Better handle duplicate destinations

luametalatex-back-pdf.lua

@@ -142,8 +142,12 @@ local function do_dest(prop, p, n, x, y)
   elseif dest_type == "fitbv" then
     data = string.format("[%i 0 R/FitBV %.5f]", cur_page, sp2bp(x))
   end
+  if pfile:written(dests[id]) then
+    texio.write_nl(string.format("Duplicate destination %q", id))
+  else
     dests[id] = pfile:indirect(dests[id], data)
   end
+end
 local function do_refobj(prop, p, n, x, y)
   pfile:reference(prop.obj)
 end

luametalatex-pdf.lua

@@ -7,6 +7,13 @@ local pairs = pairs
 local setmetatable = setmetatable
 local assigned = {}
 local delayed = {}
+-- slightly tricky interface: No/nil return means that the objects content
+-- isn't known yet, while false indicates a delayed object.
+local function written(pdf, num)
+  num = pdf[num]
+  if not num or num == assigned then return end
+  return num ~= delayed
+end
 local function stream(pdf, num, dict, content, isfile)
   if not num then num = pdf:getobj() end
   if pdf[num] ~= assigned then
@@ -117,6 +124,7 @@ local pdfmeta = {
   delayed = delayed,
   delayedstream = delayedstream,
   reference = reference,
+  written = written,
 }
 pdfmeta.__index = pdfmeta
 local function open(filename)