source-map-consumer.js

/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * Copyright 2011 Mozilla Foundation and contributors
 * Licensed under the New BSD license. See LICENSE or:
 * http://opensource.org/licenses/BSD-3-Clause
 */

var util = require('./util');
var binarySearch = require('./binary-search');
var ArraySet = require('./array-set').ArraySet;
var base64VLQ = require('./base64-vlq');
var quickSort = require('./quick-sort').quickSort;

function SourceMapConsumer(aSourceMap, aSourceMapURL) {
  var sourceMap = aSourceMap;
  if (typeof aSourceMap === 'string') {
    sourceMap = util.parseSourceMapInput(aSourceMap);
  }

  return sourceMap.sections != null
    ? new IndexedSourceMapConsumer(sourceMap, aSourceMapURL)
    : new BasicSourceMapConsumer(sourceMap, aSourceMapURL);
}

SourceMapConsumer.fromSourceMap = function(aSourceMap, aSourceMapURL) {
  return BasicSourceMapConsumer.fromSourceMap(aSourceMap, aSourceMapURL);
}

/**
 * The version of the source mapping spec that we are consuming.
 */
SourceMapConsumer.prototype._version = 3;

// `__generatedMappings` and `__originalMappings` are arrays that hold the
// parsed mapping coordinates from the source map's "mappings" attribute. They
// are lazily instantiated, accessed via the `_generatedMappings` and
// `_originalMappings` getters respectively, and we only parse the mappings
// and create these arrays once queried for a source location. We jump through
// these hoops because there can be many thousands of mappings, and parsing
// them is expensive, so we only want to do it if we must.
//
// Each object in the arrays is of the form:
//
//     {
//       generatedLine: The line number in the generated code,
//       generatedColumn: The column number in the generated code,
//       source: The path to the original source file that generated this
//               chunk of code,
//       originalLine: The line number in the original source that
//                     corresponds to this chunk of generated code,
//       originalColumn: The column number in the original source that
//                       corresponds to this chunk of generated code,
//       name: The name of the original symbol which generated this chunk of
//             code.
//     }
//
// All properties except for `generatedLine` and `generatedColumn` can be
// `null`.
//
// `_generatedMappings` is ordered by the generated positions.
//
// `_originalMappings` is ordered by the original positions.

SourceMapConsumer.prototype.__generatedMappings = null;
Object.defineProperty(SourceMapConsumer.prototype, '_generatedMappings', {
  configurable: true,
  enumerable: true,
  get: function () {
    if (!this.__generatedMappings) {
      this._parseMappings(this._mappings, this.sourceRoot);
    }

    return this.__generatedMappings;
  }
});

SourceMapConsumer.prototype.__originalMappings = null;
Object.defineProperty(SourceMapConsumer.prototype, '_originalMappings', {
  configurable: true,
  enumerable: true,
  get: function () {
    if (!this.__originalMappings) {
      this._parseMappings(this._mappings, this.sourceRoot);
    }

    return this.__originalMappings;
  }
});

SourceMapConsumer.prototype._charIsMappingSeparator =
  function SourceMapConsumer_charIsMappingSeparator(aStr, index) {
    var c = aStr.charAt(index);
    return c === ";" || c === ",";
  };

/**
 * Parse the mappings in a string in to a data structure which we can easily
 * query (the ordered arrays in the `this.__generatedMappings` and
 * `this.__originalMappings` properties).
 */
SourceMapConsumer.prototype._parseMappings =
  function SourceMapConsumer_parseMappings(aStr, aSourceRoot) {
    throw new Error("Subclasses must implement _parseMappings");
  };

SourceMapConsumer.GENERATED_ORDER = 1;
SourceMapConsumer.ORIGINAL_ORDER = 2;

SourceMapConsumer.GREATEST_LOWER_BOUND = 1;
SourceMapConsumer.LEAST_UPPER_BOUND = 2;

/**
 * Iterate over each mapping between an original source/line/column and a
 * generated line/column in this source map.
 *
 * @param Function aCallback
 *        The function that is called with each mapping.
 * @param Object aContext
 *        Optional. If specified, this object will be the value of `this` every
 *        time that `aCallback` is called.
 * @param aOrder
 *        Either `SourceMapConsumer.GENERATED_ORDER` or
 *        `SourceMapConsumer.ORIGINAL_ORDER`. Specifies whether you want to
 *        iterate over the mappings sorted by the generated file's line/column
 *        order or the original's source/line/column order, respectively. Defaults to
 *        `SourceMapConsumer.GENERATED_ORDER`.
 */
SourceMapConsumer.prototype.eachMapping =
  function SourceMapConsumer_eachMapping(aCallback, aContext, aOrder) {
    var context = aContext || null;
    var order = aOrder || SourceMapConsumer.GENERATED_ORDER;

