Replace LinkedHashMap.* with Map.*, which _is_ Linked (flutter#170713)

Pre-work to make it easier to land
flutter#170435.

The default `Map` constructor is and always has been a `LinkedHashMap`:

https://api.dart.dev/dart-core/Map/Map.html

This change make its easier to relax the type annotation rules in a
future PR.

/cc @eernstg

Author: matanlurey

dev/integration_tests/new_gallery/lib/data/demos.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:collection';
-
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
@@ -110,7 +108,7 @@ Future<void> pumpDeferredLibraries() {
 class Demos {
   static Map<String?, GalleryDemo> asSlugToDemoMap(BuildContext context) {
     final GalleryLocalizations localizations = GalleryLocalizations.of(context)!;
-    return LinkedHashMap<String?, GalleryDemo>.fromIterable(
+    return Map<String?, GalleryDemo>.fromIterable(
       all(localizations),
       // ignore: avoid_dynamic_calls
       key: (dynamic demo) => demo.slug as String?,

dev/integration_tests/new_gallery/lib/pages/settings.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:collection';
-
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_localized_locales/flutter_localized_locales.dart';
@@ -100,9 +98,9 @@ class _SettingsPageState extends State<SettingsPage> {
 
   /// Create a sorted — by native name – map of supported locales to their
   /// intended display string, with a system option as the first element.
-  LinkedHashMap<Locale, DisplayOption> _getLocaleOptions() {
-    final LinkedHashMap<Locale, DisplayOption> localeOptions =
-        LinkedHashMap<Locale, DisplayOption>.of(<Locale, DisplayOption>{
+  Map<Locale, DisplayOption> _getLocaleOptions() {
+    final Map<Locale, DisplayOption> localeOptions =
+        Map<Locale, DisplayOption>.of(<Locale, DisplayOption>{
           systemLocaleOption: DisplayOption(
             GalleryLocalizations.of(context)!.settingsSystemDefault +
                 (deviceLocale != null
@@ -123,7 +121,7 @@ class _SettingsPageState extends State<SettingsPage> {
                 compareAsciiUpperCase(l1.value.title, l2.value.title),
           );
 
-    localeOptions.addAll(LinkedHashMap<Locale, DisplayOption>.fromEntries(displayLocales));
+    localeOptions.addAll(Map<Locale, DisplayOption>.fromEntries(displayLocales));
     return localeOptions;
   }
 
