Hi,
I think there is a bug in `io.open` in --safer mode:
\directlua{
io.open(tex.jobname .. '.tex'):close()
}
\bye
If this document is run with `luatex --safer` it leads to `bad argument #1 to 'gsub' (string expected, got nil)`.
The problem is a missing `not` in luatex-core.lua, function luatex_io_open_readonly:
The default argument 'r' is used if an explicit argument is given and when no "how" argument
is given it tries to interpret the non existing argument.
hm this is tricky.. we have to check it carefully,
these "safer" modes are quite complicated things.