Make the file property optional

README.md

@@ -173,7 +173,7 @@ following attributes:
 
 * `mappings`: A string of base64 VLQs which contain the actual mappings.
 
-* `file`: The generated filename this source map is associated with.
+* `file`: Optional. The generated filename this source map is associated with.
 
 #### SourceMapConsumer.prototype.originalPositionFor(generatedPosition)
 
@@ -244,14 +244,14 @@ generated line/column in this source map.
 An instance of the SourceMapGenerator represents a source map which is being
 built incrementally.
 
-#### new SourceMapGenerator(startOfSourceMap)
+#### new SourceMapGenerator([startOfSourceMap])
 
-To create a new one, you must pass an object with the following properties:
+You may pass an object with the following properties:
 
 * `file`: The filename of the generated source that this source map is
   associated with.
 
-* `sourceRoot`: An optional root for all relative URLs in this source map.
+* `sourceRoot`: A root for all relative URLs in this source map.
 
 #### SourceMapGenerator.fromSourceMap(sourceMapConsumer)
 
@@ -291,7 +291,8 @@ is the minimium of this map and the supplied map.
 * `sourceMapConsumer`: The SourceMap to be applied.
 
 * `sourceFile`: Optional. The filename of the source file.
-  If omitted, sourceMapConsumer.file will be used.
+  If omitted, sourceMapConsumer.file will be used, if it exists.
+  Otherwise an error will be thrown.
 
 #### SourceMapGenerator.prototype.toString()
 
@@ -387,7 +388,7 @@ for trimming whitespace from the end of a source node, etc.
 Return the string representation of this source node. Walks over the tree and
 concatenates all the various snippets together to one string.
 
-### SourceNode.prototype.toStringWithSourceMap(startOfSourceMap)
+### SourceNode.prototype.toStringWithSourceMap([startOfSourceMap])
 
 Returns the string representation of this tree of source nodes, plus a
 SourceMapGenerator which contains all the mappings between the generated and

lib/source-map/source-map-consumer.js

@@ -29,7 +29,7 @@ define(function (require, exports, module) {
    *   - 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: The generated file this source map is associated with.
+   *   - file: Optional. The generated file this source map is associated with.
    *
    * Here is an example source map, taken from the source map spec[0]:
    *

lib/source-map/source-map-generator.js

@@ -15,14 +15,17 @@ define(function (require, exports, module) {
 
   /**
    * An instance of the SourceMapGenerator represents a source map which is
-   * being built incrementally. To create a new one, you must pass an object
-   * with the following properties:
+   * being built incrementally. You may pass an object with the following
+   * properties:
    *
    *   - file: The filename of the generated source.
-   *   - sourceRoot: An optional root for all URLs in this source map.
+   *   - sourceRoot: A root for all relative URLs in this source map.
    */
   function SourceMapGenerator(aArgs) {
-    this._file = util.getArg(aArgs, 'file');
+    if (!aArgs) {
+      aArgs = {};
+    }
+    this._file = util.getArg(aArgs, 'file', null);
     this._sourceRoot = util.getArg(aArgs, 'sourceRoot', null);
     this._sources = new ArraySet();
     this._names = new ArraySet();
@@ -151,12 +154,19 @@ define(function (require, exports, module) {
    *
    * @param aSourceMapConsumer The source map to be applied.
    * @param aSourceFile Optional. The filename of the source file.
-   *        If omitted, SourceMapConsumer's file property will be used.
+   *        If omitted, SourceMapConsumer's file property will be used,
+   *        if it exists. Otherwise an error is thrown.
    */
   SourceMapGenerator.prototype.applySourceMap =
     function SourceMapGenerator_applySourceMap(aSourceMapConsumer, aSourceFile) {
       // If aSourceFile is omitted, we will use the file property of the SourceMap
       if (!aSourceFile) {
+        if (!aSourceMapConsumer.file) {
+          throw new Error(
+            'SourceMapGenerator.prototype.applySourceMap requires either an explicit source file, ' +
+            'or the source map\'s "file" property. Both were omitted.'
+          );
+        }
         aSourceFile = aSourceMapConsumer.file;
       }
       var sourceRoot = this._sourceRoot;

test/source-map/test-source-map-consumer.js

@@ -12,7 +12,7 @@ define(function (require, exports, module) {
   var SourceMapConsumer = require('../../lib/source-map/source-map-consumer').SourceMapConsumer;
   var SourceMapGenerator = require('../../lib/source-map/source-map-generator').SourceMapGenerator;
 
-  exports['test that we can instantiate with a string or an objects'] = function (assert, util) {
+  exports['test that we can instantiate with a string or an object'] = function (assert, util) {
     assert.doesNotThrow(function () {
       var map = new SourceMapConsumer(util.testMap);
     });

test/source-map/test-source-map-generator.js

@@ -20,6 +20,9 @@ define(function (require, exports, module) {
       sourceRoot: '.'
     });
     assert.ok(true);
+
+    var map = new SourceMapGenerator();
+    assert.ok(true);
   };
 
   exports['test JSON serialization'] = function (assert, util) {
@@ -269,6 +272,16 @@ define(function (require, exports, module) {
     util.assertEqualMaps(assert, actualMap, expectedMap);
   };
 
+  exports['test applySourceMap throws when file is missing'] = function (assert, util) {
+    var map = new SourceMapGenerator({
+      file: 'test.js'
+    });
+    var map2 = new SourceMapGenerator();
+    assert.throws(function() {
+      map.applySourceMap(new SourceMapConsumer(map2.toJSON()));
+    })
+  };
+
   exports['test sorting with duplicate generated mappings'] = function (assert, util) {
     var map = new SourceMapGenerator({
       file: 'test.js'

test/source-map/test-source-node.js

@@ -140,8 +140,13 @@ define(function (require, exports, module) {
     var map = node.toStringWithSourceMap({
       file: 'foo.js'
     }).map;
+    var mapWithoutOptions = node.toStringWithSourceMap().map;
 
     assert.ok(map instanceof SourceMapGenerator, 'map instanceof SourceMapGenerator');
+    assert.ok(mapWithoutOptions instanceof SourceMapGenerator, 'mapWithoutOptions instanceof SourceMapGenerator');
+    mapWithoutOptions._file = 'foo.js';
+    util.assertEqualMaps(assert, map.toJSON(), mapWithoutOptions.toJSON());
+
     map = new SourceMapConsumer(map.toString());
 
     var actual;