fix _getPixelPerfectCursorOffset logic when infinite (#66845)

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

@@ -1999,15 +1999,17 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     offset.applyContentDimensions(0.0, _maxScrollExtent);
   }
 
+  /// Computes the offset to apply to the given [caretRect] so it perfectly
+  /// snaps to physical pixels.
   Offset _getPixelPerfectCursorOffset(Rect caretRect) {
     final Offset caretPosition = localToGlobal(caretRect.topLeft);
     final double pixelMultiple = 1.0 / _devicePixelRatio;
     final double pixelPerfectOffsetX = caretPosition.dx.isFinite
       ? (caretPosition.dx / pixelMultiple).round() * pixelMultiple - caretPosition.dx
-      : caretPosition.dx;
+      : 0;
     final double pixelPerfectOffsetY = caretPosition.dy.isFinite
       ? (caretPosition.dy / pixelMultiple).round() * pixelMultiple - caretPosition.dy
-      : caretPosition.dy;
+      : 0;
     return Offset(pixelPerfectOffsetX, pixelPerfectOffsetY);
   }
 

packages/flutter/test/widgets/editable_text_test.dart

@@ -3427,17 +3427,22 @@ void main() {
     });
 
     testWidgets(
-      'does not throw when sending infinite Rect',
+      'zero matrix paint transform',
       (WidgetTester tester) async {
         controller.value = TextEditingValue(text: 'a' * 100, composing: const TextRange(start: 0, end: 10));
+        // Use a FittedBox with an zero-sized child to set the paint transform
+        // to the zero matrix.
         await tester.pumpWidget(FittedBox(child: SizedBox.fromSize(size: Size.zero, child: builder())));
         await tester.showKeyboard(find.byType(EditableText));
-        expect(tester.testTextInput.log, contains(matchesMethodCall('TextInput.setMarkedTextRect', args: <String, dynamic> {
-          'width': -1,
-          'height': -1,
-          'x': 0,
-          'y': 0,
-        })));
+        expect(tester.testTextInput.log, contains(matchesMethodCall(
+          'TextInput.setMarkedTextRect',
+          args: allOf(
+            containsPair('width', isNotNaN),
+            containsPair('height', isNotNaN),
+            containsPair('x', isNotNaN),
+            containsPair('y', isNotNaN),
+          ),
+        )));
     });
   });
 
@@ -4695,7 +4700,7 @@ void main() {
 
     final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
     final Rect rect = state.renderEditable.getLocalRectForCaret(const TextPosition(offset: 0));
-    expect(rect.isFinite, false);
+    expect(rect.isFinite, true);
     expect(tester.takeException(), isNull);
   });