bug#27933: emacs25: default info dir initialization slow with remote filesystems

[Alfred M. Szmidt]

   >    > Standard info does the right thing, and shows both local (those listed
   >    > by INFOPATH) dir files, and the system ones.
   >    >
   >    > Reverting the change (5f7db63a93f0c670d6f88dd24f922462abce7d8c) makes
   >    > things work as expected.
   >
   >    "Alfred M. Szmidt" <ams@gnu.org> writes:
   >
   >    > Sorry -- too many distractions while writing, I missed to add one
   >    > additional (important) note.  Started with -Q and then evaluating:
   >    >
   >    >   (add-hook 'Info-mode-hook
   >    >         (lambda ()
   >    >                   (setq Info-additional-directory-list 
Info-default-directory-list)))
   >    >
   >    > before entering info.
   >
   >    Do you need to have both INFOPATH set and this hook set to reproduce the
   >    problem?
   >
   > Yes, exactly.

   The code here is pretty convoluted, but reading it, I think we just
   don't support doing something like that any more (since
   Info-default-directory-list isn't populated any more at this point).
   Which is why the changes here are listed under "Incompatible changes in
   Emacs 29.1".

Yes, it is convulted. :-/

But I think the situation gets slightly more convulted with this
change.  Now, there is no easy way of adding back the default
directories where Emacs searches.

The docstring could need a touch up, mentioning how
Info-default-directory-list and Info--default-directory-list work
together or hint towards it. The text is slightly misleading, since
the following is not really the case:

  This variable is used as the default for initializing
  `Info-default-directory-list' when Info is started, unless the
  environment variable INFOPATH is set.


I've tried to get the same behaviour that I had, namley that of
INFOPATH + Info-default-directory-list (in that order).  The only
thing that comes to mind is explicitly calling
Info--default-directory-list to set it up; which doesn't seem very
nice.

  (add-hook 'Info-mode-hook
          (lambda ()
            (setq Info-additional-directory-list 
                  (if (fboundp 'Info--default-directory-list)
                      (Info--default-directory-list)
                    Info-default-directory-list))))
              
If one could re-do all of this, having Info-additional-directory-list
be initialized to INFOPATH would have made most sense.  There can be
very few reasons to delete the default Emacs info directory locations,
and having INFOPATH override those always seemed backwards, and not
what stand-alone Info does -- so while the Emacs documentation says
that one should customize INFOPATH for both, the customizations aren't
really the same :-(

PS.  Shouldn't bugs become unarchived when someone replies to an
already archived one?  The discussion here is now lost in the ether...