bug#60762: 28.2; info--manual-names ignores Info-additional-directory-list

[Sean Devlin]

Hi folks,

Info.el gives the following advice for customizing the Info manual
search path:

"Normally, you should either set INFOPATH or customize
`Info-additional-directory-list' ..."

The variable Info-additional-directory-list is intended as the main
Lisp-level customization point for users. Its documentation states:

"These directories are searched after those in `Info-directory-list'."

Unfortunately, it is not used consistently across info.el.

In particular, the info--manual-names routine does not respect the
Info-additional-directory-list variable. While this function is internal
to the package, it is used to generate candidates for completing read in
some commands.

Here is a recipe to demonstrate the problem:

1. mkdir -p /tmp/emacs
2. touch /tmp/emacs/example.info
3. emacs -Q
4. M-: (setq Info-additional-directory-list '("/tmp/emacs/")) RET
5. C-h R exam TAB

Observe that there are no completion candidates.

6. C-g
7. M-: (add-to-list 'Info-directory-list "/tmp/emacs/" 'append) RET
8. C-h R exam TAB

Observe that there are completion candidates for the example info file as
expected.

There may be other instances where Info-additional-directory-list is
ignored. For example, I see that the Info-read-node-name-1 function
references Info-directory-list but not Info-additional-directory-list.

Thanks!

In GNU Emacs 28.2
System Description:  macOS 13

Configured using:
'configure --with-ns '--enable-locallisppath=/Library/Application
Support/Emacs/${version}/site-lisp:/Library/Application
Support/Emacs/site-lisp' --with-modules'

Configured features:
ACL GMP GNUTLS JSON LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER THREADS
TOOLKIT_SCROLL_BARS ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
info iso-transl tooltip eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 53964 7691)
(symbols 48 6840 1)
(strings 32 19755 1604)
(string-bytes 1 669941)
(vectors 16 14412)
(vector-slots 8 199666 13467)
(floats 8 24 38)
(intervals 56 212 4)
(buffers 992 11))