Image Lua filter new bug?

[ricopicone]

I recently upgraded to pandoc 3.1.11.1 and a trusty Lua filter (target: tex) started behaving strangely. I thought I'd ask if this is intended behavior here before reporting it as a bug. Essentially, when the Image filter runs, it wraps a generic figure environment around the custom version prescribed by the filter.

filter.lua:

function figurer(el)
  local caption = el.caption
  if caption==nil then
    caption = ""
  else
    caption = pandoc.Para(caption)
    local caption_doc = pandoc.Pandoc(caption)
    caption = pandoc.write(caption_doc,'latex')
  end
  local src = el.src
  local graphics_command = "\\includegraphics["
  local fig_begin = "\\begin{figure}[H]%\n" ..
      "\\centering\n"
  local fig_end = "\\end{figure}%\n"
  -- construct latex figure
  local fig_tex = fig_begin ..
    graphics_command.."]{"..src.."}\n\\figcaption{" ..
    el.attr.identifier.."}{" .. 
    caption.."}\n" .. 
    fig_end
  return pandoc.RawInline('latex', fig_tex)
end

function Image(el) 
  return figurer(el)
end

return {
  {Image = Image}
}

source.md:

![A caption.](figures/fig.png){#fig:fig}

Makefile:

index.tex: source.md filter.lua
	pandoc -f markdown --lua-filter filter.lua -o $@ $<

index.tex:

\begin{figure}
\centering
\begin{figure}[H]%
\centering
\includegraphics[]{figures/fig.png}
\figcaption{}{A caption.}
\end{figure}%
\caption{A caption.}\label{fig:fig}
\end{figure}

There are two problems: (1) the generic figure environment wrapped around the custom one and (2) the identifier is not getting properly passed to the filter (but it does get used in the generic outer environment). Help appreciated!

[jgm]

If you do pandoc -t native you can inspect the AST that will be manipulated by the filter.

c $ pandoc -t native
![A caption.](figures/fig.png){#fig:fig}
[ Figure
    ( "fig:fig" , [] , [] )
    (Caption
       Nothing [ Plain [ Str "A" , Space , Str "caption." ] ])
    [ Plain
        [ Image
            ( "" , [] , [] )
            [ Str "A" , Space , Str "caption." ]
            ( "figures/fig.png" , "" )
        ]
    ]
]

Your filter modifies the Image element but leaves it in the context of the Figure. (You probably recently upgraded to a version of pandoc with the Figure element.)

What you should do is match on Figure instead, extract the image, and do roughly as before.

[ricopicone]

Follow-up question: In my old filter, I was able to pass both the identifier and attributes to a custom LaTeX function. However, it looks like now the Figure gets the identifier and the Image gets the attributes. Is there a way to pass the identifier down to the Image or the attributes up to the Figure so I can still use my LaTeX function? Thanks for all your help!

[jgm]

No, but you should be able to get them in your filter from the respective elements.

[ricopicone]

It sounds like I will have to change my LaTeX function so that it doesn't require both the identifier and attributes. It's too bad I can't access both. I'm not sure why it was split up the way it is (i.e., Figure gets the identifier and the Image gets the attributes), but it's inconvenient for the way I've done things in the past. Anyway, thanks for your help.

[ricopicone]

Just to be sure, there's no way for me to access the Image attributes directly from the Figure filter? They're in there, nested inside the image:

Figure ("fig:fig",[],[]) (Caption Nothing [Plain [Str "A",Space,Str "caption."]]) [Plain [Image ("",[],[("figwidth","1\\linewidth")]) [Str "A",Space,Str "caption."] ("figures/fig.png","")]]

I just don't know how to access the nested attribute (in this case) ("figwidth","1\\linewidth") from the Figure filter.

[ricopicone]

Actually, I think I figured it out. In the Figure filter, I selected the Image with

local image = el.content[1].content[1]

Then I could get el.identifier, image.attr.attributes, and image.caption directly in the Figure filter. (It looked like I would be able to get el.caption, but that didn't work). I don't know how fragile this is, but it seems to work.