    var mappings;
    switch (order) {
    case SourceMapConsumer.GENERATED_ORDER:
      mappings = this._generatedMappings;
      break;
    case SourceMapConsumer.ORIGINAL_ORDER:
      mappings = this._originalMappings;
      break;
    default:
      throw new Error("Unknown order of iteration.");
    }

    var sourceRoot = this.sourceRoot;
    var boundCallback = aCallback.bind(context);
    var names = this._names;
    var sources = this._sources;
    var sourceMapURL = this._sourceMapURL;

    for (var i = 0, n = mappings.length; i < n; i++) {
      var mapping = mappings[i];
      var source = mapping.source === null ? null : sources.at(mapping.source);
      if(source !== null) {
        source = util.computeSourceURL(sourceRoot, source, sourceMapURL);
      }
      boundCallback({
        source: source,
        generatedLine: mapping.generatedLine,
        generatedColumn: mapping.generatedColumn,
        originalLine: mapping.originalLine,
        originalColumn: mapping.originalColumn,
        name: mapping.name === null ? null : names.at(mapping.name)
      });
    }
  };

/**
 * Returns all generated line and column information for the original source,
 * line, and column provided. If no column is provided, returns all mappings
 * corresponding to a either the line we are searching for or the next
 * closest line that has any mappings. Otherwise, returns all mappings
 * corresponding to the given line and either the column we are searching for
 * or the next closest column that has any offsets.
 *
 * The only argument is an object with the following properties:
 *
 *   - source: The filename of the original source.
 *   - line: The line number in the original source.  The line number is 1-based.
 *   - column: Optional. the column number in the original source.
 *    The column number is 0-based.
 *
 * and an array of objects is returned, each with the following properties:
 *
 *   - line: The line number in the generated source, or null.  The
 *    line number is 1-based.
 *   - column: The column number in the generated source, or null.
 *    The column number is 0-based.
 */
SourceMapConsumer.prototype.allGeneratedPositionsFor =
  function SourceMapConsumer_allGeneratedPositionsFor(aArgs) {
    var line = util.getArg(aArgs, 'line');

    // When there is no exact match, BasicSourceMapConsumer.prototype._findMapping
    // returns the index of the closest mapping less than the needle. By
    // setting needle.originalColumn to 0, we thus find the last mapping for
    // the given line, provided such a mapping exists.
    var needle = {
      source: util.getArg(aArgs, 'source'),
      originalLine: line,
      originalColumn: util.getArg(aArgs, 'column', 0)
    };

    needle.source = this._findSourceIndex(needle.source);
    if (needle.source < 0) {
      return [];
    }

    var mappings = [];

    var index = this._findMapping(needle,
                                  this._originalMappings,
                                  "originalLine",
                                  "originalColumn",
                                  util.compareByOriginalPositions,
                                  binarySearch.LEAST_UPPER_BOUND);
    if (index >= 0) {
      var mapping = this._originalMappings[index];

      if (aArgs.column === undefined) {
        var originalLine = mapping.originalLine;

        // Iterate until either we run out of mappings, or we run into
        // a mapping for a different line than the one we found. Since
        // mappings are sorted, this is guaranteed to find all mappings for
        // the line we found.
        while (mapping && mapping.originalLine === originalLine) {
          mappings.push({
            line: util.getArg(mapping, 'generatedLine', null),
            column: util.getArg(mapping, 'generatedColumn', null),
            lastColumn: util.getArg(mapping, 'lastGeneratedColumn', null)
          });

          mapping = this._originalMappings[++index];
        }
      } else {
        var originalColumn = mapping.originalColumn;

        // Iterate until either we run out of mappings, or we run into
        // a mapping for a different line than the one we were searching for.
        // Since mappings are sorted, this is guaranteed to find all mappings for
        // the line we are searching for.
        while (mapping &&
               mapping.originalLine === line &&
               mapping.originalColumn == originalColumn) {
          mappings.push({
            line: util.getArg(mapping, 'generatedLine', null),
            column: util.getArg(mapping, 'generatedColumn', null),
            lastColumn: util.getArg(mapping, 'lastGeneratedColumn', null)
          });

          mapping = this._originalMappings[++index];
        }
      }
    }

    return mappings;
  };

exports.SourceMapConsumer = SourceMapConsumer;

/**
 * A BasicSourceMapConsumer instance represents a parsed source map which we can
 * query for information about the original file positions by giving it a file
 * position in the generated source.
 *
 * The first parameter is the raw source map (either as a JSON string, or
 * already parsed to an object). According to the spec, source maps have the
 * following attributes:
 *
 *   - version: Which version of the source map spec this map is following.
 *   - sources: An array of URLs to the original source files.
 *   - names: An array of identifiers which can be referrenced by individual mappings.
 *   - sourceRoot: Optional. The URL root from which all sources are relative.
 *   - sourcesContent: Optional. An array of contents of the original source files.
 *   - mappings: A string of base64 VLQs which contain the actual mappings.
 *   - file: Optional. The generated file this source map is associated with.
 *
 * Here is an example source map, taken from the source map spec[0]:
 *
 *     {
 *       version : 3,
 *       file: "out.js",
 *       sourceRoot : "",
 *       sources: ["foo.js", "bar.js"],
 *       names: ["src", "maps", "are", "fun"],
 *       mappings: "AA,AB;;ABCDE;"
 *     }
 *
 * The second parameter, if given, is a string whose value is the URL
 * at which the source map was found.  This URL is used to compute the
 * sources array.
 *
 * [0]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit?pli=1#
 */
function BasicSourceMapConsumer(aSourceMap, aSourceMapURL) {
  var sourceMap = aSourceMap;
  if (typeof aSourceMap === 'string') {
    sourceMap = util.parseSourceMapInput(aSourceMap);
  }

