Add anchor links to all headings

Makefile

@@ -1,6 +1,6 @@
 %.html: venv
 	mkdir -p out/$(dir $@)
-	. $(VENV)/activate && pandoc -t html5 --template=template.html -F code-block-filter.py src/$*.md -o out/$*.html -s --syntax-definition=toml.xml --highlight-style=diesel.theme
+	. $(VENV)/activate && pandoc -t html5 --template=template.html -F code-block-filter.py --lua-filter=anchor-links.lua src/$*.md -o out/$*.html -s --syntax-definition=toml.xml --highlight-style=diesel.theme
 
 page: index.html compare_diesel.html guides docs news changelog
 	cp -R assets/ out

anchor-links.lua

@@ -0,0 +1,16 @@
+-- copied from https://github.com/jgm/pandoc-website/blob/master/tools/anchor-links.lua
+
+-- Adds anchor links to headings with IDs.
+function Header (h)
+  if h.identifier ~= '' then
+    -- an empty link to this header
+    local anchor_link = pandoc.Link(
+      {},                  -- content
+      '#' .. h.identifier, -- href
+      '',                  -- title
+      {class = 'anchor', ['aria-hidden'] = 'true'} -- attributes
+    )
+    h.content:insert(1, anchor_link)
+    return h
+  end
+end