src/main/java/com/google/devtools/build/lib/syntax/AssignmentStatement.java

// 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;

/**
 * Syntax node for an assignment statement.
 */
public final class AssignmentStatement extends Statement {

  private final Expression lvalue;

  private final Expression expression;

  /**
   *  Constructs an assignment: "lvalue := value".
   */
  AssignmentStatement(Expression lvalue, Expression expression) {
    this.lvalue = lvalue;
    this.expression = expression;
  }

  /**
   *  Returns the LHS of the assignment.
   */
  public Expression getLValue() {
    return lvalue;
  }

  /**
   *  Returns the RHS of the assignment.
   */
  public Expression getExpression() {
    return expression;
  }

  @Override
  public String toString() {
    return lvalue + " = " + expression + '\n';
  }

  @Override
  void exec(Environment env) throws EvalException, InterruptedException {
    if (!(lvalue instanceof Ident)) {
      throw new EvalException(getLocation(),
          "can only assign to variables, not to '" + lvalue + "'");
    }

    Ident ident = (Ident) lvalue;
    Object result = expression.eval(env);
    Preconditions.checkNotNull(result, "result of " + expression + " is null");

    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(getLocation(), "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(getLocation(), 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);
  }

  @Override
  public void accept(SyntaxTreeVisitor visitor) {
    visitor.visit(this);
  }

  @Override
  void validate(ValidationEnvironment env) throws EvalException {
    // TODO(bazel-team): Implement other validations.
    if (lvalue instanceof Ident) {
      Ident ident = (Ident) lvalue;
      SkylarkType resultType = expression.validate(env);
      env.update(ident.getName(), resultType, getLocation());
    } else {
      throw new EvalException(getLocation(),
          "can only assign to variables, not to '" + lvalue + "'");
    }
  }
}