Add InternalStyle:rootLength to implement isAbsolute and rootPrefix.

pkg/path/lib/src/style/windows.dart

Index: pkg/path/lib/src/style/windows.dart
diff --git a/pkg/path/lib/src/style/windows.dart b/pkg/path/lib/src/style/windows.dart
index 2965f1eee9230ae930e02acd11f42f36b2f82b02..9b9c239d5e11c887ac0e5c98b09f6d203634ba1f 100644
--- a/pkg/path/lib/src/style/windows.dart
+++ b/pkg/path/lib/src/style/windows.dart
@@ -34,9 +34,31 @@ class WindowsStyle extends InternalStyle {
     return !isSeparator(path.codeUnitAt(path.length - 1));
   }
 
+  int rootLength(String path) {
+    if (path.isEmpty) return 0;
+    if (path.codeUnitAt(0) == chars.SLASH) return 1;
+    if (path.codeUnitAt(0) == chars.BACKSLASH) {
+      if (path.length >= 2 && path.codeUnitAt(1) == chars.BACKSLASH) {
+        int index = path.indexOf('\\', 2);

[Bob Nystrom, 2014/08/04 17:17:32]

Document this and the next indexOf too.

[Anders Johnsen, 2014/08/05 08:57:14]

Done.

+        if (index > 0) {
+          index = path.indexOf('\\', index + 1);
+          if (index > 0) return index;
+        }
+        return path.length;

[nweiz, 2014/08/04 20:11:58]

I believe Windows considers "\\foo" and "\\foo\bar" to be equivalent to "\foo"
and "\foo\bar" respectively, rather than UNC paths.

[Anders Johnsen, 2014/08/05 08:57:14]

Surprisingly, this is not tested. Can you find some documentation behind this,
so I can change it accordingly?

[nweiz, 2014/08/05 20:22:26]

http://msdn.microsoft.com/en-us/library/gg465305.aspx

Looks like "\\foo" isn't a valid UNC path, but "\\foo\bar" is. We should
definitely add tests for these.

[Anders Johnsen, 2014/08/06 07:05:15]

But saying it's invalid doesn't indicate how we then should handle it in this
case. If I say '\\localhost' in start->run, it'll take me to a list of network
shares on my computer. I think we'll just have to treat it as the root in any
case. It's not, by any mean, a relative root. Thoughts?

[nweiz, 2014/08/06 21:05:48]

SGTM

+      }
+      return 1;

[Bob Nystrom, 2014/08/04 17:17:32]

Nit, but I would reverse this flow control to reduce the nesting:

if (path.length < 2|| path.codeUnitAt(1) != chars.BACKSLASH) return 1;

[Anders Johnsen, 2014/08/05 08:57:14]

Done.

+    }

[Bob Nystrom, 2014/08/04 17:17:32]

These could use some comments too.

[Anders Johnsen, 2014/08/05 08:57:13]

Done.

+    if (path.length < 3) return 0;
+    if (!isAlphabetic(path.codeUnitAt(0))) return 0;
+    if (path.codeUnitAt(1) != chars.COLON) return 0;
+    if (!isSeparator(path.codeUnitAt(2))) return 0;
+    return 3;
+  }
+
   String getRoot(String path) {
-    var root = _getRoot(path);
-    return root == null ? getRelativeRoot(path) : root;
+    int length = rootLength(path);
+    if (length > 0) return path.substring(0, length);
+    return getRelativeRoot(path);

[Bob Nystrom, 2014/08/04 17:17:32]

This code is the same for all three styles, isn't it? Move it up to Style or put
in a mixin?

[nweiz, 2014/08/04 20:11:58]

+1 for making it a method of InternalStyle.

[Anders Johnsen, 2014/08/05 08:57:14]

Done.

   }
 
   String getRelativeRoot(String path) {
@@ -100,39 +122,4 @@ class WindowsStyle extends InternalStyle {
       return new Uri(scheme: 'file', pathSegments: parsed.parts);
     }
   }
-
-  // A helper method for [getRoot] that doesn't handle relative roots.
-  String _getRoot(String path) {
-    if (path.length < 3) return null;
-
-    // We aren't using a RegExp for this because they're slow (issue 19090). If
-    // we could, we'd match against r'^(\\\\[^\\]+\\[^\\/]+|[a-zA-Z]:[/\\])'.
-
-    // Try roots like "C:\".
-    if (isAlphabetic(path.codeUnitAt(0))) {
-      if (path.codeUnitAt(1) != chars.COLON) return null;
-      if (!isSeparator(path.codeUnitAt(2))) return null;
-      return path.substring(0, 3);
-    }
-
-    // Try roots like "\\server\share".
-    if (!path.startsWith('\\\\')) return null;
-
-    var start = 2;
-    // The server is one or more non-"\" characters.
-    while (start < path.length && path.codeUnitAt(start) != chars.BACKSLASH) {
-      start++;
-    }
-    if (start == 2 || start == path.length) return null;
-
-    // The share is one or more non-"\" characters.
-    start += 1;
-    if (path.codeUnitAt(start) == chars.BACKSLASH) return null;
-    start += 1;
-    while (start < path.length && path.codeUnitAt(start) != chars.BACKSLASH) {
-      start++;
-    }
-
-    return path.substring(0, start);
-  }
-}
+}