[null-aware-elements] Add experiment flag 'null-aware-elements'.

Part of https://github.com/dart-lang/sdk/issues/55949
Closes https://github.com/dart-lang/sdk/issues/55926

Change-Id: Ic8c6a9226bcad54daf99e01746044045937376b1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/369960
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Reviewed-by: Keerti Parthasarathy <keertip@google.com>

pkg/_fe_analyzer_shared/lib/src/experiments/flags.dart

@@ -129,6 +129,13 @@ enum ExperimentalFlag {
       experimentEnabledVersion: const Version(2, 13),
       experimentReleasedVersion: const Version(2, 13)),
 
+  nullAwareElements(
+      name: 'null-aware-elements',
+      isEnabledByDefault: false,
+      isExpired: false,
+      experimentEnabledVersion: defaultLanguageVersion,
+      experimentReleasedVersion: defaultLanguageVersion),
+
   patterns(
       name: 'patterns',
       isEnabledByDefault: true,

pkg/analyzer/lib/dart/analysis/features.dart

@@ -49,6 +49,9 @@ abstract class Feature {
   /// Feature information for macros.
   static final macros = ExperimentalFeatures.macros;
 
+  /// Feature information for null-aware elements.
+  static final null_aware_elements = ExperimentalFeatures.null_aware_elements;
+
   /// Feature information for patterns.
   static final patterns = ExperimentalFeatures.patterns;
 

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -95,7 +95,7 @@ import 'package:meta/meta.dart';
 // TODO(scheglov): Clean up the list of implicitly analyzed files.
 class AnalysisDriver {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 368;
+  static const int DATA_VERSION = 369;
 
   /// The number of exception contexts allowed to write. Once this field is
   /// zero, we stop writing any new exception contexts in this process.

pkg/analyzer/lib/src/dart/analysis/experiments.g.dart

@@ -36,6 +36,7 @@ final _knownFeatures = <String, ExperimentalFeature>{
   EnableString.non_nullable: ExperimentalFeatures.non_nullable,
   EnableString.nonfunction_type_aliases:
       ExperimentalFeatures.nonfunction_type_aliases,
+  EnableString.null_aware_elements: ExperimentalFeatures.null_aware_elements,
   EnableString.patterns: ExperimentalFeatures.patterns,
   EnableString.records: ExperimentalFeatures.records,
   EnableString.resource_identifiers: ExperimentalFeatures.resource_identifiers,
@@ -104,6 +105,9 @@ class EnableString {
   /// String to enable the experiment "nonfunction-type-aliases"
   static const String nonfunction_type_aliases = 'nonfunction-type-aliases';
 
+  /// String to enable the experiment "null-aware-elements"
+  static const String null_aware_elements = 'null-aware-elements';
+
   /// String to enable the experiment "patterns"
   static const String patterns = 'patterns';
 
@@ -317,8 +321,18 @@ class ExperimentalFeatures {
     releaseVersion: Version.parse('2.13.0'),
   );
 
-  static final patterns = ExperimentalFeature(
+  static final null_aware_elements = ExperimentalFeature(
     index: 17,
+    enableString: EnableString.null_aware_elements,
+    isEnabledByDefault: IsEnabledByDefault.null_aware_elements,
+    isExpired: IsExpired.null_aware_elements,
+    documentation: 'Null-aware elements and map entries in collections.',
+    experimentalReleaseVersion: null,
+    releaseVersion: null,
+  );
+
+  static final patterns = ExperimentalFeature(
+    index: 18,
     enableString: EnableString.patterns,
     isEnabledByDefault: IsEnabledByDefault.patterns,
     isExpired: IsExpired.patterns,
@@ -328,7 +342,7 @@ class ExperimentalFeatures {
   );
 
   static final records = ExperimentalFeature(
-    index: 18,
+    index: 19,
     enableString: EnableString.records,
     isEnabledByDefault: IsEnabledByDefault.records,
     isExpired: IsExpired.records,
@@ -338,7 +352,7 @@ class ExperimentalFeatures {
   );
 
   static final resource_identifiers = ExperimentalFeature(
-    index: 19,
+    index: 20,
     enableString: EnableString.resource_identifiers,
     isEnabledByDefault: IsEnabledByDefault.resource_identifiers,
     isExpired: IsExpired.resource_identifiers,
@@ -348,7 +362,7 @@ class ExperimentalFeatures {
   );
 
   static final sealed_class = ExperimentalFeature(
-    index: 20,
+    index: 21,
     enableString: EnableString.sealed_class,
     isEnabledByDefault: IsEnabledByDefault.sealed_class,
     isExpired: IsExpired.sealed_class,
@@ -358,7 +372,7 @@ class ExperimentalFeatures {
   );
 
