Re: Export of this table fails LuaLaTeX compilation

[Max Nikulin]

On 12/10/2022 16:17, gerard.vermeulen@posteo.net wrote:
> On 12.10.2022 07:55, Max Nikulin wrote:
> > On 12/10/2022 12:15, gerard.vermeulen wrote:
> > > On 12.10.2022 06:45, Max Nikulin wrote:
> > > > LuaLaTeX is irrelevant. It seems \hline is allowed only immediately
> > > > after \\. Minimal LaTeX example:
> > > >
> > > > \begin{tabular}{l}
> > > > b\\\relax
> > > > \hline
> > > > \end{tabular}
> > >
> > > Your example fails on my Mac texlive-2020 with:
> > >
> > > ! Misplaced \noalign.
> > > \hline ->\noalign
> > >                    {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth 
> > > \futurelet...
> > >
> > > l.40 \hline
> > >
> > > It compiles when I remove \hline
> >
> > Gerard, we forgot to post the reason why \relax has been added after
> > \\. The intention was to  prevent errors in the case of
> >
> > | a   |
> > | [b] |
> >
> > or
> >
> > - item \\
> >   [2022-10-12]
> >
> > Stewart Thomas. [BUG] Tables with square brackets do not compile in
> > PDF (latex) export. Wed, 10 Nov 2021 11:16:10 -0500.
> > https://list.orgmode.org/CAO12V+wB18nAN0FuDPAeN94GHdt_2nbdJtc4u7n4W3HAZbaZsA@mail.gmail.com
> >
> > I can not figure out an easy way to separate \\ from [b] text but to
> > prevent the problem you have discovered. I am unsure if
> >
> >     \\[0pt]
> >
> > has no negative consequences and safe enough. I expect that LaTeX
> > sources are not easy to read when fragile sequences of tokens are
> > involved.
> >
> > I just have realized that some users might take advantage of earlier
> > behavior as a feature:
> >
> > - item \\
> >   [1cm]
> > - item
> >
> > I think that [1cm] should be treated as text, however I have no idea
> > how to allow users to specify amount of vertical space and to not
> > limit line break to LaTeX only. @@latex:\\[1cm]@@ is not suitable when
> > the same text should be exported to ascii, html, etc.
>
> Max, thanks for the background information.
>
> For your info:
> 1. I also need to remove \relax in the LaTeX export using Gentoo 
> texlive-2022 to compile.

Adding \relax is my fault, I did not expect that it may break \hline. 
Such behavior should be stable over decades. The question is how to 
allow users to have square brackets in the beginning of the line 
following \\ and not break some use case.

> 2. On my systems ws-butler removes the trailing whitespace.
> 3. I edited your example with nano to add the trailing space after 
> \relax, but it still does not compile.

Sorry, I did not get your point with trailing space. LaTeX ignores 
spaces after commands (e.g. "a\relax b" becomes "ab") and in the 
beginning of the line. What I am afraid of is unintentionally introduce 
white space at the beginning of the line, e.g. if
| a |
| b |
|---|
is exported as
{} a \\
{} b \\
\hline
then cell contents will be " a" and " b", not "a" and "b".
\relax a \\
\relax b \\
\hline
has no such problem.