Move experimental flag defaults to CFE

Change-Id: I9f1890f349fb19bbd792af071adc14ad4e50c364
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/98010
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>

pkg/compiler/lib/src/options.dart

@@ -327,7 +327,7 @@ class CompilerOptions implements DiagnosticOptions {
       {Uri librariesSpecificationUri, Uri platformBinaries}) {
     Map<fe.ExperimentalFlag, bool> languageExperiments =
         _extractExperiments(options);
-    if (equalMaps(languageExperiments, defaultExperimentalFlags)) {
+    if (equalMaps(languageExperiments, fe.defaultExperimentalFlags)) {
       platformBinaries ??= fe.computePlatformBinariesLocation();
     }
     return new CompilerOptions()
@@ -424,7 +424,7 @@ class CompilerOptions implements DiagnosticOptions {
       throw new ArgumentError("[packageRoot] must end with a /");
     }
     if (platformBinaries == null &&
-        equalMaps(languageExperiments, defaultExperimentalFlags)) {
+        equalMaps(languageExperiments, fe.defaultExperimentalFlags)) {
       throw new ArgumentError("Missing required ${Flags.platformBinaries}");
     }
   }
@@ -564,18 +564,8 @@ List<Uri> _extractUriListOption(List<String> options, String flag) {
 Map<fe.ExperimentalFlag, bool> _extractExperiments(List<String> options) {
   List<String> experiments =
       _extractOptionalCsvOption(options, Flags.enableLanguageExperiments);
-  Map<fe.ExperimentalFlag, bool> flags = fe.parseExperimentalFlags(
+  return fe.parseExperimentalFlags(
       experiments, (String error) => throw new ArgumentError(error));
-  for (fe.ExperimentalFlag flag in defaultExperimentalFlags.keys) {
-    flags[flag] ??= defaultExperimentalFlags[flag];
-  }
-  return flags;
 }
 
-const Map<fe.ExperimentalFlag, bool> defaultExperimentalFlags = {
-  fe.ExperimentalFlag.constantUpdate2018: false,
-  fe.ExperimentalFlag.controlFlowCollections: false,
-  fe.ExperimentalFlag.spreadCollections: false,
-};
-
 const String _UNDETERMINED_BUILD_ID = "build number could not be determined";

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

@@ -8,7 +8,8 @@ import 'package:kernel/target/targets.dart' show Target;
 
 import 'diagnostic_message.dart' show DiagnosticMessageHandler;
 
-import 'experimental_flags.dart' show ExperimentalFlag, parseExperimentalFlag;
+import 'experimental_flags.dart'
+    show defaultExperimentalFlags, ExperimentalFlag, parseExperimentalFlag;
 
 import 'file_system.dart' show FileSystem;
 
@@ -209,30 +210,38 @@ class CompilerOptions {
 
 /// Parse experimental flags from a list of strings, each of which is either a
 /// flag name or a flag name prefixed by 'no-'. Return a map of flags to their
-/// values that can be passed to [experimentalFlags].
+/// values that can be passed to [experimentalFlags]. The returned map is
+/// normalized to contain default values for unmentioned flags.
 ///
 /// If an unknown flag is mentioned, or a flag is mentioned more than once,
 /// the supplied error handler is called with an error message.
 Map<ExperimentalFlag, bool> parseExperimentalFlags(
     Iterable<String> experiments, void onError(String message)) {
   Map<ExperimentalFlag, bool> flags = <ExperimentalFlag, bool>{};
-  if (experiments == null) return flags;
-  for (String experiment in experiments) {
-    bool value = true;
-    if (experiment.startsWith("no-")) {
-      value = false;
-      experiment = experiment.substring(3);
-    }
-    ExperimentalFlag flag = parseExperimentalFlag(experiment);
-    if (flag == null) {
-      onError("Unknown experiment: " + experiment);
-    } else if (flags.containsKey(flag)) {
-      if (flags[flag] != value) {
-        onError("Experiment specified with conflicting values: " + experiment);
+  if (experiments != null) {
+    for (String experiment in experiments) {
+      bool value = true;
+      if (experiment.startsWith("no-")) {
+        value = false;
+        experiment = experiment.substring(3);
+      }
+      ExperimentalFlag flag = parseExperimentalFlag(experiment);
+      if (flag == null) {
+        onError("Unknown experiment: " + experiment);
+      } else if (flags.containsKey(flag)) {
+        if (flags[flag] != value) {
+          onError(
+              "Experiment specified with conflicting values: " + experiment);
+        }
+      } else {
+        flags[flag] = value;
       }
-    } else {
-      flags[flag] = value;
     }
   }
+  for (ExperimentalFlag flag in ExperimentalFlag.values) {
+    assert(defaultExperimentalFlags.containsKey(flag),
+        "No default value for $flag.");
+    flags[flag] ??= defaultExperimentalFlags[flag];
+  }
   return flags;
 }

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

@@ -24,3 +24,10 @@ ExperimentalFlag parseExperimentalFlag(String flag) {
   }
   return null;
 }
+
+const Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
+  ExperimentalFlag.constantUpdate2018: false,
+  ExperimentalFlag.controlFlowCollections: false,
+  ExperimentalFlag.setLiterals: true,
+  ExperimentalFlag.spreadCollections: false,
+};

pkg/front_end/lib/src/api_unstable/dart2js.dart

@@ -44,7 +44,8 @@ export '../api_prototype/diagnostic_message.dart'
         getMessageRelatedInformation,
         getMessageUri;
 
-export '../api_prototype/experimental_flags.dart' show ExperimentalFlag;
+export '../api_prototype/experimental_flags.dart'
+    show defaultExperimentalFlags, ExperimentalFlag;
 
 export '../api_prototype/file_system.dart'
     show FileSystem, FileSystemEntity, FileSystemException;

pkg/front_end/lib/src/base/processed_options.dart

@@ -24,7 +24,8 @@ import 'package:package_config/src/packages_impl.dart' show MapPackages;
 import '../api_prototype/compiler_options.dart'
     show CompilerOptions, DiagnosticMessage;
 
-import '../api_prototype/experimental_flags.dart' show ExperimentalFlag;
+import '../api_prototype/experimental_flags.dart'
+    show defaultExperimentalFlags, ExperimentalFlag;
 
 import '../api_prototype/file_system.dart'
     show FileSystem, FileSystemEntity, FileSystemException;
@@ -310,9 +311,11 @@ class ProcessedOptions {
       _raw.target ?? new NoneTarget(new TargetFlags(legacyMode: legacyMode));
 
   bool isExperimentEnabled(ExperimentalFlag flag) {
+    assert(defaultExperimentalFlags.containsKey(flag),
+        "No default value for $flag.");
     // TODO(askesc): Determine default flag value from specification file.
     if (flag == ExperimentalFlag.setLiterals) return true;
-    return _raw.experimentalFlags[flag] ?? false;
+    return _raw.experimentalFlags[flag] ?? defaultExperimentalFlags[flag];
   }
 
   /// Get an outline component that summarizes the SDK, if any.