master 5f7db63a93 2/2: Avoid statting directories on startup for Info

[Lars Ingebrigtsen]

branch: master
commit 5f7db63a93f0c670d6f88dd24f922462abce7d8c
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Avoid statting directories on startup for Info
    
    * doc/misc/efaq.texi (File-name conventions) Mention
    Info-directory-list instead.
    
    * doc/misc/info.texi (Emacs Info Variables): Mention
    Info--default-directory-list.
    
    * lisp/info.el (Info-default-directory-list): Default to nil to
    avoid statting directories on Emacs startup (bug#27933).
    (Info--default-directory-list): Factored out into own function.
    (Info-default-dirs): Append value of Info-default-directory-list
    to the value returned from Info--default-directory-list.
---
 doc/misc/efaq.texi |  15 +++---
 doc/misc/info.texi |   5 +-
 etc/NEWS           |   5 ++
 lisp/info.el       | 137 ++++++++++++++++++++++-------------------------------
 4 files changed, 73 insertions(+), 89 deletions(-)

diff --git a/doc/misc/efaq.texi b/doc/misc/efaq.texi
index 5d4d378d82..87a70d064e 100644
--- a/doc/misc/efaq.texi
+++ b/doc/misc/efaq.texi
@@ -259,12 +259,13 @@ name displayed by this will be the full pathname of the 
installed
 @code{data-directory}, and @kbd{C-h v} displays the value and the
 documentation of a variable.)
 
-The location of your Info directory (i.e., where Info documentation
-is stored) is kept in the variable @code{Info-default-directory-list}.  Use
-@kbd{C-h v Info-default-directory-list @key{RET}} to see the value of
-this variable, which will be a list of directory names.  The last
-directory in that list is probably where most Info files are stored.  By
-default, Emacs Info documentation is placed in @file{/usr/local/share/info}.
+The location of your Info directory (i.e., where Info documentation is
+stored) is kept in the variable @code{Info-directory-list}.  Use
+@kbd{C-h v Info-directory-list @key{RET}} to see the value of this
+variable, which will be a list of directory names (after Info has been
+started).  The last directory in that list is probably where most Info
+files are stored.  By default, Emacs Info documentation is placed in
+@file{/usr/local/share/info}.
 
 For information on some of the files in the @file{etc} directory,
 @pxref{Informational files for Emacs}.
@@ -701,7 +702,7 @@ directory which is a subdirectory of your home directory 
named @file{Info},
 you could put this in your @file{.emacs} file:
 
 @lisp
-(add-to-list 'Info-default-directory-list "~/Info")
+(add-to-list 'Info-default-directory-list "~/Info/")
 @end lisp
 
 You will need a top-level Info file named @file{dir} in this directory
diff --git a/doc/misc/info.texi b/doc/misc/info.texi
index 98e0dceb5a..6ebf60ce36 100644
--- a/doc/misc/info.texi
+++ b/doc/misc/info.texi
@@ -1191,8 +1191,9 @@ info-stnd, GNU Info}.
 The list of directories to search for Info files.  Each element is a
 string (directory name) or @code{nil} (try default directory).  If not
 initialized Info uses the environment variable @env{INFOPATH} to
-initialize it, or @code{Info-default-directory-list} if there is no
-@env{INFOPATH} variable in the environment.
+initialize it, or @code{Info-default-directory-list} in addition to
+the value returned by the @code{Info--default-directory-list} function
+if there is no @env{INFOPATH} variable in the environment.
 
 If you wish to customize the Info directory search list for both Emacs
 Info and stand-alone Info, it is best to set the @env{INFOPATH}
diff --git a/etc/NEWS b/etc/NEWS
index 8deb699978..80cf0a2f72 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -107,6 +107,11 @@ of 'user-emacs-directory'.
 
