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[debbugs-tracker] bug#35497: closed ([PATCH] Don't rewrite buffer conten
GNU bug Tracking System
[debbugs-tracker] bug#35497: closed ([PATCH] Don't rewrite buffer contents after saving by rename)
Wed, 08 May 2019 07:49:02 +0000
Your message dated Wed, 08 May 2019 09:48:07 +0200
with message-id <address@hidden>
and subject line Re: [PATCH v7] Don't rewrite buffer contents after saving by
has caused the debbugs.gnu.org bug report #35497,
regarding [PATCH] Don't rewrite buffer contents after saving by rename
to be marked as done.
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--- Begin Message ---
[PATCH] Don't rewrite buffer contents after saving by rename
Mon, 29 Apr 2019 16:20:09 -0700
When `file-precious-flag' is non-nil, files are saved by renaming a
temporary file to the new name; this is an atomic operation on POSIX
so other programs will not see the file in an intermediate state.
Unfortunately, due to a paren-matching error introduced in change
574c05e219476912db3105fa164accd9ba12b35f, we would then write the
contents again in the usual way after this rename. In addition to
being wasteful, this is a serious bug: the whole point of
`file-precious-flag' is to prevent race conditions with other programs
that might otherwise see an empty file, but with this bug the race is
actually much *more* likely to be visible: the rename will alert any
inotify watchers of a change, and then the subsequent write is very
likely to truncate the file just as those programs start to read it!
* lisp/files.el (basic-save-buffer-2): Don't rewrite file contents
* test/lisp/files-tests.el (files-tests-dont-rewrite-precious-files):
Regression test for this change.
etc/NEWS | 7 +++++++
lisp/files.el | 4 ++--
test/lisp/files-tests.el | 27 +++++++++++++++++++++++++++
3 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/etc/NEWS b/etc/NEWS
index 9b32d720b6..5bfadcbbd6 100644
@@ -340,6 +340,13 @@ longer.
** Multicolor fonts such as "Noto Color Emoji" can be displayed on
Emacs configured with Cairo drawing and linked with cairo >= 1.16.0.
+** The file-precious-flag is now respected correctly.
+A bug previously caused files to be saved twice when
+`file-precious-flag' or `break-hardlinks-on-save' were specified: once
+by renaming a temporary file to the destination name, and then again
+by truncating and rewriting the file, which is exactly what
+`file-precious-flag' is supposed to avoid.
* Editing Changes in Emacs 27.1
diff --git a/lisp/files.el b/lisp/files.el
index c05d70a00e..72518e8127 100644
@@ -5256,7 +5256,7 @@ basic-save-buffer-2
(nth 1 setmodes)))
- (logior (car setmodes) 128))))))
+ (logior (car setmodes) 128)))))
@@ -5272,7 +5272,7 @@ basic-save-buffer-2
(and setmodes (not success)
(rename-file (nth 2 setmodes) buffer-file-name t)
- (setq buffer-backed-up nil))))))
+ (setq buffer-backed-up nil)))))))
(declare-function diff-no-select "diff"
diff --git a/test/lisp/files-tests.el b/test/lisp/files-tests.el
index ae8ea41a79..07012fea6e 100644
@@ -1244,5 +1244,32 @@ files-tests-file-attributes-equal
(executable-find (file-name-nondirectory tmpfile))))))
+(ert-deftest files-tests-dont-rewrite-precious-files ()
+ "Test that `file-precious-flag' forces files to be saved by
+renaming only, rather than modified in-place."
+ (files-tests--with-temp-file temp-file-name
+ (with-current-buffer (find-file-noselect temp-file-name)
+ (let* (temp-file-events watch)
+ (setq watch
+ temp-file-name '(change)
+ (lambda (event)
+ (add-to-list 'temp-file-events (cadr event) 'append))))
+ (setq-local file-precious-flag t)
+ (insert "foobar")
+ (should (null (save-buffer)))
+ ;; file-notify callbacks are input events, so we need to
+ ;; accept input before checking results.
+ (sit-for 0.1)
+ ;; When file-precious-flag is set, the visited file
+ ;; should never be modified, only renamed-to (which may
+ ;; appear as "renamed" and/or "created" to file-notify).
+ (should (not (memq 'changed temp-file-events))))
+ (file-notify-rm-watch watch))))))
;;; files-tests.el ends here
--- End Message ---
--- Begin Message ---
Re: [PATCH v7] Don't rewrite buffer contents after saving by rename
Wed, 08 May 2019 09:48:07 +0200
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)
thanks for this final version, I've pushed it to master. I've added a
skip for Emacs < 27, since it fails there. Obviously.
Marking the bug as closed.
Best regards, Michael.
--- End Message ---
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