Fasta builders.

pkg/fasta/lib/src/modifier.dart

Index: pkg/fasta/lib/src/modifier.dart
diff --git a/pkg/fasta/lib/src/modifier.dart b/pkg/fasta/lib/src/modifier.dart
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+// Copyright (c) 2016, 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.
+
+library fasta.modifier;
+
+import 'errors.dart' show
+    internalError;
+
+enum ModifierEnum {
+  Abstract,
+  Const,
+  External,
+  Final,
+  Static,
+
+  // Not a real modifier.
+  Var,
+}
+
+const int abstractMask = 1;
+
+const int constMask = abstractMask << 1;
+
+const int externalMask = constMask << 1;
+
+const int finalMask = externalMask << 1;
+
+const int staticMask = finalMask << 1;
+
+/// Not a real modifier, and by setting it to null, it is automatically
+/// ignored by [Modifier.validate] below.
+const int varMask = 0;
+
+const Modifier Abstract = const Modifier(ModifierEnum.Abstract, abstractMask);
+
+const Modifier Const = const Modifier(ModifierEnum.Const, constMask);
+
+const Modifier External = const Modifier(ModifierEnum.External, externalMask);
+
+const Modifier Final = const Modifier(ModifierEnum.Final, finalMask);
+
+const Modifier Static = const Modifier(ModifierEnum.Static, staticMask);
+
+/// Not a real modifier.
+const Modifier Var = const Modifier(ModifierEnum.Var, varMask);
+
+class Modifier {
+  final ModifierEnum kind;
+
+  final int mask;
+
+  const Modifier(this.kind, this.mask);
+
+  factory Modifier.fromString(String string) {
+    if (identical('abstract', string)) return Abstract;
+    if (identical('const', string)) return Const;
+    if (identical('external', string)) return External;
+    if (identical('final', string)) return Final;
+    if (identical('static', string)) return Static;
+    if (identical('var', string)) return Var;
+    return internalError("Unhandled modifier: $string");
+  }
+
+  toString() => "modifier(${'$kind'.substring('ModifierEnum.'.length)})";
+
+  static int validate(List<Modifier> modifiers, {bool isAbstract: false}) {
+    // TODO(ahe): Implement modifier validation: ordering and uniqueness.
+    int result = isAbstract ? abstractMask : 0;
+    if (modifiers == null) return result;
+    for (Modifier modifier in modifiers) {
+      result |= modifier.mask;
+    }
+    return result;
+  }
+}