Update from Google.
--
MOE_MIGRATED_REVID=85702957
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Statement.java b/src/main/java/com/google/devtools/build/lib/syntax/Statement.java
new file mode 100644
index 0000000..ca89b1a
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Statement.java
@@ -0,0 +1,44 @@
+// 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;
+
+/**
+ * Base class for all statements nodes in the AST.
+ */
+public abstract class Statement extends ASTNode {
+
+ /**
+ * Executes the statement in the specified build environment, which may be
+ * modified.
+ *
+ * @throws EvalException if execution of the statement could not be completed.
+ */
+ abstract void exec(Environment env) throws EvalException, InterruptedException;
+
+ /**
+ * Checks the semantics of the Statement using the SkylarkEnvironment according to
+ * the rules of the Skylark language. The SkylarkEnvironment can be used e.g. to check
+ * variable type collision, read only variables, detecting recursion, existence of
+ * built-in variables, functions, etc.
+ *
+ * <p>The semantical check should be performed after the Skylark extension is loaded
+ * (i.e. is syntactically correct) and before is executed. The point of the semantical check
+ * is to make sure (as much as possible) that no error can occur during execution (Skylark
+ * programmers get a "compile time" error). It should also check execution branches (e.g. in
+ * if statements) that otherwise might never get executed.
+ *
+ * @throws EvalException if the Statement has a semantical error.
+ */
+ abstract void validate(ValidationEnvironment env) throws EvalException;
+}
