[text_input] prepare for custom text input sources (#72803)

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

@@ -2038,7 +2038,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
   void _closeInputConnectionIfNeeded() {
     if (_hasInputConnection) {
-      _textInputConnection!.close();
+      TextInput.detach(this);
       _textInputConnection = null;
       _lastKnownRemoteTextEditingValue = null;
     }
@@ -2056,7 +2056,6 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   @override
   void connectionClosed() {
     if (_hasInputConnection) {
-      _textInputConnection!.connectionClosedReceived();
       _textInputConnection = null;
       _lastKnownRemoteTextEditingValue = null;
       _finalizeEditing(TextInputAction.done, shouldUnfocus: true);

packages/flutter/test/services/text_input_test.dart

@@ -22,6 +22,7 @@ void main() {
     });
 
     tearDown(() {
+      TextInput.reset();
       TextInputConnection.debugResetId();
       TextInput.setChannel(SystemChannels.textInput);
     });
@@ -74,6 +75,65 @@ void main() {
             }),
       ]);
     });
+
+    test('text input client is requested to hide on detach', () async {
+      final FakeTextInputClient client = FakeTextInputClient(TextEditingValue.empty);
+      TextInput.attach(client, client.configuration);
+      fakeTextChannel.validateOutgoingMethodCalls(<MethodCall>[
+        MethodCall('TextInput.setClient', <dynamic>[1, client.configuration.toJson()]),
+      ]);
+
+      TextInput.detach(client);
+      fakeTextChannel.validateOutgoingMethodCalls(<MethodCall>[
+        // From original attach
+        MethodCall('TextInput.setClient', <dynamic>[1, client.configuration.toJson()]),
+        // From detach
+        const MethodCall('TextInput.clearClient'),
+      ]);
+
+      final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+      await binding.runAsync(() async {});
+      await expectLater(fakeTextChannel.outgoingCalls.length, 3);
+      fakeTextChannel.validateOutgoingMethodCalls(<MethodCall>[
+        // From original attach
+        MethodCall('TextInput.setClient', <dynamic>[1, client.configuration.toJson()]),
+        // From detach
+        const MethodCall('TextInput.clearClient'),
+        // From hide
+        const MethodCall('TextInput.hide'),
+      ]);
+    });
+
+    test('old client is detached when a new client is attached',() {
+      final FakeTextInputClient client1 = FakeTextInputClient(const TextEditingValue(text: '1'));
+      final TextInputConnection connection1 = TextInput.attach(client1, client1.configuration);
+      expect(connection1.attached, isTrue);
+      fakeTextChannel.validateOutgoingMethodCalls(<MethodCall>[
+        MethodCall('TextInput.setClient', <dynamic>[1, client1.configuration.toJson()]),
+      ]);
+
+      final FakeTextInputClient client2 = FakeTextInputClient(const TextEditingValue(text: '1'));
+      final TextInputConnection connection2 = TextInput.attach(client2, client2.configuration);
+      expect(connection2.attached, isTrue);
+      expect(connection1.attached, isFalse);
+      fakeTextChannel.validateOutgoingMethodCalls(<MethodCall>[
+        // From original attach
+        MethodCall('TextInput.setClient', <dynamic>[1, client1.configuration.toJson()]),
+        // From internal detach
+        const MethodCall('TextInput.clearClient'),
+        // From second attach
+        MethodCall('TextInput.setClient', <dynamic>[2, client1.configuration.toJson()]),
+      ]);
+    });
+
+    test('text input connection is reset', () async {
+      final FakeTextInputClient client = FakeTextInputClient(TextEditingValue.empty);
+      final TextInputConnection connection = TextInput.attach(client, client.configuration);
+      expect(connection.attached, isTrue);
+
+      TextInput.reset();
+      expect(connection.attached, isFalse);
+    });
   });
 
   group('TextInputConfiguration', () {