Teach dart_package to understand the packages/ subdirectory

third_party/dart-packages/path/path/src/internal_style.dart

-// Copyright (c) 2014, 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.
-
-library path.internal_style;
-
-import 'context.dart';
-import 'style.dart';
-
-/// The internal interface for the [Style] type.
-///
-/// Users should be able to pass around instances of [Style] like an enum, but
-/// the members that [Context] uses should be hidden from them. Those members
-/// are defined on this class instead.
-abstract class InternalStyle extends Style {
-  /// The default path separator for this style.
-  ///
-  /// On POSIX, this is `/`. On Windows, it's `\`.
-  String get separator;
-
-  /// Returns whether [path] contains a separator.
-  bool containsSeparator(String path);
-
-  /// Returns whether [codeUnit] is the character code of a separator.
-  bool isSeparator(int codeUnit);
-
-  /// Returns whether this path component needs a separator after it.
-  ///
-  /// Windows and POSIX styles just need separators when the previous component
-  /// doesn't already end in a separator, but the URL always needs to place a
-  /// separator between the root and the first component, even if the root
-  /// already ends in a separator character. For example, to join "file://" and
-  /// "usr", an additional "/" is needed (making "file:///usr").
-  bool needsSeparator(String path);
-
-  /// Returns the number of characters of the root part.
-  ///
-  /// Returns 0 if the path is relative.
-  ///
-  /// If the path is root-relative, the root length is 1.
-  int rootLength(String path);
-
-  /// Gets the root prefix of [path] if path is absolute. If [path] is relative,
-  /// returns `null`.
-  String getRoot(String path) {
-    var length = rootLength(path);
-    if (length > 0) return path.substring(0, length);
-    return isRootRelative(path) ? path[0] : null;
-  }
-
-  /// Returns whether [path] is root-relative.
-  ///
-  /// If [path] is relative or absolute and not root-relative, returns `false`.
-  bool isRootRelative(String path);
-
-  /// Returns the path represented by [uri] in this style.
-  String pathFromUri(Uri uri);
-
-  /// Returns the URI that represents the relative path made of [parts].
-  Uri relativePathToUri(String path) =>
-      new Uri(pathSegments: context.split(path));
-
-  /// Returns the URI that represents [path], which is assumed to be absolute.
-  Uri absolutePathToUri(String path);
-}