protected macro vs protected luacall

[Henri Menke via ntg-context <ntg-context@ntg.nl>]

Dear list,

I have noticed a somewhat strange difference between protected macros
and protected luacalls, namely that the latter cannot be expanded by
\the.  In the example below I define a Lua function that prints
\numexpr 17\relax to the token stream and I call it once from a
protected TeX macro wrapping \directlua and once from a protected
luacall registered with token.set_lua.


\directlua{
  userdata = userdata or {}
  function userdata.test()
    tex.print("\string\\numexpr 17\string\\relax")
  end
}

\tt
\protected\def\test{\directlua{userdata.test()}}
\meaning\test\par
\edef\x{\test}\meaning\x\par
\the\test

\directlua{
  local t = lua.get_functions_table()
  t[\string#t + 1] = userdata.test
  token.set_lua("test", userdata.test, \string#t, "protected")
}
\meaning\test\par
\edef\x{\test}\meaning\x\par
\the\test

\bye


However, the second \the\test fails with the following error:


! You can't use `luacall 0' after \the.
l.21 \the\test
            

Is this asymmetry between luacalls and regular macros intended? Is
there a workaround where I can have a luacall that doesn't expand
inside of \edef but still expands after \the?

Cheers, Henri
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