   static final set_literals = ExperimentalFeature(
-    index: 21,
+    index: 22,
     enableString: EnableString.set_literals,
     isEnabledByDefault: IsEnabledByDefault.set_literals,
     isExpired: IsExpired.set_literals,
@@ -368,7 +382,7 @@ class ExperimentalFeatures {
   );
 
   static final spread_collections = ExperimentalFeature(
-    index: 22,
+    index: 23,
     enableString: EnableString.spread_collections,
     isEnabledByDefault: IsEnabledByDefault.spread_collections,
     isExpired: IsExpired.spread_collections,
@@ -378,7 +392,7 @@ class ExperimentalFeatures {
   );
 
   static final super_parameters = ExperimentalFeature(
-    index: 23,
+    index: 24,
     enableString: EnableString.super_parameters,
     isEnabledByDefault: IsEnabledByDefault.super_parameters,
     isExpired: IsExpired.super_parameters,
@@ -388,7 +402,7 @@ class ExperimentalFeatures {
   );
 
   static final test_experiment = ExperimentalFeature(
-    index: 24,
+    index: 25,
     enableString: EnableString.test_experiment,
     isEnabledByDefault: IsEnabledByDefault.test_experiment,
     isExpired: IsExpired.test_experiment,
@@ -399,7 +413,7 @@ class ExperimentalFeatures {
   );
 
   static final triple_shift = ExperimentalFeature(
-    index: 25,
+    index: 26,
     enableString: EnableString.triple_shift,
     isEnabledByDefault: IsEnabledByDefault.triple_shift,
     isExpired: IsExpired.triple_shift,
@@ -409,7 +423,7 @@ class ExperimentalFeatures {
   );
 
   static final unnamed_libraries = ExperimentalFeature(
-    index: 26,
+    index: 27,
     enableString: EnableString.unnamed_libraries,
     isEnabledByDefault: IsEnabledByDefault.unnamed_libraries,
     isExpired: IsExpired.unnamed_libraries,
@@ -419,7 +433,7 @@ class ExperimentalFeatures {
   );
 
   static final variance = ExperimentalFeature(
-    index: 27,
+    index: 28,
     enableString: EnableString.variance,
     isEnabledByDefault: IsEnabledByDefault.variance,
     isExpired: IsExpired.variance,
@@ -429,7 +443,7 @@ class ExperimentalFeatures {
   );
 
   static final wildcard_variables = ExperimentalFeature(
-    index: 28,
+    index: 29,
     enableString: EnableString.wildcard_variables,
     isEnabledByDefault: IsEnabledByDefault.wildcard_variables,
     isExpired: IsExpired.wildcard_variables,
@@ -494,6 +508,9 @@ class IsEnabledByDefault {
   /// Default state of the experiment "nonfunction-type-aliases"
   static const bool nonfunction_type_aliases = true;
 
+  /// Default state of the experiment "null-aware-elements"
+  static const bool null_aware_elements = false;
+
   /// Default state of the experiment "patterns"
   static const bool patterns = true;
 
@@ -586,6 +603,9 @@ class IsExpired {
   /// Expiration status of the experiment "nonfunction-type-aliases"
   static const bool nonfunction_type_aliases = true;
 
+  /// Expiration status of the experiment "null-aware-elements"
+  static const bool null_aware_elements = false;
+
   /// Expiration status of the experiment "patterns"
   static const bool patterns = true;
 
@@ -684,6 +704,10 @@ mixin _CurrentState {
   bool get nonfunction_type_aliases =>
       isEnabled(ExperimentalFeatures.nonfunction_type_aliases);
 
+  /// Current state for the flag "null-aware-elements"
+  bool get null_aware_elements =>
+      isEnabled(ExperimentalFeatures.null_aware_elements);
+
   /// Current state for the flag "patterns"
   bool get patterns => isEnabled(ExperimentalFeatures.patterns);
 

pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart

@@ -195,6 +195,14 @@ class ExperimentalFlag {
       experimentEnabledVersion: const Version(2, 13),
       experimentReleasedVersion: const Version(2, 13));
 
+  static const ExperimentalFlag nullAwareElements = const ExperimentalFlag(
+      name: 'null-aware-elements',
+      isEnabledByDefault: false,
+      isExpired: false,
+      enabledVersion: defaultLanguageVersion,
+      experimentEnabledVersion: defaultLanguageVersion,
+      experimentReleasedVersion: defaultLanguageVersion);
+
   static const ExperimentalFlag patterns = const ExperimentalFlag(
       name: 'patterns',
       isEnabledByDefault: true,
@@ -410,6 +418,10 @@ class GlobalFeatures {
   GlobalFeature get nonfunctionTypeAliases => _nonfunctionTypeAliases ??=
       _computeGlobalFeature(ExperimentalFlag.nonfunctionTypeAliases);
 
