🐛 : FIX : Long labels overflowing in extended navigation rail.

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

@@ -698,16 +698,19 @@ class _RailDestinationState extends State<_RailDestination> {
               ),
               child: ClipRect(
                 child: Row(
+                  mainAxisSize: MainAxisSize.min,
                   children: <Widget>[
                     iconPart,
-                    Align(
-                      heightFactor: 1.0,
-                      widthFactor: widget.extendedTransitionAnimation.value,
-                      alignment: AlignmentDirectional.centerStart,
-                      child: FadeTransition(
-                        alwaysIncludeSemantics: true,
-                        opacity: labelFadeAnimation,
-                        child: styledLabel,
+                    Flexible(
+                      child: Align(
+                        heightFactor: 1.0,
+                        widthFactor: widget.extendedTransitionAnimation.value,
+                        alignment: AlignmentDirectional.centerStart,
+                        child: FadeTransition(
+                          alwaysIncludeSemantics: true,
+                          opacity: labelFadeAnimation,
+                          child: styledLabel,
+                        ),
                       ),
                     ),
                     SizedBox(width: _horizontalDestinationPadding * widget.extendedTransitionAnimation.value),

packages/flutter/test/material/navigation_rail_test.dart

@@ -7,6 +7,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
+
 import '../widgets/semantics_tester.dart';
 
 void main() {
@@ -3631,6 +3632,62 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  testWidgets('NavigationRail labels shall not overflow if longer texts provided - extended', (WidgetTester tester) async {
+
+    // The navigation rail has a narrow width constraint. The text should wrap.
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(useMaterial3: true),
+      home: Builder(
+        builder: (BuildContext context) {
+          return MediaQuery.withClampedTextScaling(
+            minScaleFactor: 1.0,
+            maxScaleFactor: 1.0,
+            child: Scaffold(
+              body: Row(
+                children: <Widget>[
+                  SizedBox(
+                    width: 140.0,
+                    child: NavigationRail(
+                      selectedIndex: 1,
+                      extended: true,
+                      destinations: const <NavigationRailDestination>[
+                        NavigationRailDestination(
+                          icon: Icon(Icons.favorite_border),
+                          selectedIcon: Icon(Icons.favorite),
+                          label: Text('Abc'),
+                        ),
+                        NavigationRailDestination(
+                          icon: Icon(Icons.bookmark_border),
+                          selectedIcon: Icon(Icons.bookmark),
+                          label: Text('Very long bookmark text for navigation destination'),
+                        ),
+                      ],
+                    ),
+                  ),
+                  const Expanded(
+                    child: Text('body'),
+                  ),
+                ],
+              ),
+            ),
+          );
+        },
+      ),
+    ));
+
+    expect(find.byType(NavigationRail), findsOneWidget);
+    final Finder normalLabelNavDestinationFinder = find.text(
+      'Abc',
+    );
+    final Finder longLabelNavDestinationFinder = find.text(
+      'Very long bookmark text for navigation destination',
+    );
+    expect(normalLabelNavDestinationFinder, findsOneWidget);
+    expect(longLabelNavDestinationFinder, findsOneWidget);
+  // If the widget manages to layout without throwing an overflow exception,
+  // the test passes.
+  });
+
   group('Material 2', () {
     // These tests are only relevant for Material 2. Once Material 2
     // support is deprecated and the APIs are removed, these tests