I addressed Martin's comments (thank you!) in
https://github.com/lelit/cpython/commits/issue22228_2, removing pointless
usage of a macro and avoiding usage of module's state to store the "next line
index", keeping it in a plain static variable.

Let me know how it looks now.

Martin Panter writes:

> Python’s “readline” module currently has runtime detection of Editline vs
> Gnu Readline. I am not sure if it is strictly needed, or just that it was
> easier than build-time detection, as hinted in
> <https://bugs.python.org/issue6877#msg92654>. It is confusing, because we
> have other build-time detection of particular Readline features.

Yes, it confused me too. Also, there is at least one spot in setup_readline()
that seems wrong to me, because it does not consider if it's effectively using
libedit:

    #ifndef __APPLE__
        if (!isatty(STDOUT_FILENO)) {
            /* Issue #19884: stdout is not a terminal. Disable meta modifier
               keys to not write the ANSI sequence "\033[1034h" into stdout. On
               terminals supporting 8 bit characters like TERM=xterm-256color
               (which is now the default Fedora since Fedora 18), the meta key is
               used to enable support of 8 bit characters (ANSI sequence
               "\033[1034h").

               With libedit, this call makes readline() crash. */
            rl_variable_bind ("enable-meta-key", "off");
        }
    #endif

> Perhaps you may be able to try out Editline using my patch for Issue 13501,
> but in my experience, the non-Apple patched Editline is too buggy to be
> useful in Python for much more than experimentation.

I will try to find some spare time to spend on this, but unfortunately I can
not promise I'll be able to do that in the near future, sorry.

> I would prefer to expose more of this at the Python level, but that seems
> hard to do.

Yeah, I know (I've been here nearly from the beginning ;-).