diagram-generator: use Figure constructor in pandoc 3 and later

Fixes: #261

Author: tarleb

diagram-generator/diagram-generator.lua

@@ -353,37 +353,53 @@ function CodeBlock(block)
 
   -- If the user defines a caption, read it as Markdown.
   local caption = block.attributes.caption
-    and pandoc.read(block.attributes.caption).blocks[1].content
-    or {}
-
-  -- A non-empty caption means that this image is a figure. We have to
-  -- set the image title to "fig:" for pandoc to treat it as such.
-  local title = #caption > 0 and "fig:" or ""
-
-  -- Transfer identifier and other relevant attributes from the code
-  -- block to the image. The `name` is kept as an attribute.
-  -- This allows a figure block starting with:
-  --
-  --     ```{#fig:example .plantuml caption="Image created by **PlantUML**."}
-  --
-  -- to be referenced as @fig:example outside of the figure when used
-  -- with `pandoc-crossref`.
-  local img_attr = {
-    id = block.identifier,
-    name = block.attributes.name,
-    width = block.attributes.width,
-    height = block.attributes.height
-  }
-
-  -- Create a new image for the document's structure. Attach the user's
-  -- caption. Also use a hack (fig:) to enforce pandoc to create a
-  -- figure i.e. attach a caption to the image.
-  local img_obj = pandoc.Image(caption, fname, title, img_attr)
-
-  -- Finally, put the image inside an empty paragraph. By returning the
-  -- resulting paragraph object, the source code block gets replaced by
-  -- the image:
-  return pandoc.Para{ img_obj }
+    and pandoc.read(block.attributes.caption).blocks
+    or pandoc.Blocks{}
+  local alt = pandoc.utils.blocks_to_inlines(caption)
+
+  if PANDOC_VERSION < 3 then
+    -- A non-empty caption means that this image is a figure. We have to
+    -- set the image title to "fig:" for pandoc to treat it as such.
+    local title = #caption > 0 and "fig:" or ""
+
+    -- Transfer identifier and other relevant attributes from the code
+    -- block to the image. The `name` is kept as an attribute.
+    -- This allows a figure block starting with:
+    --
+    --     ```{#fig:example .plantuml caption="Image created by **PlantUML**."}
+    --
+    -- to be referenced as @fig:example outside of the figure when used
+    -- with `pandoc-crossref`.
+    local img_attr = {
+      id = block.identifier,
+      name = block.attributes.name,
+      width = block.attributes.width,
+      height = block.attributes.height
+    }
+
+    -- Create a new image for the document's structure. Attach the user's
+    -- caption. Also use a hack (fig:) to enforce pandoc to create a
+    -- figure i.e. attach a caption to the image.
+    local img_obj = pandoc.Image(alt, fname, title, img_attr)
+
+    -- Finally, put the image inside an empty paragraph. By returning the
+    -- resulting paragraph object, the source code block gets replaced by
+    -- the image:
+    return pandoc.Para{ img_obj }
+  else
+    local fig_attr = {
+      id = block.identifier,
+      name = block.attributes.name,
+    }
+    local img_attr = {
+      width = block.attributes.width,
+      height = block.attributes.height,
+    }
+    local img_obj = pandoc.Image(alt, fname, "", img_attr)
+
+    -- Create a figure that contains just this image.
+    return pandoc.Figure(pandoc.Plain{img_obj}, caption, fig_attr)
+  end
 end
 
 -- Normally, pandoc will run the function in the built-in order Inlines ->