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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 2011 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.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;

/**
 * {@link CheckDebuggerStatement} checks for the presence of the "debugger" statement in JavaScript
 * code. It is appropriate to use this statement while developing JavaScript; however, it is
 * generally undesirable to include it in production code.
 */
class CheckDebuggerStatement extends AbstractPostOrderCallback implements CompilerPass {

  static final DiagnosticType DEBUGGER_STATEMENT_PRESENT =
      DiagnosticType.disabled(
          "JSC_DEBUGGER_STATEMENT_PRESENT",
          "Using the debugger statement can halt your application if the user has a JavaScript"
              + " debugger running.\n"
              + "To disable this check when you want to do debugging, you can suppress this message"
              + " like this:\n"
              // NOTE: Single quotes around curly braces are necessary to prevent them being
              // interpreted as a placeholder for replacement. See MessageFormat javadoc.
              + "  /** @suppress '{'checkDebuggerStatement'}' */\n"
              + "  debugger;");

  private final AbstractCompiler compiler;

  public CheckDebuggerStatement(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (n.isDebugger()) {
      t.report(n, DEBUGGER_STATEMENT_PRESENT);
    }
  }
}