[Dev-luatex] Re: Crash when accessing the field 'data' of a whatsit(write) node

27 May 2025

      On 5/27/2025 7:23 AM, Linas Stonys wrote:
...
I think it is a bug. Luatex tries to expand data field content like with 
\edef thats why you get \iffalse.
With older texlive (v0.76) the same example prints:
we now have luatex 1.12 so that is indeed old ... way too old to bother 
about here
...
table: 03420800
table: 034212F0
table: 03421318
\documentclass{article}
\begin{document}
\directlua{
   callback.register('vpack_filter',
     function(head)
       if node.type(head.id) == 'whatsit' and head.subtype == 1 then
         print (head.data)
       end
       return true
     end,
     'debug'
   )
}
\begin{figure}
   \caption{test}
\end{figure}
\end{document}
On 5/17/2025 1:54 PM, Josef Friedrich wrote:
...
I’m the maintainer of the nodetree package. I got a bug report: 
https://github.com/Josef-Friedrich/nodetree/issues/46
I was able to narrow down the problem:
debug.tex:
\documentclass{article}
\begin{document}
\directlua{
   luatexbase.add_to_callback('vpack_filter',
     function(head)
       if node.type(head.id) == 'whatsit' and head.subtype == 1 then
         local tmp = head.data
       end
       return true
     end,
     'debug'
   )
}
\begin{figure}
   \caption{test}
\end{figure}
\end{document}
lualatex debug.tex:
! Incomplete \iffalse; all text was ignored after line 19.
<inserted text>
\fi
l.19 \end{figure}
The line 'local tmp = head.data' causes the error. I tried also 
'print(head.data)' or 'local tmp = head['data']'. These access types 
also caused a crash.
Access to fields other than data works without any problems.
   print(head.stream)
   print(head.id)
   print(head.xxx)
Is this a bug in LuaTeX? Or how can I access the field 'data' of a 
whatsit(write) node for debugging purposes?
A tex error is not a crash and normally not a bug either. I suggest you 
look into what the "data" field gets set to which is unclear from your 
example.

\directlua{
     callback.register('vpack_filter', function(head)
         if node.type(head.id) == 'whatsit' and head.subtype == 1 then
             print(head.data)
         end
         return true
     end)
}

           \def\hello{\iftrue true\else false\fi}
           \def\world{\iftrue true\else false\fi}
\protected\def\HELLO{\iftrue TRUE\else FALSE\fi}
\protected\def\WORLD{\iftrue TRUE\else FALSE\fi}

\noindent \directlua{
     local n = node.new("whatsit",1)
     n.data = [[(\hello\world)(\HELLO\WORLD)]]
     print(n.data)
     tex.print(n)
}
test test test

\bye

So maybe use \tracingall in your latex example code to get an idea what 
is going on?

Hans

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