Change sourceRoot resolution to match the spec

The source-map library has long implemented sourceRoot resolution using
URL resolution.  However, the source map specification is reasonably
clear that concatenation is to be used instead.

There is more information in these bugs:
    mozilla#62
    https://bugzilla.mozilla.org/show_bug.cgi?id=977463

This patch changes the resolution to match what Chrome does.  This is an
incompatible change; but, I believe, better for interoperability.

This patch also adds an optional sourceMapURL parameter to the
SourceMapConsumer constructor.  This allows us to implement the full
source URL resolution algorithm in the source-map library.

Fixes mozilla#62

Author: tromey

dist/source-map.debug.js

@@ -1154,6 +1154,59 @@ return /******/ (function(modules) { // webpackBootstrap
 	}
 	exports.parseSourceMapInput = parseSourceMapInput;
 
+	/**
+	 * Compute the URL of a source given the the source root, the source's
+	 * URL, and the source map's URL.
+	 */
+	function computeSourceURL(sourceRoot, sourceURL, sourceMapURL) {
+	  sourceURL = sourceURL || '';
+
+	  if (sourceRoot) {
+	    // This follows what Chrome does.
+	    if (sourceRoot[sourceRoot.length - 1] !== '/' && sourceURL[0] !== '/') {
+	      sourceRoot += '/';
+	    }
+	    // The spec says:
+	    //   Line 4: An optional source root, useful for relocating source
+	    //   files on a server or removing repeated values in the
+	    //   “sources” entry.  This value is prepended to the individual
+	    //   entries in the “source” field.
+	    sourceURL = sourceRoot + sourceURL;
+	  }
+
+	  // Historically, SourceMapConsumer did not take the sourceMapURL as
+	  // a parameter.  This mode is still somewhat supported, which is why
+	  // this code block is conditional.  However, it's preferable to pass
+	  // the source map URL to SourceMapConsumer, so that this function
+	  // can implement the source URL resolution algorithm as outlined in
+	  // the spec.  This block is basically the equivalent of:
+	  //    new URL(sourceURL, sourceMapURL).toString()
+	  // ... except it avoids using URL, which wasn't available in the
+	  // older releases of node still supported by this library.
+	  //
+	  // The spec says:
+	  //   If the sources are not absolute URLs after prepending of the
+	  //   “sourceRoot”, the sources are resolved relative to the
+	  //   SourceMap (like resolving script src in a html document).
+	  if (sourceMapURL) {
+	    var parsed = urlParse(sourceMapURL);
+	    if (!parsed) {
+	      throw new Error("sourceMapURL could not be parsed");
+	    }
+	    if (parsed.path) {
+	      // Strip the last path component, but keep the "/".
+	      var index = parsed.path.lastIndexOf('/');
+	      if (index >= 0) {
+	        parsed.path = parsed.path.substring(0, index + 1);
+	      }
+	    }
+	    sourceURL = join(urlGenerate(parsed), sourceURL);
+	  }
+
+	  return normalize(sourceURL);
+	}
+	exports.computeSourceURL = computeSourceURL;
+
 
 /***/ }),
 /* 5 */
@@ -1384,15 +1437,15 @@ return /******/ (function(modules) { // webpackBootstrap
 	var base64VLQ = __webpack_require__(2);
 	var quickSort = __webpack_require__(9).quickSort;
 
-	function SourceMapConsumer(aSourceMap) {
+	function SourceMapConsumer(aSourceMap, aSourceMapURL) {
 	  var sourceMap = aSourceMap;
 	  if (typeof aSourceMap === 'string') {
 	    sourceMap = util.parseSourceMapInput(aSourceMap);
 	  }
 
 	  return sourceMap.sections != null
-	    ? new IndexedSourceMapConsumer(sourceMap)
-	    : new BasicSourceMapConsumer(sourceMap);
+	    ? new IndexedSourceMapConsumer(sourceMap, aSourceMapURL)
+	    : new BasicSourceMapConsumer(sourceMap, aSourceMapURL);
 	}
 
 	SourceMapConsumer.fromSourceMap = function(aSourceMap) {
@@ -1518,9 +1571,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	    var sourceRoot = this.sourceRoot;
 	    mappings.map(function (mapping) {
 	      var source = mapping.source === null ? null : this._sources.at(mapping.source);
-	      if (source != null && sourceRoot != null) {
-	        source = util.join(sourceRoot, source);
-	      }
+	      source = util.computeSourceURL(sourceRoot, source, this._sourceMapURL);
 	      return {
 	        source: source,
 	        generatedLine: mapping.generatedLine,
@@ -1634,7 +1685,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	 * query for information about the original file positions by giving it a file
 	 * position in the generated source.
 	 *
-	 * The only parameter is the raw source map (either as a JSON string, or
+	 * 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:
 	 *
@@ -1657,9 +1708,13 @@ return /******/ (function(modules) { // webpackBootstrap
 	 *       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) {
+	function BasicSourceMapConsumer(aSourceMap, aSourceMapURL) {
 	  var sourceMap = aSourceMap;
 	  if (typeof aSourceMap === 'string') {
 	    sourceMap = util.parseSourceMapInput(aSourceMap);
@@ -1711,6 +1766,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	  this.sourceRoot = sourceRoot;
 	  this.sourcesContent = sourcesContent;
 	  this._mappings = mappings;
+	  this._sourceMapURL = aSourceMapURL;
 	  this.file = file;
 	}
 
