect(formKey.currentState!.validate(), isFalse);
+    await tester.pump();
+
+    // Check error messages are displayed.
+    expect(find.text('foo/error'), findsOneWidget);
+    expect(find.text('bar/error'), findsOneWidget);
+  });
 }