On Tue, Oct 27, 2015 at 12:07 AM, Markus Triska <triska@metalevel.at> wrote:
>
>
> Steps to reproduce:
>
> 1) wget http://www.metalevel.at/ei/fault1.html
>
> 2) emacs -Q fault1.html
>
> 3) M-x delete-trailing-whitespace RET
>
> This removes several non-white-space characters, including the whole
> line containing "and use it like" (line 83 in the original file),

Apparently, the call to skip-syntax-backward is altering the match data. If you try this

--- a/lisp/simple.el

+++ b/lisp/simple.el

@@ -609,7 +609,7 @@ delete-trailing-whitespace

(start (or start (point-min))))

(goto-char start)

(while (re-search-forward "\\s-$" end-marker t)

- (skip-syntax-backward "-" (line-beginning-position))

+ (save-match-data (skip-syntax-backward "-" (line-beginning-position)))

;; Don't delete formfeeds, even if they are considered whitespace.

(if (looking-at-p ".*\f")

(goto-char (match-end 0)))

or, alternatively,

@@ -609,11 +609,12 @@ delete-trailing-whitespace

(start (or start (point-min))))

(goto-char start)

(while (re-search-forward "\\s-$" end-marker t)

- (skip-syntax-backward "-" (line-beginning-position))

- ;; Don't delete formfeeds, even if they are considered whitespace.

- (if (looking-at-p ".*\f")

- (goto-char (match-end 0)))

- (delete-region (point) (match-end 0)))

+ (let ((end (match-end 0)))

+ (skip-syntax-backward "-" (line-beginning-position))

+ ;; Don't delete formfeeds, even if they are considered whitespace.

+ (if (looking-at-p ".*\f")

+ (goto-char end))

+ (delete-region (point) end)))

;; Delete trailing empty lines.

(goto-char end-marker)

(when (and (not end)

it works. Now, the question is, should skip-syntax-backward preserve the match data, or must delete-trailing-whitespace be coded defensively? The usual policy has been that code that needs the match data preserved should make sure itself that it is so.