Fix os2.clean_path on Windows

core/os/os2/path_windows.odin

@@ -187,7 +187,6 @@ init_long_path_support :: proc() {
 	if value == 1 {
 		can_use_long_paths = true
 	}
-
 }
 
 @(require_results)
@@ -271,6 +270,11 @@ _clean_path_handle_start :: proc(path: string, buffer: []u8) -> (rooted: bool, s
 			start += 1
 		}
 		copy(buffer, path[:start])
+		for n in 0..<start {
+			if _is_path_separator(buffer[n]) {
+				buffer[n] = _Path_Separator
+			}
+		}
 	}
 	return
 }

core/os/os2/stat_windows.odin

@@ -329,42 +329,68 @@ _is_reserved_name :: proc(path: string) -> bool {
 	return false
 }
 
-_is_UNC :: proc(path: string) -> bool {
-	return _volume_name_len(path) > 2
-}
-
-_volume_name_len :: proc(path: string) -> int {
+_volume_name_len :: proc(path: string) -> (length: int) {
 	if len(path) < 2 {
 		return 0
 	}
-	c := path[0]
+
 	if path[1] == ':' {
-		switch c {
+		switch path[0] {
 		case 'a'..='z', 'A'..='Z':
 			return 2
 		}
 	}
 
-	// URL: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
-	if l := len(path); l >= 5 && _is_path_separator(path[0]) && _is_path_separator(path[1]) &&
-		!_is_path_separator(path[2]) && path[2] != '.' {
-		for n := 3; n < l-1; n += 1 {
-			if _is_path_separator(path[n]) {
-				n += 1
-				if !_is_path_separator(path[n]) {
-					if path[n] == '.' {
-						break
-					}
-				}
-				for ; n < l; n += 1 {
-					if _is_path_separator(path[n]) {
-						break
-					}
-				}
-				return n
+	/*
+		See: URL: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
+		Further allowed paths can be of the form of:
+		- \\server\share or \\server\share\more\path
+		- \\?\C:\...
+		- \\.\PhysicalDriveX
+	*/
+	// Any remaining kind of path has to start with two slashes.
+	if !_is_path_separator(path[0]) || !_is_path_separator(path[1]) {
+		return 0
+	}
+
+	// Device path. The volume name is the whole string
+	if len(path) >= 5 && path[2] == '.' && _is_path_separator(path[3]) {
+		return len(path)
+	}
+
+	// We're a UNC share `\\host\share`, file namespace `\\?\C:` or UNC in file namespace `\\?\\host\share`
+	prefix := 2
+
+	// File namespace.
+	if len(path) >= 5 && path[2] == '?' && _is_path_separator(path[3]) {
+		if _is_path_separator(path[4]) {
+			// `\\?\\` UNC path in file namespace
+			prefix = 5
+		}
+
+		if len(path) >= 6 && path[5] == ':' {
+			switch path[4] {
+			case 'a'..='z', 'A'..='Z':
+				return 6
+			case:
+				return 0
 			}
-			break
 		}
 	}
-	return 0
-}
+
+	// UNC path, minimum version of the volume is `\\h\s` for host, share.
+	// Can also contain an IP address in the host position.
+	slash_count := 0
+	for i in prefix..<len(path) {
+		// Host needs to be at least 1 character
+		if _is_path_separator(path[i]) && i > 0 {
+			slash_count += 1
+
+			if slash_count == 2 {
+				return i
+			}
+		}
+	}
+
+	return len(path)
+}