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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2004 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;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.ImmutableList;

import java.io.IOException;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;

/**
 * Extracts messages and message comments from JS code.
 *
 *  Uses a special prefix (e.g. {@code MSG_}) to determine which variables
 * are messages. Here are the recognized formats:
 *
 *   
 *   var MSG_FOO = "foo";
 *   var MSG_FOO_HELP = "this message is used for foo";
 *   
 *
 *   
 *   var MSG_BAR = function(a, b) {
 *     return a + " bar " + b;
 *   }
 *   var MSG_BAR_HELP = "the bar message";
 *   
 *
 * This class enforces the policy that message variable names must be unique
 * across all JS files.
 *
 */
@GwtIncompatible("JsMessage.Builder")
public final class JsMessageExtractor {

  private final JsMessage.Style style;
  private final JsMessage.IdGenerator idGenerator;
  private final CompilerOptions options;
  private final boolean extractExternalMessages;

  public JsMessageExtractor(
      JsMessage.IdGenerator idGenerator,
      JsMessage.Style style) {
    this(idGenerator, style, new CompilerOptions(), false /* extractExternalMessages */);
  }

  public JsMessageExtractor(
      JsMessage.IdGenerator idGenerator,
      JsMessage.Style style,
      CompilerOptions options,
      boolean extractExternalMessages) {
    this.idGenerator = idGenerator;
    this.style = style;
    this.options = options;
    this.extractExternalMessages = extractExternalMessages;
  }

  /**
   * Visitor that collects messages.
   */
  private class ExtractMessagesVisitor extends JsMessageVisitor {
    // We use List here as we want to preserve insertion-order for found
    // messages.
    // Take into account that messages with the same id could be present in the
    // result list. Message could have the same id only in case if they are
    // unnamed and have the same text but located in different source files.
    private final List messages = new LinkedList<>();

    private ExtractMessagesVisitor(AbstractCompiler compiler) {
      super(compiler, true, style, idGenerator);
    }

    @Override
    protected void processJsMessage(JsMessage message,
        JsMessageDefinition definition) {
      if (extractExternalMessages || !message.isExternal()) {
        messages.add(message);
      }
    }

    /**
     * Returns extracted messages.
     *
     * @return collection of JsMessage objects that was found in js sources.
     */
    public Collection getMessages() {
      return messages;
    }
  }

  /**
   * Extracts JS messages from JavaScript code.
   */
  public Collection extractMessages(SourceFile... inputs)
      throws IOException {
    return extractMessages(ImmutableList.copyOf(inputs));
  }


  /**
   * Extracts JS messages from JavaScript code.
   *
   * @param inputs  the JavaScript source code inputs
   * @return the extracted messages collection
   * @throws RuntimeException if there are problems parsing the JS code or the
   *     JS messages, or if two messages have the same key
   */
  public  Collection extractMessages(Iterable inputs) {
    Compiler compiler = new Compiler();
    compiler.init(
        ImmutableList.of(),
        ImmutableList.copyOf(inputs),
        options);
    compiler.parseInputs();

    ExtractMessagesVisitor extractCompilerPass =
        new ExtractMessagesVisitor(compiler);
    if (compiler.getErrors().length == 0) {
      extractCompilerPass.process(null, compiler.getRoot());
    }

    JSError[] errors = compiler.getErrors();
    // Check for errors.
    if (errors.length > 0) {
      StringBuilder msg = new StringBuilder("JSCompiler errors\n");
      MessageFormatter formatter = new LightweightMessageFormatter(compiler);
      for (JSError e : errors) {
        msg.append(formatter.formatError(e));
      }
      throw new RuntimeException(msg.toString());
    }

    return extractCompilerPass.getMessages();
  }
}