@@ -138,7 +136,7 @@ class _SettingsPageState extends State<SettingsPage> {
       SettingsListItem<double?>(
         title: localizations.settingsTextScaling,
         selectedOption: options.textScaleFactor(context, useSentinel: true),
-        optionsMap: LinkedHashMap<double?, DisplayOption>.of(<double?, DisplayOption>{
+        optionsMap: Map<double?, DisplayOption>.of(<double?, DisplayOption>{
           systemTextScaleFactorOption: DisplayOption(localizations.settingsSystemDefault),
           0.8: DisplayOption(localizations.settingsTextScalingSmall),
           1.0: DisplayOption(localizations.settingsTextScalingNormal),
@@ -154,15 +152,14 @@ class _SettingsPageState extends State<SettingsPage> {
       SettingsListItem<CustomTextDirection?>(
         title: localizations.settingsTextDirection,
         selectedOption: options.customTextDirection,
-        optionsMap: LinkedHashMap<CustomTextDirection?, DisplayOption>.of(
-          <CustomTextDirection?, DisplayOption>{
-            CustomTextDirection.localeBased: DisplayOption(
-              localizations.settingsTextDirectionLocaleBased,
-            ),
-            CustomTextDirection.ltr: DisplayOption(localizations.settingsTextDirectionLTR),
-            CustomTextDirection.rtl: DisplayOption(localizations.settingsTextDirectionRTL),
-          },
-        ),
+        optionsMap:
+            Map<CustomTextDirection?, DisplayOption>.of(<CustomTextDirection?, DisplayOption>{
+              CustomTextDirection.localeBased: DisplayOption(
+                localizations.settingsTextDirectionLocaleBased,
+              ),
+              CustomTextDirection.ltr: DisplayOption(localizations.settingsTextDirectionLTR),
+              CustomTextDirection.rtl: DisplayOption(localizations.settingsTextDirectionRTL),
+            }),
         onOptionChanged:
             (CustomTextDirection? newTextDirection) => GalleryOptions.update(
               context,
@@ -187,14 +184,13 @@ class _SettingsPageState extends State<SettingsPage> {
       SettingsListItem<TargetPlatform?>(
         title: localizations.settingsPlatformMechanics,
         selectedOption: options.platform,
-        optionsMap:
-            LinkedHashMap<TargetPlatform?, DisplayOption>.of(<TargetPlatform?, DisplayOption>{
-              TargetPlatform.android: DisplayOption('Android'),
-              TargetPlatform.iOS: DisplayOption('iOS'),
-              TargetPlatform.macOS: DisplayOption('macOS'),
-              TargetPlatform.linux: DisplayOption('Linux'),
-              TargetPlatform.windows: DisplayOption('Windows'),
-            }),
+        optionsMap: Map<TargetPlatform?, DisplayOption>.of(<TargetPlatform?, DisplayOption>{
+          TargetPlatform.android: DisplayOption('Android'),
+          TargetPlatform.iOS: DisplayOption('iOS'),
+          TargetPlatform.macOS: DisplayOption('macOS'),
+          TargetPlatform.linux: DisplayOption('Linux'),
+          TargetPlatform.windows: DisplayOption('Windows'),
+        }),
         onOptionChanged:
             (TargetPlatform? newPlatform) =>
                 GalleryOptions.update(context, options.copyWith(platform: newPlatform)),
@@ -204,7 +200,7 @@ class _SettingsPageState extends State<SettingsPage> {
       SettingsListItem<ThemeMode?>(
         title: localizations.settingsTheme,
         selectedOption: options.themeMode,
-        optionsMap: LinkedHashMap<ThemeMode?, DisplayOption>.of(<ThemeMode?, DisplayOption>{
+        optionsMap: Map<ThemeMode?, DisplayOption>.of(<ThemeMode?, DisplayOption>{
           ThemeMode.system: DisplayOption(localizations.settingsSystemDefault),
           ThemeMode.dark: DisplayOption(localizations.settingsDarkTheme),
           ThemeMode.light: DisplayOption(localizations.settingsLightTheme),

dev/integration_tests/new_gallery/lib/pages/settings_list_item.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:collection';
-
 import 'package:flutter/material.dart';
 
 // Common constants between SlowMotionSetting and SettingsListItem.
@@ -81,7 +79,7 @@ class SettingsListItem<T> extends StatefulWidget {
     required this.isExpanded,
   });
 
-  final LinkedHashMap<T, DisplayOption> optionsMap;
+  final Map<T, DisplayOption> optionsMap;
   final String title;
   final T selectedOption;
   final ValueChanged<T> onOptionChanged;

packages/flutter/lib/src/foundation/observer_list.dart

@@ -106,7 +106,7 @@ class ObserverList<T> extends Iterable<T> {
 ///
 ///  * [ObserverList] for a list that is fast for small numbers of observers.
 class HashedObserverList<T> extends Iterable<T> {
-  final LinkedHashMap<T, int> _map = LinkedHashMap<T, int>();
+  final Map<T, int> _map = <T, int>{};
 
   /// Adds an item to the end of this list.
   ///

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

@@ -5,7 +5,6 @@
 /// @docImport 'package:flutter/cupertino.dart';
 library;
 
-import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:ui' as ui show BoxHeightStyle, BoxWidthStyle, LineMetrics, SemanticsInputType, TextBox;
 
@@ -1308,7 +1307,7 @@ class RenderEditable extends RenderBox
   // can be re-used when [assembleSemanticsNode] is called again. This ensures
   // stable ids for the [SemanticsNode]s of [TextSpan]s across
   // [assembleSemanticsNode] invocations.
-  LinkedHashMap<Key, SemanticsNode>? _cachedChildNodes;
+  Map<Key, SemanticsNode>? _cachedChildNodes;
 
