Fix scroll offset when caret larger than viewport (flutter#93248)

Fixing a calculation when jumping to an offset with a large caret as compared to the viewport.

Author: tgucio

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

@@ -2151,7 +2151,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     if (!_isMultiline) {
       additionalOffset = rect.width >= editableSize.width
         // Center `rect` if it's oversized.
-        ? editableSize.width / 2 - rect.center.dx
+        ? rect.center.dx - editableSize.width / 2
         // Valid additional offsets range from (rect.right - size.width)
         // to (rect.left). Pick the closest one if out of range.
         : 0.0.clamp(rect.right - editableSize.width, rect.left);
@@ -2167,7 +2167,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       );
 
       additionalOffset = expandedRect.height >= editableSize.height
-        ? editableSize.height / 2 - expandedRect.center.dy
+        ? expandedRect.center.dy - editableSize.height / 2
         : 0.0.clamp(expandedRect.bottom - editableSize.height, expandedRect.top);
       unitOffset = const Offset(0, 1);
     }

packages/flutter/test/widgets/editable_text_test.dart

@@ -5812,12 +5812,111 @@ void main() {
     state.bringIntoView(TextPosition(offset: controller.text.length));
 
     await tester.pumpAndSettle();
-    // The SingleChildScrollView is scrolled instead of the EditableText to
-    // reveal the caret.
+    // The SingleChildScrollView is scrolled instead of the EditableText to reveal the caret.
     expect(outerController.offset, outerController.position.maxScrollExtent);
     expect(editableScrollController.offset, 0);
   });
 
+  testWidgets('bringIntoView centers the viewport on caret when the caret is wider than the viewport', (WidgetTester tester) async {
+    const String text = 'to coz ze ze Szwecji';
+    final TextEditingController controller = TextEditingController(text: text);
+
+    await tester.pumpWidget(MaterialApp(
+      home: Align(
+        alignment: Alignment.topLeft,
+        child: SizedBox(
+          width: 32.0,
+          height: 100.0,
+          child: EditableText(
+            showSelectionHandles: true,
+            controller: controller,
+            focusNode: FocusNode(),
+            style: const TextStyle(fontFamily: 'Ahem', fontSize: 48.0, height: 1.0),
+            cursorColor: Colors.blue,
+            cursorWidth: 48.0,
+            backgroundCursorColor: Colors.grey,
+            selectionControls: materialTextSelectionControls,
+            keyboardType: TextInputType.text,
+          ),
+        ),
+      ),
+    ));
+
+    final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+    final RenderEditable renderEditable = state.renderEditable;
+    final Scrollable scrollable = tester.widget<Scrollable>(find.byType(Scrollable));
+
+    expect(scrollable.controller!.position.viewportDimension, equals(32.0));
+    expect(scrollable.controller!.offset, 0.0);
+    expect(renderEditable.maxScrollExtent, equals(977.0));
+
+    state.bringIntoView(const TextPosition(offset: 2));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 2 * 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 5));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 5 * 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 7));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 7 * 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 9));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 9 * 48.0 + 48.0 / 2 - 32.0 / 2);
+  });
+
+  testWidgets('bringIntoView centers the viewport on caret when the caret is taller than the viewport', (WidgetTester tester) async {
+    const String text = 'to\ncoz\nze\nze\nSzwecji';
+    final TextEditingController controller = TextEditingController(text: text);
+
+    await tester.pumpWidget(MaterialApp(
+      home: Align(
+        alignment: Alignment.topLeft,
+        child: SizedBox(
+          width: 500.0,
+          height: 32.0,
+          child: EditableText(
+            showSelectionHandles: true,
+            maxLines: null,
+            controller: controller,
+            focusNode: FocusNode(),
+            style: const TextStyle(fontFamily: 'Ahem', fontSize: 48.0, height: 1.0),
+            cursorColor: Colors.blue,
+            backgroundCursorColor: Colors.grey,
+            selectionControls: materialTextSelectionControls,
+            keyboardType: TextInputType.text,
+          ),
+        ),
+      ),
+    ));
+
+    final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+    final RenderEditable renderEditable = state.renderEditable;
+    final Scrollable scrollable = tester.widget<Scrollable>(find.byType(Scrollable));
+
+    expect(scrollable.controller!.position.viewportDimension, equals(32.0));
+    expect(scrollable.controller!.offset, 0.0);
+    expect(renderEditable.maxScrollExtent, equals(208.0));
+
+    state.bringIntoView(const TextPosition(offset: 3));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 7));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 2 * 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 10));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 3 * 48.0 + 48.0 / 2 - 32.0 / 2);
+
+    state.bringIntoView(const TextPosition(offset: 13));
+    await tester.pumpAndSettle();
+    expect(scrollable.controller!.offset, 4 * 48.0 + 48.0 / 2 - 32.0 / 2);
+  });
+
   testWidgets('bringIntoView does nothing if the physics prohibits implicit scrolling', (WidgetTester tester) async {
     final TextEditingController controller = TextEditingController(text: testText * 20);
     final ScrollController scrollController = ScrollController();
@@ -5844,7 +5943,6 @@ void main() {
       ));
     }
 
-
     await buildWithPhysics();
     expect(scrollController.offset, 0);