data/pandoc.lua: fix attribute names of Citation

The fields were named like the Haskell fields, not like the documented,
shorter version.  The names are changed to match the documentation and
Citations are given a shared metatable to enable simple extensibility.

Fixes: #4222

data/pandoc.lua

@@ -764,6 +764,8 @@ M.Attr.__newindex = function(t, k, v)
 end
 setmetatable(M.Attr, M.Attr)
 
+-- Citation
+M.Citation = {}
 
 --- Creates a single citation.
 -- @function Citation
@@ -773,20 +775,20 @@ setmetatable(M.Attr, M.Attr)
 -- @tparam[opt] {Inline,...} suffix   citation suffix
 -- @tparam[opt] int          note_num note number
 -- @tparam[opt] int          hash  hash number
-M.Citation = function(id, mode, prefix, suffix, note_num, hash)
-  prefix = prefix or {}
-  suffix = suffix or {}
-  note_num = note_num or 0
-  hash = hash or 0
-  return {
-    citationId = id,
-    citationPrefix = prefix,
-    citationSuffix = suffix,
-    citationMode = mode,
-    citationNoteNum = note_num,
-    citationHash = hash,
-  }
+M.Citation.__call = function(t, id, mode, prefix, suffix, note_num, hash)
+  return setmetatable(
+    {
+      id = id,
+      mode = mode,
+      prefix = prefix or {},
+      suffix = suffix or {},
+      note_num = note_num or 0,
+      hash = hash or 0,
+    },
+    t
+  )
 end
+setmetatable(M.Citation, M.Citation)
 
 
 ------------------------------------------------------------------------

src/Text/Pandoc/Lua/StackInstances.hs

@@ -84,12 +84,12 @@ instance ToLuaStack Citation where
 
 instance FromLuaStack Citation where
   peek idx = do
-    id' <- getTable idx "citationId"
-    prefix <- getTable idx "citationPrefix"
-    suffix <- getTable idx "citationSuffix"
-    mode <- getTable idx "citationMode"
-    num <- getTable idx "citationNoteNum"
-    hash <- getTable idx "citationHash"
+    id' <- getTable idx "id"
+    prefix <- getTable idx "prefix"
+    suffix <- getTable idx "suffix"
+    mode <- getTable idx "mode"
+    num <- getTable idx "note_num"
+    hash <- getTable idx "hash"
     return $ Citation id' prefix suffix mode num hash
 
 instance ToLuaStack Alignment where