bug#67615: [PATCH v3] * lisp/info.el (Info-url-alist): New option mapping manuals to URLs.

[Mekeor Melire]

>From 1e9b31174ab4cfb2edb73f23aa1a3ec86943ba42 Mon Sep 17 00:00:00 2001
From: Mekeor Melire <mekeor@posteo.de>
Date: Mon, 4 Dec 2023 16:37:37 +0100
Subject: [PATCH] * lisp/info.el (Info-url-alist): New option mapping manuals
 to URLs.

---
 ChangeLog.4  |   8 +++++
 etc/NEWS     |   9 +++++
 lisp/info.el | 100 ++++++++++++++++++++++++++++++++++++++++-----------
 3 files changed, 96 insertions(+), 21 deletions(-)

diff --git a/ChangeLog.4 b/ChangeLog.4
index 24afabdbbb1..0aabd9f52bb 100644
--- a/ChangeLog.4
+++ b/ChangeLog.4
@@ -1,3 +1,11 @@
+2023-12-08  Mekeor Melire  <mekeor@posteo.de>
+
+       Support online-browsing all Emacs-contained manuals or any other.
+
+       * lisp/info.el (Info-url-alist): New defcustom that maps
+       manual-names to URL-specifications.
+       (Info-url-for-node): Use it.
+
 2023-10-16  Po Lu  <luangruo@yahoo.com>
 
        Correctly register focus events concomitant with alpha changes
diff --git a/etc/NEWS b/etc/NEWS
index 29f4e5c0b66..4730cc3a351 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -356,6 +356,15 @@ respectively, in addition to the existing translations 
'C-x 8 / e' and
 
 * Changes in Specialized Modes and Packages in Emacs 30.1
 
+** Info
+
+---
+*** New user option 'Info-url-alist'.
+This user option associates manual-names with URLs. It affects the
+'Info-goto-node-web' command.  By default, associations for all
+Emacs-included manuals are set.  Further associations can be added for
+arbitrary info manuals.
+
 +++
 ** New command 'lldb'.
 Run the LLDB debugger, analogous to the 'gud-gdb' command.  Note that
diff --git a/lisp/info.el b/lisp/info.el
index 51e9eb72edf..c0e342a62d6 100644
--- a/lisp/info.el
+++ b/lisp/info.el
@@ -213,6 +213,52 @@ Info-additional-directory-list
 These directories are searched after those in `Info-directory-list'."
   :type '(repeat directory))
 
+(defcustom Info-url-alist
+  '((("auth" "autotype" "bovine" "calc" "ccmode" "cl" "dbus" "dired-x"
+      "ebrowse" "ede" "ediff" "edt" "efaq" "efaq-w32" "eglot" "eieio"
+      "eintr" "elisp" "emacs" "emacs-gnutls" "emacs-mime" "epa" "erc"
+      "ert" "eshell" "eudc" "eww" "flymake" "forms" "gnus"
+      "htmlfontify" "idlwave" "ido" "info" "mairix-el" "message"
+      "mh-e" "modus-themes" "newsticker" "nxml-mode" "octave-mode"
+      "org" "pcl-cvs" "pgg" "rcirc" "reftex" "remember" "sasl" "sc"
+      "semantic" "ses" "sieve" "smtpmail" "speedbar" "srecode"
+      "todo-mode" "tramp" "transient" "url" "use-package" "vhdl-mode"
+      "vip" "viper" "vtable" "widget" "wisent" "woman") .
+     "https://www.gnu.org/software/emacs/manual/html_node/%m/%e";))
+  "Alist telling `Info-mode' where manuals are accessible online.
+
+Each element of this list should match the pattern (MANUALS
+. URL-SPEC).  MANUALS represents the name of one or many manuals.
+It can either be a string or a list of strings.  URL-SPEC can be
+a string in which the substring \"%m\" will be expanded to the
+manual-name, \"%n\" to the node-name, and \"%e\" to the
+URL-encoded node-name with a `.html' suffix.  (The URL-encoding
+of the node-name mimics GNU Texinfo, as documented at info
+node `(texinfo)HTML Xref Node Name Expansion'.)  Alternatively,
+URL-SPEC can be a function which is given manual-name, node-name
+and URL-encoded node-name as arguments, and is expected to return
+the corresponding URL as string.
+
+This variable particularly affects the command
+`Info-goto-node-web', which see.
+
+The default value of this variable refers to the official,
+HTTPS-accessible HTML-representations of all manuals that Emacs
+includes.  These URLs refer to the most recently released version
+of Emacs, disregarding the version of the running Emacs.  In
+other words, the content of your local info node and the
+associated online node may differ.  The resource represented by
+the generated URL may even be not found by the gnu.org server."
+  :type '(alist
+           :tag "Mapping from manual-name(s) to URL-specification"
+           :key-type (choice
+                       (string :tag "A single manual-name")
+                       (repeat :tag "List of manual-names" string))
+           :value-type (choice
+                         (string :tag "URL-specification string")
+                         (function
+                           :tag "URL-specification function"))))
+
 (defcustom Info-scroll-prefer-subnodes nil
   "If non-nil, \\<Info-mode-map>\\[Info-scroll-up] in a menu visits subnodes.
 
