Re: Mystery: Why does yylineno cause backing up tables?

[Vern Paxson]

> (Rephrase of my question.) 
> Why are the following three lines in the flex source?
> 
>     if ( do_yylineno )
>         /* This should really be "maintain_backup_tables = true" */
>         reject_really_used = true;

Well, I've scrutinized the code a fair bit and I'm embarrassed to say that
I can't figure out why that comment is there :-(.  It certainly appears
that yylineno as presently implemented shouldn't require the full backup
tables.  So one possibility is that the comment reflects bit-rot, coming
from an earlier time when I had implemented yylineno some other way that
*did* require the backup tables, but they no longer do.  However, the
second possiblity is that there's some horrible subtle gotcha that really
does require the tables, but it won't readily manifest itself.  In general,
I was loathe to turn on reject_really_used, so I have to imagine that I had
a good reason for doing so; and I'd also think that if I did manage to
reimplement things to not require reject_really_used, then I would've
happily removed the restriction.  But at this point, this is simply
speculation, alas ...

                Vern