bizarre bug in xml

bizarre bug in xml

[Thomas A. Schmitz]

Hi all,

this is the most bizarre bug I've ever seen in context. I would be 
grateful if others could try to replicate it. Test file:

\startbuffer[test]
<document>
     <hskip width="1em"/>Materiam vati da Venus alma tuo.
</document>
\stopbuffer

\startxmlsetups xml:testsetups
         \xmlsetsetup{#1}{*}{-}
	\xmlsetsetup{#1}{document|
			hskip}{xml:*}
\stopxmlsetups

\xmlregistersetup{xml:testsetups}

\startxmlsetups xml:document
    \xmlflush{#1}
\stopxmlsetups

\startxmlsetups xml:hskip
	\hskip\xmlatt{#1}{width}
\stopxmlsetups

\starttext
	\xmlprocessbuffer{main}{test}{}
\stoptext

This gives an error with the latest lmtx (2020.11.19 11:28, linux 64 bit):

tex error       > tex error on line 10 in file ./xmltest.tex: Valid 
keyword expected, likely 'minus'


<lua output> Ma
     teriam vati da Venus alma tuo.
<macro> \22>:xml:document #1->\xmlflush {#1}

<lua output> }


<macro> \22>:xml:process #1->\xmlregistereddocumentsetups 
{#1}{#1}\xmlmain {#1}


<macro> \lxml_process ...ocument {#3}#2{#3}{#4}\setcatcodetable 
\notcatcodes \doifelsenothing {#5}{\xmlsetup 
{#3}{xml:process}}{\xmlsetup {#3}{#5}}
     \endgroup

<line 4.24>     \xmlprocessbuffer{main}{test}{}

The file compiles cleanly if I give the --luatex switch.

Now for the bizarre part: if you delete the capital M of "Materiam" or 
replace it by any other capital letter, the file compiles. What's going 
on here?

Thanks, and all best

Thomas
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Re: bizarre bug in xml

[Wolfgang Schuster]

Thomas A. Schmitz schrieb am 20.11.2020 um 22:44:
> 
> Hi all,
> 
> this is the most bizarre bug I've ever seen in context. I would be 
> grateful if others could try to replicate it. Test file:
> 
> \startbuffer[test]
> <document>
>      <hskip width="1em"/>Materiam vati da Venus alma tuo.
> </document>
> \stopbuffer
> 
> \startxmlsetups xml:testsetups
>          \xmlsetsetup{#1}{*}{-}
>      \xmlsetsetup{#1}{document|
>              hskip}{xml:*}
> \stopxmlsetups
> 
> \xmlregistersetup{xml:testsetups}
> 
> \startxmlsetups xml:document
>     \xmlflush{#1}
> \stopxmlsetups
> 
> \startxmlsetups xml:hskip
>      \hskip\xmlatt{#1}{width}

     \hskip\xmlatt{#1}{width}\relax

> The file compiles cleanly if I give the --luatex switch.
> 
> Now for the bizarre part: if you delete the capital M of "Materiam" or 
> replace it by any other capital letter, the file compiles. What's going 
> on here?

Optional arguments (e.g. plus/minus values for \hskip) for commands are 
handled different in LMTX but it was always recommended to add \relax 
after the last value.

Wolfgang
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Re: bizarre bug in xml

[Pablo Rodriguez]

On 11/20/20 10:52 PM, Wolfgang Schuster wrote:
> [...]
> Optional arguments (e.g. plus/minus values for \hskip) for commands are
> handled different in LMTX but it was always recommended to add \relax
> after the last value.

Hi Wolfgang,

the same would apply to \vskip, wouldn’t it?

Many thanks for your help,

Pablo
--
http://www.ousia.tk
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Re: bizarre bug in xml

[Hans Hagen]

On 11/21/2020 2:09 AM, Pablo Rodriguez wrote:
> On 11/20/20 10:52 PM, Wolfgang Schuster wrote:
>> [...]
>> Optional arguments (e.g. plus/minus values for \hskip) for commands are
>> handled different in LMTX but it was always recommended to add \relax
>> after the last value.
> 
> Hi Wolfgang,
> 
> the same would apply to \vskip, wouldn’t it?
also for \hrule and \vrule (and in pdftex/luatex some backend related 
primitives); primitives like \hbox have their keyword scan terminated by 
a leftbrace token

Hans

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Re: bizarre bug in xml

[Wolfgang Schuster]

Thomas A. Schmitz schrieb am 20.11.2020 um 22:57:
>
> On 11/20/20 10:52 PM, Wolfgang Schuster wrote:
>> Optional arguments (e.g. plus/minus values for \hskip) for commands 
>> are handled different in LMTX but it was always recommended to add 
>> \relax after the last value.
>
> Thank you Wolfgang, that makes the file indeed compile again! Any 
> explanation for the strange behavior of the error?

In LMTX the order of the plus and minus values of \hskip can be written 
in any order and it's even possible to set them multiple times (try the 
example below with LuaTeX and LMTX).

To check whether a stretch or shrink value is set LMTX takes a look at 
the next character (p, P, m or M) before it makes a decision, when you 
have now a word after \hskip which start with one of these characters 
(e.g. Materiam) you trigger the scanner which fails because it didn't 
find a keyword. To avoid such problems always add \relax after the last 
value of \hskip, this is even explained in one of the exercises in the 
TeXbook.

\starttext

a\hskip 1cm plus 5mm minus 5mm b

a\hskip 1cm minus 5mm plus 5mm b

a\hskip 1cm pLuS 5mm MiNuS 5mm b

a\hskip 1cm plus 5mm minus 5mm plus 1cm b

\stoptext

Wolfgang

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Re: bizarre bug in xml

[Thomas A. Schmitz]

On 11/21/20 11:04 AM, Wolfgang Schuster wrote:
> To check whether a stretch or shrink value is set LMTX takes a look at 
> the next character (p, P, m or M) before it makes a decision, when you 
> have now a word after \hskip which start with one of these characters 
> (e.g. Materiam) you trigger the scanner which fails because it didn't 
> find a keyword. To avoid such problems always add \relax after the last 
> value of \hskip, this is even explained in one of the exercises in the 
> TeXbook.

Thank you Wolfgang, now it all makes sense. I will relax more and dust 
off my copy of the TeXbook. I used to read small chapters in the tramway 
on my way to the university, but with the lockdown, I didn't have this 
opportunity. Nah, just kidding, I haven't looked at it in a long time.

Thomas
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