Unsafe unwrap in parser

[RadicalZephyr]

Found with the new fuzz testing setup!

This input export\x09AA causes the Lexer to fail.

extern crate just;

fn lex_and_parse<'a>(input: &'a str) -> Result<(), just::CompilationError<'a>> {
  let tokens = just::Lexer::lex(input)?;
  let parser = just::Parser::new(input, tokens);
  let _justfile = parser.justfile()?;
  Ok(())
}

fn main() {
  let input = "export	AA";
  lex_and_parse(&input);
}

[casey]

Awesome, nice find!

The parser uses an itertools adapter that allows putting items back into an iterator. However, if you put back two items in a row, it overwrites the previous item. The bug was caused by removing and putting back an Eof token, and then putting back another token, overwriting the Eof token. The parser assumes that it will never advance past the last token, but since the Eof token was overwritten, it does so and crashes.

[casey]

I'm surprised that nobody ever hit this organically!