Searching for lua files in --data-dir and --resource-path

[massifrg]

I wrote some lua filters, readers and writers for Pandoc that share some common functions, so I put those functions in a base module that is loaded with the require lua command.

Sometimes I need to use those filters, readers and writers outside their directory, like this:

pandoc -f path_to_custom_reader/custom_reader.lua \
       -t path_to_custom_writer/custom_writer.lua \
       -L path_to_filter/filter.lua \
       document.ext

If those lua files require some base lua module in their directory, pandoc can't find it and it tells you something like this (a real case of mine):

Error running Lua:
../src/indices2json.lua:22: module './pandoc-indices' not found:
...

I thought that passing the path of the shared lua module with --data-dir or --resource-path options would make it work, but it does not.

Eventually @tarleb pointed me to the sluaggo repo where I found a section about the same problem.

This is a code you may use in your lua code that needs to load other lua files in the --data-dir and/or --resource-path directories:

---Add paths to look in for Lua code to be loaded with `require`.
---@param paths string[]
local function addPathsToLuaPath(paths)
  local luapaths = {}
  local path
  for i = 1, #paths do
    path = paths[i]
    if path and type(path) == "string" then
      table.insert(luapaths, path .. "/?.lua")
      table.insert(luapaths, path .. "/?/init.lua")
    end
  end
  package.path = package.path .. ";" .. table.concat(luapaths, ";")
end

If you want to look for lua code in the --resource-path, just add:

addPathsToLuaPath(PANDOC_STATE.resource_path)

If you want to look for lua code in the --data-dir, just add:

addPathsToLuaPath({ PANDOC_STATE.user_data_dir })

[massifrg]

Some further notes.

Paths precedence

The addPathsToLuaPath defined in the first message gives precedence to the lua files you may have installed in usual, default lua paths:

package.path = package.path .. ";" .. table.concat(luapaths, ";")

If you want to search first in the paths added with addPathsToLuaPath, change it like this:

package.path = table.concat(luapaths, ";") .. ";" .. package.path

Looking in the same directory of the script

Without specifying any path with --data-dir and --resource-path, you can search for lua files in the directory of your script this way:

addPathsToLuaPath({ pandoc.path.directory(PANDOC_SCRIPT_FILE) })