Implementing null-aware operators throughout the repository (#143804)

This pull request fixes #143803 by taking advantage of Dart's null-aware operators.

And unlike `switch` expressions ([9 PRs](flutter/flutter#143634) and counting), the Flutter codebase is already fantastic when it comes to null-aware coding. After refactoring the entire repo, all the changes involving `?.` and `??` can fit into a single pull request.

dev/benchmarks/microbenchmarks/lib/language/sync_star_semantics_bench.dart

@@ -91,11 +91,7 @@ Iterable<InlineSpanSemanticsInformation> combineSemanticsInfoSyncStar(List<Inlin
       workingText += info.text;
       workingLabel ??= '';
       final String? infoSemanticsLabel = info.semanticsLabel;
-      if (infoSemanticsLabel != null) {
-        workingLabel += infoSemanticsLabel;
-      } else {
-        workingLabel += info.text;
-      }
+      workingLabel += infoSemanticsLabel ?? info.text;
     }
   }
   assert(workingLabel != null);
@@ -115,11 +111,7 @@ Iterable<InlineSpanSemanticsInformation> combineSemanticsInfoList(List<InlineSpa
       workingText += info.text;
       workingLabel ??= '';
       final String? infoSemanticsLabel = info.semanticsLabel;
-      if (infoSemanticsLabel != null) {
-        workingLabel += infoSemanticsLabel;
-      } else {
-        workingLabel += info.text;
-      }
+      workingLabel += infoSemanticsLabel ?? info.text;
     }
   }
   assert(workingLabel != null);

dev/bots/tool_subsharding.dart

@@ -16,20 +16,13 @@ class TestSpecs {
   int startTime;
   int? _endTime;
 
-  int get milliseconds {
-    return endTime - startTime;
-  }
+  int get milliseconds => endTime - startTime;
 
   set endTime(int value) {
     _endTime = value;
   }
 
-  int get endTime {
-    if (_endTime == null) {
-      return 0;
-    }
-    return _endTime!;
-  }
+  int get endTime => _endTime ?? 0;
 
   String toJson() {
     return json.encode(

dev/conductor/core/lib/src/version.dart

@@ -158,13 +158,10 @@ class Version {
     int nextZ = previousVersion.z;
     int? nextM = previousVersion.m;
     int? nextN = previousVersion.n;
-    if (nextVersionType == null) {
-      if (previousVersion.type == VersionType.latest || previousVersion.type == VersionType.gitDescribe) {
-        nextVersionType = VersionType.development;
-      } else {
-        nextVersionType = previousVersion.type;
-      }
-    }
+    nextVersionType ??= switch (previousVersion.type) {
+      VersionType.stable => VersionType.stable,
+      VersionType.latest || VersionType.gitDescribe || VersionType.development => VersionType.development,
+    };
 
     switch (increment) {
       case 'x':

dev/devicelab/bin/tasks/flavors_test.dart

@@ -32,11 +32,7 @@ Future<void> main() async {
         final TaskResult? firstInstallFailure = testResults
           .firstWhereOrNull((TaskResult element) => element.failed);
 
-        if (firstInstallFailure != null) {
-          return firstInstallFailure;
-        }
-
-        return TaskResult.success(null);
+        return firstInstallFailure ?? TaskResult.success(null);
       },
     );
 

dev/devicelab/bin/tasks/flavors_test_ios.dart

@@ -32,11 +32,7 @@ Future<void> main() async {
         final TaskResult? firstInstallFailure = testResults
           .firstWhereOrNull((TaskResult element) => element.failed);
 
-        if (firstInstallFailure != null) {
-          return firstInstallFailure;
-        }
-
-        return TaskResult.success(null);
+        return firstInstallFailure ?? TaskResult.success(null);
       },
     );
 

dev/devicelab/lib/framework/browser.dart

@@ -572,12 +572,7 @@ class BlinkTraceEvent {
 /// Returns null if the value is null.
 int? _readInt(Map<String, dynamic> json, String key) {
   final num? jsonValue = json[key] as num?;
-
-  if (jsonValue == null) {
-    return null;
-  }
-
-  return jsonValue.toInt();
+  return jsonValue?.toInt();
 }
 
