* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
@ 2012-07-10 1:46 Dmitry Gutov
2012-07-18 12:53 ` Stefan Monnier
0 siblings, 1 reply; 6+ messages in thread
From: Dmitry Gutov @ 2012-07-10 1:46 UTC (permalink / raw)
To: 11894
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This applies both to context and unified diffs.
To get a 0-context hunk, you invoke diff command with -c0 or -U0 argument.
1. Example files (4 and 3 lines long):
test:
z
abc
def
test2:
z
abc
def
2. Run `diff -c0 test test2 > test.diff`:
*** test 2012-07-09 06:04:04.572209000 +0400
--- test2 2012-07-09 06:04:11.987150600 +0400
***************
*** 3 ****
-
--- 2 ----
3. Open test.diff in Emacs, then:
a) Do `C-u C-c C-a' (reverse hunk) -> see the empty line appear after
"z", instead of after "abc".
b) Open test2, add empty line after "abc", go to test.diff window, do
`C-c C-a' (apply hunk), see the newline between "z" and "abc" disappear
instead.
Not sure if we can rely on the line number being always off by 1 in such
hunks (there's no insertion, so, technically, the second line number in
the header could be arbitrary), but at least 3 versions of diff across 2
different OSes work the same in this regard.
Note that if you try to create such hunk with `diff-split-hunk' (by
slicing it off a bigger hunk), the line number won't be off by 1.
Maybe that's a bug in `diff-split-hunk'.
--Dmitry
[-- Attachment #2: diff-mode.diff --]
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diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 9034ffe..e27b60f 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -1675,7 +1675,11 @@ NOPROMPT, if non-nil, means not to prompt the user."
(when (> (prefix-numeric-value other-file) 8)
(setq diff-jump-to-old-file other))
(with-current-buffer buf
- (goto-char (point-min)) (forward-line (1- (string-to-number line)))
+ (let ((line-num (string-to-number line)))
+ ;; When the hunk is pure deletion, line number is off by 1.
+ (when (string= (if reverse (car old) (car new)) "")
+ (incf line-num))
+ (goto-char (point-min)) (forward-line (1- line-num)))
(let* ((orig-pos (point))
(switched nil)
;; FIXME: Check for case where both OLD and NEW are found.
^ permalink raw reply related [flat|nested] 6+ messages in thread* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
2012-07-10 1:46 bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal Dmitry Gutov
@ 2012-07-18 12:53 ` Stefan Monnier
2012-07-18 13:28 ` Andreas Schwab
2012-07-18 17:25 ` Dmitry Gutov
0 siblings, 2 replies; 6+ messages in thread
From: Stefan Monnier @ 2012-07-18 12:53 UTC (permalink / raw)
To: Dmitry Gutov; +Cc: 11894
> Not sure if we can rely on the line number being always off by 1 in such
> hunks (there's no insertion, so, technically, the second line number in the
> header could be arbitrary), but at least 3 versions of diff across
> 2 different OSes work the same in this regard.
This looks like a bug in those versions of diff (not that I know
a non-buggy version, tho). Could you report it to GNU diffutils.
> Note that if you try to create such hunk with `diff-split-hunk' (by slicing
> it off a bigger hunk), the line number won't be off by 1.
Oh, right, so there is a "version of diff" that doesn't have this bug ;-)
> Maybe that's a bug in `diff-split-hunk'.
I doubt it. At least `patch' seems to agree with diff-mode.el:
% diff -c0 footest1 footest2 |patch -o footest3 footest1
patching file footest1
patch: **** replacement text or line numbers mangled in hunk at line 8
%
> - (goto-char (point-min)) (forward-line (1- (string-to-number line)))
> + (let ((line-num (string-to-number line)))
> + ;; When the hunk is pure deletion, line number is off by 1.
> + (when (string= (if reverse (car old) (car new)) "")
> + (incf line-num))
> + (goto-char (point-min)) (forward-line (1- line-num)))
Context/unified diffs with 0 context are pretty rare, so I'd rather not
work around such a bug if I don't really have to.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
2012-07-18 12:53 ` Stefan Monnier
@ 2012-07-18 13:28 ` Andreas Schwab
2012-07-19 7:58 ` Stefan Monnier
2012-07-18 17:25 ` Dmitry Gutov
1 sibling, 1 reply; 6+ messages in thread
From: Andreas Schwab @ 2012-07-18 13:28 UTC (permalink / raw)
To: Stefan Monnier; +Cc: 11894, Dmitry Gutov
Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
> This looks like a bug in those versions of diff (not that I know
> a non-buggy version, tho).
