Subject: bug#69305: outline-minor-mode for tabulated-list-mode

From: Juri Linkov <[email-masked]>
Date: Wed, 21 Feb 2024 19:34:17 +0200

[From emacs-devel]

>> +(defcustom Buffer-menu-group-by nil
>> +  "If non-nil, buffers are grouped by function."
>> +  :type 'function
>> +  :group 'Buffer-menu
>> +  :version "30.1")
>
> Please consider letting users choose a symbol, not a function.  Each
> symbol can be mapped to a function, but having a user option whose
> values are functions makes it harder for users to customize the
> option.

Ok, now the type is changed to 'symbol'.  Here is the complete patch:

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 70d1a40f836..bb2100dbb4d 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1239,6 +1239,21 @@ Tabulated List Mode
 above form when called with no arguments.
 @end defvar
 
+@defvar tabulated-list-groups
+This buffer-local variable specifies the groups of entries displayed in
+the Tabulated List buffer.  Its value should be either a list, or a
+function.
+
+If the value is a list, each list element corresponds to one group, and
+should have the form @w{@code{(@var{group-name} @var{entries})}}, where
+@var{group-name} is a string inserted before all group entries, and
+@var{entries} have the same format as @code{tabulated-list-entries}
+(see above).
+
+Otherwise, the value should be a function which returns a list of the
+above form when called with no arguments.
+@end defvar
+
 @defvar tabulated-list-revert-hook
 This normal hook is run prior to reverting a Tabulated List buffer.  A
 derived mode can add a function to this hook to recompute
diff --git a/etc/NEWS b/etc/NEWS
index 7b248c3fe78..b549eab9f0b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1332,6 +1332,11 @@ will return the URL for that bug.
 This allows for rcirc logs to use a custom timestamp format, than the
 chat buffers use by default.
 
+---
+*** New user option 'Buffer-menu-group-by'.
+It splits buffers by groups that are displayed with headings in
+Outline minor mode.
+
 ---
 *** New command 'Buffer-menu-toggle-internal'.
 This command toggles the display of internal buffers in Buffer Menu mode;
@@ -1997,6 +2002,10 @@ inside 'treesit-language-source-alist', so that calling
 It may be useful, for example, for the purposes of bisecting a
 treesitter grammar.
 
++++
+** New buffer-local variable 'tabulated-list-groups'.
+It prints and sorts the groups of entries separately.
+
 
 * Changes in Emacs 30.1 on Non-Free Operating Systems
 
diff --git a/lisp/buff-menu.el b/lisp/buff-menu.el
index e13c3b56b4e..62717c4625b 100644
--- a/lisp/buff-menu.el
+++ b/lisp/buff-menu.el
@@ -95,6 +95,18 @@ Buffer-menu-use-frame-buffer-list
   :group 'Buffer-menu
   :version "22.1")
 
+(defcustom Buffer-menu-group-by nil
+  "If non-nil, buffers are grouped by function.
+This function takes one argument: a list of entries in the same format
+as in `tabulated-list-entries', and should return a list in the format
+suitable for `tabulated-list-groups'.  Also when this variable is non-nil,
+then `outline-minor-mode' is enabled in the Buffer Menu.  Then with the
+default value of `outline-regexp' you can use Outline minor mode commands
+to show/hide groups of buffers."
+  :type 'symbol
+  :group 'Buffer-menu
+  :version "30.1")
+
 (defvar-local Buffer-menu-files-only nil
   "Non-nil if the current Buffer Menu lists only file buffers.
 This is set by the prefix argument to `buffer-menu' and related
@@ -674,7 +684,12 @@ list-buffers-noselect
       (setq Buffer-menu-buffer-list buffer-list)
       (setq Buffer-menu-filter-predicate filter-predicate)
       (list-buffers--refresh buffer-list old-buffer)
-      (tabulated-list-print))
+      (tabulated-list-print)
+      (when tabulated-list-groups
+        (setq-local outline-minor-mode-cycle t
+                    outline-minor-mode-highlight t
+                    outline-minor-mode-use-buttons 'in-margins)
+        (outline-minor-mode 1)))
     buffer))
 
 (defun Buffer-menu-mouse-select (event)
@@ -750,7 +765,11 @@ list-buffers--refresh
 		  `("Mode" ,Buffer-menu-mode-width t)
 		  '("File" 1 t)))
     (setq tabulated-list-use-header-line Buffer-menu-use-header-line)
-    (setq tabulated-list-entries (nreverse entries)))
+    (setq tabulated-list-entries (nreverse entries))
+    (when Buffer-menu-group-by
+      (setq tabulated-list-groups
+            (seq-group-by Buffer-menu-group-by
+                          tabulated-list-entries))))
   (tabulated-list-init-header))
 
 (defun tabulated-list-entry-size-> (entry1 entry2)
diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index 9884a2fc24b..a78e1726c26 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -139,6 +139,21 @@ tabulated-list-entries
 arguments and must return a list of the above form.")
 (put 'tabulated-list-entries 'permanent-local t)
 
+(defvar-local tabulated-list-groups nil
+  "Groups displayed in the current Tabulated List buffer.
+This should be either a function, or a list.
+If a list, each element has the form (GROUP-NAME ENTRIES),
+where:
+
+ - GROUP-NAME is a group name as a string, which is displayed
+   at the top line of each group.
+
+ - ENTRIES is a list described in `tabulated-list-entries'.
+
+If `tabulated-list-groups' is a function, it is called with no
+arguments and must return a list of the above form.")
+(put 'tabulated-list-groups 'permanent-local t)
+
 (defvar-local tabulated-list-padding 0
   "Number of characters preceding each Tabulated List mode entry.
 By default, lines are padded with spaces, but you can use the
@@ -427,6 +444,9 @@ tabulated-list-print
 specified by `tabulated-list-sort-key'.  It then erases the
 buffer and inserts the entries with `tabulated-list-printer'.
 
