Revert rematching DropdownMenu.initialSelection (#160643)

## Description

This PR reverts `DropdownMenu` changes from
https://github.com/flutter/flutter/pull/155757.
Automatically rematching the `initialSelection` breaks some use cases.
It is more flexible to let users manipulate the text field content using
the TextEditingController.

## Related Issue

Fixes [Dropdown Menu Creates Infinite Build
Loop](https://github.com/flutter/flutter/issues/160196)
Fixes [Can no longer initialize non selectable value in DropdownMenu as
of flutter version
3.27.1](https://github.com/flutter/flutter/issues/160555)

## Tests

Removes 2 regression tests from
https://github.com/flutter/flutter/pull/155757.
Keeps 2 tests from the original PR (missing test for the
initialSelection behavior).
Adds 1 tests to avoid regressing this revert.

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

@@ -521,18 +521,6 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
   TextEditingController? _localTextEditingController;
   final FocusNode _internalFocudeNode = FocusNode();
 
-  TextEditingValue get _initialTextEditingValue {
-    for (final DropdownMenuEntry<T> entry in filteredEntries) {
-      if (entry.value == widget.initialSelection) {
-        return TextEditingValue(
-          text: entry.label,
-          selection: TextSelection.collapsed(offset: entry.label.length),
-        );
-      }
-    }
-    return TextEditingValue.empty;
-  }
-
   @override
   void initState() {
     super.initState();
@@ -545,8 +533,15 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
     filteredEntries = widget.dropdownMenuEntries;
     buttonItemKeys = List<GlobalKey>.generate(filteredEntries.length, (int index) => GlobalKey());
     _menuHasEnabledItem = filteredEntries.any((DropdownMenuEntry<T> entry) => entry.enabled);
-    _localTextEditingController?.value = _initialTextEditingValue;
+    final int index = filteredEntries.indexWhere(
-
+      (DropdownMenuEntry<T> entry) => entry.value == widget.initialSelection,
+    );
+    if (index != -1) {
+      _localTextEditingController?.value = TextEditingValue(
+        text: filteredEntries[index].label,
+        selection: TextSelection.collapsed(offset: filteredEntries[index].label.length),
+      );
+    }
     refreshLeadingPadding();
   }
 
@@ -585,19 +580,20 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
       filteredEntries = widget.dropdownMenuEntries;
       buttonItemKeys = List<GlobalKey>.generate(filteredEntries.length, (int index) => GlobalKey());
       _menuHasEnabledItem = filteredEntries.any((DropdownMenuEntry<T> entry) => entry.enabled);
-      // If the text field content matches one of the new entries do not rematch the initialSelection.
-      final bool isCurrentSelectionValid = filteredEntries.any(
-        (DropdownMenuEntry<T> entry) => entry.label == _localTextEditingController?.text,
-      );
-      if (!isCurrentSelectionValid) {
-        _localTextEditingController?.value = _initialTextEditingValue;
-      }
     }
     if (oldWidget.leadingIcon != widget.leadingIcon) {
       refreshLeadingPadding();
     }
     if (oldWidget.initialSelection != widget.initialSelection) {
-      _localTextEditingController?.value = _initialTextEditingValue;
+      final int index = filteredEntries.indexWhere(
+        (DropdownMenuEntry<T> entry) => entry.value == widget.initialSelection,
+      );
+      if (index != -1) {
+        _localTextEditingController?.value = TextEditingValue(
+          text: filteredEntries[index].label,
+          selection: TextSelection.collapsed(offset: filteredEntries[index].label.length),
+        );
+      }
     }
   }
 

packages/flutter/test/material/dropdown_menu_test.dart

@@ -2174,83 +2174,30 @@ void main() {
     expect(controller.text, isEmpty);
   });
 
-  // Regression test for https://github.com/flutter/flutter/issues/155660.
-  testWidgets('Updating the menu entries refreshes the initial selection', (
-    WidgetTester tester,
-  ) async {
-    final TextEditingController controller = TextEditingController();
-    addTearDown(controller.dispose);
-
-    Widget boilerplate(List<DropdownMenuEntry<TestMenu>> entries) {
-      return MaterialApp(
-        home: StatefulBuilder(
-          builder: (BuildContext context, StateSetter setState) {
-            return Scaffold(
-              body: DropdownMenu<TestMenu>(
-                initialSelection: TestMenu.mainMenu3,
-                dropdownMenuEntries: entries,
-                controller: controller,
-              ),
-            );
-          },
-        ),
-      );
-    }
-
-    // The text field should be empty when the initial selection does not match
-    // any menu items.
-    await tester.pumpWidget(boilerplate(menuChildren.getRange(0, 1).toList()));
-    expect(controller.text, '');
-
-    // When the menu entries is updated the initial selection should be rematched.
-    await tester.pumpWidget(boilerplate(menuChildren));
-    expect(controller.text, TestMenu.mainMenu3.label);
-
-    // Update the entries with none matching the initial selection.
-    await tester.pumpWidget(boilerplate(menuChildren.getRange(0, 1).toList()));
-    expect(controller.text, '');
-  });
-
-  // Regression test for https://github.com/flutter/flutter/issues/155660.
   testWidgets(
-    'Updating the menu entries refreshes the initial selection only if the current selection is no more valid',
+    'Text field content is not cleared when the initial selection does not match any menu entries',
     (WidgetTester tester) async {
-      final TextEditingController controller = TextEditingController();
+      final TextEditingController controller = TextEditingController(text: 'Flutter');
       addTearDown(controller.dispose);
 
-      Widget boilerplate(List<DropdownMenuEntry<TestMenu>> entries) {
+      await tester.pumpWidget(
-        return MaterialApp(
+        MaterialApp(
           home: StatefulBuilder(
             builder: (BuildContext context, StateSetter setState) {
               return Scaffold(
                 body: DropdownMenu<TestMenu>(
                   initialSelection: TestMenu.mainMenu3,
-                  dropdownMenuEntries: entries,
+                  // Use a menu entries which does not contain TestMenu.mainMenu3.
+                  dropdownMenuEntries: menuChildren.getRange(0, 1).toList(),
                   controller: controller,
                 ),
               );
             },
           ),
-        );
+        ),
-      }
+      );
 
-      await tester.pumpWidget(boilerplate(menuChildren));
+      expect(controller.text, 'Flutter');
-      expect(controller.text, TestMenu.mainMenu3.label);
-
-      // Open the menu.
-      await tester.tap(find.byType(DropdownMenu<TestMenu>));
-      await tester.pump();
-
-      // Select another item.
-      final Finder item2 = findMenuItemButton('Item 2');
-      await tester.tap(item2);
-      await tester.pumpAndSettle();
-      expect(controller.text, TestMenu.mainMenu2.label);
-
-      // Update the menu entries with another instance of list containing the
-      // same entries.
-      await tester.pumpWidget(boilerplate(List<DropdownMenuEntry<TestMenu>>.from(menuChildren)));
-      expect(controller.text, TestMenu.mainMenu2.label);
     },
   );