feature: tag tests; choose tags on command line

lib/src/backend/metadata.dart

Index: lib/src/backend/metadata.dart
diff --git a/lib/src/backend/metadata.dart b/lib/src/backend/metadata.dart
index 7fb37ba8402133feab972f7ddd96d94fdd8e9462..d3991e23e884d7b66478f46bf9d974797ffe70c2 100644
--- a/lib/src/backend/metadata.dart
+++ b/lib/src/backend/metadata.dart
@@ -33,6 +33,9 @@ class Metadata {
   /// The reason the test or suite should be skipped, if given.
   final String skipReason;
 
+  /// A set of tags attached to a test
+  final List<String> tags;
+
   /// Platform-specific metadata.
   ///
   /// Each key identifies a platform, and its value identifies the specific
@@ -88,27 +91,30 @@ class Metadata {
   /// [testOn] defaults to [PlatformSelector.all].
   Metadata({PlatformSelector testOn, Timeout timeout, bool skip: false,
           this.verboseTrace: false, this.skipReason,
-          Map<PlatformSelector, Metadata> onPlatform})
+          Map<PlatformSelector, Metadata> onPlatform, List<String> tags})
       : testOn = testOn == null ? PlatformSelector.all : testOn,
         timeout = timeout == null ? const Timeout.factor(1) : timeout,
         skip = skip,
         onPlatform = onPlatform == null
             ? const {}
-            : new UnmodifiableMapView(onPlatform);
+            : new UnmodifiableMapView(onPlatform),
+        this.tags = tags ?? const <String>[];

[nweiz, 2015/10/13 23:28:12]

Unfortunately "??" isn't usable here. Anything that gets loaded by Dartium,
which is basically everything in backend/, needs to work on an extra-wide range
of Dart versions since there's no good way to constrain the Dartium version.

[yjbanov, 2015/10/30 20:13:59]

Done.

 
   /// Creates a new Metadata, but with fields parsed from caller-friendly values
   /// where applicable.
   ///
   /// Throws a [FormatException] if any field is invalid.
   Metadata.parse({String testOn, Timeout timeout, skip,
-          this.verboseTrace: false, Map<String, dynamic> onPlatform})
+          this.verboseTrace: false, Map<String, dynamic> onPlatform,
+          List<String> tags})
       : testOn = testOn == null
             ? PlatformSelector.all
             : new PlatformSelector.parse(testOn),
         timeout = timeout == null ? const Timeout.factor(1) : timeout,
         skip = skip != null && skip != false,
         skipReason = skip is String ? skip : null,
-        onPlatform = _parseOnPlatform(onPlatform) {
+        onPlatform = _parseOnPlatform(onPlatform),
+        this.tags = tags ?? const <String>[] {
     if (skip != null && skip is! String && skip is! bool) {
       throw new ArgumentError(
           '"skip" must be a String or a bool, was "$skip".');
@@ -124,6 +130,7 @@ class Metadata {
         skip = serialized['skip'],
         skipReason = serialized['skipReason'],
         verboseTrace = serialized['verboseTrace'],
+        tags = serialized['tags'] ?? const <String>[],
         onPlatform = new Map.fromIterable(serialized['onPlatform'],
             key: (pair) => new PlatformSelector.parse(pair.first),
             value: (pair) => new Metadata.deserialize(pair.last));
@@ -147,7 +154,8 @@ class Metadata {
           skip: skip || other.skip,
           verboseTrace: verboseTrace || other.verboseTrace,
           skipReason: other.skipReason == null ? skipReason : other.skipReason,
-          onPlatform: mergeMaps(onPlatform, other.onPlatform));
+          onPlatform: mergeMaps(onPlatform, other.onPlatform),
+          tags: mergeLists(tags, other.tags));
 
   /// Returns a copy of [this] with the given fields changed.
   Metadata change({PlatformSelector testOn, Timeout timeout, bool skip,
@@ -192,7 +200,8 @@ class Metadata {
       'skip': skip,
       'skipReason': skipReason,
       'verboseTrace': verboseTrace,
-      'onPlatform': serializedOnPlatform
+      'onPlatform': serializedOnPlatform,
+      'tags': tags.isEmpty ? null : tags,

[nweiz, 2015/10/13 23:28:12]

Just pass an empty list here rather than adding a special case to null it out.

[yjbanov, 2015/10/30 20:13:59]

Done.

     };
   }