[tex-k] [NTG-pdftex] Bug#458059:

[David Kastrup]

Taco Hoekwater <taco at elvenkind.com> writes:

> David Kastrup wrote:
>> Frank Küster <frank at debian.org> writes:
>>
>>> There is a configuration variable nest_size level, but it doesn't seem
>>> to help in this case: The attached file gives an error
>>>
>>> ! TeX capacity exceeded, sorry [grouping levels=255].
>>>
>>> although my texmf.cnf has nest_size=500.
>>
>> I find it awfully hard to reliably trigger a semantic nest size
>> overflow.  The best I have been able to come up with was
>>
>> Can anybody think of a semantic nest without grouping apart from
>> unrestricted hmode (which I use above)?
>
> The example that was attached by Frank (or Stijn?) does just fine.

But that's not without grouping as far as I can see, so it is not really
different from what I had.  If you put a line
{{{{{{{{{{{{{{{{{{{{{
before the problem, then it will again bomb out with a grouping error
instead.  At least that is what I think I see when looking at the error
message and context.

In short: I don't see how one can trigger semantic nest errors when the
semantic nest limit is more than twice the grouping limit (which it
isn't right now).  I might still be overlooking something, though.
Already the single possibility to switch between semantic lists without
a corresponding group switch that I can think of (basically
\leavevmode/\par) escaped Knuth in the TeXbook Appendix D.  As a result,
the next edition (if we will see it) will have a quite simpler version
of \removevboxes in it than previous ones.

But there may be some rationale behind the current semantic nest size
limit...

> \bm at command ...nd \z@ {\bm at gr@@p \boldmath {{b^c}}
>                                                   }
> \makebm #1$->\bm {#1}
>                      $
> \bm at mchoice ... {\hbox {#1$\displaystyle \m at th #2$
>                                                   }}{\hbox
> {#1$\textstyle \m...
>
> \bm at gr@@p ...fmmode \bm at mchoice #1{#2}{#2}{#2}{#2}
>                                                   \else \bfseries #1#2\fi
> \bm at command ...nd \z@ {\bm at gr@@p \boldmath {{b^c}}
>                                                   }
> \makebm #1$->\bm {#1}
>                      $
> \bm at mchoice ... {\hbox {#1$\displaystyle \m at th #2$
>                                                   }}{\hbox
> {#1$\textstyle \m...
>
> \bm at gr@@p ...fmmode \bm at mchoice #1{#2}{#2}{#2}{#2}
>                                                   \else \bfseries #1#2\fi
> \bm at command ...30049 ^{\bm at gr@@p \boldmath {{b^c}}
>                                                   }
> \makebm #1$->\bm {#1}
>                      $
> \makelabel ...h {\makebm }\normalfont \bfseries #1
>                                                   :}
> \sbox #1#2->\setbox #1\hbox {\color at setgroup #2
>                                                \color at endgroup }
> \@item ...i \fi \sbox \@tempboxa {\makelabel {#1}}
>                                                   \global \setbox
> \@labels \...
> l.11 \item[$a^{b^c}$]
>                       $a^{b^c}$
> !  ==> Fatal error occurred, no output PDF file produced!

-- 
David Kastrup