build.rs: imp. function to show weird paths as hex

* previously char range 0x00 to 0x1F weren't hexified
* even if valid utf-8, still show \0 as \x00
(even though in our use case \0 wouldn't be seen due to being converted
by Command::arg/args earlier to "<string-with-nul>")

* passes the tests that were there thus far but got removed by prev. commit

build.rs

@@ -1162,16 +1162,32 @@ struct MyArgs<'a>(Vec<&'a OsStr>);
 
 fn humanly_visible_os_chars(f: &mut fmt::Formatter<'_>, arg: &OsStr) -> fmt::Result {
  if let Some(arg_str) = arg.to_str() {
- // If the argument is valid UTF-8, simply display it
- write!(f, "\"{}\"", arg_str)?;
+ // If the argument is valid UTF-8,
+ if arg_str.contains('\0') {
+ write!(f, "\"")?;
+ // has \0 in it, show them as \x00 but keep the rest as they are such as ♥
+ for c in arg_str.chars() {
+ if c == '\0' {
+ write!(f,"\\x00")?
+ } else {
+ write!(f,"{}",c)?
+ }
+ }
+ write!(f, "\"")?;
+ } else {
+ // has no \0 in it
+ write!(f, "\"{}\"", arg_str)?;
+ }
  } else {
  //None aka not fully utf8 arg
  //then we show it as ascii + hex
  write!(f, "\"")?;
  #[cfg(not(target_os = "windows"))]
  for byte in arg.as_bytes() {
  match std::char::from_u32(u32::from(*byte)) {
- Some(c) if c.is_ascii() => write!(f, "{}", c)?,
+ //chars in range 0x20..0x7E (presumably printable) are shown as they are
+ Some(c) if (*byte >= 0x20) && (*byte <= 0x7E) => write!(f, "{}", c)?,
+ //anything else including \0 and ♥ become hex, eg. ♥ is \xE2\x99\xA5
  _ => {
  write!(f, "\\x{:02X}", byte)?;
  }