text_formatter: detect tty based on fd

terminal_windows.go

@@ -19,9 +19,13 @@ var (
 )
 
 // IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	fd := syscall.Stderr
-	var st uint32
-	r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, uintptr(fd), uintptr(unsafe.Pointer(&st)), 0)
-	return r != 0 && e == 0
+func IsTerminal(f io.Writer) bool {
+	switch v := f.(type) {
+	case *os.File:
+		var st uint32
+		r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, uintptr(v.Fd()), uintptr(unsafe.Pointer(&st)), 0)
+		return r != 0 && e == 0
+	default:
+		return false
+	}
 }