1 files changed, 93 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java b/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java
new file mode 100644
index 0000000000..26c5f1557f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java
@@ -0,0 +1,93 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.syntax;
+
+import javax.annotation.Nullable;
+
+// TODO(bazel-team): for extra performance:
+// (1) intern the strings, so we can use == to compare, and have .equals use the assumption.
+// Then have Argument and Parameter use Identifier again instead of String as keys.
+// (2) Use Identifier, not String, as keys in the Environment, which will be cleaner.
+// (3) For performance, avoid doing HashMap lookups at runtime, and compile local variable access
+// into array reference with a constant index. Variable lookups are currently a speed bottleneck,
+// as previously measured in an experiment.
+/**
+ *  Syntax node for an identifier.
+ */
+public final class Identifier extends Expression {
+
+  private final String name;
+
+  public Identifier(String name) {
+    this.name = name;
+  }
+
+  /**
+   *  Returns the name of the Identifier.
+   */
+  public String getName() {
+    return name;
+  }
+  
+  public boolean isPrivate() {
+    return name.startsWith("_");
+  }
+
+  @Override
+  public String toString() {
+    return name;
+  }
+
+  @Override
+  Object eval(Environment env) throws EvalException {
+    try {
+      return env.lookup(name);
+    } catch (Environment.NoSuchVariableException e) {
+      throw createInvalidIdentifierException();
+    }
+  }
+
+  @Override
+  public boolean equals(@Nullable Object object) {
+    if (object instanceof Identifier) {
+      Identifier that = (Identifier) object;
+      return this.name.equals(that.name);
+    }
+    return false;
+  }
+  
+  @Override
+  public int hashCode() {
+    return name.hashCode();
+  }
+
+  @Override
+  public void accept(SyntaxTreeVisitor visitor) {
+    visitor.visit(this);
+  }
+
+  @Override
+  void validate(ValidationEnvironment env) throws EvalException {
+    if (!env.hasSymbolInEnvironment(name)) {
+      throw createInvalidIdentifierException();
+    }
+  }
+
+  private EvalException createInvalidIdentifierException() {
+    return name.equals("$error$")
+        ? new EvalException(getLocation(), "contains syntax error(s)", true)
+        : new EvalException(getLocation(), "name '" + name + "' is not defined");
+  }
+}