Re: Bug#793067: Bug#792328: info: can no longer find the Emacs manual

[Gavin Smith <gavinsmith0123@gmail.com>]

I implemented an option in the standalone Info browser to search the
subdirectory containing the current Info file when following a
cross-reference to another manual, before searching through the Info
file search path. Emacs Info could have a similar option.

The variable is called "follow-strategy": in Emacs the variable could
be "Info-follow-strategy". The two possible values at the moment are
"remain" and "path". "remain" is the default: it means to try to
remain in the current subdirectory. The other is "path" which means
search through the search path, which was the previous default
behaviour. If you can think of better names please email.

The intention behind this change is to improve support for
installation of multiple versions of manuals at once. For example,
with a dir entry of

* Emacs-23: (emacs-23/emacs)Top.

and with files emacs-23/emacs.info, emacs-23/calc.info
doing "info Emacs-23" gives the emacs-23/emacs.info file. Then
following a cross-reference "*Note (calc)Top::." will find
emacs-23/calc.info, instead of whatever calc.info file was earlier in
the search path. Likewise there can be other subdirectories under the
main Info subdirectory for other versions, like "emacs-24" or
"emacs-25", containing the corresponding Info files.

This should be useful for projects like Emacs with many manuals that
all reference each other, and when finding the manual for the same
version is desirable.

This appears to provide the functionality that some users wanted, for
example the Debian maintainers. However, let me point out what this
doesn't accomplish:

* References to the "emacs" manual from outwith the "emacs-23"
subdirectory will not be capable of finding "emacs-23/emacs.info",
unless "emacs-23" is in the search path.
* Such dir entries cannot at present be automatically generated by
appropriately invoking install-info (the program to update dir files),
or by Automake-generated build systems that install Info files. So
there still isn't a convenient way to install and access multiple
versions of Info manuals at once.
* References to subdirectories in node specifications aren't treated
the way they need to be for this to work by the Info browser from the
Texinfo 6.0 release; this has been changed since then in the
development sources.

Please email bug-texinfo@gnu.org with any suggestions that could be
useful for the Texinfo project.

Eli Zaretskii asked me to file this bug report. I emailed
bug-gnu-emacs because M-x report-emacs-bug isn't set up to send emails
for me.