Re: How to add a `\usepackage` in a Lua filter meant to support LaTeX?

[Norman Ramsey <fellswalker-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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I can work out a solution for my own personal use.  But other people are 
using my infrastructure.  Ideally I'd like to be able to tell them, "If you 
want this effect, use this filter."  Asking them also to use a custom 
template is not only a greater burden, but it's a solution that doesn't 
compose in the same way that filters do.  You can think of the problem I'm 
trying to solve like this: I want to extend Pandoc with a new capability.  
The capability is going to be supported by new markup, new CSS (for the 
HTML writer), and new LaTeX packages (for the LaTeX/PDF writer).  But I'm 
writing more than one extension, and I want my extensions to coexist 
peacefully with other extensions.  I can manage stuff like name-space 
collisions for element classes.  But a custom template become 
non-compositional.

One of the many issues I looked at today mentioned the idea of extending 
the standard template with a `filter-header-includes` variable, or even a 
`filter-header-includes.writer` variable.  As the OP in that thread 
observed, it's a bit clunky, but with discipline from filter authors, it 
could work.  The key would be this: filter authors would need to rely on 
and invariant saying that variable is not set on the command line. @jgm, 
I'm not sure whether you considered such an extension to the default 
templates?  (Pardon my poor memory, but I got deep into the weeds.)


On Thursday, November 19, 2020 at 2:50:51 PM UTC-5 denis...-FfwAq0itz3ofv37vnLkPlQ@public.gmane.org 
wrote:

> I don't know how that would work with a filter, but wouldn't a custom 
> template be an easier solution? Or what speaks against this?
>
> Best,
> Denis
>
>
> ________________________________________
> Von: pandoc-...-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org <pandoc-...-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org> im Auftrag 
> von Norman Ramsey <fells...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Gesendet: Donnerstag, 19. November 2020 20:27:18
> An: pandoc-discuss
> Betreff: How to add a `\usepackage` in a Lua filter meant to support LaTeX?
>
> I've got a Lua filter that is meant to render certain document elements in 
> a `boxedminipage` environment. To accomplish this feat, I give the element 
> in a suitable `div`, and a Lua filter inserts the LaTeX environment. The 
> document itself remains universal, but the Lua filter is resolutely 
> intended for LaTeX.
>
> The filter adds a raw `\usepackage{boxedminipage2e}` to the 
> `header-includes` of the metadata, but unfortunately when `-V 
> header-includes=...` appears on the command line, it takes precedence and 
> the document metadata is ignored.
>
> I thought of trying to use `-M header-includes=...` instead of `-V 
> header-includes=...`, but that comes with its own problems: using the `-M` 
> option, the argument on the command line is escaped. It is not clear to me 
> if there is a mechanism I can use to put raw LaTeX in that spot.
>
> The issue of the command line overriding metadata has been discussed at 
> some length on the issue tracker (
> https://github.com/jgm/pandoc/issues/3139) and in pandoc-discuss, where a 
> related issue is laid out in the last post (
> https://groups.google.com/g/pandoc-discuss/c/N6WhlmSPXbY/m/UYJJBdZwAAAJ).
> The discussion thread in pandoc-discuss is now two and a half years old, 
> and it seemed to be in favor of a change. But as of pandoc version 
> 2.11.1.1, no change appears to have been made, and issue #3139 remains open.
>
> Is there a workaround I can add to my Lua filter that will make it work in 
> a self-contained way even in the presence of assignments to the 
> `header-includes` variable on the command line? And is there any thought of 
> #3139 being resolved one way or the other?
>
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