 /// Used by [Chrome.launch] to detect a glibc bug and retry launching the

dev/devicelab/lib/tasks/perf_tests.dart

@@ -1290,11 +1290,7 @@ class PerfTest {
   }) {
     return inDirectory<TaskResult>(testDirectory, () async {
       late Device selectedDevice;
-      if (device != null) {
-        selectedDevice = device!;
-      } else {
-        selectedDevice = await devices.workingDevice;
-      }
+      selectedDevice = device ?? await devices.workingDevice;
       await selectedDevice.unlock();
       final String deviceId = selectedDevice.deviceId;
       final String? localEngine = localEngineFromEnv;

dev/integration_tests/android_semantics_testing/lib/src/matcher.dart

@@ -223,10 +223,7 @@ class _AndroidSemanticsMatcher extends Matcher {
   Description describeMismatch(dynamic item, Description mismatchDescription,
       Map<dynamic, dynamic> matchState, bool verbose) {
     final String? failure = matchState['failure'] as String?;
-    if (failure == null) {
-      return mismatchDescription.add('hasAndroidSemantics matcher does not complete successfully');
-    }
-    return mismatchDescription.add(failure);
+    return mismatchDescription.add(failure ?? 'hasAndroidSemantics matcher does not complete successfully');
   }
 
   bool _failWithMessage(String value, Map<dynamic, dynamic> matchState) {

dev/integration_tests/flutter_gallery/lib/demo/shrine/model/app_state_model.dart

@@ -62,12 +62,8 @@ class AppStateModel extends Model {
 
   // Adds a product to the cart.
   void addProductToCart(int productId) {
-    final int? value = _productsInCart[productId];
-    if (value == null) {
-      _productsInCart[productId] = 1;
-    } else {
-      _productsInCart[productId] = value+1;
-    }
+    final int value = _productsInCart[productId] ?? 0;
+    _productsInCart[productId] = value + 1;
 
     notifyListeners();
   }

dev/tools/gen_defaults/bin/gen_defaults.dart

@@ -86,9 +86,7 @@ Future<void> main(List<String> args) async {
     final Map<String, dynamic> tokenFileTokens = _readTokenFile(tokenFile as File);
     final String version = tokenFileTokens['version'] as String;
     tokenFileTokens.remove('version');
-    if (versionMap[version] == null) {
-      versionMap[version] = List<String>.empty(growable: true);
-    }
+    versionMap[version] ??= <String>[];
     versionMap[version]!.add(tokenFile.uri.pathSegments.last);
 
     tokens.addAll(tokenFileTokens);

packages/flutter/lib/src/cupertino/colors.dart

@@ -953,9 +953,6 @@ class CupertinoDynamicColor extends Color with Diagnosticable {
   ///  * [resolve], which is similar to this function, but returns a
   ///    non-nullable value, and does not allow a null `resolvable` color.
   static Color? maybeResolve(Color? resolvable, BuildContext context) {
-    if (resolvable == null) {
-      return null;
-    }
     return (resolvable is CupertinoDynamicColor)
       ? resolvable.resolveFrom(context)
       : resolvable;

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -684,10 +684,8 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
 
