I just realized that I have bug in my GPS driver. It operates on ASCII data, so [] operator is safe, BUT data can be corrupted (low chance, but non-zero), so it can form valid multibyte character, so my code will panic on it, trying to parse and validate NMEA message.

Panicking on parsing corrupted data seem like a feature to me...

It's like the default rule in a lexer, if it ever gets to it then it's an unrecognized character and lexing stops so error handling can proceed.

--edit--

Which I now realize was probably your point.

Truncating a string to fit in a fixed-size storage field is probably the most common reason to split at a particular byte position. If you’re throwing data away anyway, you probably don’t care too much about the little bit of corruption.

Granted, this is certainly incorrect but has little to do with safety, especially if the downstream code has to revalidate everything anyway.