bug#13705: 24.2.93; "^M" characters in diff buffers

bug#13705: 24.2.93; "^M" characters in diff buffers

[Dani Moncayo]

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Recipe from "emacs -Q":
1. Download the two attached files `fa' and `fb'.
2. M-x diff RET fb RET fa RET

In the *Diff* buffer, I see annoying/inappropriate "^M" characters at
the end of the compared lines. (see attached screenshot)

I see this bug both in the emacs-24 branch and the trunk.

In GNU Emacs 24.2.93.1 (i386-mingw-nt6.1.7601)
 of 2013-02-10 on VBOX-W7
Bzr revision: 111243 michael.albinus@gmx.de-20130210100709-s22fi7zl9w92a8sa
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -IC:/emacs/libs/libXpm-3.5.10/include -IC:/emacs/libs/libXpm-3.5.10/src
 -IC:/emacs/libs/libpng-dev_1.4.3-1_win32/include
 -IC:/emacs/libs/zlib-dev_1.2.5-2_win32/include
 -IC:/emacs/libs/giflib-4.1.4-1-lib/include
 -IC:/emacs/libs/jpeg-6b-4-lib/include
 -IC:/emacs/libs/tiff-3.8.2-1-lib/include
 -IC:/emacs/libs/libxml2-2.7.8-w32-bin/include/libxml2
 -IC:/emacs/libs/gnutls-3.1.5-w32/include
 -IC:/emacs/libs/libiconv-1.14-2-mingw32-dev/include'


-- 
Dani Moncayo

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a

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á

bug#13705: 24.2.93; "^M" characters in diff buffers

[Eli Zaretskii]

> Date: Wed, 13 Feb 2013 10:40:22 +0100
> From: Dani Moncayo <dmoncayo@gmail.com>
> 
> Recipe from "emacs -Q":
> 1. Download the two attached files `fa' and `fb'.
> 2. M-x diff RET fb RET fa RET
> 
> In the *Diff* buffer, I see annoying/inappropriate "^M" characters at
> the end of the compared lines. (see attached screenshot)

It's most probably your Diff, not Emacs.  I cannot reproduce the
problem with the version of Diff I have here (which is a GnuWin32
port).  My crystal says that yours is from MSYS or maybe Cygwin, and
writes its output with Unix-style LF-only EOL format.  That presents
to Emacs text that has inconsistent EOLs (because the files you diff
have DOS CR-LF EOLs), so Emacs punts and doesn't decode the EOL
format.

To see if my crystal ball is as clear as it gets, try this:

  (let ((coding-system-for-read 'no-conversion))
    (call-process shell-file-name nil t nil
		  shell-command-switch "diff -c fa fb"))

and look at the lines generated by Diff, like these:

 *** fa	2013-02-12 18:41:03.201375000 +0200
 --- fb	2013-02-08 16:25:03.161000000 +0200

If they don't have the ^M character at their end, your problem is as I
described.

With my Diff, the above snippet gives me _all_ the lines with ^M,
which is consistent.

bug#13705: 24.2.93; "^M" characters in diff buffers

[Dani Moncayo]

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> It's most probably your Diff, not Emacs.  I cannot reproduce the
> problem with the version of Diff I have here (which is a GnuWin32
> port).  My crystal says that yours is from MSYS or maybe Cygwin

Yes, my diff (at that moment) was from MSYS.

>, and
> writes its output with Unix-style LF-only EOL format.  That presents
> to Emacs text that has inconsistent EOLs (because the files you diff
> have DOS CR-LF EOLs), so Emacs punts and doesn't decode the EOL
> format.
>
> To see if my crystal ball is as clear as it gets, try this:
>
>   (let ((coding-system-for-read 'no-conversion))
>     (call-process shell-file-name nil t nil
>                   shell-command-switch "diff -c fa fb"))
>
> and look at the lines generated by Diff, like these:
>
>  *** fa 2013-02-12 18:41:03.201375000 +0200
>  --- fb 2013-02-08 16:25:03.161000000 +0200

The above expression produces the output shown in
"Screenshot-MS-Windows.png" (attached).

> If they don't have the ^M character at their end, your problem is as I
> described.
>
> With my Diff, the above snippet gives me _all_ the lines with ^M,
> which is consistent.

Yes, the problem seems to be the one you've spotted, but note that
I've just reproduced the exact same problem on Ubuntu [1].  See the
screenshot "Screenshot-Ubuntu.png" (attached).

Therefore, the problem seems to be more general: it affects to every
diff made from two files with DOS-type EOLs, unless the "diff" program
is adapted to deal with this scenario (like the one from GnuWin32).

But anyway, if there is a problem here, it is not in Emacs, and
therefore, I'm closing this bug report.

As always, thanks for your time Eli.


---- Footnotes ----

[1]
In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.13)
 of 2013-02-11 on LeG570-ubuntu
Bzr revision: 111735 eliz@gnu.org-20130211173232-odvn6s0c9gs3jclc
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:	Ubuntu 12.10


-- 
Dani Moncayo

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bug#13705: 24.2.93; "^M" characters in diff buffers

[Eli Zaretskii]

> Date: Wed, 13 Feb 2013 19:59:23 +0100
> From: Dani Moncayo <dmoncayo@gmail.com>
> Cc: 13705-done@debbugs.gnu.org
> 
> >   (let ((coding-system-for-read 'no-conversion))
> >     (call-process shell-file-name nil t nil
> >                   shell-command-switch "diff -c fa fb"))
> >
> > and look at the lines generated by Diff, like these:
> >
> >  *** fa 2013-02-12 18:41:03.201375000 +0200
> >  --- fb 2013-02-08 16:25:03.161000000 +0200
> 
> The above expression produces the output shown in
> "Screenshot-MS-Windows.png" (attached).

As expected.

> Yes, the problem seems to be the one you've spotted, but note that
> I've just reproduced the exact same problem on Ubuntu [1].  See the
> screenshot "Screenshot-Ubuntu.png" (attached).

On Ubuntu, it is expected to see the ^M characters, because that's
what you'd see if you invoke Diff from the shell prompt as well.

IOW, on Windows, two files which have DOS EOLs should not show ^M in
the Diff output, because DOS EOLs are native on Windows, and ^M at the
end of the line is not considered part of the text there.  On Unix,
files with DOS EOLs are expected to be seen with the ^M explicit,
because it _is_ part of the text.

> Therefore, the problem seems to be more general: it affects to every
> diff made from two files with DOS-type EOLs, unless the "diff" program
> is adapted to deal with this scenario (like the one from GnuWin32).

It _is_ general, but it is not a problem.  When Emacs sees
inconsistent EOL format it _always_ refrains from decoding the EOLs.