Re: [NTG-pdftex] Bug#458059:

28 May 2008

      Taco Hoekwater  writes:
...
David Kastrup wrote:
...
Frank Küster  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@command ...nd \z@ {\bm@gr@@p \boldmath {{b^c}}
                                                  }
\makebm #1$->\bm {#1}
                     $
\bm@mchoice ... {\hbox {#1$\displaystyle \m@th #2$
                                                  }}{\hbox
{#1$\textstyle \m...
\bm@gr@@p ...fmmode \bm@mchoice #1{#2}{#2}{#2}{#2}
                                                  \else \bfseries #1#2\fi
\bm@command ...nd \z@ {\bm@gr@@p \boldmath {{b^c}}
                                                  }
\makebm #1$->\bm {#1}
                     $
\bm@mchoice ... {\hbox {#1$\displaystyle \m@th #2$
                                                  }}{\hbox
{#1$\textstyle \m...
\bm@gr@@p ...fmmode \bm@mchoice #1{#2}{#2}{#2}{#2}
                                                  \else \bfseries #1#2\fi
\bm@command ...30049 ^{\bm@gr@@p \boldmath {{b^c}}
                                                  }
\makebm #1$->\bm {#1}
                     $
\makelabel ...h {\makebm }\normalfont \bfseries #1
                                                  :}
\sbox #1#2->\setbox #1\hbox {\color@setgroup #2
                                               \color@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