Description

Using the (very handy!) pandoc.List type in a Lua filter causes the value to be serialized by pandoc.json as a JSON object rather than an array.

To demonstrate, if you create the following filter as test.lua

function Pandoc(doc)
  local t1 = {"one", "two", "three"} -- two identical tables, indexed by integer
  local t2 = {"one", "two", "three"}

  pandoc.List(t2) -- make the second a List

  print(pandoc.json.encode(t1)) -- this serializes as a JSON array
  print(pandoc.json.encode(t2)) -- but this does not
  os.exit()
end

and run it

echo | pandoc -L test.lua

it outputs the following:

["one","two","three"]
{"1":"one","2":"two","3":"three"}

These two lines should be the same.

Possible cause

The pandoc.List type adds an "__index" function to the metatable. Is this the culprit? (Perhaps using string indexes rather than numbers?)

Version info

Tested on pandoc 3.1.13