@@ -1807,33 +1853,45 @@ Info-goto-node-web
      (Info-url-for-node (format "(%s)%s" filename node)))))
 
 (defun Info-url-for-node (node)
-  "Return a URL for NODE, a node in the GNU Emacs or Elisp manual.
-NODE should be a string on the form \"(manual)Node\".  Only emacs
-and elisp manuals are supported."
+  "Return a URL for NODE.  NODE should be a string of the form
+\"(manual)Node\"."
   (unless (string-match "\\`(\\(.+\\))\\(.+\\)\\'" node)
-    (error "Invalid node name %s" node))
-  (let ((manual (match-string 1 node))
-        (node (match-string 2 node)))
-    (unless (member manual '("emacs" "elisp"))
-      (error "Only emacs/elisp manuals are supported"))
-    ;; Encode a bunch of characters the way that makeinfo does.
-    (setq node
-          (mapconcat (lambda (ch)
-                       (if (or (< ch 32)        ; ^@^A-^Z^[^\^]^^^-
+    (error "Invalid node-name %s" node))
+  ;; use `if-let*' instead of `let*' so we check if an association was
+  ;; found.
+  (if-let* ((manual (match-string 1 node))
+             (node (match-string 2 node))
+             (association (seq-find
+                            (lambda (pair)
+                              (seq-contains (ensure-list (car pair))
+                                manual #'string-equal-ignore-case))
+                            Info-url-alist))
+             (url-spec (cdr association))
+             (encoded-node
+               ;; Reproduce GNU Texinfo's way of URL-encoding.
+               ;; (info "(texinfo) HTML Xref Node Name Expansion")
+               (if (equal node "Top")
+                 ""
+                 (url-hexify-string
+                   (string-replace " " "-"
+                     (mapconcat
+                       (lambda (ch)
+                         (if (or (< ch 32)      ; ^@^A-^Z^[^\^]^^^-
                                (<= 33 ch 47)    ; !"#$%&'()*+,-./
                                (<= 58 ch 64)    ; :;<=>?@
                                (<= 91 ch 96)    ; [\]_`
                                (<= 123 ch 127)) ; {|}~ DEL
                            (format "_00%x" ch)
-                         (char-to-string ch)))
-                     node
-                     ""))
-    (concat "https://www.gnu.org/software/emacs/manual/html_node/";
-            manual "/"
-            (and (not (equal node "Top"))
-                 (concat
-                  (url-hexify-string (string-replace " " "-" node))
-                  ".html")))))
+                           (char-to-string ch)))
+                       node ""))))))
+    (cond
+      ((stringp url-spec)
+        (format-spec url-spec
+          `((?m . ,manual) (?n . ,node) (?e . ,encoded-node))))
+      ((functionp url-spec)
+        (funcall url-spec manual node encoded-node))
+      (t (error "URL-specification neither string nor function")))
+    (error "No URL-specification associated with manual-name `%s'")))
 
 (defvar Info-read-node-completion-table)
 
-- 
2.41.0