fix tap detection and call focus

lib/web_ui/lib/src/engine/semantics/text_field.dart

@@ -288,24 +288,24 @@ class TextField extends RoleManager {
       _initializeForBlink();
       return;
     }
-    num? lastTouchStartOffsetX;
-    num? lastTouchStartOffsetY;
+    num? lastPointerDownOffsetX;
+    num? lastPointerDownOffsetY;
 
-    editableElement.addEventListener('touchstart',
+    editableElement.addEventListener('pointerdown',
         allowInterop((DomEvent event) {
-          final DomTouchEvent touchEvent = event as DomTouchEvent;
-          lastTouchStartOffsetX = touchEvent.changedTouches!.last.clientX;
-          lastTouchStartOffsetY = touchEvent.changedTouches!.last.clientY;
+          final DomPointerEvent pointerEvent = event as DomPointerEvent;
+          lastPointerDownOffsetX = pointerEvent.clientX;
+          lastPointerDownOffsetY = pointerEvent.clientY;
         }), true);
 
     editableElement.addEventListener(
-        'touchend', allowInterop((DomEvent event) {
-      final DomTouchEvent touchEvent = event as DomTouchEvent;
+        'pointerup', allowInterop((DomEvent event) {
+      final DomPointerEvent pointerEvent = event as DomPointerEvent;
 
-      if (lastTouchStartOffsetX != null) {
-        assert(lastTouchStartOffsetY != null);
-        final num offsetX = touchEvent.changedTouches!.last.clientX;
-        final num offsetY = touchEvent.changedTouches!.last.clientY;
+      if (lastPointerDownOffsetX != null) {
+        assert(lastPointerDownOffsetY != null);
+        final num offsetX = pointerEvent.clientX - lastPointerDownOffsetX!;
+        final num offsetY = pointerEvent.clientY - lastPointerDownOffsetY!;
 
         // This should match the similar constant defined in:
         //
@@ -318,13 +318,25 @@ class TextField extends RoleManager {
           // Recognize it as a tap that requires a keyboard.
           EnginePlatformDispatcher.instance.invokeOnSemanticsAction(
               semanticsObject.id, ui.SemanticsAction.tap, null);
+
+          // We need to call focus for the following scenario:
+          // 1. The virtial keyboard in iOS gets dismissed by the 'Done' button
+          // located at the top right of the keyboard.
+          // 2. The user tries to focus on the input field again, either by
+          // VoiceOver or manually, but the keyboard does not show up.
+          // In this scenario, the Flutter framework does not send a semantic update,
+          // so we need to call focus after detecting a tap to make sure that the
+          // the virtual keyboard will show.
+          if (semanticsObject.hasFocus) {
+            editableElement.focus();
+          }
         }
       } else {
-        assert(lastTouchStartOffsetY == null);
+        assert(lastPointerDownOffsetY == null);
       }
 
-      lastTouchStartOffsetX = null;
-      lastTouchStartOffsetY = null;
+      lastPointerDownOffsetX = null;
+      lastPointerDownOffsetY = null;
     }), true);
   }
 

lib/web_ui/test/engine/semantics/text_field_test.dart

@@ -63,6 +63,29 @@ void testMain() {
     semantics().semanticsEnabled = false;
   });
 
+  test('tap detection works', () async {
+    debugBrowserEngineOverride = BrowserEngine.webkit;
+    debugOperatingSystemOverride = OperatingSystem.iOs;
+
+    final SemanticsActionLogger logger = SemanticsActionLogger();
+    semantics()
+      ..debugOverrideTimestampFunction(() => _testTime)
+      ..semanticsEnabled = true;
+
+    createTextFieldSemantics(value: 'hello');
+
+    final DomElement textField = appHostNode
+        .querySelector('input[data-semantics-role="text-field"]')!;
+
+    textField.dispatchEvent(createDomPointerEvent('pointerdown'));
+    textField.dispatchEvent(createDomPointerEvent('pointerup'));
+
+    expect(await logger.idLog.first, 0);
+    expect(await logger.actionLog.first, ui.SemanticsAction.tap);
+
+    semantics().semanticsEnabled = false;
+  });
+
   // TODO(yjbanov): this test will need to be adjusted for Safari when we add
   //                Safari testing.
   test('sends a tap action when browser requests focus', () async {