Experimental flags in Fasta

Change-Id: Ifc807059d9b434934e077f8fe5845d723807640c
Reviewed-on: https://dart-review.googlesource.com/c/87843
Reviewed-by: Peter von der Ahé <ahe@google.com>

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

@@ -8,6 +8,8 @@ import 'package:kernel/target/targets.dart' show Target;
 
 import 'diagnostic_message.dart' show DiagnosticMessageHandler;
 
+import 'experimental_flags.dart' show ExperimentalFlag;
+
 import 'file_system.dart' show FileSystem;
 
 import 'standard_file_system.dart' show StandardFileSystem;
@@ -120,6 +122,11 @@ class CompilerOptions {
   // libraries.json)
   Map<String, List<Uri>> targetPatches = {};
 
+  /// Enable or disable experimental features. Features mapping to `true` are
+  /// explicitly enabled. Features mapping to `false` are explicitly disabled.
+  /// Features not mentioned in the map will have their default value.
+  Map<ExperimentalFlag, bool> experimentalFlags = {};
+
   /// The target platform that will consume the compiled code.
   ///
   /// Used to provide platform-specific details to the compiler like:

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

@@ -0,0 +1,15 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// TODO(askesc): Generate this file from a flag specification.
+
+enum ExperimentalFlag { setLiterals }
+
+ExperimentalFlag parseExperimentalFlag(String flag) {
+  switch (flag) {
+    case "set-literals":
+      return ExperimentalFlag.setLiterals;
+  }
+  return null;
+}

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

@@ -24,6 +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/file_system.dart'
     show FileSystem, FileSystemEntity, FileSystemException;
 
@@ -293,6 +295,11 @@ class ProcessedOptions {
   Target get target => _target ??=
       _raw.target ?? new NoneTarget(new TargetFlags(legacyMode: legacyMode));
 
+  bool isExperimentEnabled(ExperimentalFlag flag) {
+    // TODO(askesc): Determine default flag value from specification file.
+    return _raw.experimentalFlags[flag] ?? false;
+  }
+
   /// Get an outline component that summarizes the SDK, if any.
   // TODO(sigmund): move, this doesn't feel like an "option".
   Future<Component> loadSdkSummary(CanonicalName nameRoot) async {

pkg/front_end/lib/src/fasta/fasta_codes_generated.dart

@@ -3320,7 +3320,12 @@ const MessageCode messageFastaUsageLong =
     Makes messages of the given kinds fatal, that is, immediately stop the
     compiler with a non-zero exit-code. In --verbose mode, also display an
     internal stack trace from the compiler. Multiple kinds can be separated by
-    commas, for example, --fatal=errors,warnings.""");
+    commas, for example, --fatal=errors,warnings.
+
+  --enable-experiment=<flag>
+  --disable-experiment=<flag>
+    Enable or disable an experimental flag, used to guard features currently
+    in development. Multiple experiments can be separated by commas.""");
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeFastaUsageShort = messageFastaUsageShort;

pkg/front_end/lib/src/fasta/target_implementation.dart

@@ -18,6 +18,8 @@ import 'ticker.dart' show Ticker;
 
 import 'uri_translator.dart' show UriTranslator;
 
+import '../api_prototype/experimental_flags.dart' show ExperimentalFlag;
+
 /// Provides the implementation details used by a loader for a target.
 abstract class TargetImplementation extends Target {
   final UriTranslator uriTranslator;
@@ -33,8 +35,12 @@ abstract class TargetImplementation extends Target {
   Declaration cachedNativeAnnotation;
   Declaration cachedNativeExtensionAnnotation;
 
+  bool enableSetLiterals;
+
   TargetImplementation(Ticker ticker, this.uriTranslator, this.backendTarget)
-      : super(ticker);
+      : enableSetLiterals = CompilerContext.current.options
+            .isExperimentEnabled(ExperimentalFlag.setLiterals),
+        super(ticker);
 
   /// Creates a [LibraryBuilder] corresponding to [uri], if one doesn't exist
   /// already.

pkg/front_end/messages.yaml

@@ -1582,6 +1582,11 @@ FastaUsageLong:
         internal stack trace from the compiler. Multiple kinds can be separated by
         commas, for example, --fatal=errors,warnings.
 
+      --enable-experiment=<flag>
+      --disable-experiment=<flag>
+        Enable or disable an experimental flag, used to guard features currently
+        in development. Multiple experiments can be separated by commas.
+
 FastaCLIArgumentRequired:
   template: "Expected value after '#name'."
 

pkg/front_end/tool/_fasta/command_line.dart

@@ -14,6 +14,9 @@ import 'package:build_integration/file_system/single_root.dart'
 import 'package:front_end/src/api_prototype/compiler_options.dart'
     show CompilerOptions;
 
+import 'package:front_end/src/api_prototype/experimental_flags.dart'
+    show ExperimentalFlag, parseExperimentalFlag;
+
 import 'package:front_end/src/api_prototype/file_system.dart' show FileSystem;
 
 import 'package:front_end/src/api_prototype/standard_file_system.dart'
@@ -237,7 +240,9 @@ class ParsedArguments {
 const Map<String, dynamic> optionSpecification = const <String, dynamic>{
   "--bytecode": false,
   "--compile-sdk": Uri,
+  "--disable-experiment": ",",
   "--dump-ir": false,
+  "--enable-experiment": ",",
   "--exclude-source": false,
   "--omit-platform": false,
   "--fatal": ",",
@@ -338,6 +343,31 @@ ProcessedOptions analyzeCommandLine(
     });
   }
 
+  final List<String> enabledExperiments = options["--enable-experiment"];
+  final List<String> disabledExperiments = options["--disable-experiment"];
+
+  Map<ExperimentalFlag, bool> experimentalFlags = {};
+
+  void setExperimentalFlags(List<String> experiments, bool value) {
+    if (experiments != null) {
+      for (String experiment in experiments) {
+        ExperimentalFlag flag = parseExperimentalFlag(experiment);
+        if (flag == null) {
+          throw new CommandLineProblem.deprecated(
+              "Unknown experiment: " + experiment);
+        }
+        if (experimentalFlags.containsKey(flag)) {
+          throw new CommandLineProblem.deprecated(
+              "Experiment mentioned more than once: " + experiment);
+        }
+        experimentalFlags[flag] = value;
+      }
+    }
+  }
+
+  setExperimentalFlags(enabledExperiments, true);
+  setExperimentalFlags(disabledExperiments, false);
+
   if (programName == "compile_platform") {
     if (arguments.length != 5) {
       return throw new CommandLineProblem.deprecated(
@@ -369,7 +399,8 @@ ProcessedOptions analyzeCommandLine(
           ..omitPlatform = omitPlatform
           ..verbose = verbose
           ..verify = verify
-          ..bytecode = bytecode,
+          ..bytecode = bytecode
+          ..experimentalFlags = experimentalFlags,
         inputs: <Uri>[Uri.parse(arguments[0])],
         output: resolveInputUri(arguments[3], extraSchemes: extraSchemes));
   } else if (arguments.isEmpty) {
@@ -403,7 +434,8 @@ ProcessedOptions analyzeCommandLine(
     ..debugDump = dumpIr
     ..omitPlatform = omitPlatform
     ..verbose = verbose
-    ..verify = verify;
+    ..verify = verify
+    ..experimentalFlags = experimentalFlags;
 
   // TODO(ahe): What about chase dependencies?