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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2008 The Closure Compiler Authors.
 *
 * 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.javascript.jscomp.disambiguate;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.MoreObjects;
import com.google.errorprone.annotations.DoNotCall;
import com.google.javascript.jscomp.colors.Color;
import java.util.BitSet;

/**
 * A struct representing a {@link Color} for use in ambiguation.
 *
 * "Flat" refers to the coercion of multiple {@link Color}s, which should behave the same during
 * disambiguation, into a single {@link ColorGraphNode}.
 *
 * 
Each instance pairs a type with the information required for ambiguation to map this type to
 * the set of associated properties.
 *
 * Note: this design now depends on the implementation of Color to preserve invariants about
 * recursive Colors. The node factory can't be depended on for post-processing Colors without
 * losing type safety.
 */
final class ColorGraphNode {

  private final Color color;

  private final int id;

  private final BitSet subtypeIds = new BitSet();

  static ColorGraphNode create(Color single, int id) {
    checkNotNull(single);

    checkArgument(id >= 0);

    return new ColorGraphNode(single, id);
  }

  @VisibleForTesting
  static ColorGraphNode createForTesting(int id) {
    checkArgument(id < 0); // All test types have negative ids to differentiate them.

    return new ColorGraphNode(null, id);
  }

  private ColorGraphNode(Color single, int id) {
    this.id = id;
    this.color = single;
  }

  Color getColor() {
    return checkNotNull(this.color);
  }

  /**
   * An ID used to efficiently construct a unique name for any cluster this node becomes the
   * represenative of.
   */
  int getId() {
    return this.id;
  }

  /** The IDs of other ColorGraphNodes that have been found to be subtypes of this type. */
  BitSet getSubtypeIds() {
    return this.subtypeIds;
  }

  @Override
  @DoNotCall // For debugging only.
  public String toString() {
    return MoreObjects.toStringHelper(this).add("id", this.id).add("color", this.color).toString();
  }
}