  var version = util.getArg(sourceMap, 'version');
  var sources = util.getArg(sourceMap, 'sources');
  // Sass 3.3 leaves out the 'names' array, so we deviate from the spec (which
  // requires the array) to play nice here.
  var names = util.getArg(sourceMap, 'names', []);
  var sourceRoot = util.getArg(sourceMap, 'sourceRoot', null);
  var sourcesContent = util.getArg(sourceMap, 'sourcesContent', null);
  var mappings = util.getArg(sourceMap, 'mappings');
  var file = util.getArg(sourceMap, 'file', null);

  // Once again, Sass deviates from the spec and supplies the version as a
  // string rather than a number, so we use loose equality checking here.
  if (version != this._version) {
    throw new Error('Unsupported version: ' + version);
  }

  if (sourceRoot) {
    sourceRoot = util.normalize(sourceRoot);
  }

  sources = sources
    .map(String)
    // Some source maps produce relative source paths like "./foo.js" instead of
    // "foo.js".  Normalize these first so that future comparisons will succeed.
    // See bugzil.la/1090768.
    .map(util.normalize)
    // Always ensure that absolute sources are internally stored relative to
    // the source root, if the source root is absolute. Not doing this would
    // be particularly problematic when the source root is a prefix of the
    // source (valid, but why??). See github issue #199 and bugzil.la/1188982.
    .map(function (source) {
      return sourceRoot && util.isAbsolute(sourceRoot) && util.isAbsolute(source)
        ? util.relative(sourceRoot, source)
        : source;
    });

  // Pass `true` below to allow duplicate names and sources. While source maps
  // are intended to be compressed and deduplicated, the TypeScript compiler
  // sometimes generates source maps with duplicates in them. See Github issue
  // #72 and bugzil.la/889492.
  this._names = ArraySet.fromArray(names.map(String), true);
  this._sources = ArraySet.fromArray(sources, true);

  this._absoluteSources = this._sources.toArray().map(function (s) {
    return util.computeSourceURL(sourceRoot, s, aSourceMapURL);
  });

  this.sourceRoot = sourceRoot;
  this.sourcesContent = sourcesContent;
  this._mappings = mappings;
  this._sourceMapURL = aSourceMapURL;
  this.file = file;
}

BasicSourceMapConsumer.prototype = Object.create(SourceMapConsumer.prototype);
BasicSourceMapConsumer.prototype.consumer = SourceMapConsumer;

/**
 * Utility function to find the index of a source.  Returns -1 if not
 * found.
 */
BasicSourceMapConsumer.prototype._findSourceIndex = function(aSource) {
  var relativeSource = aSource;
  if (this.sourceRoot != null) {
    relativeSource = util.relative(this.sourceRoot, relativeSource);
  }

  if (this._sources.has(relativeSource)) {
    return this._sources.indexOf(relativeSource);
  }

  // Maybe aSource is an absolute URL as returned by |sources|.  In
  // this case we can't simply undo the transform.
  var i;
  for (i = 0; i < this._absoluteSources.length; ++i) {
    if (this._absoluteSources[i] == aSource) {
      return i;
    }
  }

  return -1;
};

/**
 * Create a BasicSourceMapConsumer from a SourceMapGenerator.
 *
 * @param SourceMapGenerator aSourceMap
 *        The source map that will be consumed.
 * @param String aSourceMapURL
 *        The URL at which the source map can be found (optional)
 * @returns BasicSourceMapConsumer
 */
BasicSourceMapConsumer.fromSourceMap =
  function SourceMapConsumer_fromSourceMap(aSourceMap, aSourceMapURL) {
    var smc = Object.create(BasicSourceMapConsumer.prototype);

    var names = smc._names = ArraySet.fromArray(aSourceMap._names.toArray(), true);
    var sources = smc._sources = ArraySet.fromArray(aSourceMap._sources.toArray(), true);
    smc.sourceRoot = aSourceMap._sourceRoot;
    smc.sourcesContent = aSourceMap._generateSourcesContent(smc._sources.toArray(),
                                                            smc.sourceRoot);
    smc.file = aSourceMap._file;
    smc._sourceMapURL = aSourceMapURL;
    smc._absoluteSources = smc._sources.toArray().map(function (s) {
      return util.computeSourceURL(smc.sourceRoot, s, aSourceMapURL);
    });

