Use filepath.clean instead of path.clean (#26404)

* internal/flags: use filepath.Clean instead of path.Clean

* internal/flags: fix windows pipe issue

* internal/flags: modify test for windows

* internal/flags: use backticks, fix test

internal/flags/flags_test.go

@@ -19,23 +19,43 @@ package flags
 import (
 	"os"
 	"os/user"
+	"runtime"
 	"testing"
 )
 
 func TestPathExpansion(t *testing.T) {
 	user, _ := user.Current()
-	tests := map[string]string{
-		"/home/someuser/tmp": "/home/someuser/tmp",
-		"~/tmp":              user.HomeDir + "/tmp",
-		"~thisOtherUser/b/":  "~thisOtherUser/b",
-		"$DDDXXX/a/b":        "/tmp/a/b",
-		"/a/b/":              "/a/b",
+	var tests map[string]string
+
+	if runtime.GOOS == "windows" {
+		tests = map[string]string{
+			`/home/someuser/tmp`:        `\home\someuser\tmp`,
+			`~/tmp`:                     user.HomeDir + `\tmp`,
+			`~thisOtherUser/b/`:         `~thisOtherUser\b`,
+			`$DDDXXX/a/b`:               `\tmp\a\b`,
+			`/a/b/`:                     `\a\b`,
+			`C:\Documents\Newsletters\`: `C:\Documents\Newsletters`,
+			`C:\`:                       `C:\`,
+			`\\.\pipe\\pipe\geth621383`: `\\.\pipe\\pipe\geth621383`,
+		}
+	} else {
+		tests = map[string]string{
+			`/home/someuser/tmp`:        `/home/someuser/tmp`,
+			`~/tmp`:                     user.HomeDir + `/tmp`,
+			`~thisOtherUser/b/`:         `~thisOtherUser/b`,
+			`$DDDXXX/a/b`:               `/tmp/a/b`,
+			`/a/b/`:                     `/a/b`,
+			`C:\Documents\Newsletters\`: `C:\Documents\Newsletters\`,
+			`C:\`:                       `C:\`,
+			`\\.\pipe\\pipe\geth621383`: `\\.\pipe\\pipe\geth621383`,
+		}
 	}
-	os.Setenv("DDDXXX", "/tmp")
+
+	os.Setenv(`DDDXXX`, `/tmp`)
 	for test, expected := range tests {
 		got := expandPath(test)
 		if got != expected {
-			t.Errorf("test %s, got %s, expected %s\n", test, got, expected)
+			t.Errorf(`test %s, got %s, expected %s\n`, test, got, expected)
 		}
 	}
 }