path/filepath: add support for plan9

R=paulzhol, ality, r, fhs
CC=golang-dev
https://golang.org/cl/4316054

src/pkg/path/filepath/Makefile

@@ -18,6 +18,9 @@ GOFILES_darwin=\
 GOFILES_linux=\
 	path_unix.go
 
+GOFILES_plan9=\
+	path_plan9.go
+
 GOFILES_windows=\
 	path_windows.go
 

src/pkg/path/filepath/path_plan9.go

@@ -0,0 +1,28 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package filepath
+
+import "strings"
+
+const (
+	Separator     = '/' // OS-specific path separator
+	ListSeparator = 0   // OS-specific path list separator
+)
+
+// isSeparator returns true if c is a directory separator character.
+func isSeparator(c uint8) bool {
+	return Separator == c
+}
+
+// IsAbs returns true if the path is absolute.
+func IsAbs(path string) bool {
+	return strings.HasPrefix(path, "/") || strings.HasPrefix(path, "#")
+}
+
+// volumeName returns the leading volume name on Windows.
+// It returns "" elsewhere
+func volumeName(path string) string {
+	return ""
+}

src/pkg/path/filepath/path_unix.go

@@ -22,7 +22,7 @@ func IsAbs(path string) bool {
 }
 
 // volumeName returns the leading volume name on Windows.
-// It returns "" on Unix.
+// It returns "" elsewhere.
 func volumeName(path string) string {
 	return ""
 }