Fix absolute paths on Windows without a drive letter.

runtime/bin/builtin.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.
 
 library builtin;
 import 'dart:io';
 
 // Corelib 'print' implementation.
 void _print(arg) {
   _Logger._printString(arg.toString());
@@ skipping 59 matching lines @@
               _requestCompleted(builder.takeBytes(), response);
             });
       }).catchError((error) {
         _requestFailed(error);
       });
 }
 
 
 // Are we running on Windows?
 var _isWindows = false;
+var _workingWindowsDrivePrefix;
 // The current working directory
 var _workingDirectoryUri;
 // The URI that the entry point script was loaded from. Remembered so that
 // package imports can be resolved relative to it.
 var _entryPointScript;
 // The directory to look in to resolve "package:" scheme URIs.
 var _packageRoot;
 
 
 void _setWindows() {
   _isWindows = true;
 }
 
 
 _sanitizeWindowsPath(path) {

[zra, 2013/08/14 16:38:12]

If it's easy/makes sense, maybe collect all Windows path futzery in here.
Otherwise, giving a name that has something to do with slashes might make things
a bit more clear.

   // For Windows we need to massage the paths a bit according to
   // http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-windows.aspx
   //
   // Convert
   // C:\one\two\three
   // to
   // /C:/one/two/three
 
   if (_isWindows == false) {
     // Do nothing when not running Windows.
@@ skipping 11 matching lines @@
 }
 
 _enforceTrailingSlash(uri) {
   // Ensure we have a trailing slash character.
   if (!uri.endsWith('/')) {
     return '$uri/';
   }
   return uri;
 }
 
+_extractDriveLetterPrefix(cwd) {
+  if (!_isWindows) {
+    return null;
+  }
+  if (cwd.length > 1 && cwd[1] == ':') {
+    return '/${cwd[0]}:';
+  }
+  return null;
+}
 
 void _setWorkingDirectory(cwd) {
+  _workingWindowsDrivePrefix = _extractDriveLetterPrefix(cwd);
   cwd = _sanitizeWindowsPath(cwd);
   cwd = _enforceTrailingSlash(cwd);
   _workingDirectoryUri = new Uri(scheme: 'file', path: cwd);
   _logResolution('# Working Directory: $cwd');
 }
 
 
 _setPackageRoot(String packageRoot) {
   packageRoot = _enforceTrailingSlash(packageRoot);
   _packageRoot = _workingDirectoryUri.resolve(packageRoot);
@@ skipping 77 matching lines @@
     //
     // Drop the leading / before the drive letter.
     path = path.substring(1);
     _logResolution('# Path: Removed leading / -> $path');
   }
 
   return path;
 }
 
 
 String _filePathFromFileUri(Uri uri) {

[zra, 2013/08/14 16:38:12]

It looks like this code is only running under the file: URI scheme. Does
Uri.parse give the file: scheme when no scheme is in the URI?

[Cutch, 2013/08/14 20:29:08]

For absolute paths with no scheme, yes. 

   if (!uri.host.isEmpty) {
     throw "URIs using the 'file:' scheme may not contain a host.";
   }
 
-  _logResolution('# Path: $uri -> ${uri.path}');
-  return uri.path;
+  String path = uri.path;
+  _logResolution('# Path: $uri -> ${path}');
+  if (_isWindows && (path.length > 2) && path.startsWith('/') &&
+      (path[2] != ':')) {

[zra, 2013/08/14 16:38:12]

Is this (path[2] != ':') checking that the path is not already of the form
/C:/...? A comment to that effect might be helpful.

[Cutch, 2013/08/14 20:29:08]

Done.

+    if (_workingWindowsDrivePrefix == null) {
+      throw 'Could not determine windows drive letter prefix.';
+    }
+    // Absolute path on Windows without a drive letter.
+    _logResolution('# Path: Windows absolute path needs a drive letter.'
+                   ' Prepending $_workingWindowsDrivePrefix.');
+    path = '$_workingWindowsDrivePrefix$path';
+  }
+  return path;
 }
 
 
 String _filePathFromOtherUri(Uri uri) {
   if (!uri.host.isEmpty) {
     throw 'URIs whose paths are used as file paths may not contain a host.';
   }
 
   _logResolution('# Path: $uri -> ${uri.path}');
   return uri.path;
@@ skipping 27 matching lines @@
   }
   _logResolution('# Package: $uri -> $path');
   return path;
 }
 
 
 String _filePathFromHttpUri(Uri uri) {
   _logResolution('# Path: $uri -> $uri');
   return uri.toString();
 }