Allow nonexhaustive rules

[dario23]

I had a try at allowing nonexhaustive rules, as proposed in #179.

[kevinmehall]

Thanks!

I'm not sure "nonexhaustive" is the right term for this -- in the context of Rust, "a non-exhaustive" match is when not all cases are covered by patterns. In rust-peg, one might expect exhaustive / non-exhaustive to mean that the parser covers all possible inputs / will fail for some inputs.

Not sure of a better term, though. #[no_eof]?

This attribute should also probably only be allowed with pub as it has no effect when calling the rule from other rules.

[kevinmehall]

Merged as #[no_eof] pub rule name() = ...

[jocutajar]

Excellent. Might be worthwhile adding how to detect the non-eof match. I suppose we can check end position and compare to input length. Haven't tried yet.

I also notice in the MR:

To opt in to non exhaustive parsing, add the nonexhaustive modifier before the rule keyword.

But here you say #[no_eof]. Which one then? :)

Thanks a lot!