Use 'no-' prefix to disable an experiment.

Change-Id: I597a98802f6900d57ed4583c35b20790738e2f3a
Reviewed-on: https://dart-review.googlesource.com/c/88712
Reviewed-by: Paul Berry <[email protected]>
Reviewed-by: Kevin Millikin <[email protected]>
Commit-Queue: Aske Simon Christensen <[email protected]>

Author: askeksa

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

@@ -120,12 +120,12 @@ class CompilerOptions {
   /// directly, while relative URIs are resolved from the [sdkRoot].
   // TODO(sigmund): provide also a flag to load this data from a file (like
   // libraries.json)
-  Map<String, List<Uri>> targetPatches = {};
+  Map<String, List<Uri>> targetPatches = <String, List<Uri>>{};
 
   /// 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 = {};
+  Map<ExperimentalFlag, bool> experimentalFlags = <ExperimentalFlag, bool>{};
 
   /// The target platform that will consume the compiled code.
   ///

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

@@ -3323,9 +3323,9 @@ const MessageCode messageFastaUsageLong =
     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.""");
+    in development. Prefix an experiment name with 'no-' to disable it.
+    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/messages.yaml

@@ -1587,9 +1587,9 @@ FastaUsageLong:
         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.
+        in development. Prefix an experiment name with 'no-' to disable it.
+        Multiple experiments can be separated by commas.
 
 FastaCLIArgumentRequired:
   template: "Expected value after '#name'."

pkg/front_end/tool/_fasta/command_line.dart

@@ -240,7 +240,6 @@ 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,
@@ -343,31 +342,25 @@ 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;
-      }
+  Map<ExperimentalFlag, bool> experimentalFlags = <ExperimentalFlag, bool>{};
+  for (String experiment in options["--enable-experiment"] ?? <String>[]) {
+    bool value = true;
+    if (experiment.startsWith("no-")) {
+      value = false;
+      experiment = experiment.substring(3);
+    }
+    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(