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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 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.regex.RegExpTree;
import com.google.javascript.rhino.Node;

/**
 * Simplifies regular expression patterns and flags.
 *
 * @author Mike Samuel 
 */
class PeepholeSimplifyRegExp extends AbstractPeepholeOptimization {

  @Override
  Node optimizeSubtree(Node subtree) {
    if (subtree.isRegExp()) {
      // Split regexp into pattern and flags.
      String pattern = subtree.getFirstChild().getString();
      String flags = subtree.hasTwoChildren() ? subtree.getLastChild().getString() : "";
      // Parse to an AST and optimize.
      RegExpTree regexTree;
      try {
        regexTree = RegExpTree.parseRegExp(pattern, flags);
      } catch (IllegalArgumentException ex) {
        // Warnings are propagated in the CheckRegExp pass.
        return subtree;
      }
      regexTree = regexTree.simplify(flags);
      // Decompose the AST.
      String literal = regexTree.toString();
      String newPattern = literal.substring(1, literal.length() - 1);
      // Remove unnecessary flags and order them consistently for gzip.
      String newFlags = (
          // The g flags cannot match or replace more than one instance if it is
          // anchored at the front and back as in /^foo$/ and if the anchors are
          // relative to the whole string.
          // But if the regex has capturing groups, then the match operator
          // would return capturing groups without the g flag.
          (flags.contains("g")
           && (!RegExpTree.matchesWholeInput(regexTree, flags)
               || regexTree.hasCapturingGroup())
           ? "g" : "")
          // Remove the i flag if it doesn't have any effect.
          // E.g. /[a-z0-9_]/i -> /\w/
          + (flags.contains("i") && regexTree.isCaseSensitive() ? "i" : "")
          // If the regular expression contains no anchors, then the m flag has
          // no effect.
          + (flags.contains("m") && regexTree.containsAnchor() ? "m" : ""));
      // Update the original if something was done.
      if (!(newPattern.equals(pattern) && newFlags.equals(flags))) {
        subtree.getFirstChild().setString(newPattern);
        if (!newFlags.isEmpty()) {
          subtree.getLastChild().setString(newFlags);
        } else if (subtree.hasTwoChildren()) {
          subtree.getLastChild().detach();
        }
        reportCodeChange();
      }
    }
    return subtree;
  }
}