    // Because we are modifying the entries (by converting string sources and
    // names to indices into the sources and names ArraySets), we have to make
    // a copy of the entry or else bad things happen. Shared mutable state
    // strikes again! See github issue #191.

    var generatedMappings = aSourceMap._mappings.toArray().slice();
    var destGeneratedMappings = smc.__generatedMappings = [];
    var destOriginalMappings = smc.__originalMappings = [];

    for (var i = 0, length = generatedMappings.length; i < length; i++) {
      var srcMapping = generatedMappings[i];
      var destMapping = new Mapping;
      destMapping.generatedLine = srcMapping.generatedLine;
      destMapping.generatedColumn = srcMapping.generatedColumn;

      if (srcMapping.source) {
        destMapping.source = sources.indexOf(srcMapping.source);
        destMapping.originalLine = srcMapping.originalLine;
        destMapping.originalColumn = srcMapping.originalColumn;

        if (srcMapping.name) {
          destMapping.name = names.indexOf(srcMapping.name);
        }

        destOriginalMappings.push(destMapping);
      }

      destGeneratedMappings.push(destMapping);
    }

    quickSort(smc.__originalMappings, util.compareByOriginalPositions);

    return smc;
  };

/**
 * The version of the source mapping spec that we are consuming.
 */
BasicSourceMapConsumer.prototype._version = 3;

/**
 * The list of original sources.
 */
Object.defineProperty(BasicSourceMapConsumer.prototype, 'sources', {
  get: function () {
    return this._absoluteSources.slice();
  }
});

/**
 * Provide the JIT with a nice shape / hidden class.
 */
function Mapping() {
  this.generatedLine = 0;
  this.generatedColumn = 0;
  this.source = null;
  this.originalLine = null;
  this.originalColumn = null;
  this.name = null;
}

/**
 * Parse the mappings in a string in to a data structure which we can easily
 * query (the ordered arrays in the `this.__generatedMappings` and
 * `this.__originalMappings` properties).
 */

const compareGenerated = util.compareByGeneratedPositionsDeflatedNoLine;
function sortGenerated(array, start) {
  let l = array.length;
  let n = array.length - start;
  if (n <= 1) {
    return;
  } else if (n == 2) {
    let a = array[start];
    let b = array[start + 1];
    if (compareGenerated(a, b) > 0) {
      array[start] = b;
      array[start + 1] = a;
    }
  } else if (n < 20) {
    for (let i = start; i < l; i++) {
      for (let j = i; j > start; j--) {
        let a = array[j - 1];
        let b = array[j];
        if (compareGenerated(a, b) <= 0) {
          break;
        }
        array[j - 1] = b;
        array[j] = a;
      }
    }
  } else {
    quickSort(array, compareGenerated, start);
  }
}
BasicSourceMapConsumer.prototype._parseMappings =
  function SourceMapConsumer_parseMappings(aStr, aSourceRoot) {
    var generatedLine = 1;
    var previousGeneratedColumn = 0;
    var previousOriginalLine = 0;
    var previousOriginalColumn = 0;
    var previousSource = 0;
    var previousName = 0;
    var length = aStr.length;
    var index = 0;
    var cachedSegments = {};
    var temp = {};
    var originalMappings = [];
    var generatedMappings = [];
    var mapping, str, segment, end, value;

    let subarrayStart = 0;
    while (index < length) {
      if (aStr.charAt(index) === ';') {
        generatedLine++;
        index++;
        previousGeneratedColumn = 0;

        sortGenerated(generatedMappings, subarrayStart);
        subarrayStart = generatedMappings.length;
      }
      else if (aStr.charAt(index) === ',') {
        index++;
      }
      else {
        mapping = new Mapping();
        mapping.generatedLine = generatedLine;

        for (end = index; end < length; end++) {
          if (this._charIsMappingSeparator(aStr, end)) {
            break;
          }
        }
        str = aStr.slice(index, end);

        segment = [];
        while (index < end) {
          base64VLQ.decode(aStr, index, temp);
          value = temp.value;
          index = temp.rest;
          segment.push(value);
        }

        if (segment.length === 2) {
          throw new Error('Found a source, but no line and column');
        }

        if (segment.length === 3) {
          throw new Error('Found a source and line, but no column');
        }

        // Generated column.
        mapping.generatedColumn = previousGeneratedColumn + segment[0];
        previousGeneratedColumn = mapping.generatedColumn;

        if (segment.length > 1) {
          // Original source.
          mapping.source = previousSource + segment[1];
          previousSource += segment[1];

          // Original line.
          mapping.originalLine = previousOriginalLine + segment[2];
          previousOriginalLine = mapping.originalLine;
          // Lines are stored 0-based
          mapping.originalLine += 1;

