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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.graph;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.base.Predicate;
import com.google.javascript.jscomp.graph.FixedPointGraphTraversal.EdgeCallback;
import org.jspecify.nullness.Nullable;

/**
 * Computes all the reachable nodes. Upon execution of {@link #compute(Object)},
 * the graph nodes will be annotated with {@link #REACHABLE} if it is reachable
 * from the specified entry node.
 *
 * @param  The type of data that the graph node holds.
 * @param  The type of data that the graph edge holds.
 *
 * @see GraphNode#getAnnotation()
 */
public final class GraphReachability implements EdgeCallback {

  // TODO(user): This should work for undirected graphs when
  // FixedPointGraphTraversal accepts them.
  private final DiGraph graph;

  private final Predicate> edgePredicate;

  public GraphReachability(DiGraph graph) {
    this(graph, null);
  }

  /**
   * @param graph The graph.
   * @param edgePredicate Given the predecessor P of the a node S and the edge coming from P to S,
   *     this predicate should return true if S is reachable from P using the edge.
   */
  public GraphReachability(
      DiGraph graph, @Nullable Predicate> edgePredicate) {
    this.graph = graph;
    this.edgePredicate = edgePredicate;
  }

  public void compute(N entry) {
    graph.clearNodeAnnotations();
    graph.getNode(entry).setAnnotation(REACHABLE);
    FixedPointGraphTraversal.newTraversal(this)
        .computeFixedPoint(graph, entry);
  }

  public void recompute(N reachableNode) {
    GraphNode newReachable = graph.getNode(reachableNode);
    checkState(newReachable.getAnnotation() != REACHABLE);
    newReachable.setAnnotation(REACHABLE);
    FixedPointGraphTraversal.newTraversal(this)
        .computeFixedPoint(graph, reachableNode);
  }

  @Override
  public boolean traverseEdge(N source, E e, N destination) {
    if (graph.getNode(source).getAnnotation() == REACHABLE &&
        (edgePredicate == null ||
            edgePredicate.apply(new EdgeTuple<>(source, e, destination)))) {
      GraphNode destNode = graph.getNode(destination);
      if (destNode.getAnnotation() != REACHABLE) {
        destNode.setAnnotation(REACHABLE);
        return true;
      }
    }
    return false;
  }

  public static final Annotation REACHABLE = new Annotation() {};

  /**
   * Represents a Source Node and an Edge.
   */
  public static final class EdgeTuple {
    public final N sourceNode;
    public final E edge;
    public EdgeTuple(N sourceNode, E edge, N destNode) {
      this.sourceNode = sourceNode;
      this.edge = edge;
    }
  }
}