render double-bracketed wiki links, roughly in Obsidian style

Makefile

@@ -4,7 +4,9 @@ all: html
 # (including README, maybe useful for local preview. $(filter-out README.md, ...) to exclude).
 html: $(patsubst src/%,out/%,$(patsubst %.md,%.html,$(wildcard src/*.md src/quickref/*.md))) Makefile
 
-PANDOC=pandoc -f markdown-smart-tex_math_dollars+autolink_bare_uris
+PANDOC=pandoc \
+	-f markdown-smart-tex_math_dollars+autolink_bare_uris+wikilinks_title_after_pipe \
+	--lua-filter=fixwikilinks.lua
 
 # generate html from a md file
 out/%.html: src/%.md page.tmpl

fixwikilinks.lua

@@ -0,0 +1,26 @@
+-- Pandoc's wikilinks_title_after_pipe extension makes a start at linking
+-- [[bracketed wiki links]]. This lua filter finishes the job and tries to
+-- mimic Obsidian's wiki linking, by
+-- - either hyphen-replacing or dropping all problem characters in the uri
+-- - adding ".html" to the uri path
+-- - preserving the uri fragment if any
+-- - lower-casing the uri fragment
+
+function Link(elem)
+   if elem.title == "wikilink" then
+      t = elem.target .. "#"
+      t = string.gsub(t, " ", "-")
+      t = string.gsub(t, "'", "")
+      path, frag = string.match(t, "([^#]*)#([^#]*)")
+      t = path
+      if string.len(path) > 0 then
+         t = t .. ".html"
+      end
+      if string.len(frag) > 0 then
+         frag = pandoc.text.lower(frag)
+         t = t .. "#" .. frag
+      end
+      elem.target = t
+   end
+   return elem
+end