Don't assume the pubspec is only one level up from a library

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 1401 matching lines @@
 
   /// For a library's [mirror], determine the name of the package (if any) we
   /// believe it came from (because of its file URI).
   ///
   /// If no package could be determined, we return an empty string.
   String _findPackage(LibraryMirror mirror) {
     if (mirror == null) return '';
     if (_hasBeenCheckedForPackage) return packageName;
     _hasBeenCheckedForPackage = true;
     if (mirror.uri.scheme != 'file') return '';
-    // We assume that we are documenting only libraries under package/lib
     packageName = _packageName(mirror);
     // Associate the package readme with all the libraries. This is a bit
     // wasteful, but easier than trying to figure out which partial match
     // is best.
     packageIntro = _packageIntro(_getRootdir(mirror));
     return packageName;
   }
 
   String _packageIntro(packageDir) {
+    if (packageDir == null) return null;
     var dir = new Directory(packageDir);
     var files = dir.listSync();
     var readmes = files.where((FileSystemEntity each) => (each is File &&
         each.path.substring(packageDir.length + 1, each.path.length)
           .startsWith('README'))).toList();
     if (readmes.isEmpty) return '';
     // If there are multiples, pick the shortest name.
     readmes.sort((a, b) => a.path.length.compareTo(b.path.length));
     var readme = readmes.first;
     var linkResolver = (name) => Indexable.globalFixReference(name);
     var contents = markdown.markdownToHtml(readme
       .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()));
+  /// holding the package information for that library. If the library is not 
+  /// part of a package, return null.
+  static String _getRootdir(LibraryMirror mirror) {
+    var file = mirror.uri.toFilePath();
+    // Any file that's in a package will be in a directory of the form 
+    // packagename/lib/.../filename.dart, so we know that a possible
+    // package directory is at least in the directory above the one containing
+    // [file]
+    var directoryAbove = path.dirname(path.dirname(file));
+    return _packageDirectoryFor(directoryAbove);
+  }
 
   /// 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);
+    if (rootdir == null) return '';
     return packageNameFor(rootdir);
   }
 
+  /// Recursively walk up from directory name looking for a pubspec. Return
+  /// the directory that contains it, or null if none is found.
+  static String _packageDirectoryFor(String directoryName) {
+    var dir = directoryName;
+    while (!_pubspecFor(dir).existsSync()) {
+      var newDir = path.dirname(dir);
+      if (newDir == dir) return null;
+      dir = newDir;
+    }
+    return dir;
+  }
+
+  static File _pubspecFor(String directoryName) =>
+      new File(path.join(directoryName, 'pubspec.yaml'));
+
   /// 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"];
   }
 
@@ skipping 759 matching lines @@
         .map((e) => originalMirror.getField(e.simpleName).reflectee)
         .where((e) => e != null)
         .toList();
   }
 
   Map toMap() => {
     'name': Indexable.getDocgenObject(mirror, owningLibrary).docName,
     'parameters': parameters
   };
 }