Re: [FR] Recognize L3 \msg_line_context: on warning parsing

[Florent Rougon]

Hi,

Tassilo Horn <tsdh@gnu.org> wrote:

> We could do that only if l3msg is loaded for the current document.  I
> would like to try it but cannot find out which TeXLive package I need
> for l3msg.  I have
>
>   texlive-{bin,core,latexextra,bibtexextra,pictures,science,fontsextra}
>
> but apparently there is no l3msg...  Any hints?

l3msg is just this:

  https://github.com/latex3/latex3/blob/main/l3kernel/l3msg.dtx

It's a “chapter” of the LaTeX kernel in its literate programming form
('texdoc interface3' calls it a module). There is no \usepackage nor any
'import'-alike thingy needed to have it available. If you run current
LaTeX, l3msg is there, in the format (in earlier releases of the LaTeX
kernel, \usepackage{expl3} was needed).

Unrelated to your question but related to the thread: there is another,
less common way to print error messages, which works in expansion-only
contexts: \msg_expandable_error:nnn and friends. Since neither \message
nor \write work in expansion-only contexts, \msg_expandable_error:nnn
works by triggering a specially crafted “Undefined control sequence”
error, as it seems. The result is slightly ugly as compared to normal
error messages, but this is the only way I know to print error messages
in expansion-only contexts. The attached document shows an example,
which yields the following output on the terminal:

./document.tex:19: Undefined control sequence.
<argument> \::error 
                    ! foo: This is an error message: 'some stuff'.
l.19 \edef\zzz{\foomsg{some stuff}
                                  }

Regards

-- 
Florent

document.tex
Description: Expandable message printing