How to check for used pdf-engine in lua filters?

How to check for used pdf-engine in lua filters?

[Johannes Maibaum]

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Hello,

I have the following lua filter function that uses fontspec's 
\addfontfeature to activate certain OpenType font features, in this case 
diagonal fractions for all Spans with the custom 'frac' class:

if FORMAT:match 'latex' then
    function Span (elem)
        -- Surround with fontspec's \addfontfeature{Fractions=On}
        if elem.classes:includes('frac', 1) then
            return {
                pandoc.RawInline('latex', '{\\addfontfeature{Fractions=On}
'),
                elem,
                pandoc.RawInline('latex', '}'),
            }
        else
            return elem
        end
    end
end

However, this does only work when I set `pdf-engine` to `xelatex` or 
`lualatex`. When I forget this, pandoc defaults to pdflatex which doesn't 
support fontspec, and this breaks compilation as expected:

Error producing PDF.
> ! Undefined control sequence.
> l.59 {\addfontfeature
>

Is it possible to check the value of `pdf-engine` (or if a certain LaTeX 
package like `fontspec` has been loaded) from the filter API? I would like 
to add a check like this to my filter.


Johannes

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Re: How to check for used pdf-engine in lua filters?

[John MacFarlane]

> However, this does only work when I set `pdf-engine` to `xelatex` or 
> `lualatex`. When I forget this, pandoc defaults to pdflatex which doesn't 
> support fontspec, and this breaks compilation as expected:
>
> Error producing PDF.
>> ! Undefined control sequence.
>> l.59 {\addfontfeature
>>

No, not possible.  Using a --defaults file that specifies both
the lua filter and the tex engine might help.

Re: How to check for used pdf-engine in lua filters?

[BPJ]

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Or add a metadata variable which the filter can check. You need to type both

--pdf-engine=...

and

-M pdf-engine=...

but maybe you can put that ugliness in a defaults file.

Den mån 13 apr. 2020 23:52John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> skrev:

>
> > However, this does only work when I set `pdf-engine` to `xelatex` or
> > `lualatex`. When I forget this, pandoc defaults to pdflatex which
> doesn't
> > support fontspec, and this breaks compilation as expected:
> >
> > Error producing PDF.
> >> ! Undefined control sequence.
> >> l.59 {\addfontfeature
> >>
>
> No, not possible.  Using a --defaults file that specifies both
> the lua filter and the tex engine might help.
>
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> .
>

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Re: How to check for used pdf-engine in lua filters?

[Johannes Maibaum]

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>
> Den mån 13 apr. 2020 23:52John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> skrev:
>
>>
>> No, not possible.  Using a --defaults file that specifies both
>> the lua filter and the tex engine might help.
>>
>
BPJ <bpj-J3H7GcXPSITLoDKTGw+V6w@public.gmane.org> schrieb am Di., 14. Apr. 2020, 13:47:

Or add a metadata variable which the filter can check. You need to type both

--pdf-engine=...

and

-M pdf-engine=...

but maybe you can put that ugliness in a defaults file.


I knew about the default file workaround, but wanted to ask if I was
missing an API feature. This question has now been answered. Thanks to you
both for your explanations and suggestions!

>

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