[BottomNavigationBar] Adds more control to ToolTip (#71079)

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

@@ -397,6 +397,9 @@ class _BottomNavigationTile extends StatelessWidget {
     // (or zero if the unselected icons are not any bigger than the selected icon).
     final double unselectedIconDiff = math.max(unselectedIconSize - selectedIconSize, 0);
 
+    // The effective tool tip message to be shown on the BottomNavigationBarItem.
+    final String? effectiveTooltip = item.tooltip == '' ? null : item.tooltip ?? item.label;
+
     // Defines the padding for the animating icons + labels.
     //
     // The animations go from "Unselected":
@@ -487,9 +490,9 @@ class _BottomNavigationTile extends StatelessWidget {
       ),
     );
 
-    if (item.label != null) {
+    if (effectiveTooltip != null) {
       result = Tooltip(
-        message: item.label!,
+        message: effectiveTooltip,
         preferBelow: false,
         verticalOffset: selectedIconSize + selectedFontSize,
         excludeFromSemantics: true,

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

@@ -32,6 +32,7 @@ class BottomNavigationBarItem {
     this.label,
     Widget? activeIcon,
     this.backgroundColor,
+    this.tooltip,
   }) : activeIcon = activeIcon ?? icon,
        assert(label == null || title == null),
        assert(icon != null);
@@ -77,9 +78,7 @@ class BottomNavigationBarItem {
 
   /// The text label for this [BottomNavigationBarItem].
   ///
-  /// This will be used to create a [Text] widget to put in the bottom navigation bar,
-  /// and in Material Design [BottomNavigationBar]s, this will be used to display
-  /// a tooltip on long press of an item in the [BottomNavigationBar].
+  /// This will be used to create a [Text] widget to put in the bottom navigation bar.
   final String? label;
 
   /// The color of the background radial animation for material [BottomNavigationBar].
@@ -96,4 +95,13 @@ class BottomNavigationBarItem {
   ///  * [Icon.color] and [ImageIcon.color] to control the foreground color of
   ///    the icons themselves.
   final Color? backgroundColor;
+
+  /// The text to display in the tooltip for this [BottomNavigationBarItem], when
+  /// the user long presses the item.
+  ///
+  /// The [Tooltip] will only appear on an item in a Material design [BottomNavigationBar], and
+  /// when the string is not empty.
+  ///
+  /// Defaults to null, in which case the [label] text will be used.
+  final String? tooltip;
 }

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -1121,6 +1121,7 @@ void main() {
                             BottomNavigationBarItem(
                               label: label,
                               icon: Icon(Icons.ac_unit),
+                              tooltip: label,
                             ),
                             BottomNavigationBarItem(
                               label: 'B',
@@ -1151,6 +1152,45 @@ void main() {
     expect(tester.getSize(find.text(label).last), equals(const Size(168.0, 56.0)));
   });
 
+  testWidgets('Different behaviour of tool tip in BottomNavigationBarItem', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          bottomNavigationBar: BottomNavigationBar(
+            items: const <BottomNavigationBarItem>[
+              BottomNavigationBarItem(
+                label: 'A',
+                tooltip: 'A tooltip',
+                icon: Icon(Icons.ac_unit),
+              ),
+              BottomNavigationBarItem(
+                label: 'B',
+                icon: Icon(Icons.battery_alert),
+              ),
+              BottomNavigationBarItem(
+                label: 'C',
+                icon: Icon(Icons.cake),
+                tooltip: '',
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    expect(find.text('A'), findsOneWidget);
+    await tester.longPress(find.text('A'));
+    expect(find.byTooltip('A tooltip'), findsOneWidget);
+
+    expect(find.text('B'), findsOneWidget);
+    await tester.longPress(find.text('B'));
+    expect(find.byTooltip('B'), findsOneWidget);
+
+    expect(find.text('C'), findsOneWidget);
+    await tester.longPress(find.text('C'));
+    expect(find.byTooltip('C'), findsNothing);
+  });
+
   testWidgets('BottomNavigationBar limits width of tiles with long titles', (WidgetTester tester) async {
     final Text longTextA = Text(''.padLeft(100, 'A'));
     final Text longTextB = Text(''.padLeft(100, 'B'));