src/main/java/com/google/devtools/common/options/OptionsBase.java

// Copyright 2014 The Bazel Authors. 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.common.options;

import com.google.common.collect.Maps;
import com.google.common.escape.CharEscaperBuilder;
import com.google.common.escape.Escaper;
import java.util.List;
import java.util.Map;
import java.util.Objects;

/**
 * Base class for all options classes. Extend this class, adding public instance fields annotated
 * with {@link Option}. Then you can create instances either programmatically:
 *
 * <pre>
 *   X x = Options.getDefaults(X.class);
 *   x.host = "localhost";
 *   x.port = 80;
 * </pre>
 *
 * or from an array of command-line arguments:
 *
 * <pre>
 *   OptionsParser parser = OptionsParser.builder()
 *       .optionsClasses(X.class)
 *       .build();
 *   parser.parse("--host", "localhost", "--port", "80");
 *   X x = parser.getOptions(X.class);
 * </pre>
 *
 * <p>Subclasses of {@code OptionsBase} <i>must</i> be constructed reflectively, i.e. using not
 * {@code new MyOptions()}, but one of the above methods instead. (Direct construction creates an
 * empty instance, not containing default values. This leads to surprising behavior and often {@code
 * NullPointerExceptions}, etc.)
 */
public abstract class OptionsBase {

  private static final Escaper ESCAPER = new CharEscaperBuilder()
      .addEscape('\\', "\\\\").addEscape('"', "\\\"").toEscaper();

  /**
   * Subclasses must provide a default (no argument) constructor.
   */
  protected OptionsBase() {
    // There used to be a sanity check here that checks the stack trace of this constructor
    // invocation; unfortunately, that makes the options construction about 10x slower. So be
    // careful with how you construct options classes.
  }

  /**
   * Returns a mapping from option names to values, for each option on this object, including
   * inherited ones. The mapping is a copy, so subsequent mutations to it or to this object are
   * independent. Entries are sorted alphabetically.
   */
  public final Map<String, Object> asMap() {
    List<OptionDefinition> definitions = OptionsData.getAllOptionDefinitionsForClass(getClass());
    Map<String, Object> map = Maps.newLinkedHashMapWithExpectedSize(definitions.size());
    for (OptionDefinition definition : definitions) {
      map.put(definition.getOptionName(), getValueFromDefinition(definition));
    }
    return map;
  }

  /** Returns the value of the option described by {@code definition}. */
  public final Object getValueFromDefinition(OptionDefinition definition) {
    try {
      return definition.getField().get(this);
    } catch (IllegalAccessException e) {
      throw new IllegalStateException("All options fields of options classes should be public", e);
    }
  }

  @Override
  public final String toString() {
    return getClass().getName() + asMap();
  }

  /**
   * Returns a string that uniquely identifies the options. This value is
   * intended for analysis caching.
   */
  public final String cacheKey() {
    StringBuilder result = new StringBuilder(getClass().getName()).append("{");
    result.append(mapToCacheKey(asMap()));
    return result.append("}").toString();
  }

  public static String mapToCacheKey(Map<String, Object> optionsMap) {
    StringBuilder result = new StringBuilder();
    for (Map.Entry<String, Object> entry : optionsMap.entrySet()) {
      result.append(entry.getKey()).append("=");

      Object value = entry.getValue();
      // This special case is needed because List.toString() prints the same
      // ("[]") for an empty list and for a list with a single empty string.
      if (value instanceof List<?> && ((List<?>) value).isEmpty()) {
        result.append("EMPTY");
      } else if (value == null) {
        result.append("NULL");
      } else {
        result
            .append('"')
            .append(ESCAPER.escape(value.toString()))
            .append('"');
      }
      result.append(", ");
    }
    return result.toString();
  }

  @Override
  @SuppressWarnings("EqualsGetClass") // Options can only be equal if they are of the same type.
  public final boolean equals(Object that) {
    if (this == that) {
      return true;
    }
    if (that == null || !getClass().equals(that.getClass())) {
      return false;
    }
    OptionsBase other = (OptionsBase) that;
    for (OptionDefinition def : OptionsParser.getOptionDefinitions(getClass())) {
      if (!Objects.equals(getValueFromDefinition(def), other.getValueFromDefinition(def))) {
        return false;
      }
    }
    return true;
  }

  @Override
  public final int hashCode() {
    return this.getClass().hashCode() + asMap().hashCode();
  }
}