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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 2010 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.collect.ImmutableSet;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.regex.RegExpTree;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

/**
 * Look for references to the global RegExp object that would cause
 * regular expressions to be unoptimizable, and checks that regular expressions
 * are syntactically valid.
 */
class CheckRegExp extends AbstractPostOrderCallback implements CompilerPass {

  static final DiagnosticType REGEXP_REFERENCE =
    DiagnosticType.warning("JSC_REGEXP_REFERENCE",
        "References to the global RegExp object prevents " +
        "optimization of regular expressions.");
  static final DiagnosticType MALFORMED_REGEXP = DiagnosticType.warning(
        "JSC_MALFORMED_REGEXP",
        "Malformed Regular Expression: {0}");

  private static final ImmutableSet REGEXP_PROPERTY_SKIPLIST =
      ImmutableSet.of(
          "$1",
          "$2",
          "$3",
          "$4",
          "$5",
          "$6",
          "$7",
          "$8",
          "$9",
          "$_",
          "$input",
          // The following would also be skiplisted, but they aren't valid
          // identifiers, so can't be accessed with the '.' operator anyway.
          // "$*", "$&", "$+", "$`", "$'",
          "input",
          "lastMatch",
          "lastParen",
          "leftContext",
          "rightContext",
          "global",
          "ignoreCase",
          "lastIndex",
          "multiline",
          "source");

  private final AbstractCompiler compiler;
  private final boolean reportErrors;
  private boolean globalRegExpPropertiesUsed = false;

  public boolean isGlobalRegExpPropertiesUsed() {
    return globalRegExpPropertiesUsed;
  }

  public CheckRegExp(AbstractCompiler compiler, boolean reportErrors) {
    this.compiler = compiler;
    this.reportErrors = reportErrors;
  }

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

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (NodeUtil.isReferenceName(n)) {
      String name = n.getString();
      if (name.equals("RegExp") && t.getScope().getVar(name) == null) {
        Token parentType = parent.getToken();
        boolean first = (n == parent.getFirstChild());
        if (!((parentType == Token.NEW && first)
            || (parentType == Token.CALL && first)
            || (parentType == Token.INSTANCEOF && !first)
            || parentType == Token.EQ
            || parentType == Token.NE
            || parentType == Token.SHEQ
            || parentType == Token.SHNE
            || parentType == Token.CASE
            || (parentType == Token.GETPROP
                && first
                && !REGEXP_PROPERTY_SKIPLIST.contains(parent.getString())))) {
          if (reportErrors) {
            t.report(n, REGEXP_REFERENCE);
          }
          globalRegExpPropertiesUsed = true;
        }
      }

      // Check the syntax of regular expression patterns.
    } else if (reportErrors && n.isRegExp()) {
      String pattern = n.getFirstChild().getString();
      String flags = n.hasTwoChildren() ? n.getLastChild().getString() : "";
      try {
        RegExpTree.parseRegExp(pattern, flags);
      } catch (IllegalArgumentException | IndexOutOfBoundsException ex) {
        t.report(n, MALFORMED_REGEXP, ex.getMessage());
      }
    }
  }
}