Fixing guile-debugger.ly - Some investigations

[Michael Käppler]

Hi all,
while trying to debug a problem concerning scheme code I stumbled upon
the somewhat broken
state of the "guile-debugger.ly"-interface.
This was discussed several times on the list, seemingly without a good
solution.
See:
https://lists.gnu.org/archive/html/lilypond-user/2014-05/msg00595.html
and more recently
https://lists.gnu.org/archive/html/lilypond-user/2019-09/msg00284.html

I found that guile-debugger.ly will only work on my Ubuntu 18.04 system
if there's an additional guile-1.8 installation present.
This is true for the vanilla installers 2.18.2 and also for 2.19.83 from
http://lilypond.org/download.html and also for the 2.18.2 package in the
Ubuntu 18.04 repo.
Ubuntu 18.04 does not provide guile-1.8 anymore, AFAIK. Self-compiling
worked flawlessly for me, but I think it would
be better to provide the libraries needed for guile-debugger.ly with the
lilypond installer. (Or, as a quick and dirty "solution", add
an error message to guile-debugger.scm stating that guile-1.8 has to be
installed in order to make guile-debugger.ly work)

There a two different problems, though.
1. With the help of strace I could figure out that guile does load
libguilereadline, which is provided
in /lilypond/usr/lib. Then for some reason which I could not find out it
does not (not even try to) load libreadline, however.
It does not output an error, either.
If I copy a self-compiled libguilereadline from my own guile 1.8.8 build
to /lilypond/usr/lib, it does succeed to load libreadline.
The very different sizes of the provided libguilereadline (4352 bytes)
compared to the packaged one (52032 bytes) seemed a bit strange to me, too.
I do not know anything about library linking etc., so maybe this is normal.
2. the whole 'debugger' directory is missing in
/lilypond/usr/share/guile/1.8/ice-9.
After copying this directory from my own guile-1.8 build, the debugger
works fine. (At least loading the debugger; I did not try any real
debugging yet)

See the full test procedure in the log attached, for which I used a
fresh vanilla 2.19.83 install.

Seems that for further investigation I need a GUB setup, which I do not
have currently.
Are the instructions that Knut(?) posted some time ago still valid?
I vaguely remember having read some about some commits that have to be
cherry-picked in order to make GUB work,
quite unsure about this.

Cheers,
Michael

lilyreadlinedebug_7_1_2020.log
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