@@ -1722,10 +1778,12 @@ return /******/ (function(modules) { // webpackBootstrap
 	 *
 	 * @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) {
+	  function SourceMapConsumer_fromSourceMap(aSourceMap, aSourceMapURL) {
 	    var smc = Object.create(BasicSourceMapConsumer.prototype);
 
 	    var names = smc._names = ArraySet.fromArray(aSourceMap._names.toArray(), true);
@@ -1734,6 +1792,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	    smc.sourcesContent = aSourceMap._generateSourcesContent(smc._sources.toArray(),
 	                                                            smc.sourceRoot);
 	    smc.file = aSourceMap._file;
+	    smc._sourceMapURL = 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
@@ -1781,7 +1840,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	Object.defineProperty(BasicSourceMapConsumer.prototype, 'sources', {
 	  get: function () {
 	    return this._sources.toArray().map(function (s) {
-	      return this.sourceRoot != null ? util.join(this.sourceRoot, s) : s;
+	      return util.computeSourceURL(this.sourceRoot, s, this._sourceMapURL);
 	    }, this);
 	  }
 	});
@@ -2005,9 +2064,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	        var source = util.getArg(mapping, 'source', null);
 	        if (source !== null) {
 	          source = this._sources.at(source);
-	          if (this.sourceRoot != null) {
-	            source = util.join(this.sourceRoot, source);
-	          }
+	          source = util.computeSourceURL(this.sourceRoot, source, this._sourceMapURL);
 	        }
 	        var name = util.getArg(mapping, 'name', null);
 	        if (name !== null) {
@@ -2054,12 +2111,23 @@ return /******/ (function(modules) { // webpackBootstrap
 	      return null;
 	    }
 
+	    var relativeSource = aSource;
 	    if (this.sourceRoot != null) {
-	      aSource = util.relative(this.sourceRoot, aSource);
+	      relativeSource = util.relative(this.sourceRoot, relativeSource);
+	    }
+
+	    if (this._sources.has(relativeSource)) {
+	      return this.sourcesContent[this._sources.indexOf(relativeSource)];
 	    }
 
-	    if (this._sources.has(aSource)) {
-	      return this.sourcesContent[this._sources.indexOf(aSource)];
+	    // Maybe aSource is an absolute URL as returned by |sources|.  In
+	    // this case we can't simply undo the transform.
+	    var sourceArray = this.sources;
+	    var i;
+	    for (i = 0; i < sourceArray.length; ++i) {
+	      if (sourceArray[i] == aSource) {
+	        return this.sourcesContent[i];
+	      }
 	    }
 
 	    var url;
@@ -2069,15 +2137,15 @@ return /******/ (function(modules) { // webpackBootstrap
 	      // 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 = aSource.replace(/^file:\/\//, "");
+	      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("/" + aSource)) {
-	        return this.sourcesContent[this._sources.indexOf("/" + aSource)];
+	          && this._sources.has("/" + relativeSource)) {
+	        return this.sourcesContent[this._sources.indexOf("/" + relativeSource)];
 	      }
 	    }
 
@@ -2089,7 +2157,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	      return null;
 	    }
 	    else {
-	      throw new Error('"' + aSource + '" is not in the SourceMap.');
+	      throw new Error('"' + relativeSource + '" is not in the SourceMap.');
 	    }
 	  };
 
@@ -2173,7 +2241,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	 * that it takes "indexed" source maps (i.e. ones with a "sections" field) as
 	 * input.
 	 *
-	 * The only parameter is a raw source map (either as a JSON string, or already
+	 * 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:
 	 *
@@ -2210,9 +2278,13 @@ return /******/ (function(modules) { // webpackBootstrap
 	 *    }],
 	 *  }
 	 *
+	 * 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) {
+	function IndexedSourceMapConsumer(aSourceMap, aSourceMapURL) {
 	  var sourceMap = aSourceMap;
 	  if (typeof aSourceMap === 'string') {
 	    sourceMap = util.parseSourceMapInput(aSourceMap);
@@ -2255,7 +2327,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	        generatedLine: offsetLine + 1,
 	        generatedColumn: offsetColumn + 1
 	      },
-	      consumer: new SourceMapConsumer(util.getArg(s, 'map'))
+	      consumer: new SourceMapConsumer(util.getArg(s, 'map'), aSourceMapURL)
 	    }
 	  });
 	}
@@ -2441,9 +2513,7 @@ return /******/ (function(modules) { // webpackBootstrap
 	        var mapping = sectionMappings[j];
 
 	        var source = section.consumer._sources.at(mapping.source);
-	        if (section.consumer.sourceRoot !== null) {
-	          source = util.join(section.consumer.sourceRoot, source);
-	        }
+	        source = util.computeSourceURL(section.consumer.sourceRoot, source, this._sourceMapURL);
 	        this._sources.add(source);
 	        source = this._sources.indexOf(source);