Use reasonable defaults for docgen if invoked on a single package

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.
 ///
 ///      $ dart docgen.dart [OPTIONS] [FILE/DIR]
@@ skipping 393 matching lines @@
     }
     _writeOutputFiles(libraryMap, filteredEntities, outputToYaml, append,
         startPage);
   }
 
   /// Output all of the libraries and classes into json or yaml files for
   /// consumption by a viewer.
   static void _writeOutputFiles(libraryMap,
       Iterable<Indexable> filteredEntities, bool outputToYaml, bool append,
       String startPage) {
-    if (startPage != null) libraryMap['startPage'] = startPage;
+    if (startPage != null) libraryMap['start-page'] = startPage;
 
     _writeToFile(JSON.encode(libraryMap), 'library_list.json');
 
     // Output libraries and classes to file after all information is generated.
     filteredEntities.where((e) => e is Class || e is Library).forEach((output) {
       _writeIndexableToFile(output, outputToYaml);
     });
 
     // Outputs all the qualified names documented with their type.
     // This will help generate search results.
@@ skipping 159 matching lines @@
             contents.startsWith(new RegExp('part of ')))) {
           libraries.add(new Uri.file(path.normalize(path.absolute(f))));
           logger.info('Added to libraries: $f');
         }
       }
     });
     return libraries;
   }
 
   /// All of the directories for our dependent packages
+  /// If this is not a package, return an empty list.
   static List<String> _allDependentPackageDirs(String packageDirectory) {
+    var packageName = Library.packageNameFor(packageDirectory);
+    if (packageName == '') return [];
     var dependentsJson = Process.runSync('pub', ['list-package-dirs'],
         workingDirectory: packageDirectory, runInShell: true);
     if (dependentsJson.exitCode != 0) {
       print(dependentsJson.stderr);
      }
     var dependents = JSON.decode(dependentsJson.stdout)['packages'];
     return dependents.values.toList();
   }
 
   /// For all the libraries, return a list of the libraries that are part of
@@ skipping 782 matching lines @@
       .readAsStringSync(), linkResolver: linkResolver,
       inlineSyntaxes: _MARKDOWN_SYNTAXES);
     return contents;
   }
 
   /// Given a LibraryMirror that is a library, return the name of the directory
   /// holding that library.
   static String _getRootdir(LibraryMirror mirror) =>
       path.dirname(path.dirname(mirror.uri.toFilePath()));
 
-  /// Read a pubspec and return the library name.
+  /// Read a pubspec and return the library name given a [LibraryMirror].
   static String _packageName(LibraryMirror mirror) {
     if (mirror.uri.scheme != 'file') return '';
     var rootdir = _getRootdir(mirror);
-    var pubspecName = path.join(rootdir, 'pubspec.yaml');
+    return packageNameFor(rootdir);
+  }
+
+  /// Read a pubspec and return the library name, given a directory
+  static String packageNameFor(String directoryName) {
+    var pubspecName = path.join(directoryName, 'pubspec.yaml');
     File pubspec = new File(pubspecName);
     if (!pubspec.existsSync()) return '';
     var contents = pubspec.readAsStringSync();
     var spec = loadYaml(contents);
     return spec["name"];
   }
 
   String get packagePrefix => packageName == null || packageName.isEmpty ?
       '' : '$packageName/';
 
@@ skipping 754 matching lines @@
         .map((e) => originalMirror.getField(e.simpleName).reflectee)
         .where((e) => e != null)
         .toList();
   }
 
   Map toMap() => {
     'name': Indexable.getDocgenObject(mirror, owningLibrary).docName,
     'parameters': parameters
   };
 }