Re: [Emacs-diffs] master c66aaa6: Recomplexify ‘delete-trailing-whitespace’ by treating \n as whitespace again

[Noam Postavsky <npostavs@users.sourceforge.net>]

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On Wed, Mar 15, 2017 at 10:52 PM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
> Yes, it's normal: the "search" attempts a "match" from every whitespace.
> So if you have N consecutive whitespace chars in the middle of line,
> that gives you N attempts to "match" and every attempt takes O(N) steps
> to find that the end of the whitespace is not an LF.
>
> I don't understand how "\\s-+$" can be significantly faster than
> "[\s\t]+$" in this respect.

What?  I though I said "\\s-+" is *slower* (though only by a factor of 2).

Anyway, how about the attached which removes the syntax table stuff.

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From 2275487232b96ca782ca671d60be002e3948a764 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Wed, 15 Mar 2017 23:01:13 -0400
Subject: [PATCH] Simplify delete-trailing-whitespace by dropping syntax tables

* lisp/simple.el (delete-trailing-whitespace): Just match [[:blank:]]
independently of current syntax table.
---
 lisp/simple.el | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/lisp/simple.el b/lisp/simple.el
index 369fbf7192..2cf8c13225 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -630,14 +630,13 @@ delete-trailing-whitespace
     (save-excursion
       (let ((end-marker (and end (copy-marker end))))
         (goto-char (or start (point-min)))
-        (with-syntax-table (make-syntax-table (syntax-table))
-          ;; Don't delete formfeeds, even if they are considered whitespace.
-          (modify-syntax-entry ?\f "_")
-          (while (re-search-forward "\\s-$" end-marker t)
-            (skip-syntax-backward "-" (line-beginning-position))
-            (let ((b (point)) (e (match-end 0)))
-              (when (region-modifiable-p b e)
-                (delete-region b e)))))
+        ;; Note that trying to match all the trailing whitespace with
+        ;; just the regexp can be very slow (Bug#26079).
+        (while (re-search-forward "[[:blank:]]$" end-marker t)
+          (skip-syntax-backward "-" (line-beginning-position))
+          (let ((b (point)) (e (match-end 0)))
+            (when (region-modifiable-p b e)
+              (delete-region b e))))
         (if end
             (set-marker end-marker nil)
           ;; Delete trailing empty lines.
-- 
2.11.1