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

1 Jun 2025

First of all, thank you for the new `value` field for `write` whatsit nodes!

So that I have understood it correctly: A debugging package such as nodetree must not 
access the `data` field, as access to the `data` field expands the token list, 
which may cause in some circumstances the document to stop compiling? 
Access to the new value field is safe as it does not expand?

I have compiled the latest LuaTeX with the lastet commit from Luigi and tried to test the new `value` field.

          \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)]]
    local output = ''
    for index, token in pairs(n.value) do
        output = output .. string.char(token[2])
    end
    print(output)
}
test

This is LuaTeX, Version 1.23.2 (TeX Live 2026/dev) 
 restricted system commands enabled.
(./hans.tex(truetrue)(\HELLO \WORLD )
 [1{/usr/local/texlive/2025/texmf-var/fonts/map/pdftex/updmap/pdftex
.map}])

Instead of the output ‘(truetrue)(\HELLO \WORLD )’ I would have expected ‘(\hello\world)(\HELLO\WORLD)’?

I also noticed the following:

I think the field `value` would still have to be entered in the file `texnodes.c` so that the `node.fields()` function can output it.

```tex
\directlua{
for index, field in pairs(node.fields(node.id('whatsit'), 1)) do
  print(field)
end
}
``

diff --git a/source/texk/web2c/luatexdir/tex/texnodes.c b/source/texk/web2c/luatexdir/tex/texnodes.c
index 47eda07cb..0c8275d10 100644
--- a/source/texk/web2c/luatexdir/tex/texnodes.c
+++ b/source/texk/web2c/luatexdir/tex/texnodes.c
@@ -1049,7 +1049,8 @@ void l_set_whatsit_data(void) {
     init_field_key(node_fields_whatsit_write, 0, attr);
     init_field_key(node_fields_whatsit_write, 1, stream);
     init_field_key(node_fields_whatsit_write, 2, data);
-    init_field_nop(node_fields_whatsit_write, 3);
+    init_field_key(node_fields_whatsit_write, 3, value);
+    init_field_nop(node_fields_whatsit_write, 4);
 
     init_node_key(whatsit_node_data, pdf_literal_node,     pdf_literal)
     init_node_key(whatsit_node_data, pdf_late_literal_node,pdf_late_literal)

Josef

On 30.05.25 16:17, luigi scarso wrote:
...
On Fri, 30 May 2025 at 10:45, Linas Stonys mailto:lstonys@vtex.lt> wrote:
life is running so fast that change in TL2026 sounds legit.
Just pushed in  https://gitlab.lisn.upsaclay.fr/texlive/luatex.git https://gitlab.lisn.upsaclay.fr/texlive/luatex.git
commit ea28673465c4d9445bbb582ccdb5dbea75cafc19 (HEAD -> master, origin/master, origin/HEAD)
Author: Luigi Scarso mailto:luigi.scarso@gmail.com>
Date:   Fri May 30 16:07:24 2025 +0200
    Additional 'value' field for write nodes (getfield) for unexpanded token tables (H.Hagen). LaTeX 1.23.2
--
luigi
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[Dev-luatex] Re: Crash when accessing the field 'data' of a whatsit(write) node

Josef Friedrich