Re: [luatex-plain] disappearing math-on node

[Hans Hagen <pragma@wxs.nl>]

On 4/5/2014 3:12 PM, Philipp Gesang wrote:
> ···<date: 2014-04-03, Thursday>···<from: Hans Hagen>···
>
>> On 4/3/2014 6:29 PM, Dohyun Kim wrote:
>>> This is a bug report based on the issue discussed at
>>> https://github.com/lualatex/luaotfload/issues/212
>>>
>>> \font\tenrm{file:lmroman10-regular.otf:mode=node;script=latn}\tenrm
>>> \setbox0\vbox{%
>>>     x\penalty-10000
>>>     $a$x$a$
>>> }
>>> \unvbox0
>>> \setbox0\lastbox
>>> \unhbox0
>>> \end
>>>
>>> The plain tex code shown above fails with a lua error:
>>> luatex-fonts-merged.lua:9616: attempt to index local 'current' (a nil value)
>>>
>>> My guess is: as math-on (math-off too) is a "discardable" item after a
>>> linebreak, the first math-on node has gone away. So the
>>> math-on/math-off pair has become broken, by which the behavior of
>>> "node.end_of_math" is confused.
>>
>> mtxrun --script plain test.tex
>>
>> runs ok here so i need an example that fails with context or luatex-plain
>
> It fails with the luatex-plain format from the minimals as of
> yesterday and Luatex 4972:
>
>      error: .../context/tex/texmf-context/tex/context/base/font-ota.lua:144: attempt to index local 'current' (a nil value)
>      .
>      \bye ^^@-\par
>                  \vfill \supereject \end
>      l.17 \bye
>
> Though the issue arises only in node mode.
>
>> normally the font callback is called on a hlist and there are always
>> paired math nodes
>>
>> (what is line 9616 in the current beta?)
>
> Line 9626 with yesterday’s code. Attached are patches for
> font-ota.lua and luatex-fonts-otn.lua that guard all invocations
> of end_of_math() with checks for the subtype.

I think that the removed math node is a bad thing so that will change in 
a next luatex release (i tested a patch but it will not go in the tl 
release). (Just like the math node at the end of a line it will have 
zero surround in order to make the backend happy.)

In order to avoid the 'current' issue I'll use an overload of 
end_of_math in the generic code.

The real solution is to make the built-in end_of_math more strict 
(trivial patch ready and tested so that can end up in the next luatex).

In the context code i won't intercept it because end_of_math will do 
that at some point.

Hans

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                                           Hans Hagen | PRAGMA ADE
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