Maybe, but that's how POSIX wants it:
The ending line number of an empty range shall be the number of the
preceding line, or 0 if the range is at the start of the file.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
^ permalink raw reply [flat|nested] 6+ messages in thread* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
2012-07-18 13:28 ` Andreas Schwab
@ 2012-07-19 7:58 ` Stefan Monnier
2012-07-19 8:40 ` Andreas Schwab
0 siblings, 1 reply; 6+ messages in thread
From: Stefan Monnier @ 2012-07-19 7:58 UTC (permalink / raw)
To: Andreas Schwab; +Cc: 11894, Dmitry Gutov
>> This looks like a bug in those versions of diff (not that I know
>> a non-buggy version, tho).
> Maybe, but that's how POSIX wants it:
> The ending line number of an empty range shall be the number of the
> preceding line, or 0 if the range is at the start of the file.
Hmm... but the number we're talking about is the starting-line-number,
isn't it?
In any case I think that we're OK in the sense that we're not doing
much worse than `patch'.
Stefan
^ permalink raw reply [flat|nested] 6+ messages in thread* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
2012-07-19 7:58 ` Stefan Monnier
@ 2012-07-19 8:40 ` Andreas Schwab
0 siblings, 0 replies; 6+ messages in thread
From: Andreas Schwab @ 2012-07-19 8:40 UTC (permalink / raw)
To: Stefan Monnier; +Cc: 11894, Dmitry Gutov
Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
>>> This looks like a bug in those versions of diff (not that I know
>>> a non-buggy version, tho).
>> Maybe, but that's how POSIX wants it:
>
>> The ending line number of an empty range shall be the number of the
>> preceding line, or 0 if the range is at the start of the file.
>
> Hmm... but the number we're talking about is the starting-line-number,
> isn't it?
There is no starting-line-number.
Next, the range of lines in file1 shall be written in the following
format if the range contains two or more lines:
"*** %d,%d ****\n", <beginning line number>, <ending line number>
and the following format otherwise:
"*** %d ****\n", <ending line number>
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal
2012-07-18 12:53 ` Stefan Monnier
2012-07-18 13:28 ` Andreas Schwab
@ 2012-07-18 17:25 ` Dmitry Gutov
1 sibling, 0 replies; 6+ messages in thread
From: Dmitry Gutov @ 2012-07-18 17:25 UTC (permalink / raw)
To: Stefan Monnier; +Cc: 11894, Andreas Schwab
On 18.07.2012 16:53, Stefan Monnier wrote:
>> Not sure if we can rely on the line number being always off by 1 in such
>> hunks (there's no insertion, so, technically, the second line number in the
>> header could be arbitrary), but at least 3 versions of diff across
>> 2 different OSes work the same in this regard.
>
> This looks like a bug in those versions of diff (not that I know
> a non-buggy version, tho). Could you report it to GNU diffutils.
As per Andreas' comment, this is probably not a bug.
>> Note that if you try to create such hunk with `diff-split-hunk' (by slicing
>> it off a bigger hunk), the line number won't be off by 1.
>
> Oh, right, so there is a "version of diff" that doesn't have this bug ;-)
Yep, and I'll use it as a workaround if this bug won't be fixed.
>> Maybe that's a bug in `diff-split-hunk'.
>
> I doubt it. At least `patch' seems to agree with diff-mode.el:
>
> % diff -c0 footest1 footest2 |patch -o footest3 footest1
> patching file footest1
> patch: **** replacement text or line numbers mangled in hunk at line 8
> %
`info diff` says: "For proper operation, `patch' typically needs at
least two lines of context.", so this just may be a documented problem
nobody cares about.
>> - (goto-char (point-min)) (forward-line (1- (string-to-number line)))
>> + (let ((line-num (string-to-number line)))
>> + ;; When the hunk is pure deletion, line number is off by 1.
>> + (when (string= (if reverse (car old) (car new)) "")
>> + (incf line-num))
>> + (goto-char (point-min)) (forward-line (1- line-num)))
>
> Context/unified diffs with 0 context are pretty rare, so I'd rather not
> work around such a bug if I don't really have to.
I'm fine either way, just wanted to report this.
--Dmitry
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-07-19 8:40 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2012-07-10 1:46 bug#11894: 24.1.50; [PATCH] diff-apply-hunk can be off by 1 line when the hunk is 0-context pure removal Dmitry Gutov
2012-07-18 12:53 ` Stefan Monnier
2012-07-18 13:28 ` Andreas Schwab
2012-07-19 7:58 ` Stefan Monnier
2012-07-19 8:40 ` Andreas Schwab
2012-07-18 17:25 ` Dmitry Gutov
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