From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: Don't complain about changed file when it hasn't changed
Date: Fri, 02 Sep 2016 11:22:15 -0400 [thread overview]
Message-ID: <jwvy43ajpk5.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: 83k2evg26c.fsf@gnu.org
> My preference would be to have the test in the caller, because I doubt
> that anyone who replaces that function would want to lose the test.
> But that preference is not very strong.
How 'bout the patch below, then,
Stefan
diff --git a/doc/lispref/buffers.texi b/doc/lispref/buffers.texi
index 740d7cf..e4ef4d5 100644
--- a/doc/lispref/buffers.texi
+++ b/doc/lispref/buffers.texi
@@ -669,8 +669,9 @@ Modification Time
This function is used to ask a user how to proceed after an attempt to
modify an buffer visiting file @var{filename} when the file is newer
than the buffer text. Emacs detects this because the modification
-time of the file on disk is newer than the last save-time of the
-buffer. This means some other program has probably altered the file.
+time of the file on disk is newer than the last save-time and its contents
+have changed.
+This means some other program has probably altered the file.
@kindex file-supersession
Depending on the user's answer, the function may return normally, in
diff --git a/etc/NEWS b/etc/NEWS
index 1290fa4..cdabeda 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -213,6 +213,10 @@ In modes where form feed was treated as a whitespace character,
It now deletes whitespace after the last form feed thus behaving the
same as in modes where the character is not whitespace.
+** No more prompt about changed file when the file's content is unchanged.
+Instead of only checking the modification time, Emacs now also checks
+the file's actual content before prompting the user.
+
\f
* Changes in Specialized Modes and Packages in Emacs 25.2
diff --git a/lisp/userlock.el b/lisp/userlock.el
index a0c55fd..1cfc3b9 100644
--- a/lisp/userlock.el
+++ b/lisp/userlock.el
@@ -97,6 +97,41 @@ ask-user-about-lock-help
(define-error 'file-supersession nil 'file-error)
+(defun userlock--check-content-unchanged (fn)
+ (with-demoted-errors "Unchanged content check: %S"
+ ;; Even tho we receive `fn', we know that `fn' refers to the current
+ ;; buffer's file.
+ (cl-assert (equal fn (expand-file-name buffer-file-truename)))
+ ;; Note: rather than read the file and compare to the buffer, we could save
+ ;; the buffer and compare to the file, but for encrypted data this
+ ;; wouldn't work well (and would risk exposing the data).
+ (save-restriction
+ (widen)
+ (let ((buf (current-buffer))
+ (cs buffer-file-coding-system)
+ (start (point-min))
+ (end (point-max)))
+ ;; FIXME: To avoid a slow `insert-file-contents' on large or
+ ;; remote files, it'd be good to include file size in the
+ ;; "visited-modtime" check.
+ (when (with-temp-buffer
+ (let ((coding-system-for-read cs)
+ (non-essential t))
+ (insert-file-contents fn))
+ (when (= (buffer-size) (- end start)) ;Minor optimization.
+ (= 0 (let ((case-fold-search nil))
+ (compare-buffer-substrings
+ buf start end
+ (current-buffer) (point-min) (point-max))))))
+ (set-visited-file-modtime)
+ 'unchanged)))))
+
+;;;###autoload
+(defun userlock--ask-user-about-supersession-threat (fn)
+ ;; Called from filelock.c.
+ (unless (userlock--check-content-unchanged fn)
+ (ask-user-about-supersession-threat fn)))
+
;;;###autoload
(defun ask-user-about-supersession-threat (fn)
"Ask a user who is about to modify an obsolete buffer what to do.
