% Bugs:
% 0-3: \prevdepth/\prevgraf problems.
% 4-5: node fields problems.
%
% Bug #3 seems to be the crux of the biscuit, but I'm no good judge.

% Choose your bug:
\chardef\bug=0


\ifcase\bug % 0
% tex.prevdepth is supposed to be read-only, according to the manual. Yet:
% (Also with prevgraf.)
\directlua{
  tex.prevdepth = 100
  texio.write_nl(tex.prevdepth)
  }





\or % 1
% Improper prevdepth? Disappears if the following line is uncommented.
%\directlua{tex.prevdepth = 0}
\quitvmode\directlua{texio.write_nl(tex.prevdepth)}





\or % 2
% (This might be just a side-effect/particular case of the following problem.)
%
% Disconnection between tex.prevdepth and \prevdepth.  (Also with prevgraf.)
% Less clear to me, though, I might have misunderstood something.
%
% write_nl prints -65536000 as expected for the first paragraph.  For the
% second, however, it prints 0, i.e. the \prevdepth declaration isn't taken
% into account. Now it is taken into account if you remove the line:
%
% tex.prevdepth = info.prevdepth
%
% But then prevdepth isn't automatically updated; so I guess setting
% tex.prevdepth to info.prevdepth is required when breaking paragraph by hand
% (unless, well, see next bug).

\directlua{
callback.register("linebreak_filter",
function (head)
  texio.write_nl(tex.prevdepth)
  local par, info = tex.linebreak(head)
  tex.prevdepth = info.prevdepth
  return par
end)}

abc\par \prevdepth=-10000pt abc





\or % 3
% The paragraph's first node is an hlist for the first two paragraphs, and a
% glue for the third (and any following paragraphs). In other words, it is as
% if tex.linebreak takes prevdepth into account if and only if it has already
% been set with \prevdepth (not tex.prevdepth).
\directlua{
callback.register("linebreak_filter",
function (head)
  local par = tex.linebreak(head)
  texio.write_nl(par.id)
  return par
end)}

abc\par
abc\par
\prevdepth=0pt
%\directlua{tex.prevdepth = 0} % Doesn't work the Lua way.
abc\par





\or % 4
% Prints "subtype" among others, although temp nodes have no subtype (also
% with action items 49, and probably other); also, prints "next" (for 50) and
% "next" and "prev" (for others), which is probably on purpose, although it
% might lead to error when investigating an isolated node.
\directlua{
for _, f in pairs(node.fields(0)) do
  texio.write_nl(f)
end}

% Correlatively, validates an unexisting field:
\directlua{
local n = node.new(50)
if node.has_field(n, "subtype") then
  texio.write_nl("Something's wrong.")
end
}





\or % 5
% And a crash (only with 50, as far as I can tell):
\directlua{
local n = node.new(50)
local x = node.has_field(n, "foo")
}



\fi

\end