Properly support UNC paths in pkg/path.

pkg/path/lib/path.dart

 // Copyright (c) 2012, 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.
 
 /// A comprehensive, cross-platform path manipulation library.
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 951 matching lines @@
 }
 
 /// The style for Windows paths.
 class _WindowsStyle extends Style {
   _WindowsStyle();
 
   final name = 'windows';
   final separator = '\\';
   final separatorPattern = new RegExp(r'[/\\]');
   final needsSeparatorPattern = new RegExp(r'[^/\\]$');
-  final rootPattern = new RegExp(r'^(\\\\|[a-zA-Z]:[/\\])');
+  final rootPattern = new RegExp(r'^(\\\\[^\\]+\\[^\\/]+|[a-zA-Z]:[/\\])');
 
   String pathFromUri(Uri uri) {
     if (uri.scheme != '' && uri.scheme != 'file') {
       throw new ArgumentError("Uri $uri must have scheme 'file:'.");
     }
 
     var path = uri.path;
     if (uri.host == '') {
       // Drive-letter paths look like "file:///C:/path/to/file". The
       // replaceFirst removes the extra initial slash.
       if (path.startsWith('/')) path = path.replaceFirst("/", "");
     } else {
       // Network paths look like "file://hostname/path/to/file".
       path = '\\\\${uri.host}$path';
     }
     return Uri.decodeComponent(path.replaceAll("/", "\\"));
   }
 
   Uri absolutePathToUri(String path) {
     var parsed = builder._parse(path);
-    if (parsed.root == r'\\') {
-      // Network paths become "file://hostname/path/to/file".
+    if (parsed.root.startsWith(r'\\')) {
+      // Network paths become "file://server/share/path/to/file".
 
-      var host = parsed.parts.removeAt(0);
+      // The root is of the form "\\server\share". We want "server" to be the
+      // URI host, and "share" to be the first element of the path.
+      var rootParts = parsed.root.split('\\').where((part) => part != '');
+      parsed.parts.insert(0, rootParts.last);
 
-      if (parsed.parts.isEmpty) {
-        // If the path is a bare root (e.g. "\\hostname"), [parsed.parts] will
-        // currently be empty. We add two empty components so the URL
-        // constructor produces "file://hostname/", with a trailing slash.
-        parsed.parts.addAll(["", ""]);
-      } else if (parsed.hasTrailingSeparator) {
+      if (parsed.hasTrailingSeparator) {
         // If the path has a trailing slash, add a single empty component so the
         // URI has a trailing slash as well.
         parsed.parts.add("");
       }
 
-      return new Uri(scheme: 'file', host: host, pathSegments: parsed.parts);
+      return new Uri(scheme: 'file', host: rootParts.first,
+          pathSegments: parsed.parts);
     } else {
       // Drive-letter paths become "file:///C:/path/to/file".
 
       // If the path is a bare root (e.g. "C:\"), [parsed.parts] will currently
       // be empty. We add an empty component so the URL constructor produces
       // "file:///C:/", with a trailing slash. We also add an empty component if
       // the URL otherwise has a trailing slash.
       if (parsed.parts.length == 0 || parsed.hasTrailingSeparator) {
         parsed.parts.add("");
       }
@@ skipping 159 matching lines @@
     // doesn't count.
     if (lastDot <= 0) return [file, ''];
 
     return [file.substring(0, lastDot), file.substring(lastDot)];
   }
 
   _ParsedPath clone() => new _ParsedPath(
       style, root, isRootRelative,
       new List.from(parts), new List.from(separators));
 }