diff --git a/src/filelock.c b/src/filelock.c
index 2f92e0f..bde34e2 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -684,7 +684,7 @@ lock_file (Lisp_Object fn)
if (!NILP (subject_buf)
&& NILP (Fverify_visited_file_modtime (subject_buf))
&& !NILP (Ffile_exists_p (fn)))
- call1 (intern ("ask-user-about-supersession-threat"), fn);
+ call1 (intern ("userlock--ask-user-about-supersession-threat"), fn);
}
next prev parent reply other threads:[~2016-09-02 15:22 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-29 0:29 Don't complain about changed file when it hasn't changed Stefan Monnier
2016-08-29 3:36 ` Clément Pit--Claudel
2016-08-29 3:39 ` Daniel Colascione
2016-08-29 3:43 ` Clément Pit--Claudel
2016-08-29 6:44 ` Michael Albinus
2016-08-29 14:42 ` Eli Zaretskii
2016-08-29 16:18 ` Michael Albinus
2016-08-29 17:42 ` Davis Herring
2016-08-29 17:57 ` Clément Pit--Claudel
2016-08-29 19:10 ` Davis Herring
2016-08-29 13:17 ` Stefan Monnier
2016-08-30 9:20 ` Michael Albinus
2016-08-30 15:00 ` Stefan Monnier
2016-08-30 13:40 ` Clément Pit--Claudel
2016-08-30 15:01 ` Stefan Monnier
2016-08-30 15:23 ` Clément Pit--Claudel
2016-08-30 15:48 ` Stefan Monnier
2016-08-30 16:55 ` Eli Zaretskii
2016-08-30 16:11 ` Eli Zaretskii
2016-08-30 16:38 ` Clément Pit--Claudel
2016-08-29 14:34 ` Eli Zaretskii
2016-08-29 14:50 ` Stefan Monnier
2016-08-30 15:26 ` Eli Zaretskii
2016-08-30 15:44 ` Stefan Monnier
2016-08-30 16:15 ` Eli Zaretskii
2016-08-30 17:13 ` Stefan Monnier
2016-08-30 17:26 ` Eli Zaretskii
2016-08-30 18:02 ` Stefan Monnier
2016-08-30 15:46 ` Stefan Monnier
2016-08-30 16:19 ` Eli Zaretskii
2016-08-30 17:16 ` Stefan Monnier
2016-08-30 17:32 ` Eli Zaretskii
2016-08-30 18:06 ` Stefan Monnier
2016-09-01 13:49 ` Eli Zaretskii
2016-09-02 15:22 ` Stefan Monnier [this message]
2016-09-02 15:26 ` Eli Zaretskii
2016-09-02 15:44 ` Stefan Monnier
2016-09-02 15:39 ` Joost Kremers
2016-08-29 16:01 ` Stefan Monnier
2016-08-29 16:26 ` Eli Zaretskii
2016-08-30 0:35 ` Stefan Monnier
2016-08-29 17:50 ` Davis Herring
2016-08-29 18:09 ` Eli Zaretskii
2016-08-29 19:22 ` Davis Herring
2016-08-30 0:39 ` Stefan Monnier
2016-08-30 7:55 ` Andreas Schwab
2016-08-30 0:37 ` Stefan Monnier
2016-08-30 1:23 ` Rolf Ade
2016-08-30 15:12 ` Eli Zaretskii
2016-08-30 15:34 ` Clément Pit--Claudel
2016-08-30 16:14 ` Eli Zaretskii
2016-09-06 16:29 ` John Wiegley
2016-09-06 17:50 ` Stefan Monnier
2016-09-06 17:52 ` John Wiegley
2016-09-06 19:00 ` Andreas Röhler
2016-09-06 21:00 ` Stefan Monnier
2016-09-06 21:29 ` Drew Adams
2016-09-06 21:41 ` Karl Fogel
2016-09-06 21:59 ` Paul Eggert
2016-09-06 22:01 ` Karl Fogel
2016-09-06 22:07 ` Davis Herring
2016-09-06 22:21 ` Karl Fogel
2016-09-06 22:46 ` Clément Pit--Claudel
2016-09-07 0:24 ` Stefan Monnier
2016-09-07 16:49 ` Karl Fogel
2016-09-07 18:41 ` Andreas Röhler
2016-09-07 20:02 ` Karl Fogel
2016-09-06 22:03 ` Karl Fogel
2016-12-24 1:03 ` Rolf Ade
2016-12-25 15:44 ` Stefan Monnier
2016-12-26 0:29 ` Rolf Ade
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