          // Original column.
          mapping.originalColumn = previousOriginalColumn + segment[3];
          previousOriginalColumn = mapping.originalColumn;

          if (segment.length > 4) {
            // Original name.
            mapping.name = previousName + segment[4];
            previousName += segment[4];
          }
        }

        generatedMappings.push(mapping);
        if (typeof mapping.originalLine === 'number') {
          let currentSource = mapping.source;
          while (originalMappings.length <= currentSource) {
            originalMappings.push(null);
          }
          if (originalMappings[currentSource] === null) {
            originalMappings[currentSource] = [];
          }
          originalMappings[currentSource].push(mapping);
        }
      }
    }

    sortGenerated(generatedMappings, subarrayStart);
    this.__generatedMappings = generatedMappings;

    for (var i = 0; i < originalMappings.length; i++) {
      if (originalMappings[i] != null) {
        quickSort(originalMappings[i], util.compareByOriginalPositionsNoSource);
      }
    }
    this.__originalMappings = [].concat(...originalMappings);
  };

/**
 * Find the mapping that best matches the hypothetical "needle" mapping that
 * we are searching for in the given "haystack" of mappings.
 */
BasicSourceMapConsumer.prototype._findMapping =
  function SourceMapConsumer_findMapping(aNeedle, aMappings, aLineName,
                                         aColumnName, aComparator, aBias) {
    // To return the position we are searching for, we must first find the
    // mapping for the given position and then return the opposite position it
    // points to. Because the mappings are sorted, we can use binary search to
    // find the best mapping.

    if (aNeedle[aLineName] <= 0) {
      throw new TypeError('Line must be greater than or equal to 1, got '
                          + aNeedle[aLineName]);
    }
    if (aNeedle[aColumnName] < 0) {
      throw new TypeError('Column must be greater than or equal to 0, got '
                          + aNeedle[aColumnName]);
    }

    return binarySearch.search(aNeedle, aMappings, aComparator, aBias);
  };

/**
 * Compute the last column for each generated mapping. The last column is
 * inclusive.
 */
BasicSourceMapConsumer.prototype.computeColumnSpans =
  function SourceMapConsumer_computeColumnSpans() {
    for (var index = 0; index < this._generatedMappings.length; ++index) {
      var mapping = this._generatedMappings[index];

      // Mappings do not contain a field for the last generated columnt. We
      // can come up with an optimistic estimate, however, by assuming that
      // mappings are contiguous (i.e. given two consecutive mappings, the
      // first mapping ends where the second one starts).
      if (index + 1 < this._generatedMappings.length) {
        var nextMapping = this._generatedMappings[index + 1];

        if (mapping.generatedLine === nextMapping.generatedLine) {
          mapping.lastGeneratedColumn = nextMapping.generatedColumn - 1;
          continue;
        }
      }

      // The last mapping for each line spans the entire line.
      mapping.lastGeneratedColumn = Infinity;
    }
  };

/**
 * Returns the original source, line, and column information for the generated
 * source's line and column positions provided. The only argument is an object
 * with the following properties:
 *
 *   - line: The line number in the generated source.  The line number
 *     is 1-based.
 *   - column: The column number in the generated source.  The column
 *     number is 0-based.
 *   - bias: Either 'SourceMapConsumer.GREATEST_LOWER_BOUND' or
 *     'SourceMapConsumer.LEAST_UPPER_BOUND'. Specifies whether to return the
 *     closest element that is smaller than or greater than the one we are
 *     searching for, respectively, if the exact element cannot be found.
 *     Defaults to 'SourceMapConsumer.GREATEST_LOWER_BOUND'.
 *
 * and an object is returned with the following properties:
 *
 *   - source: The original source file, or null.
 *   - line: The line number in the original source, or null.  The
 *     line number is 1-based.
 *   - column: The column number in the original source, or null.  The
 *     column number is 0-based.
 *   - name: The original identifier, or null.
 */
BasicSourceMapConsumer.prototype.originalPositionFor =
  function SourceMapConsumer_originalPositionFor(aArgs) {
    var needle = {
      generatedLine: util.getArg(aArgs, 'line'),
      generatedColumn: util.getArg(aArgs, 'column')
    };

    var index = this._findMapping(
      needle,
      this._generatedMappings,
      "generatedLine",
      "generatedColumn",
      util.compareByGeneratedPositionsDeflated,
      util.getArg(aArgs, 'bias', SourceMapConsumer.GREATEST_LOWER_BOUND)
    );

    if (index >= 0) {
      var mapping = this._generatedMappings[index];

      if (mapping.generatedLine === needle.generatedLine) {
        var source = util.getArg(mapping, 'source', null);
        if (source !== null) {
          source = this._sources.at(source);
          source = util.computeSourceURL(this.sourceRoot, source, this._sourceMapURL);
        }
        var name = util.getArg(mapping, 'name', null);
        if (name !== null) {
          name = this._names.at(name);
        }
        return {
          source: source,
          line: util.getArg(mapping, 'originalLine', null),
          column: util.getArg(mapping, 'originalColumn', null),
          name: name
        };
      }
    }

    return {
      source: null,
      line: null,
      column: null,
      name: null
    };
  };