+  GlobalFeature? _nullAwareElements;
+  GlobalFeature get nullAwareElements => _nullAwareElements ??=
+      _computeGlobalFeature(ExperimentalFlag.nullAwareElements);
+
   GlobalFeature? _patterns;
   GlobalFeature get patterns =>
       _patterns ??= _computeGlobalFeature(ExperimentalFlag.patterns);
@@ -567,6 +579,11 @@ class LibraryFeatures {
           canonicalUri,
           libraryVersion);
 
+  LibraryFeature? _nullAwareElements;
+  LibraryFeature get nullAwareElements =>
+      _nullAwareElements ??= globalFeatures._computeLibraryFeature(
+          ExperimentalFlag.nullAwareElements, canonicalUri, libraryVersion);
+
   LibraryFeature? _patterns;
   LibraryFeature get patterns =>
       _patterns ??= globalFeatures._computeLibraryFeature(
@@ -665,6 +682,8 @@ class LibraryFeatures {
         return nonNullable;
       case shared.ExperimentalFlag.nonfunctionTypeAliases:
         return nonfunctionTypeAliases;
+      case shared.ExperimentalFlag.nullAwareElements:
+        return nullAwareElements;
       case shared.ExperimentalFlag.patterns:
         return patterns;
       case shared.ExperimentalFlag.records:
@@ -731,6 +750,8 @@ ExperimentalFlag? parseExperimentalFlag(String flag) {
       return ExperimentalFlag.nonNullable;
     case "nonfunction-type-aliases":
       return ExperimentalFlag.nonfunctionTypeAliases;
+    case "null-aware-elements":
+      return ExperimentalFlag.nullAwareElements;
     case "patterns":
       return ExperimentalFlag.patterns;
     case "records":
@@ -793,6 +814,8 @@ final Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
   ExperimentalFlag.nonNullable: ExperimentalFlag.nonNullable.isEnabledByDefault,
   ExperimentalFlag.nonfunctionTypeAliases:
       ExperimentalFlag.nonfunctionTypeAliases.isEnabledByDefault,
+  ExperimentalFlag.nullAwareElements:
+      ExperimentalFlag.nullAwareElements.isEnabledByDefault,
   ExperimentalFlag.patterns: ExperimentalFlag.patterns.isEnabledByDefault,
   ExperimentalFlag.records: ExperimentalFlag.records.isEnabledByDefault,
   ExperimentalFlag.resourceIdentifiers:
@@ -844,6 +867,7 @@ const Map<shared.ExperimentalFlag, ExperimentalFlag> sharedExperimentalFlags = {
   shared.ExperimentalFlag.nonNullable: ExperimentalFlag.nonNullable,
   shared.ExperimentalFlag.nonfunctionTypeAliases:
       ExperimentalFlag.nonfunctionTypeAliases,
+  shared.ExperimentalFlag.nullAwareElements: ExperimentalFlag.nullAwareElements,
   shared.ExperimentalFlag.patterns: ExperimentalFlag.patterns,
   shared.ExperimentalFlag.records: ExperimentalFlag.records,
   shared.ExperimentalFlag.resourceIdentifiers:

pkg/front_end/test/coverage_suite_expected.dart

@@ -18,10 +18,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 66,
     missCount: 8,
   ),
-  // 55.28846153846154%.
+  // 54.07925407925408%.
   "package:front_end/src/api_prototype/experimental_flags_generated.dart": (
-    hitCount: 230,
-    missCount: 186,
+    hitCount: 232,
+    missCount: 197,
   ),
   // 33.33333333333333%.
   "package:front_end/src/api_prototype/file_system.dart": (
@@ -753,10 +753,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 118,
     missCount: 6,
   ),
-  // 93.60488798370672%.
+  // 93.47120843471208%.
   "package:front_end/src/source/outline_builder.dart": (
-    hitCount: 2298,
-    missCount: 157,
+    hitCount: 2305,
+    missCount: 161,
   ),
   // 94.44444444444444%.
   "package:front_end/src/source/redirecting_factory_body.dart": (
@@ -809,9 +809,9 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 295,
     missCount: 35,
   ),
-  // 85.36585365853658%.
+  // 85.3836784409257%.
   "package:front_end/src/source/source_library_builder.dart": (
-    hitCount: 3500,
+    hitCount: 3505,
     missCount: 600,
   ),
   // 81.8988464951198%.

tools/experimental_features.yaml

@@ -358,6 +358,9 @@ features:
       }
     expired: true
 
+  null-aware-elements:
+    help: "Null-aware elements and map entries in collections."
+
   extension-methods:
     help: "Extension Methods"
     enabledIn: '2.6.0'