Add lisp-data-mode for editing non-code Lisp data

Fixes: bug#40573

The new mode can be used stand-alone or inherited from by modes
intended to edit programs. The existing emacs-lisp-mode and lisp-mode
are examples.

Thanks to Juri Linkov and Basil L. Contovounesios for researching some
data files in Emacs that can be automatically set to use the new mode.

* lisp/files.el (auto-mode-alist): Add entry for ".dir-locals" and
".dir-locals-2"

* lisp/emacs-lisp/lisp-mode.el: (lisp-data-mode): New major mode.
(lisp-mode): Inherit from lisp-data-mode.  Set special lisp-mode
stuff here.

* lisp/progmodes/elisp-mode.el (emacs-lisp-mode): Inherit from
lisp-data-mode.

* lisp/bookmark.el (bookmark-insert-file-format-version-stamp):
Use lisp-data-mode.

* lisp/saveplace.el (save-place-alist-to-file): Use
lisp-data-mode.

* lisp/net/eww.el (eww-write-bookmarks): Use lisp-data-mode.

* lisp/net/nsm.el (nsm-write-settings): Use lisp-data-mode.

* lisp/net/tramp-cache.el (tramp-dump-connection-properties): Use
lisp-data-mode.

* etc/NEWS: Mention lisp-data-mode.

* doc/lispref/modes.texi (Example Major Modes): Update example.

1 files changed, 4 insertions, 13 deletions

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index fc68ee1b322..eaee56f0a32 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1352,19 +1352,11 @@ illustrate how these modes are written.
 @end smallexample
 
   The three modes for Lisp share much of their code.  For instance,
-each calls the following function to set various variables:
-
-@smallexample
-@group
-(defun lisp-mode-variables (&optional syntax keywords-case-insensitive elisp)
-  (when syntax
-    (set-syntax-table lisp-mode-syntax-table))
-  @dots{}
-@end group
-@end smallexample
+Lisp mode and Emacs Lisp mode inherit from Lisp Data mode and Lisp
+Interaction Mode inherits from Emacs Lisp mode.
 
 @noindent
-Amongst other things, this function sets up the @code{comment-start}
+Amongst other things, Lisp Data mode sets up the @code{comment-start}
 variable to handle Lisp comments:
 
 @smallexample
@@ -1414,7 +1406,7 @@ Finally, here is the major mode command for Lisp mode:
 
 @smallexample
 @group
-(define-derived-mode lisp-mode prog-mode "Lisp"
+(define-derived-mode lisp-mode lisp-data-mode "Lisp"
   "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
 Commands:
 Delete converts tabs to spaces as it moves back.
@@ -1425,7 +1417,6 @@ Note that `run-lisp' may be used either to start an inferior Lisp job
 or to switch back to an existing one."
 @end group
 @group
-  (lisp-mode-variables nil t)
   (setq-local find-tag-default-function 'lisp-find-tag-default)
   (setq-local comment-start-skip
               "\\(\\(^\\|[^\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")