X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/7be313ea3b46a5877b0f2b2ee6639f1c3d660fef..b336bfcdf39f1e4d35bff4a7bd01d3b4bca8f516:/lisp/tabify.el

diff --git a/lisp/tabify.el b/lisp/tabify.el
index 62d50aa033..c8cf877cb9 100644
--- a/lisp/tabify.el
+++ b/lisp/tabify.el
@@ -1,15 +1,16 @@
 ;;; tabify.el --- tab conversion commands for Emacs
 
-;; Copyright (C) 1985, 1994 Free Software Foundation, Inc.
+;; Copyright (C) 1985, 1994, 2001, 2002, 2003, 2004,
+;;   2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
 
 ;; Maintainer: FSF
 
 ;; This file is part of GNU Emacs.
 
-;; GNU Emacs is free software; you can redistribute it and/or modify
+;; GNU Emacs is free software: you can redistribute it and/or modify
 ;; it under the terms of the GNU General Public License as published by
-;; the Free Software Foundation; either version 2, or (at your option)
-;; any later version.
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
 
 ;; GNU Emacs is distributed in the hope that it will be useful,
 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -17,8 +18,7 @@
 ;; GNU General Public License for more details.
 
 ;; You should have received a copy of the GNU General Public License
-;; along with GNU Emacs; see the file COPYING.  If not, write to
-;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
 
 ;;; Commentary:
 
@@ -39,13 +39,20 @@ The variable `tab-width' controls the spacing of tab stops."
       (narrow-to-region (point-min) end)
       (goto-char start)
       (while (search-forward "\t" nil t)	; faster than re-search
+	(forward-char -1)
 	(let ((tab-beg (point))
-	      (column (current-column))
-	      (indent-tabs-mode nil))
-	  (skip-chars-backward "\t" start)
+	      (indent-tabs-mode nil)
+	      column)
+	  (skip-chars-forward "\t")
+	  (setq column (current-column))
 	  (delete-region tab-beg (point))
 	  (indent-to column))))))
 
+(defvar tabify-regexp " [ \t]+"
+  "Regexp matching whitespace that tabify should consider.
+Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
+\"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
+
 ;;;###autoload
 (defun tabify (start end)
   "Convert multiple spaces in region to tabs when possible.
@@ -63,12 +70,24 @@ The variable `tab-width' controls the spacing of tab stops."
       (beginning-of-line)
       (narrow-to-region (point) end)
       (goto-char start)
-      (while (re-search-forward "[ \t][ \t][ \t]*" nil t)
-	(let ((column (current-column))
-	      (indent-tabs-mode t))
-	  (delete-region (match-beginning 0) (point))
-	  (indent-to column))))))
+      (let ((indent-tabs-mode t))
+        (while (re-search-forward tabify-regexp nil t)
+          ;; The region between (match-beginning 0) and (match-end 0) is just
+          ;; spacing which we want to adjust to use TABs where possible.
+          (let ((end-col (current-column))
+                (beg-col (save-excursion (goto-char (match-beginning 0))
+                                         (skip-chars-forward "\t")
+                                         (current-column))))
+            (if (= (/ end-col tab-width) (/ beg-col tab-width))
+                ;; The spacing (after some leading TABs which we wouldn't
+                ;; want to touch anyway) does not straddle a TAB boundary,
+                ;; so it neither contains a TAB, nor will we be able to use
+                ;; a TAB here anyway: there's nothing to do.
+                nil
+              (delete-region (match-beginning 0) (point))
+              (indent-to end-col))))))))
 
 (provide 'tabify)
 
+;; arch-tag: c83893b1-e0cc-4e57-8a09-73fd03466416
 ;;; tabify.el ends here