io/fs: backslash is always a glob meta character

Fixes #44171

Change-Id: I2d3437a2f5b9fa0358e4664e1a8eacebed975eed
Reviewed-on: https://go-review.googlesource.com/c/go/+/290512
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/io/fs/glob.go

@@ -6,7 +6,6 @@ package fs
 
 import (
 	"path"
-	"runtime"
 )
 
 // A GlobFS is a file system with a Glob method.
@@ -111,8 +110,8 @@ func glob(fs FS, dir, pattern string, matches []string) (m []string, e error) {
 // recognized by path.Match.
 func hasMeta(path string) bool {
 	for i := 0; i < len(path); i++ {
-		c := path[i]
-		if c == '*' || c == '?' || c == '[' || runtime.GOOS == "windows" && c == '\\' {
+		switch path[i] {
+		case '*', '?', '[', '\\':
 			return true
 		}
 	}

src/io/fs/glob_test.go

@@ -17,6 +17,7 @@ var globTests = []struct {
 }{
 	{os.DirFS("."), "glob.go", "glob.go"},
 	{os.DirFS("."), "gl?b.go", "glob.go"},
+	{os.DirFS("."), `gl\ob.go`, "glob.go"},
 	{os.DirFS("."), "*", "glob.go"},
 	{os.DirFS(".."), "*/glob.go", "fs/glob.go"},
 }
@@ -32,7 +33,7 @@ func TestGlob(t *testing.T) {
 			t.Errorf("Glob(%#q) = %#v want %v", tt.pattern, matches, tt.result)
 		}
 	}
-	for _, pattern := range []string{"no_match", "../*/no_match"} {
+	for _, pattern := range []string{"no_match", "../*/no_match", `\*`} {
 		matches, err := Glob(os.DirFS("."), pattern)
 		if err != nil {
 			t.Errorf("Glob error for %q: %s", pattern, err)