/**
 * Return true if we have the source content for every source in the source
 * map, false otherwise.
 */
BasicSourceMapConsumer.prototype.hasContentsOfAllSources =
  function BasicSourceMapConsumer_hasContentsOfAllSources() {
    if (!this.sourcesContent) {
      return false;
    }
    return this.sourcesContent.length >= this._sources.size() &&
      !this.sourcesContent.some(function (sc) { return sc == null; });
  };

/**
 * Returns the original source content. The only argument is the url of the
 * original source file. Returns null if no original source content is
 * available.
 */
BasicSourceMapConsumer.prototype.sourceContentFor =
  function SourceMapConsumer_sourceContentFor(aSource, nullOnMissing) {
    if (!this.sourcesContent) {
      return null;
    }

    var index = this._findSourceIndex(aSource);
    if (index >= 0) {
      return this.sourcesContent[index];
    }

    var relativeSource = aSource;
    if (this.sourceRoot != null) {
      relativeSource = util.relative(this.sourceRoot, relativeSource);
    }

    var url;
    if (this.sourceRoot != null
        && (url = util.urlParse(this.sourceRoot))) {
      // XXX: file:// URIs and absolute paths lead to unexpected behavior for
      // many users. We can help them out when they expect file:// URIs to
      // behave like it would if they were running a local HTTP server. See
      // https://bugzilla.mozilla.org/show_bug.cgi?id=885597.
      var fileUriAbsPath = relativeSource.replace(/^file:\/\//, "");
      if (url.scheme == "file"
          && this._sources.has(fileUriAbsPath)) {
        return this.sourcesContent[this._sources.indexOf(fileUriAbsPath)]
      }

      if ((!url.path || url.path == "/")
          && this._sources.has("/" + relativeSource)) {
        return this.sourcesContent[this._sources.indexOf("/" + relativeSource)];
      }
    }

    // This function is used recursively from
    // IndexedSourceMapConsumer.prototype.sourceContentFor. In that case, we
    // don't want to throw if we can't find the source - we just want to
    // return null, so we provide a flag to exit gracefully.
    if (nullOnMissing) {
      return null;
    }
    else {
      throw new Error('"' + relativeSource + '" is not in the SourceMap.');
    }
  };

/**
 * Returns the generated line and column information for the original source,
 * line, and column positions provided. The only argument is an object with
 * the following properties:
 *
 *   - source: The filename of the original source.
 *   - line: The line number in the original source.  The line number
 *     is 1-based.
 *   - column: The column number in the original source.  The column
 *     number is 0-based.
 *   - bias: Either 'SourceMapConsumer.GREATEST_LOWER_BOUND' or
 *     'SourceMapConsumer.LEAST_UPPER_BOUND'. Specifies whether to return the
 *     closest element that is smaller than or greater than the one we are
 *     searching for, respectively, if the exact element cannot be found.
 *     Defaults to 'SourceMapConsumer.GREATEST_LOWER_BOUND'.
 *
 * and an object is returned with the following properties:
 *
 *   - line: The line number in the generated source, or null.  The
 *     line number is 1-based.
 *   - column: The column number in the generated source, or null.
 *     The column number is 0-based.
 */
BasicSourceMapConsumer.prototype.generatedPositionFor =
  function SourceMapConsumer_generatedPositionFor(aArgs) {
    var source = util.getArg(aArgs, 'source');
    source = this._findSourceIndex(source);
    if (source < 0) {
      return {
        line: null,
        column: null,
        lastColumn: null
      };
    }

    var needle = {
      source: source,
      originalLine: util.getArg(aArgs, 'line'),
      originalColumn: util.getArg(aArgs, 'column')
    };

    var index = this._findMapping(
      needle,
      this._originalMappings,
      "originalLine",
      "originalColumn",
      util.compareByOriginalPositions,
      util.getArg(aArgs, 'bias', SourceMapConsumer.GREATEST_LOWER_BOUND)
    );

    if (index >= 0) {
      var mapping = this._originalMappings[index];

      if (mapping.source === needle.source) {
        return {
          line: util.getArg(mapping, 'generatedLine', null),
          column: util.getArg(mapping, 'generatedColumn', null),
          lastColumn: util.getArg(mapping, 'lastGeneratedColumn', null)
        };
      }
    }

    return {
      line: null,
      column: null,
      lastColumn: null
    };
  };

exports.BasicSourceMapConsumer = BasicSourceMapConsumer;