   // Lazily calculate the column width of the column being displayed only.
   double _getEstimatedColumnWidth(_PickerColumnType columnType) {
-    if (estimatedColumnWidths[columnType.index] == null) {
-      estimatedColumnWidths[columnType.index] =
-          CupertinoDatePicker._getColumnWidth(columnType, localizations, context, widget.showDayOfWeek);
-    }
+    estimatedColumnWidths[columnType.index] ??=
+        CupertinoDatePicker._getColumnWidth(columnType, localizations, context, widget.showDayOfWeek);
 
     return estimatedColumnWidths[columnType.index]!;
   }

packages/flutter/lib/src/cupertino/interface_level.dart

@@ -94,10 +94,7 @@ class CupertinoUserInterfaceLevel extends InheritedWidget {
   ///    [CupertinoUserInterfaceLevel] encloses the given context.
   static CupertinoUserInterfaceLevelData? maybeOf(BuildContext context) {
     final CupertinoUserInterfaceLevel? query = context.dependOnInheritedWidgetOfExactType<CupertinoUserInterfaceLevel>();
-    if (query != null) {
-      return query._data;
-    }
-    return null;
+    return query?._data;
   }
 
   @override

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

@@ -2257,10 +2257,7 @@ class EnumProperty<T extends Enum?> extends DiagnosticsProperty<T> {
 
   @override
   String valueToString({ TextTreeConfiguration? parentConfiguration }) {
-    if (value == null) {
-      return value.toString();
-    }
-    return value!.name;
+    return value?.name ?? 'null';
   }
 }
 

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

@@ -47,13 +47,9 @@ class PersistentHashMap<K extends Object, V> {
   /// is not in the map.
   @pragma('dart2js:as:trust')
   V? operator[](K key) {
-    if (_root == null) {
-      return null;
-    }
-
     // Unfortunately can not use unsafeCast<V?>(...) here because it leads
     // to worse code generation on VM.
-    return _root.get(0, key, key.hashCode) as V?;
+    return _root?.get(0, key, key.hashCode) as V?;
   }
 }
 

packages/flutter/lib/src/gestures/recognizer.dart

@@ -461,10 +461,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   }
 
   GestureArenaEntry _addPointerToArena(int pointer) {
-    if (_team != null) {
-      return _team!.add(pointer, this);
-    }
-    return GestureBinding.instance.gestureArena.add(pointer, this);
+    return _team?.add(pointer, this) ?? GestureBinding.instance.gestureArena.add(pointer, this);
   }
 
   /// Causes events related to the given pointer ID to be routed to this recognizer.

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

@@ -560,10 +560,8 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
 
   double get _width {
     final RenderBox? box = _drawerKey.currentContext?.findRenderObject() as RenderBox?;
-    if (box != null) {
-      return box.size.width;
-    }
-    return _kWidth; // drawer not being shown currently
+    // return _kWidth if drawer not being shown currently
+    return box?.size.width ?? _kWidth;
   }
 
   bool _previouslyOpened = false;

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

@@ -154,10 +154,7 @@ class _RenderMenuItem extends RenderShiftedBox {
 
   @override
   Size computeDryLayout(BoxConstraints constraints) {
-    if (child == null) {
-      return Size.zero;
-    }
-    return child!.getDryLayout(constraints);
+    return child?.getDryLayout(constraints) ?? Size.zero;
   }
 
   @override

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

@@ -442,10 +442,8 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
       if (isActive) MaterialState.selected else MaterialState.disabled,
     };
     final Color? resolvedConnectorColor = widget.connectorColor?.resolve(states);
-    if (resolvedConnectorColor != null) {
-      return resolvedConnectorColor;
-    }
-    return isActive ? colorScheme.primary : Colors.grey.shade400;
+
+    return resolvedConnectorColor ?? (isActive ? colorScheme.primary : Colors.grey.shade400);
   }
 
   Widget _buildLine(bool visible, bool isActive) {

packages/flutter/lib/src/painting/border_radius.dart

@@ -238,13 +238,7 @@ abstract class BorderRadiusGeometry {
     if (visual != null && logical != null) {
       return '$visual + $logical';
     }
-    if (visual != null) {
-      return visual;
-    }
-    if (logical != null) {
-      return logical;
-    }
-    return 'BorderRadius.zero';
+    return visual ?? logical ?? 'BorderRadius.zero';
   }
 
