Label should always be aligned with text in filled input decoration (#115540)

Co-authored-by: Qun Cheng <quncheng@google.com>

packages/flutter/lib/src/material/input_decorator.dart

@@ -1555,14 +1555,14 @@ class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin
         case TextDirection.rtl: // origin is on the right
           startX = labelOffset.dx + labelWidth * (1.0 - scale);
           floatStartX = startX;
-          if (prefixIcon != null && !decoration.alignLabelWithHint) {
+          if (prefixIcon != null && !decoration.alignLabelWithHint && isOutlineBorder) {
             floatStartX += material3 ? _boxSize(prefixIcon).width - contentPadding.left : 0.0;
           }
           break;
         case TextDirection.ltr: // origin on the left
           startX = labelOffset.dx;
           floatStartX = startX;
-          if (prefixIcon != null && !decoration.alignLabelWithHint) {
+          if (prefixIcon != null && !decoration.alignLabelWithHint && isOutlineBorder) {
             floatStartX += material3 ? -_boxSize(prefixIcon).width + contentPadding.left : 0.0;
           }
           break;

packages/flutter/test/material/input_decorator_test.dart

@@ -2842,6 +2842,25 @@ void main() {
         expect(tester.getBottomLeft(find.text('text')).dx, 48.0);
         expect(getBorderWeight(tester), 2.0);
       });
+
+      testWidgets('Floating label for filled input decoration is aligned with text', (WidgetTester tester) async {
+        await tester.pumpWidget(
+          buildInputDecorator(
+            useMaterial3: useMaterial3,
+            decoration: const InputDecoration(
+              prefixIcon: Icon(Icons.ac_unit),
+              labelText: 'label',
+              filled: true,
+            ),
+            isFocused: true,
+          ),
+        );
+
+        expect(tester.getSize(find.byType(InputDecorator)), const Size(800.0, 56.0));
+        expect(tester.getTopLeft(find.text('label')).dx, 48.0);
+        expect(tester.getBottomLeft(find.text('text')).dx, 48.0);
+        expect(getBorderWeight(tester), 2.0);
+      });
     });
 
     group('3 point interpolation alignment', () {