+If `tabulated-list-groups' is non-nil, each group of entries
+is sorted separately after printing the group header line.
+
 Optional argument REMEMBER-POS, if non-nil, means to move point
 to the entry with the same ID element as the current line.
 
@@ -437,6 +457,9 @@ tabulated-list-print
 `tabulated-list-put-tag').  Don't use this immediately after
 changing `tabulated-list-sort-key'."
   (let ((inhibit-read-only t)
+        (groups (if (functionp tabulated-list-groups)
+		    (funcall tabulated-list-groups)
+		  tabulated-list-groups))
 	(entries (if (functionp tabulated-list-entries)
 		     (funcall tabulated-list-entries)
 		   tabulated-list-entries))
@@ -447,7 +470,14 @@ tabulated-list-print
 	 (setq saved-col (current-column)))
     ;; Sort the entries, if necessary.
     (when sorter
-      (setq entries (sort entries sorter)))
+      (if groups
+          (setq groups
+                (mapcar (lambda (group)
+                          (cons (car group) (sort (cdr group) sorter)))
+                        groups))
+        (setq entries (sort entries sorter))))
+    (unless (functionp tabulated-list-groups)
+      (setq tabulated-list-groups groups))
     (unless (functionp tabulated-list-entries)
       (setq tabulated-list-entries entries))
     ;; Without a sorter, we have no way to just update.
@@ -459,6 +489,25 @@ tabulated-list-print
       (unless tabulated-list-use-header-line
         (tabulated-list-print-fake-header)))
     ;; Finally, print the resulting list.
+    (if groups
+        (dolist (group groups)
+          (insert (car group) ?\n)
+          (when-let ((saved-pt-new (tabulated-list-print-entries
+                                    (cdr group) sorter update entry-id)))
+            (setq saved-pt saved-pt-new)))
+      (setq saved-pt (tabulated-list-print-entries
+                      entries sorter update entry-id)))
+    (when update
+      (delete-region (point) (point-max)))
+    (set-buffer-modified-p nil)
+    ;; If REMEMBER-POS was specified, move to the "old" location.
+    (if saved-pt
+	(progn (goto-char saved-pt)
+	       (move-to-column saved-col))
+      (goto-char (point-min)))))
+
+(defun tabulated-list-print-entries (entries sorter update entry-id)
+  (let (saved-pt)
     (while entries
       (let* ((elt (car entries))
              (tabulated-list--near-rows
@@ -495,14 +544,7 @@ tabulated-list-print
               (forward-line 1)
               (delete-region old (point))))))
       (setq entries (cdr entries)))
-    (when update
-      (delete-region (point) (point-max)))
-    (set-buffer-modified-p nil)
-    ;; If REMEMBER-POS was specified, move to the "old" location.
-    (if saved-pt
-	(progn (goto-char saved-pt)
-	       (move-to-column saved-col))
-      (goto-char (point-min)))))
+    saved-pt))
 
 (defun tabulated-list-print-entry (id cols)
   "Insert a Tabulated List entry at point.
diff --git a/test/lisp/emacs-lisp/tabulated-list-tests.el b/test/lisp/emacs-lisp/tabulated-list-tests.el
index 8be2be3139e..e53268b3f14 100644
--- a/test/lisp/emacs-lisp/tabulated-list-tests.el
+++ b/test/lisp/emacs-lisp/tabulated-list-tests.el
@@ -130,4 +130,45 @@ tabulated-list-sort
    (should-error (tabulated-list-sort) :type 'user-error)
    (should-error (tabulated-list-sort 4) :type 'user-error)))
 
+(ert-deftest tabulated-list-groups ()
+  (with-temp-buffer
+    (tabulated-list-mode)
+    (setq tabulated-list-groups
+          (reverse
+           (seq-group-by (lambda (b) (concat "* " (aref (cadr b) 3)))
+                         tabulated-list--test-entries)))
+    (setq tabulated-list-format tabulated-list--test-format)
+    (setq tabulated-list-padding 7)
+    (tabulated-list-init-header)
+    (tabulated-list-print)
+    ;; Basic printing.
+    (should (string-equal
+             (buffer-substring-no-properties (point-min) (point-max))
+             "\
+* installed
+       zzzz-game  zzzz-game  2113      installed   play zzzz in Emacs
+       mode       mode       1128      installed   A simple mode for editing Actionscript 3 files
+* available
+       abc-mode   abc-mode   944       available   Major mode for editing abc music files
+* obsolete
+       4clojure   4clojure   1507      obsolete    Open and evaluate 4clojure.com questions
+"))
+    ;; Sort and preserve position.
+    (forward-line 2)
+    (let ((pos (thing-at-point 'line)))
+      (tabulated-list-next-column 2)
+      (tabulated-list-sort)
+      (should (equal (thing-at-point 'line) pos))
+      (should (string-equal
+               (buffer-substring-no-properties (point-min) (point-max))
+               "\
+* installed
+       mode       mode       1128      installed   A simple mode for editing Actionscript 3 files
+       zzzz-game  zzzz-game  2113      installed   play zzzz in Emacs
+* available
+       abc-mode   abc-mode   944       available   Major mode for editing abc music files
+* obsolete
+       4clojure   4clojure   1507      obsolete    Open and evaluate 4clojure.com questions
+")))))
+
 ;;; tabulated-list-tests.el ends here