Added a flag --append to docgen.

pkg/docgen/lib/docgen.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * **docgen** is a tool for creating machine readable representations of Dart
  * code metadata, including: classes, members, comments and annotations.
  *
  * docgen is run on a `.dart` file or a directory containing `.dart` files.
  *
@@ skipping 49 matching lines @@
  * [packageRoot] is the packages directory of the directory being analyzed.
  * If [includeSdk] is `true`, then any SDK libraries explicitly imported will
  * also be documented.
  * If [parseSdk] is `true`, then all Dart SDK libraries will be documented.
  * This option is useful when only the SDK libraries are needed.
  *
  * Returns `true` if docgen sucessfuly completes.
  */
 Future<bool> docgen(List<String> files, {String packageRoot,
     bool outputToYaml: true, bool includePrivate: false, bool includeSdk: false,
-    bool parseSdk: false}) {
+    bool parseSdk: false, bool append: false}) {
+  if (!append) {
+    var dir = new Directory('docs');
+    if (dir.existsSync()) dir.deleteSync(recursive: true);
+  }
+  
   if (packageRoot == null && !parseSdk) {
     // TODO(janicejl): At the moment, if a single file is passed it, it is
     // assumed that it does not have a package root unless it is passed in by
     // the user. In future, find a better way to find the packageRoot and also
     // fully test finding the packageRoot.
     if (FileSystemEntity.typeSync(files.first)
         == FileSystemEntityType.DIRECTORY) {
       packageRoot = _findPackageRoot(files.first);
     }
   }
   logger.info('Package Root: ${packageRoot}');
 
   linkResolver = (name) =>
       fixReference(name, _currentLibrary, _currentClass, _currentMember);
 
   return getMirrorSystem(files, packageRoot: packageRoot, parseSdk: parseSdk)
     .then((MirrorSystem mirrorSystem) {
       if (mirrorSystem.libraries.isEmpty) {
         throw new StateError('No library mirrors were created.');
       }
       _documentLibraries(mirrorSystem.libraries.values,
           includeSdk: includeSdk, includePrivate: includePrivate,
-          outputToYaml: outputToYaml);
+          outputToYaml: outputToYaml, append: append);
 
       return true;
     });
 }
 
 List<String> _listLibraries(List<String> args) {
   // TODO(janicejl): At the moment, only have support to have either one file,
   // or one directory. This is because there can only be one package directory
   // since only one docgen is created per run.
   if (args.length != 1) throw new UnsupportedError(USAGE);
@@ skipping 85 matching lines @@
         // system, and it is not possible to use the stack trace. BUG(#11622)
         // To avoid printing the stack trace.
         exit(1);
       });
 }
 
 /**
  * Creates documentation for filtered libraries.
  */
 void _documentLibraries(List<LibraryMirror> libraries,
-    {bool includeSdk:false, bool includePrivate:false, bool
-     outputToYaml:true}) {
+    {bool includeSdk:false, bool includePrivate:false, 
+    bool outputToYaml:true, bool append: false}) {

[Bob Nystrom, 2013/07/30 16:23:29]

Style nit: add spaces after other ":" in param list.

   libraries.forEach((lib) {
     // Files belonging to the SDK have a uri that begins with 'dart:'.
     if (includeSdk || !lib.uri.toString().startsWith('dart:')) {
       var library = generateLibrary(lib, includePrivate: includePrivate);
       _writeLibraryToFile(library, outputToYaml);
     }
   });
   // Outputs a text file with a list of files available after creating all
   // the libraries. This will help the viewer know what files are available
   // to read in.
   _writeToFile(listDir('docs').join('\n').replaceAll('docs/', ''),
-      'library_list.txt');
+      'library_list.txt', append: append);
   // Outputs all the qualified names documented. This will help generate search
   // results. 
-  _writeToFile(qualifiedNameIndex.join('\n'), 'index.txt');
+  _writeToFile(qualifiedNameIndex.join('\n'), 'index.txt', append: append);
 }
 
 Library generateLibrary(dart2js.Dart2JsLibraryMirror library,
   {bool includePrivate:false}) {
   _currentLibrary = library;
   var result = new Library(library.qualifiedName, _getComment(library),
       _getVariables(library.variables, includePrivate),
       _getMethods(library.functions, includePrivate),
       _getClasses(library.classes, includePrivate));
   logger.fine('Generated library for ${result.name}');
@@ skipping 210 matching lines @@
       innerList.add(new Type(e.qualifiedName, _typeGenerics(e)));
     });
     return innerList;
   }
   return [];
 }
 
 /**
  * Writes text to a file in the 'docs' directory.
  */
-void _writeToFile(String text, String filename) {
+void _writeToFile(String text, String filename, {bool append: false}) {
   Directory dir = new Directory('docs');
   if (!dir.existsSync()) {
     dir.createSync();
   }
   File file = new File('docs/$filename');
   if (!file.existsSync()) {
     file.createSync();
   }
-  file.openSync();
-  file.writeAsString(text);
+  file.writeAsString(text, mode: append ? FileMode.APPEND : FileMode.WRITE);
 }
 
 /**
  * Transforms the map by calling toMap on each value in it.
  */
 Map recurseMap(Map inputMap) {
   var outputMap = {};
   inputMap.forEach((key, value) {
     if (value is Map) {
       outputMap[key] = recurseMap(value);
@@ skipping 263 matching lines @@
   String outer;
   List<Type> inner;
   
   Type(this.outer, this.inner);
   
   Map toMap() => {
       'outer': outer,
       'inner': new List.from(inner.map((e) => e.toMap()))
     };
 }