 * Incompatible changes in Emacs 29.1
 
+---
+** 'Info-default-directory-list' is no longer populated at Emacs startup.
+If you have code in your init file that removes directories from
+'Info-default-directory-list', this will no longer work.
+
 ---
 ** 'C-k' no longer deletes files in 'ido-mode'.
 To get the previous action back, put something like the following in
diff --git a/lisp/info.el b/lisp/info.el
index 0565663c38..db95574bf7 100644
--- a/lisp/info.el
+++ b/lisp/info.el
@@ -161,59 +161,8 @@ A header-line does not scroll with the rest of the buffer."
   "Face used to highlight matches in an index entry."
   :version "24.4")
 
-;; This is a defcustom largely so that we can get the benefit
-;; of `custom-initialize-delay'.  Perhaps it would work to make it a
-;; `defvar' and explicitly give it a `standard-value' property, and
-;; call `custom-initialize-delay' on it.
-;; The value is initialized at startup time, when command-line calls
-;; `custom-reevaluate-setting' on all the defcustoms in
-;; `custom-delayed-init-variables'.  This is somewhat sub-optimal, as ideally
-;; this should be done when Info mode is first invoked.
 ;;;###autoload
-(defcustom Info-default-directory-list
-  (let* ((config-dir
-         (file-name-as-directory
-          ;; Self-contained NS build with info/ in the app-bundle.
-          (or (and (featurep 'ns)
-                   (let ((dir (expand-file-name "../info" data-directory)))
-                     (if (file-directory-p dir) dir)))
-              configure-info-directory)))
-        (prefixes
-         ;; Directory trees in which to look for info subdirectories
-         (prune-directory-list '("/usr/local/" "/usr/" "/opt/")))
-        (suffixes
-         ;; Subdirectories in each directory tree that may contain info
-         ;; directories.
-         '("share/" ""))
-        (standard-info-dirs
-         (apply #'nconc
-                (mapcar (lambda (pfx)
-                          (let ((dirs
-                                 (mapcar (lambda (sfx)
-                                           (concat pfx sfx "info/"))
-                                         suffixes)))
-                            (prune-directory-list dirs)))
-                        prefixes)))
-        ;; If $(prefix)/share/info is not one of the standard info
-        ;; directories, they are probably installing an experimental
-        ;; version of Emacs, so make sure that experimental version's Info
-        ;; files override the ones in standard directories.
-        (dirs
-         (if (member config-dir standard-info-dirs)
-             ;; FIXME?  What is the point of adding it again at the end
-             ;; when it is already present earlier in the list?
-             (nconc standard-info-dirs (list config-dir))
-           (cons config-dir standard-info-dirs))))
-    (if (not (eq system-type 'windows-nt))
-       dirs
-      ;; Include the info directory near where Emacs executable was installed.
-      (let* ((instdir (file-name-directory invocation-directory))
-            (dir1 (expand-file-name "../info/" instdir))
-            (dir2 (expand-file-name "../../../info/" instdir)))
-       (cond ((file-exists-p dir1) (append dirs (list dir1)))
-             ((file-exists-p dir2) (append dirs (list dir2)))
-             (t dirs)))))
-
+(defcustom Info-default-directory-list nil
   "Default list of directories to search for Info documentation files.
 They are searched in the order they are given in the list.
 Therefore, the directory of Info files that come with Emacs
@@ -224,15 +173,12 @@ first in this list.
 
 Once Info is started, the list of directories to search
 comes from the variable `Info-directory-list'.
-This variable `Info-default-directory-list' is used as the default
-for initializing `Info-directory-list' when Info is started, unless
-the environment variable INFOPATH is set.
-
-Although this is a customizable variable, that is mainly for technical
-reasons.  Normally, you should either set INFOPATH or customize
-`Info-additional-directory-list', rather than changing this variable."
-  :initialize #'custom-initialize-delay
-  :type '(repeat directory))
+
+This variable is used as the default for initializing
+`Info-directory-list' when Info is started, unless the
+environment variable INFOPATH is set."
+  :type '(repeat directory)
+  :version "29.1")
 
