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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 2019 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.diagnostic;

import com.google.common.collect.Multimap;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.TypeAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;

/** A Gson instance tailored to generating logs output. */
public final class LogsGson {

  /**
   * A conversion to a preferred logging representation.
   *
   * When an implementor is logged, the result of this method will be JSON stringified in place
   * of the implementor.
   *
   * Use this interface when the default Gson serialization for a class is bad and the class
   * should always be logged another way. Primitive wrappers and entity type are ideal candidates.
   */
  public interface Able {
    Object toLogsGson();
  }

  static String toJson(Object o) {
    return GSON.toJson(o);
  }

  private static final Gson GSON =
      new GsonBuilder()
          .registerTypeHierarchyAdapter(
              Able.class,
              new TypeAdapter() {
                @Override
                public Able read(JsonReader in) {
                  throw new AssertionError();
                }

                @Override
                public void write(JsonWriter out, Able value) throws IOException {
                  out.jsonValue(GSON.toJson(value.toLogsGson()));
                }
              })
          .registerTypeHierarchyAdapter(
              Multimap.class,
              new TypeAdapter>() {
                @Override
                public Multimap read(JsonReader in) {
                  throw new AssertionError();
                }

                @Override
                public void write(JsonWriter out, Multimap value) throws IOException {
                  out.jsonValue(GSON.toJson(value.asMap()));
                }
              })
          .create();

  private LogsGson() {
    throw new AssertionError();
  }
}