Make checking for sequence more stringent.

lib/lyaml/init.lua

@@ -199,9 +199,24 @@ local dumper_mt = {
  elseif itsa == 'string' or itsa == 'boolean' or itsa == 'number' then
  return self:dump_scalar(node)
  elseif itsa == 'table' then
- if #node > 0 then
+ -- Something is only a sequence if its keys start at 1
+ -- and are consecutive integers without any jumps.
+ local prior_key = 0
+ local is_pure_sequence = true
+ local i, v = next(node, nil)
+ while i and is_pure_sequence do
+ if type(i) ~= "number" or (prior_key + 1 ~= i) then
+ is_pure_sequence = false -- breaks the loop
+ else
+ prior_key = i
+ i, v = next(node, prior_key)
+ end
+ end
+ if is_pure_sequence then
+ -- Only sequentially numbered integer keys starting from 1.
  return self:dump_sequence(node)
  else
+ -- Table contains non sequential integer keys or mixed keys.
  return self:dump_mapping(node)
  end
  else -- unsupported Lua type