Enable credential autofill for signup and login (#56)

frontend/app/test/autofill_test.dart

@@ -0,0 +1,149 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:sxchnge_app/main.dart';
+import 'package:sxchnge_app/providers/locale.dart';
+
+Finder field(String key) => find.byKey(ValueKey(key));
+
+EditableTextState editor(WidgetTester tester, String key) =>
+    tester.state<EditableTextState>(
+      find.descendant(of: field(key), matching: find.byType(EditableText)),
+    );
+
+void main() {
+  for (final language in ['en', 'ru']) {
+    testWidgets(
+      'platform autofill fills the signup credential group ($language)',
+      (tester) async {
+        tester.view.physicalSize = const Size(1440, 1200);
+        tester.view.devicePixelRatio = 1;
+        addTearDown(tester.view.resetPhysicalSize);
+        addTearDown(tester.view.resetDevicePixelRatio);
+        await tester.pumpWidget(
+          SxchngeApp(
+            localeProvider: LocaleProvider(initialLocale: Locale(language)),
+          ),
+        );
+        await tester.pumpAndSettle();
+        await tester.tap(
+          find.text(language == 'ru' ? 'Регистрация' : 'Sign up'),
+        );
+        await tester.pumpAndSettle();
+        await tester.showKeyboard(field('email'));
+
+        final configuration = tester.testTextInput.setClientArgs!;
+        expect(
+          configuration['inputType']['name'],
+          'TextInputType.emailAddress',
+        );
+        final fields = (configuration['fields'] as List).cast<Map>();
+        expect(fields, hasLength(4));
+        expect(
+          fields.map((field) => field['autofill']['hints'].first),
+          containsAll(['name', 'username', 'newPassword', 'newPassword']),
+        );
+
+        const values = {
+          'name': 'Alex Example',
+          'email': 'alex@example.com',
+          'password': 'generated-example-password',
+          'confirmation': 'generated-example-password',
+        };
+        await tester.binding.defaultBinaryMessenger.handlePlatformMessage(
+          SystemChannels.textInput.name,
+          SystemChannels.textInput.codec.encodeMethodCall(
+            MethodCall('TextInputClient.updateEditingStateWithTag', [
+              0,
+              {
+                for (final entry in values.entries)
+                  editor(tester, entry.key).autofillId: TextEditingValue(
+                    text: entry.value,
+                  ).toJSON(),
+              },
+            ]),
+          ),
+          (_) {},
+        );
+        await tester.pumpAndSettle();
+        for (final entry in values.entries) {
+          expect(
+            editor(tester, entry.key).currentTextEditingValue.text,
+            entry.value,
+          );
+        }
+
+        // A visibility change must retain both the supplied value and its role.
+        await tester.tap(
+          find.byTooltip(
+            language == 'ru' ? 'Показать пароль' : 'Show password',
+          ),
+        );
+        await tester.pump();
+        expect(editor(tester, 'password').widget.obscureText, isFalse);
+        expect(editor(tester, 'password').widget.autofillHints, [
+          'newPassword',
+        ]);
+        expect(
+          editor(tester, 'password').currentTextEditingValue.text,
+          values['password'],
+        );
+
+        await tester.tap(find.text(language == 'ru' ? 'Войти' : 'Log in'));
+        await tester.pumpAndSettle();
+        await tester.showKeyboard(field('email'));
+        final loginFields =
+            (tester.testTextInput.setClientArgs!['fields'] as List).cast<Map>();
+        expect(loginFields, hasLength(2));
+        expect(loginFields.map((field) => field['autofill']['hints'].first), [
+          'username',
+          'password',
+        ]);
+        expect(
+          editor(tester, 'password').currentTextEditingValue.text,
+          isEmpty,
+        );
+        expect(
+          tester.testTextInput.log,
+          contains(
+            isMethodCall('TextInput.finishAutofillContext', arguments: false),
+          ),
+        );
+        expect(
+          tester.testTextInput.log,
+          isNot(
+            contains(
+              isMethodCall('TextInput.finishAutofillContext', arguments: true),
+            ),
+          ),
+        );
+      },
+    );
+  }
+
+  testWidgets('leaving an unfinished auth form cancels saving', (tester) async {
+    await tester.pumpWidget(const SxchngeApp());
+    await tester.pumpAndSettle();
+    await tester.enterText(field('email'), 'alex@example.com');
+    await tester.enterText(field('password'), 'unfinished-password');
+    tester.testTextInput.log.clear();
+    await tester.pumpWidget(const SizedBox.shrink());
+    await tester.pumpAndSettle();
+    expect(
+      tester.testTextInput.log,
+      contains(
+        isMethodCall('TextInput.finishAutofillContext', arguments: false),
+      ),
+    );
+    expect(
+      tester.testTextInput.log,
+      isNot(
+        contains(
+          isMethodCall('TextInput.finishAutofillContext', arguments: true),
+        ),
+      ),
+    );
+  });
+}