From 82e357d6d5944fc5b0293085a0305fe328c505ea Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@golang.org>
Date: Fri, 26 Aug 2022 19:22:50 -0700
Subject: [PATCH] os: use backslashes for DirFS on Windows

Otherwise DirFS of a UNC path does not work.

Fixes #54694

Change-Id: I82c1c436f7c26b3935c2cc4fd238daf094fc4d86
Reviewed-on: https://go-review.googlesource.com/c/go/+/426094
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: hopehook <hopehook@golangcn.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
---
 src/os/file.go | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/os/file.go b/src/os/file.go
index e2eef8ec5d30dc..78677c2f8fdfd8 100644
--- a/src/os/file.go
+++ b/src/os/file.go
@@ -642,7 +642,7 @@ func (dir dirFS) Open(name string) (fs.File, error) {
 	if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
 		return nil, &PathError{Op: "open", Path: name, Err: ErrInvalid}
 	}
-	f, err := Open(string(dir) + "/" + name)
+	f, err := Open(dir.join(name))
 	if err != nil {
 		return nil, err // nil fs.File
 	}
@@ -653,13 +653,28 @@ func (dir dirFS) Stat(name string) (fs.FileInfo, error) {
 	if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
 		return nil, &PathError{Op: "stat", Path: name, Err: ErrInvalid}
 	}
-	f, err := Stat(string(dir) + "/" + name)
+	f, err := Stat(dir.join(name))
 	if err != nil {
 		return nil, err
 	}
 	return f, nil
 }
 
+// join returns the path for name in dir. We can't always use "/"
+// because that fails on Windows for UNC paths.
+func (dir dirFS) join(name string) string {
+	if runtime.GOOS == "windows" && containsAny(name, "/") {
+		buf := []byte(name)
+		for i, b := range buf {
+			if b == '/' {
+				buf[i] = '\\'
+			}
+		}
+		name = string(buf)
+	}
+	return string(dir) + string(PathSeparator) + name
+}
+
 // ReadFile reads the named file and returns the contents.
 // A successful call returns err == nil, not err == EOF.
 // Because ReadFile reads the whole file, it does not treat an EOF from Read