cmd/go/internal/lockedfile/internal/filelock: re-use filelock_other.go for plan9

The implementation for lockType, lock, unlock and isNotSupported is the
same on plan9 as on other platforms where filelocks are unsupported.

Change-Id: I8b9c0bdc429e23346ab9145ec3814622319427fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/476915
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

2 files changed, 1 insertions, 37 deletions

diff --git a/src/cmd/go/internal/lockedfile/internal/filelock/filelock_other.go b/src/cmd/go/internal/lockedfile/internal/filelock/filelock_other.go
index c18dbdf850..7bdd62bd9b 100644
--- a/src/cmd/go/internal/lockedfile/internal/filelock/filelock_other.go
+++ b/src/cmd/go/internal/lockedfile/internal/filelock/filelock_other.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !unix && !plan9 && !windows
+//go:build !unix && !windows
 
 package filelock
 
diff --git a/src/cmd/go/internal/lockedfile/internal/filelock/filelock_plan9.go b/src/cmd/go/internal/lockedfile/internal/filelock/filelock_plan9.go
deleted file mode 100644
index 54b2c946e0..0000000000
--- a/src/cmd/go/internal/lockedfile/internal/filelock/filelock_plan9.go
+++ /dev/null
@@ -1,36 +0,0 @@
-// Copyright 2018 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.
-
-//go:build plan9
-
-package filelock
-
-import "io/fs"
-
-type lockType int8
-
-const (
-	readLock = iota + 1
-	writeLock
-)
-
-func lock(f File, lt lockType) error {
-	return &fs.PathError{
-		Op:   lt.String(),
-		Path: f.Name(),
-		Err:  ErrNotSupported,
-	}
-}
-
-func unlock(f File) error {
-	return &fs.PathError{
-		Op:   "Unlock",
-		Path: f.Name(),
-		Err:  ErrNotSupported,
-	}
-}
-
-func isNotSupported(err error) bool {
-	return err == ErrNotSupported
-}