* lisp/files.el: Use a fixed file name for the second dir-locals file

(dir-locals-file): Revert to its original fixed value.
(dir-locals-file-2): New const.
(dir-locals--all-files): Don't use `file-name-all-completions'.
Instead, just check for the 2 dir-locals files and return a list
of the ones that exit (if any).

* etc/NEWS: Document the change.

* doc/emacs/custom.texi (Directory Variables): Document the change.

* doc/lispref/variables.texi (Directory Local Variables): Update
accordingly.

doc/emacs/custom.texi

@@ -1299,8 +1299,8 @@ named @file{.dir-locals.el}@footnote{ On MS-DOS, the name of this file
 should be @file{_dir-locals.el}, due to limitations of the DOS
 filesystems.  If the filesystem is limited to 8+3 file names, the name
 of the file will be truncated by the OS to @file{_dir-loc.el}.
-}@footnote{ You can also use files like @file{.dir-locals2.el}, which
-are loaded in addition.  This is useful when @file{.dir-locals.el} is
+}@footnote{ You can also use @file{.dir-locals-2.el}, which
+is loaded in addition.  This is useful when @file{.dir-locals.el} is
 under version control in a shared repository and can't be used for
 personal customizations.  } in a
 directory.  Whenever Emacs visits any file in that directory or any of

doc/lispref/variables.texi

@@ -1765,33 +1765,20 @@ variables: by putting them in a special file, or by defining a
 @dfn{project class} for that directory.
 
 @defvr Constant dir-locals-file
-This constant is a wildcard pattern matching the name of files where
-Emacs expects to find directory-local variables.  Its value is
-@file{.dir-locals*.el}@footnote{
-The MS-DOS version of Emacs uses @file{_dir-locals*.el} instead, due to
+This constant is the name of the file where Emacs expects to find the
+directory-local variables.  The name of the file is
+@file{.dir-locals.el}@footnote{
+The MS-DOS version of Emacs uses @file{_dir-locals.el} instead, due to
 limitations of the DOS filesystems.
-}, and the most common file name to use is @file{.dir-locals.el}.
-
-Any file matching this name pattern in a directory causes Emacs to
-apply its settings when visiting files in that directory or any of its
-subdirectories (optionally, you can exclude subdirectories; see
-below).
-If some of the subdirectories have their own file matching
-@file{.dir-locals*.el}, Emacs uses the settings from the deepest file
-it finds starting from the file's directory and moving up the
-directory tree.  The file specifies local variables as a specially
-formatted list; see @ref{Directory Variables, , Per-directory Local
-Variables, emacs, The GNU Emacs Manual}, for more details.
-
-If the same directory contains multiple such files (for instance,
-@file{.dir-locals.el} and @file{.dir-locals2.el}), then all of them
-are used in @code{string<} order.  This means that, if two files
-specify different values for the same variable, the file sorted after
-will override the value of the previous file (for instance, values in
-@file{.dir-locals2.el} override those in @file{.dir-locals.el}).  Note
-that, because of how lexicographic order works, values in
-@file{.dir-locals10.el} are overridden by values in @file{.dir-locals2.el}.
-This can be avoided by using @file{.dir-locals02.el} instead.
+}.  A file by that name in a directory causes Emacs to apply its
+settings to any file in that directory or any of its subdirectories
+(optionally, you can exclude subdirectories; see below).
+If some of the subdirectories have their own @file{.dir-locals.el}
+files, Emacs uses the settings from the deepest file it finds starting
+from the file's directory and moving up the directory tree.  The file
+specifies local variables as a specially formatted list; see
+@ref{Directory Variables, , Per-directory Local Variables, emacs, The
+GNU Emacs Manual}, for more details.
 @end defvr
 
 @defun hack-dir-local-variables

etc/NEWS

@@ -179,9 +179,8 @@ by default, and must be enabled by using the `--with-modules' option
 at configure time.
 
 +++
-** Any file of the form .dir-locals*.el is now considered a dir-local
-file, and multiple such files can be used in the same directory.  See
-the variable `dir-locals-file' for more information.
+** A second dir-local file (.dir-locals-2.el) is now accepted.
+See the variable `dir-locals-file-2' for more information.
 
 +++
 ** Network security (TLS/SSL certificate validity and the like) is

lisp/files.el

@@ -3713,37 +3713,43 @@ VARIABLES list of the class.  The list is processed in order.
   applied by recursively following these rules."
   (setf (alist-get class dir-locals-class-alist) variables))
 
-(defconst dir-locals-file ".dir-locals"
-  "Pattern for files that contain directory-local variables.
+(defconst dir-locals-file ".dir-locals.el"
+  "File that contains directory-local variables.
 It has to be constant to enforce uniform values across different
 environments and users.
+See also `dir-locals-file-2', whose values override this one's.
+See Info node `(elisp)Directory Local Variables' for details.")
 
-Multiple dir-locals files in the same directory are loaded in
-`string<' order.
+(defconst dir-locals-file-2 ".dir-locals-2.el"
+  "File that contains directory-local variables.
+This essentially a second file that can be used like
+`dir-locals-file', so that users can have specify their personal
+dir-local variables even if the current directory already has a
+`dir-locals-file' that is shared with other users (such as in a
+git repository).
 See Info node `(elisp)Directory Local Variables' for details.")
 
-(defun dir-locals--all-files (file-or-dir)
-  "Return a list of all readable dir-locals files matching FILE-OR-DIR.
-If FILE-OR-DIR is a file pattern, expand wildcards in it and
-return a sorted list of the results.  If it is a directory name,
-return a sorted list of all files matching `dir-locals-file' in
-this directory.
-The returned list is sorted by `string<' order."
-  (require 'seq)
-  (let ((dir (if (file-directory-p file-or-dir)
-                 file-or-dir
-               (or (file-name-directory file-or-dir)
-                   default-directory)))
-        (file (cond ((not (file-directory-p file-or-dir)) (file-name-nondirectory file-or-dir))
-                    ((eq system-type 'ms-dos) (dosified-file-name dir-locals-file))
-                    (t dir-locals-file))))
-    (seq-filter (lambda (f) (and (file-readable-p f)
-                            (file-regular-p f)
-                            (not (file-directory-p f))))
-                (mapcar (lambda (f) (expand-file-name f dir))
-                        (nreverse
-                         (let ((completion-regexp-list '("\\.el\\'")))
-                           (file-name-all-completions file dir)))))))
+(defun dir-locals--all-files (directory)
+  "Return a list of all readable dir-locals files in DIRECTORY.
+The returned list is sorted by increasing priority.  That is,
+values specified in the last file should take precedence over
+those in the first."
+  (when (file-readable-p directory)
+    (let* ((file-1 (expand-file-name (if (eq system-type 'ms-dos)
+                                        (dosified-file-name dir-locals-file)
+                                      dir-locals-file)
+                                    directory))
+           (file-2 (when (string-match "\\.el\\'" file-1)
+                     (replace-match "-2.el" t nil file-1)))
+          (out nil))
+      ;; The order here is important.
+      (dolist (f (list file-2 file-1))
+        (when (and f
+                   (file-readable-p f)
+                   (file-regular-p f)
+                   (not (file-directory-p f)))
+          (push f out)))
+      out)))
 
 (defun dir-locals-find-file (file)
   "Find the directory-local variables for FILE.