1 files changed, 97 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/LValue.java b/src/main/java/com/google/devtools/build/lib/syntax/LValue.java
new file mode 100644
index 0000000000..a328118a6e
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+++ b/src/main/java/com/google/devtools/build/lib/syntax/LValue.java
@@ -0,0 +1,97 @@
+// 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 com.google.common.base.Preconditions;
+import com.google.devtools.build.lib.events.Location;
+
+import java.io.Serializable;
+
+/**
+ * Class representing an LValue.
+ * It appears in assignment, for loop and comprehensions, e.g.
+ *    lvalue = 2
+ *    [for lvalue in exp]
+ *    for lvalue in exp: pass
+ * An LValue can be a simple variable or something more complex like a tuple.
+ */
+public class LValue implements Serializable {
+  // Currently, expr can only be an Ident, but we plan to support more.
+  private final Expression expr;
+
+  public LValue(Expression expr) {
+    this.expr = expr;
+  }
+
+  public Expression getExpression() {
+    return expr;
+  }
+
+  /**
+   * Assign a value to an LValue and update the environment.
+   */
+  public void assign(Environment env, Location loc, Expression rvalue)
+      throws EvalException, InterruptedException {
+    if (!(expr instanceof Ident)) {
+      throw new EvalException(loc,
+          "can only assign to variables, not to '" + expr + "'");
+    }
+
+    Ident ident = (Ident) expr;
+    Object result = rvalue.eval(env);
+    Preconditions.checkNotNull(result, "result of %s is null", rvalue);
+
+    if (env.isSkylarkEnabled()) {
+      // The variable may have been referenced successfully if a global variable
+      // with the same name exists. In this case an Exception needs to be thrown.
+      SkylarkEnvironment skylarkEnv = (SkylarkEnvironment) env;
+      if (skylarkEnv.hasBeenReadGlobalVariable(ident.getName())) {
+        throw new EvalException(loc, "Variable '" + ident.getName()
+            + "' is referenced before assignment."
+            + "The variable is defined in the global scope.");
+      }
+      Class<?> variableType = skylarkEnv.getVariableType(ident.getName());
+      Class<?> resultType = EvalUtils.getSkylarkType(result.getClass());
+      if (variableType != null && !variableType.equals(resultType)
+          && !resultType.equals(Environment.NoneType.class)
+          && !variableType.equals(Environment.NoneType.class)) {
+        throw new EvalException(loc, String.format("Incompatible variable types, "
+            + "trying to assign %s (type of %s) to variable %s which is already %s",
+            EvalUtils.prettyPrintValue(result),
+            EvalUtils.getDataTypeName(result),
+            ident.getName(),
+            EvalUtils.getDataTypeNameFromClass(variableType)));
+      }
+    }
+    env.update(ident.getName(), result);
+  }
+
+  void validate(ValidationEnvironment env, Location loc, SkylarkType rvalueType)
+      throws EvalException {
+    // TODO(bazel-team): Implement other validations.
+    if (expr instanceof Ident) {
+      Ident ident = (Ident) expr;
+      env.update(ident.getName(), rvalueType, loc);
+      return;
+    }
+    throw new EvalException(loc,
+        "can only assign to variables, not to '" + expr + "'");
+  }
+
+  @Override
+  public String toString() {
+    return expr.toString();
+  }
+}