   /// Returns a list of rects that bound the given selection, and the text
   /// direction. The text direction is used by the engine to calculate
@@ -1436,7 +1435,7 @@ class RenderEditable extends RenderBox
     int placeholderIndex = 0;
     int childIndex = 0;
     RenderBox? child = firstChild;
-    final LinkedHashMap<Key, SemanticsNode> newChildCache = LinkedHashMap<Key, SemanticsNode>();
+    final Map<Key, SemanticsNode> newChildCache = <Key, SemanticsNode>{};
     _cachedCombinedSemanticsInfos ??= combineSemanticsInfo(_semanticsInfo!);
     for (final InlineSpanSemanticsInformation info in _cachedCombinedSemanticsInfos!) {
       final TextSelection selection = TextSelection(

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

@@ -5,7 +5,6 @@
 /// @docImport 'binding.dart';
 library;
 
-import 'dart:collection' show LinkedHashMap;
 import 'dart:ui';
 
 import 'package:flutter/foundation.dart';
@@ -27,16 +26,13 @@ class _MouseState {
   _MouseState({required PointerEvent initialEvent}) : _latestEvent = initialEvent;
 
   // The list of annotations that contains this device.
-  //
-  // It uses [LinkedHashMap] to keep the insertion order.
-  LinkedHashMap<MouseTrackerAnnotation, Matrix4> get annotations => _annotations;
-  LinkedHashMap<MouseTrackerAnnotation, Matrix4> _annotations =
-      LinkedHashMap<MouseTrackerAnnotation, Matrix4>();
+  Map<MouseTrackerAnnotation, Matrix4> get annotations => _annotations;
+  Map<MouseTrackerAnnotation, Matrix4> _annotations = <MouseTrackerAnnotation, Matrix4>{};
 
-  LinkedHashMap<MouseTrackerAnnotation, Matrix4> replaceAnnotations(
-    LinkedHashMap<MouseTrackerAnnotation, Matrix4> value,
+  Map<MouseTrackerAnnotation, Matrix4> replaceAnnotations(
+    Map<MouseTrackerAnnotation, Matrix4> value,
   ) {
-    final LinkedHashMap<MouseTrackerAnnotation, Matrix4> previous = _annotations;
+    final Map<MouseTrackerAnnotation, Matrix4> previous = _annotations;
     _annotations = value;
     return previous;
   }
@@ -93,12 +89,12 @@ class _MouseTrackerUpdateDetails with Diagnosticable {
   /// The annotations that the device is hovering before the update.
   ///
   /// It is never null.
-  final LinkedHashMap<MouseTrackerAnnotation, Matrix4> lastAnnotations;
+  final Map<MouseTrackerAnnotation, Matrix4> lastAnnotations;
 
   /// The annotations that the device is hovering after the update.
   ///
   /// It is never null.
-  final LinkedHashMap<MouseTrackerAnnotation, Matrix4> nextAnnotations;
+  final Map<MouseTrackerAnnotation, Matrix4> nextAnnotations;
 
   /// The last event that the device observed before the update.
   ///
@@ -232,11 +228,8 @@ class MouseTracker extends ChangeNotifier {
         lastEvent.position != event.position;
   }
 
-  LinkedHashMap<MouseTrackerAnnotation, Matrix4> _hitTestInViewResultToAnnotations(
-    HitTestResult result,
-  ) {
-    final LinkedHashMap<MouseTrackerAnnotation, Matrix4> annotations =
-        LinkedHashMap<MouseTrackerAnnotation, Matrix4>();
+  Map<MouseTrackerAnnotation, Matrix4> _hitTestInViewResultToAnnotations(HitTestResult result) {
+    final Map<MouseTrackerAnnotation, Matrix4> annotations = <MouseTrackerAnnotation, Matrix4>{};
     for (final HitTestEntry entry in result.path) {
       final Object target = entry.target;
       if (target is MouseTrackerAnnotation) {
@@ -251,12 +244,12 @@ class MouseTracker extends ChangeNotifier {
   //
   // If the device is not connected or not a mouse, an empty map is returned
   // without calling `hitTest`.
-  LinkedHashMap<MouseTrackerAnnotation, Matrix4> _findAnnotations(_MouseState state) {
+  Map<MouseTrackerAnnotation, Matrix4> _findAnnotations(_MouseState state) {
     final Offset globalPosition = state.latestEvent.position;
     final int device = state.device;
     final int viewId = state.latestEvent.viewId;
     if (!_mouseStates.containsKey(device)) {
-      return LinkedHashMap<MouseTrackerAnnotation, Matrix4>();
+      return <MouseTrackerAnnotation, Matrix4>{};
     }
 