 (defvar Info-directory-list nil
   "List of directories to search for Info documentation files.
@@ -679,6 +625,51 @@ in `Info-file-supports-index-cookies-list'."
   (cdr (assoc file Info-file-supports-index-cookies-list)))
 
 
+(defun Info--default-directory-list ()
+  "Compute a directory list suitable for Info."
+  (let* ((config-dir
+         (file-name-as-directory
+          ;; Self-contained NS build with info/ in the app-bundle.
+          (or (and (featurep 'ns)
+                   (let ((dir (expand-file-name "../info" data-directory)))
+                     (if (file-directory-p dir) dir)))
+              configure-info-directory)))
+        (prefixes
+         ;; Directory trees in which to look for info subdirectories
+         (prune-directory-list '("/usr/local/" "/usr/" "/opt/")))
+        (suffixes
+         ;; Subdirectories in each directory tree that may contain info
+         ;; directories.
+         '("share/" ""))
+        (standard-info-dirs
+         (apply #'nconc
+                (mapcar (lambda (pfx)
+                          (let ((dirs
+                                 (mapcar (lambda (sfx)
+                                           (concat pfx sfx "info/"))
+                                         suffixes)))
+                            (prune-directory-list dirs)))
+                        prefixes)))
+        ;; If $(prefix)/share/info is not one of the standard info
+        ;; directories, they are probably installing an experimental
+        ;; version of Emacs, so make sure that experimental version's Info
+        ;; files override the ones in standard directories.
+        (dirs
+         (if (member config-dir standard-info-dirs)
+             ;; FIXME?  What is the point of adding it again at the end
+             ;; when it is already present earlier in the list?
+             (nconc standard-info-dirs (list config-dir))
+           (cons config-dir standard-info-dirs))))
+    (if (not (eq system-type 'windows-nt))
+       dirs
+      ;; Include the info directory near where Emacs executable was installed.
+      (let* ((instdir (file-name-directory invocation-directory))
+            (dir1 (expand-file-name "../info/" instdir))
+            (dir2 (expand-file-name "../../../info/" instdir)))
+       (cond ((file-exists-p dir1) (append dirs (list dir1)))
+             ((file-exists-p dir2) (append dirs (list dir2)))
+             (t dirs))))))
+
 (defun Info-default-dirs ()
   (let ((source (expand-file-name "info/" source-directory))
        (sibling (if installation-directory
@@ -701,25 +692,11 @@ in `Info-file-supports-index-cookies-list'."
              sibling
            ;; Uninstalled, builddir == srcdir
            source))
-    (if (or (member alternative Info-default-directory-list)
-           ;; On DOS/NT, we use movable executables always,
-           ;; and we must always find the Info dir at run time.
-           (if (memq system-type '(ms-dos windows-nt))
-               nil
-             ;; Use invocation-directory for Info
-             ;; only if we used it for exec-directory also.
-             (not (string= exec-directory
-                           (expand-file-name "lib-src/"
-                                             installation-directory))))
-           (not (file-exists-p alternative)))
-       Info-default-directory-list
-      ;; `alternative' contains the Info files that came with this
-      ;; version, so we should look there first.  `Info-insert-dir'
-      ;; currently expects to find `alternative' first on the list.
-      (cons alternative
-           ;; Don't drop the last part, it might contain non-Emacs stuff.
-           ;; (reverse (cdr (reverse
-           Info-default-directory-list)))) ;; )))
+    ;; `alternative' contains the Info files that came with this
+    ;; version, so we should look there first.  `Info-insert-dir'
+    ;; currently expects to find `alternative' first on the list.
+    (append (cons alternative Info-default-directory-list)
+            (Info--default-directory-list))))
 
 (defun info-initialize ()
   "Initialize `Info-directory-list', if that hasn't been done yet."