/**
 * An IndexedSourceMapConsumer instance represents a parsed source map which
 * we can query for information. It differs from BasicSourceMapConsumer in
 * that it takes "indexed" source maps (i.e. ones with a "sections" field) as
 * input.
 *
 * The first parameter is a raw source map (either as a JSON string, or already
 * parsed to an object). According to the spec for indexed source maps, they
 * have the following attributes:
 *
 *   - version: Which version of the source map spec this map is following.
 *   - file: Optional. The generated file this source map is associated with.
 *   - sections: A list of section definitions.
 *
 * Each value under the "sections" field has two fields:
 *   - offset: The offset into the original specified at which this section
 *       begins to apply, defined as an object with a "line" and "column"
 *       field.
 *   - map: A source map definition. This source map could also be indexed,
 *       but doesn't have to be.
 *
 * Instead of the "map" field, it's also possible to have a "url" field
 * specifying a URL to retrieve a source map from, but that's currently
 * unsupported.
 *
 * Here's an example source map, taken from the source map spec[0], but
 * modified to omit a section which uses the "url" field.
 *
 *  {
 *    version : 3,
 *    file: "app.js",
 *    sections: [{
 *      offset: {line:100, column:10},
 *      map: {
 *        version : 3,
 *        file: "section.js",
 *        sources: ["foo.js", "bar.js"],
 *        names: ["src", "maps", "are", "fun"],
 *        mappings: "AAAA,E;;ABCDE;"
 *      }
 *    }],
 *  }
 *
 * The second parameter, if given, is a string whose value is the URL
 * at which the source map was found.  This URL is used to compute the
 * sources array.
 *
 * [0]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit#heading=h.535es3xeprgt
 */
function IndexedSourceMapConsumer(aSourceMap, aSourceMapURL) {
  var sourceMap = aSourceMap;
  if (typeof aSourceMap === 'string') {
    sourceMap = util.parseSourceMapInput(aSourceMap);
  }

  var version = util.getArg(sourceMap, 'version');
  var sections = util.getArg(sourceMap, 'sections');

  if (version != this._version) {
    throw new Error('Unsupported version: ' + version);
  }

  this._sources = new ArraySet();
  this._names = new ArraySet();

  var lastOffset = {
    line: -1,
    column: 0
  };
  this._sections = sections.map(function (s) {
    if (s.url) {
      // The url field will require support for asynchronicity.
      // See https://github.com/mozilla/source-map/issues/16
      throw new Error('Support for url field in sections not implemented.');
    }
    var offset = util.getArg(s, 'offset');
    var offsetLine = util.getArg(offset, 'line');
    var offsetColumn = util.getArg(offset, 'column');

    if (offsetLine < lastOffset.line ||
        (offsetLine === lastOffset.line && offsetColumn < lastOffset.column)) {
      throw new Error('Section offsets must be ordered and non-overlapping.');
    }
    lastOffset = offset;

    return {
      generatedOffset: {
        // The offset fields are 0-based, but we use 1-based indices when
        // encoding/decoding from VLQ.
        generatedLine: offsetLine + 1,
        generatedColumn: offsetColumn + 1
      },
      consumer: new SourceMapConsumer(util.getArg(s, 'map'), aSourceMapURL)
    }
  });
}

IndexedSourceMapConsumer.prototype = Object.create(SourceMapConsumer.prototype);
IndexedSourceMapConsumer.prototype.constructor = SourceMapConsumer;

/**
 * The version of the source mapping spec that we are consuming.
 */
IndexedSourceMapConsumer.prototype._version = 3;

/**
 * The list of original sources.
 */
Object.defineProperty(IndexedSourceMapConsumer.prototype, 'sources', {
  get: function () {
    var sources = [];
    for (var i = 0; i < this._sections.length; i++) {
      for (var j = 0; j < this._sections[i].consumer.sources.length; j++) {
        sources.push(this._sections[i].consumer.sources[j]);
      }
    }
    return sources;
  }
});

/**
 * Returns the original source, line, and column information for the generated
 * source's line and column positions provided. The only argument is an object
 * with the following properties:
 *
 *   - line: The line number in the generated source.  The line number
 *     is 1-based.
 *   - column: The column number in the generated source.  The column
 *     number is 0-based.
 *
 * and an object is returned with the following properties:
 *
 *   - source: The original source file, or null.
 *   - line: The line number in the original source, or null.  The
 *     line number is 1-based.
 *   - column: The column number in the original source, or null.  The
 *     column number is 0-based.
 *   - name: The original identifier, or null.
 */
IndexedSourceMapConsumer.prototype.originalPositionFor =
  function IndexedSourceMapConsumer_originalPositionFor(aArgs) {
    var needle = {
      generatedLine: util.getArg(aArgs, 'line'),
      generatedColumn: util.getArg(aArgs, 'column')
    };

    // Find the section containing the generated position we're trying to map
    // to an original position.
    var sectionIndex = binarySearch.search(needle, this._sections,
      function(needle, section) {
        var cmp = needle.generatedLine - section.generatedOffset.generatedLine;
        if (cmp) {
          return cmp;
        }

        return (needle.generatedColumn -
                section.generatedOffset.generatedColumn);
      });
    var section = this._sections[sectionIndex];

    if (!section) {
      return {
        source: null,
        line: null,
        column: null,
        name: null
      };
    }

    return section.consumer.originalPositionFor({
      line: needle.generatedLine -
        (section.generatedOffset.generatedLine - 1),
      column: needle.generatedColumn -
        (section.generatedOffset.generatedLine === needle.generatedLine
         ? section.generatedOffset.generatedColumn - 1
         : 0),
      bias: aArgs.bias
    });
  };