     return _hitTestInViewResultToAnnotations(_hitTestInView(globalPosition, viewId));
@@ -341,12 +334,13 @@ class MouseTracker extends ChangeNotifier {
         final _MouseState targetState = _mouseStates[device] ?? existingState!;
 
         final PointerEvent lastEvent = targetState.replaceLatestEvent(event);
-        final LinkedHashMap<MouseTrackerAnnotation, Matrix4> nextAnnotations =
+        final Map<MouseTrackerAnnotation, Matrix4> nextAnnotations =
             event is PointerRemovedEvent
-                ? LinkedHashMap<MouseTrackerAnnotation, Matrix4>()
+                ? <MouseTrackerAnnotation, Matrix4>{}
                 : _hitTestInViewResultToAnnotations(result);
-        final LinkedHashMap<MouseTrackerAnnotation, Matrix4> lastAnnotations = targetState
-            .replaceAnnotations(nextAnnotations);
+        final Map<MouseTrackerAnnotation, Matrix4> lastAnnotations = targetState.replaceAnnotations(
+          nextAnnotations,
+        );
 
         _handleDeviceUpdate(
           _MouseTrackerUpdateDetails.byPointerEvent(
@@ -374,11 +368,10 @@ class MouseTracker extends ChangeNotifier {
     _deviceUpdatePhase(() {
       for (final _MouseState dirtyState in _mouseStates.values) {
         final PointerEvent lastEvent = dirtyState.latestEvent;
-        final LinkedHashMap<MouseTrackerAnnotation, Matrix4> nextAnnotations = _findAnnotations(
-          dirtyState,
+        final Map<MouseTrackerAnnotation, Matrix4> nextAnnotations = _findAnnotations(dirtyState);
+        final Map<MouseTrackerAnnotation, Matrix4> lastAnnotations = dirtyState.replaceAnnotations(
+          nextAnnotations,
         );
-        final LinkedHashMap<MouseTrackerAnnotation, Matrix4> lastAnnotations = dirtyState
-            .replaceAnnotations(nextAnnotations);
 
         _handleDeviceUpdate(
           _MouseTrackerUpdateDetails.byNewFrame(
@@ -407,8 +400,8 @@ class MouseTracker extends ChangeNotifier {
   static void _handleDeviceUpdateMouseEvents(_MouseTrackerUpdateDetails details) {
     final PointerEvent latestEvent = details.latestEvent;
 
-    final LinkedHashMap<MouseTrackerAnnotation, Matrix4> lastAnnotations = details.lastAnnotations;
-    final LinkedHashMap<MouseTrackerAnnotation, Matrix4> nextAnnotations = details.nextAnnotations;
+    final Map<MouseTrackerAnnotation, Matrix4> lastAnnotations = details.lastAnnotations;
+    final Map<MouseTrackerAnnotation, Matrix4> nextAnnotations = details.nextAnnotations;
 
     // Order is important for mouse event callbacks. The
     // `_hitTestInViewResultToAnnotations` returns annotations in the visual order

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

@@ -7,7 +7,6 @@
 /// @docImport 'editable.dart';
 library;
 
-import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:ui'
     as ui
@@ -1268,7 +1267,7 @@ class RenderParagraph extends RenderBox
   // can be re-used when [assembleSemanticsNode] is called again. This ensures
   // stable ids for the [SemanticsNode]s of [TextSpan]s across
   // [assembleSemanticsNode] invocations.
-  LinkedHashMap<Key, SemanticsNode>? _cachedChildNodes;
+  Map<Key, SemanticsNode>? _cachedChildNodes;
 
   @override
   void assembleSemanticsNode(
@@ -1285,7 +1284,7 @@ class RenderParagraph extends RenderBox
     int placeholderIndex = 0;
     int childIndex = 0;
     RenderBox? child = firstChild;
-    final LinkedHashMap<Key, SemanticsNode> newChildCache = LinkedHashMap<Key, SemanticsNode>();
+    final Map<Key, SemanticsNode> newChildCache = <Key, SemanticsNode>{};
     _cachedCombinedSemanticsInfos ??= combineSemanticsInfo(_semanticsInfo!);
     for (final InlineSpanSemanticsInformation info in _cachedCombinedSemanticsInfos!) {
       final TextSelection selection = TextSelection(