os: deduplicate File definition

Fixes #16993.

Change-Id: Ibe406f97d2a49acae94531d969c56dbac8ce53b2
Reviewed-on: https://go-review.googlesource.com/28511
Run-TryBot: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/file_plan9.go

@@ -11,11 +11,6 @@ import (
 	"time"
 )
 
-// File represents an open file descriptor.
-type File struct {
-	*file
-}
-
 // file is the real representation of *File.
 // The extra level of indirection ensures that no clients of os
 // can overwrite this data, which could cause the finalizer

src/os/file_unix.go

@@ -19,11 +19,6 @@ func rename(oldname, newname string) error {
 	return nil
 }
 
-// File represents an open file descriptor.
-type File struct {
-	*file
-}
-
 // file is the real representation of *File.
 // The extra level of indirection ensures that no clients of os
 // can overwrite this data, which could cause the finalizer

src/os/file_windows.go

@@ -15,11 +15,6 @@ import (
 	"unsafe"
 )
 
-// File represents an open file descriptor.
-type File struct {
-	*file
-}
-
 // file is the real representation of *File.
 // The extra level of indirection ensures that no clients of os
 // can overwrite this data, which could cause the finalizer

src/os/types.go

@@ -12,6 +12,11 @@ import (
 // Getpagesize returns the underlying system's memory page size.
 func Getpagesize() int { return syscall.Getpagesize() }
 
+// File represents an open file descriptor.
+type File struct {
+	*file // os specific
+}
+
 // A FileInfo describes a file and is returned by Stat and Lstat.
 type FileInfo interface {
 	Name() string       // base name of the file