   @override

packages/flutter/lib/src/painting/borders.dart

@@ -510,13 +510,7 @@ abstract class ShapeBorder {
     if (identical(a, b)) {
       return a;
     }
-    ShapeBorder? result;
-    if (b != null) {
-      result = b.lerpFrom(a, t);
-    }
-    if (result == null && a != null) {
-      result = a.lerpTo(b, t);
-    }
+    final ShapeBorder? result = b?.lerpFrom(a, t) ?? a?.lerpTo(b, t);
     return result ?? (t < 0.5 ? a : b);
   }
 
@@ -700,13 +694,7 @@ abstract class OutlinedBorder extends ShapeBorder {
     if (identical(a, b)) {
       return a;
     }
-    ShapeBorder? result;
-    if (b != null) {
-      result = b.lerpFrom(a, t);
-    }
-    if (result == null && a != null) {
-      result = a.lerpTo(b, t);
-    }
+    final ShapeBorder? result = b?.lerpFrom(a, t) ?? a?.lerpTo(b, t);
     return result as OutlinedBorder? ?? (t < 0.5 ? a : b);
   }
 }

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

@@ -468,43 +468,31 @@ class RenderAspectRatio extends RenderProxyBox {
     if (height.isFinite) {
       return height * _aspectRatio;
     }
-    if (child != null) {
-      return child!.getMinIntrinsicWidth(height);
-    }
-    return 0.0;
+    return child?.getMinIntrinsicWidth(height) ?? 0.0;
   }
 
   @override
   double computeMaxIntrinsicWidth(double height) {
     if (height.isFinite) {
       return height * _aspectRatio;
     }
-    if (child != null) {
-      return child!.getMaxIntrinsicWidth(height);
-    }
-    return 0.0;
+    return child?.getMaxIntrinsicWidth(height) ?? 0.0;
   }
 
   @override
   double computeMinIntrinsicHeight(double width) {
     if (width.isFinite) {
       return width / _aspectRatio;
     }
-    if (child != null) {
-      return child!.getMinIntrinsicHeight(width);
-    }
-    return 0.0;
+    return child?.getMinIntrinsicHeight(width) ?? 0.0;
   }
 
   @override
   double computeMaxIntrinsicHeight(double width) {
     if (width.isFinite) {
       return width / _aspectRatio;
     }
-    if (child != null) {
-      return child!.getMaxIntrinsicHeight(width);
-    }
-    return 0.0;
+    return child?.getMaxIntrinsicHeight(width) ?? 0.0;
   }
 
   Size _applyAspectRatio(BoxConstraints constraints) {

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

@@ -51,10 +51,7 @@ class DisposableBuildContext<T extends State> {
   /// Otherwise, asserts the [_state] is still mounted and returns its context.
   BuildContext? get context {
     assert(_debugValidate());
-    if (_state == null) {
-      return null;
-    }
-    return _state!.context;
+    return _state?.context;
   }
 
   /// Called from asserts or tests to determine whether this object is in a

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

@@ -1039,10 +1039,7 @@ class DraggableScrollableActuator extends StatefulWidget {
   /// otherwise.
   static bool reset(BuildContext context) {
     final _InheritedResetNotifier? notifier = context.dependOnInheritedWidgetOfExactType<_InheritedResetNotifier>();
-    if (notifier == null) {
-      return false;
-    }
-    return notifier._sendReset();
+    return notifier?._sendReset() ?? false;
   }
 
   @override

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

@@ -578,10 +578,7 @@ abstract class Route<T> {
   /// rendered. It is even possible for the route to be active but for the stateful
   /// widgets within the route to not be instantiated. See [ModalRoute.maintainState].
   bool get isActive {
-    if (_navigator == null) {
-      return false;
-    }
-    return _navigator!._firstRouteEntryWhereOrNull(_RouteEntry.isRoutePredicate(this))?.isPresent ?? false;
+    return _navigator?._firstRouteEntryWhereOrNull(_RouteEntry.isRoutePredicate(this))?.isPresent ?? false;
   }
 }