Fix that RenderEditable (TextField) ignores offset in painting, making text...

Fix that RenderEditable (TextField) ignores offset in painting, making text selections shifted when offset is nonzero (#109287)

Small fix in text layout math, unlikely to affect most normal usages.

packages/flutter/lib/src/rendering/editable.dart

@@ -2540,14 +2540,14 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     }
   }
 
-  void _paintHandleLayers(PaintingContext context, List<TextSelectionPoint> endpoints) {
+  void _paintHandleLayers(PaintingContext context, List<TextSelectionPoint> endpoints, Offset offset) {
     Offset startPoint = endpoints[0].point;
     startPoint = Offset(
       clampDouble(startPoint.dx, 0.0, size.width),
       clampDouble(startPoint.dy, 0.0, size.height),
     );
     context.pushLayer(
-      LeaderLayer(link: startHandleLayerLink, offset: startPoint),
+      LeaderLayer(link: startHandleLayerLink, offset: startPoint + offset),
       super.paint,
       Offset.zero,
     );
@@ -2558,7 +2558,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
         clampDouble(endPoint.dy, 0.0, size.height),
       );
       context.pushLayer(
-        LeaderLayer(link: endHandleLayerLink, offset: endPoint),
+        LeaderLayer(link: endHandleLayerLink, offset: endPoint + offset),
         super.paint,
         Offset.zero,
       );
@@ -2582,7 +2582,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
       _paintContents(context, offset);
     }
     if (selection!.isValid) {
-      _paintHandleLayers(context, getEndpointsForSelection(selection!));
+      _paintHandleLayers(context, getEndpointsForSelection(selection!), offset);
     }
   }
 

packages/flutter/test/rendering/editable_test.dart

@@ -113,6 +113,37 @@ void main() {
     expect(visited, true);
   });
 
+  test('RenderEditable.paint respects offset argument', () {
+    const BoxConstraints viewport = BoxConstraints(maxHeight: 1000.0, maxWidth: 1000.0);
+    final TestPushLayerPaintingContext context = TestPushLayerPaintingContext();
+
+    const Offset paintOffset = Offset(100, 200);
+    const double fontSize = 20.0;
+    const Offset endpoint = Offset(0.0, fontSize);
+
+    final RenderEditable editable = RenderEditable(
+      text: const TextSpan(
+        text: 'text',
+        style: TextStyle(
+          fontSize: fontSize,
+          height: 1.0,
+        ),
+      ),
+      textDirection: TextDirection.ltr,
+      startHandleLayerLink: LayerLink(),
+      endHandleLayerLink: LayerLink(),
+      offset: ViewportOffset.zero(),
+      textSelectionDelegate: _FakeEditableTextState(),
+      selection: const TextSelection(baseOffset: 0, extentOffset: 0),
+    );
+    layout(editable, constraints: viewport, phase: EnginePhase.composite);
+    editable.paint(context, paintOffset);
+
+    final List<LeaderLayer> leaderLayers = context.pushedLayers.whereType<LeaderLayer>().toList();
+    expect(leaderLayers, hasLength(1), reason: '_paintHandleLayers will paint a LeaderLayer');
+    expect(leaderLayers.single.offset, endpoint + paintOffset, reason: 'offset should respect paintOffset');
+  });
+
   test('editable intrinsics', () {
     final TextSelectionDelegate delegate = _FakeEditableTextState();
     final RenderEditable editable = RenderEditable(

packages/flutter/test/rendering/rendering_tester.dart

@@ -365,6 +365,23 @@ class TestClipPaintingContext extends PaintingContext {
   Clip clipBehavior = Clip.none;
 }
 
+class TestPushLayerPaintingContext extends PaintingContext {
+  TestPushLayerPaintingContext() : super(ContainerLayer(), Rect.zero);
+
+  final List<ContainerLayer> pushedLayers = <ContainerLayer>[];
+
+  @override
+  void pushLayer(
+    ContainerLayer childLayer,
+    PaintingContextCallback painter,
+    Offset offset, {
+    Rect? childPaintBounds
+  }) {
+    pushedLayers.add(childLayer);
+    super.pushLayer(childLayer, painter, offset, childPaintBounds: childPaintBounds);
+  }
+}
+
 void expectOverflowedErrors() {
   final FlutterErrorDetails errorDetails = TestRenderingFlutterBinding.instance.takeFlutterErrorDetails()!;
   final bool overflowed = errorDetails.toString().contains('overflowed');