Re: Assertion failure in AnnotationList.c on IELR grammar with a useless nonterminal

[Akim Demaille]

Hi Dwight,

> Le 17 déc. 2020 à 00:09, Dwight Guth <dwight.guth@runtimeverification.com> a 
> écrit :
> 
> I have reproduced this error with Bison 3.7.4, but it is also present
> in versions as old as 3.0.4, the oldest version I have tried.

Wow...

> Note that the terminal output mentions that C is a useless
> nonterminal, but if C is removed from the grammar, the error
> disappears. While I am aware that the problem could be solved by
> simply removing the useless nonterminal from the grammar (and have
> been able to reproduce this behavior on my real-world example), the
> real-world grammar is autogenerated and it would be nice if this just
> worked and the useless nonterminal was ignored. Regardless, I figured
> an assertion error is probably not an appropriate failure mode, so I
> wanted to report the error to you.

Yes, this is definitely not expected, thanks a lot for the (complete)
report!


> We have plans to modify our grammar generator on our end to fix the
> issue in the way I described above, so this is not terribly high
> priority for us, since by the time bison releases trickle out into
> Linux distros, we will have already worked around the issue. But I
> have seen this same error message in other contexts in the past, so
> it's possible we may run into it again in a situation where it will be
> harder for us to simply work around it, so a fix would still be
> helpful to us long-term.

I will not work on this immediately (I expect this one to be tricky,
and I have ongoing business in Bison I'd like to finish first), but
this is definitely in the TODO list.

> I should have already completed a copyright assignment form that is
> applicable for changes to Bison, and am happy to follow any steps you
> have in mind in order to incorporate this minimized test into your
> test suite. Just let me know what you need.

I believe your test case is small enough so that we can call it
"trivial" (although, I agree, finding it was not), and therefore
I can use it as a contributions of yours that does not require
paperwork.  If, however, you'd like to contribute to Bison (for
instance there's a bug report about IELR that has just arrived :-),
you'll have to sign these papers.

Cheers!