From: Tom Jones <thj@freebsd.org>
Subject: Re: diff: handle missing new lines in trailing context
To: gameoftrees@openbsd.org
Date: Thu, 29 Sep 2022 10:46:35 +0100

On Thu, Sep 29, 2022 at 11:35:45AM +0200, Stefan Sperling wrote:
> On Thu, Sep 29, 2022 at 10:00:37AM +0100, Tom Jones wrote:
> > Hi folks,
> > 
> > If there is a missing new line in the context we currently miss it and
> > fail to print the warning. This trips up patch and leads to failures.
> > 
> > This patch uses the chunk at result->chunks.head[cc->chunk.end] for
> > checking the final atom. I am not sure if can assume there is a chunk
> > there, but I haven't seen another way to access this correctly.
> 
> Using chunk.end as an index will end up indexing one item beyond the
> end of the array.
> 
> Does your test still work when checking at index chunk.end - 1 instead?

This seems obviously wrong to me too, but there is another chunk there,
but not accounted for. 

Sadly checking chunk.end -1 doesn't handle this. If it did the check in
the loop would handle this case. This block after the loop might be
suspect, my tests show that result.len is 1 more than chunk.end.

I didn't figure out why we end up trailing context as atoms rather than
a chunk, looking in a debugger shows a correct chunk there. Is there a
reason why?

- Tom