/**
 * Return true if we have the source content for every source in the source
 * map, false otherwise.
 */
IndexedSourceMapConsumer.prototype.hasContentsOfAllSources =
  function IndexedSourceMapConsumer_hasContentsOfAllSources() {
    return this._sections.every(function (s) {
      return s.consumer.hasContentsOfAllSources();
    });
  };

/**
 * Returns the original source content. The only argument is the url of the
 * original source file. Returns null if no original source content is
 * available.
 */
IndexedSourceMapConsumer.prototype.sourceContentFor =
  function IndexedSourceMapConsumer_sourceContentFor(aSource, nullOnMissing) {
    for (var i = 0; i < this._sections.length; i++) {
      var section = this._sections[i];

      var content = section.consumer.sourceContentFor(aSource, true);
      if (content || content === '') {
        return content;
      }
    }
    if (nullOnMissing) {
      return null;
    }
    else {
      throw new Error('"' + aSource + '" is not in the SourceMap.');
    }
  };

/**
 * Returns the generated line and column information for the original source,
 * line, and column positions provided. The only argument is an object with
 * the following properties:
 *
 *   - source: The filename of the original source.
 *   - line: The line number in the original source.  The line number
 *     is 1-based.
 *   - column: The column number in the original source.  The column
 *     number is 0-based.
 *
 * and an object is returned with the following properties:
 *
 *   - line: The line number in the generated source, or null.  The
 *     line number is 1-based. 
 *   - column: The column number in the generated source, or null.
 *     The column number is 0-based.
 */
IndexedSourceMapConsumer.prototype.generatedPositionFor =
  function IndexedSourceMapConsumer_generatedPositionFor(aArgs) {
    for (var i = 0; i < this._sections.length; i++) {
      var section = this._sections[i];

      // Only consider this section if the requested source is in the list of
      // sources of the consumer.
      if (section.consumer._findSourceIndex(util.getArg(aArgs, 'source')) === -1) {
        continue;
      }
      var generatedPosition = section.consumer.generatedPositionFor(aArgs);
      if (generatedPosition) {
        var ret = {
          line: generatedPosition.line +
            (section.generatedOffset.generatedLine - 1),
          column: generatedPosition.column +
            (section.generatedOffset.generatedLine === generatedPosition.line
             ? section.generatedOffset.generatedColumn - 1
             : 0)
        };
        return ret;
      }
    }

    return {
      line: null,
      column: null
    };
  };

/**
 * Parse the mappings in a string in to a data structure which we can easily
 * query (the ordered arrays in the `this.__generatedMappings` and
 * `this.__originalMappings` properties).
 */
IndexedSourceMapConsumer.prototype._parseMappings =
  function IndexedSourceMapConsumer_parseMappings(aStr, aSourceRoot) {
    this.__generatedMappings = [];
    this.__originalMappings = [];
    for (var i = 0; i < this._sections.length; i++) {
      var section = this._sections[i];
      var sectionMappings = section.consumer._generatedMappings;
      for (var j = 0; j < sectionMappings.length; j++) {
        var mapping = sectionMappings[j];

        var source = section.consumer._sources.at(mapping.source);
        if(source !== null) {
          source = util.computeSourceURL(section.consumer.sourceRoot, source, this._sourceMapURL);
        }
        this._sources.add(source);
        source = this._sources.indexOf(source);

        var name = null;
        if (mapping.name) {
          name = section.consumer._names.at(mapping.name);
          this._names.add(name);
          name = this._names.indexOf(name);
        }

        // The mappings coming from the consumer for the section have
        // generated positions relative to the start of the section, so we
        // need to offset them to be relative to the start of the concatenated
        // generated file.
        var adjustedMapping = {
          source: source,
          generatedLine: mapping.generatedLine +
            (section.generatedOffset.generatedLine - 1),
          generatedColumn: mapping.generatedColumn +
            (section.generatedOffset.generatedLine === mapping.generatedLine
            ? section.generatedOffset.generatedColumn - 1
            : 0),
          originalLine: mapping.originalLine,
          originalColumn: mapping.originalColumn,
          name: name
        };

        this.__generatedMappings.push(adjustedMapping);
        if (typeof adjustedMapping.originalLine === 'number') {
          this.__originalMappings.push(adjustedMapping);
        }
      }
    }

    quickSort(this.__generatedMappings, util.compareByGeneratedPositionsDeflated);
    quickSort(this.__originalMappings, util.compareByOriginalPositions);
  };

exports.IndexedSourceMapConsumer = IndexedSourceMapConsumer;