Filesystem: Support Windows shares/DFS roots in wp_normalize_path().

Props rilwis for initial patch.
Fixes #35996.


git-svn-id: https://develop.svn.wordpress.org/trunk@36881 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -1687,17 +1687,19 @@ function path_join( $base, $path ) {
  *
  * On windows systems, replaces backslashes with forward slashes
  * and forces upper-case drive letters.
- * Ensures that no duplicate slashes exist.
+ * Allows for two leading slashes for Windows network shares, but
+ * ensures that all other duplicate slashes are reduced to a single.
  *
  * @since 3.9.0
  * @since 4.4.0 Ensures upper-case drive letters on Windows systems.
+ * @since 4.5.0 Allows for Windows network shares.
  *
  * @param string $path Path to normalize.
  * @return string Normalized path.
  */
 function wp_normalize_path( $path ) {
 	$path = str_replace( '\\', '/', $path );
-	$path = preg_replace( '|/+|','/', $path );
+	$path = preg_replace( '|(?<=.)/+|', '/', $path );
 	if ( ':' === substr( $path, 1, 1 ) ) {
 		$path = ucfirst( $path );
 	}