src/main/java/com/google/devtools/build/lib/syntax/DotExpression.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.collect.Iterables;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.syntax.FuncallExpression.MethodDescriptor;

import java.lang.reflect.InvocationTargetException;
import java.util.List;
import java.util.concurrent.ExecutionException;

/**
 * Syntax node for a dot expression.
 * e.g.  obj.field, but not obj.method()
 */
public final class DotExpression extends Expression {

  private final Expression obj;

  private final Ident field;

  public DotExpression(Expression obj, Ident field) {
    this.obj = obj;
    this.field = field;
  }

  public Expression getObj() {
    return obj;
  }

  public Ident getField() {
    return field;
  }

  @Override
  public String toString() {
    return obj + "." + field;
  }

  @Override
  Object eval(Environment env) throws EvalException, InterruptedException {
    Object objValue = obj.eval(env);
    String name = field.getName();
    Object result = eval(objValue, name, getLocation());
    if (result == null) {
      if (objValue instanceof ClassObject) {
        String customErrorMessage = ((ClassObject) objValue).errorMessage(name);
        if (customErrorMessage != null) {
          throw new EvalException(getLocation(), customErrorMessage);
        }
      }
      throw new EvalException(getLocation(), "Object of type '"
          + EvalUtils.getDatatypeName(objValue) + "' has no field '" + name + "'");
    }
    return result;
  }

  /**
   * Returns the field of the given name of the struct objValue, or null if no such field exists.
   */
  public static Object eval(Object objValue, String name, Location loc) throws EvalException {
    Object result = null;
    if (objValue instanceof ClassObject) {
      result = ((ClassObject) objValue).getValue(name);
      result = SkylarkType.convertToSkylark(result, loc);
      // If we access NestedSets using ClassObject.getValue() we won't know the generic type,
      // so we have to disable it. This should not happen.
      SkylarkType.checkTypeAllowedInSkylark(result, loc);
    } else {
      try {
        List<MethodDescriptor> methods = FuncallExpression.getMethods(objValue.getClass(), name, 0);
        if (methods != null && methods.size() > 0) {
          MethodDescriptor method = Iterables.getOnlyElement(methods);
          if (method.getAnnotation().structField()) {
            result = FuncallExpression.callMethod(
                method, name, objValue, new Object[] {}, loc);
          }
        }
      } catch (ExecutionException | IllegalAccessException | InvocationTargetException e) {
        throw new EvalException(loc, "Method invocation failed: " + e);
      }
    }

    return result;
  }

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

  @Override
  SkylarkType validate(ValidationEnvironment env) throws EvalException {
    obj.validate(env);
    // TODO(bazel-team): check existance of field
    return SkylarkType.UNKNOWN;
  }
}