From 2cdd76d8d98835fa42ebd8b503bfc416563b1bd1 Mon Sep 17 00:00:00 2001
From: Stefan Kangas <address@hidden>
Date: Mon, 16 Sep 2019 03:48:47 +0200
Subject: [PATCH] Add new function to clear tags in tabulated list

* lisp/emacs-lisp/tabulated-list.el (tabulated-list-clear-all-tags):
New function to clear all tags from padding area in current buffer.
* doc/lispref/modes.texi (Tabulated List Mode): Document it.
* etc/NEWS: Announce it.
---
 doc/lispref/modes.texi            |  5 +++++
 etc/NEWS                          |  5 +++++
 lisp/emacs-lisp/tabulated-list.el | 13 +++++++++++++
 3 files changed, 23 insertions(+)

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 7185c243e2..2e0c9e4655 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1201,6 +1201,11 @@ Tabulated List Mode
 function advances point by one line.
 @end defun
 
+@defun tabulated-list-clear-all-tags
+This function clears all tags from the padding area in the current
+buffer.
+@end defun
+
 @defun tabulated-list-set-col col desc &optional change-entry-data
 This function changes the tabulated list entry at point, setting
 @var{col} to @var{desc}.  @var{col} is the column number to change, or
diff --git a/etc/NEWS b/etc/NEWS
index 252c6bf9b9..2204d34b00 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1707,6 +1707,11 @@ near the current column in Tabulated Lists (see variables
 list mode: 'w' (which widens the current column) and 'c' which makes
 the current column contract.
 
++++
+*** New function 'tabulated-list-clear-all-tags'.
+This function clears all tags from the padding area in the current
+buffer.  Tags are typically added by calling 'tabulated-list-put-tag'.
+
 ** Text mode
 
 +++
diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index 63ae1f8c07..4392fbd1e8 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -192,6 +192,19 @@ tabulated-list-put-tag
   (if advance
       (forward-line)))
 
+(defun tabulated-list-clear-all-tags ()
+  "Clear all tags from the padding area in the current buffer."
+  (unless (> tabulated-list-padding 0)
+    (error "There can be no tags in current buffer"))
+  (save-excursion
+    (goto-char (point-min))
+    (let ((inhibit-read-only t)
+          ;; Match non-space in the first n characters.
+          (re (format "^ \\{0,%s\\}[^ ]" (1- tabulated-list-padding)))
+          (empty (make-string tabulated-list-padding ? )))
+      (while (re-search-forward re nil 'noerror)
+        (tabulated-list-put-tag empty)))))
+
 (defvar tabulated-list-mode-map
   (let ((map (make-sparse-keymap)))
     (set-keymap-parent map (make-composed-keymap
-- 
2.20.1