Silence all citeproc warnings if possible

This requires the `pandoc.log` Lua module, which first became available
in pandoc 3.2.

Fixes: #13

Author: tarleb

_extensions/multibib/multibib.lua

@@ -54,17 +54,21 @@ local refs_div_with_properties
 local supports_quiet_arg = false
 
 --- Run citeproc on a pandoc document
-local function citeproc(doc, quiet)
-  -- utils.citeproc() was added in 2.19.1
-  if utils.citeproc and supports_quiet_arg then
-    -- Built-in Lua function
-    return utils.citeproc(doc, quiet)
-  else
-    -- Use pandoc as a citeproc processor
-    local path = PANDOC_STATE.resource_path
-    local opts = {'--from=json', '--to=json', '--citeproc',
-                  '--resource-path=' .. table.concat(path, ':'),
-                  quiet and '--quiet' or nil}
+--
+-- Falls back to the external `pandoc-citeproc` filter if the built-in
+-- citeproc processor is not available. Tries to silence all citeproc
+-- warnings, which isn't possible in some versions.
+local citeproc = utils.citeproc
+if pcall(require, 'pandoc.log') and citeproc then
+  -- silence all warnings if possible
+  local log = require 'pandoc.log'
+  citeproc = function (...)
+    return select(2, log.silence(utils.citeproc, ...))
+  end
+elseif not citeproc then
+  -- Use pandoc as a citeproc processor
+  citeproc = function (doc)
+    local opts = {'--from=json', '--to=json', '--citeproc', '--quiet'}
     return run_json_filter(doc, 'pandoc', opts)
   end
 end