From: Andreas Gruenbacher <agruen@suse.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH] Improve the "diff --git" format documentation
Date: Thu, 14 Oct 2010 14:39:42 +0200 [thread overview]
Message-ID: <201010141439.43168.agruen@suse.de> (raw)
In-Reply-To: <7v8w21fsgr.fsf@alter.siamese.dyndns.org>
On Thursday 14 October 2010 03:55:48 Junio C Hamano wrote:
> Andreas Gruenbacher <agruen@suse.de> writes:
>
> > The `a/` and `b/` filenames are the same unless rename/copy is
> > involved. Especially, even for a creation or a deletion,
> > -`/dev/null` is _not_ used in place of `a/` or `b/` filenames.
> > +`/dev/null` is _not_ used in place of the `a/` or `b/` filenames
> > +for nonexisting files (unlike in the unified diff headers).
>
> The description in the parentheses is wrong, unless you qualify whose
> "unified diff headers" you are talking about.
I was referring to the unified diff headers that git emits, not any other
utility's output.
POSIX does not say anything about nonexisting files, and GNU diff with -rN uses an
Epoch timestamp instead of /dev/null to distinguish between missing and empty
files:
http://www.gnu.org/software/diffutils/manual/html_node/Creating-and-Removing.html
> For example:
>
> http://www.opengroup.org/onlinepubs/9699919799/utilities/diff.html#tag_20_34_10_07
>
> does not mention anything about file creation/deletion events.
Fine, let's make this clear in the "combined diff" format description too
then.
> Perhaps you are referring to cvs or svn output, but I think we can safely
> drop the parenthesized part without losing clarity.
I still believe that the documentation should make it very clear how it
handles created and deleted files; it really is not obvious to everyone.
Can you live with the attached patch?
Thanks,
Andreas
--
[PATCH] Clarify how /dev/null is used in diffs
Say where the unified diff header comes in the "git diff" format, and
make it clear that /dev/null is used there.
In the description of the "combined diff" format, do not claim that
traditional unified diffs use /dev/null to signal created or deleted files.
Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
---
Documentation/diff-generate-patch.txt | 26 ++++++++++++++++++--------
1 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt
index 3ac2bea..21c4923 100644
--- a/Documentation/diff-generate-patch.txt
+++ b/Documentation/diff-generate-patch.txt
@@ -53,12 +53,22 @@ The index line includes the SHA-1 checksum before and after the change.
The <mode> is included if the file mode does not change; otherwise,
separate lines indicate the old and the new mode.
-3. TAB, LF, double quote and backslash characters in pathnames
+3. It is followed by a 'unified' diff which starts with a two-line
+ from-file/to-file header:
+
+ --- a/file1
+ +++ b/file2
++
+This header is omitted if the contents of `file1` and `file2` are identical.
+To signal created or deleted files, `/dev/null` is used instead of `a/file1`
+or `b/file2`.
+
+4. TAB, LF, double quote and backslash characters in pathnames
are represented as `\t`, `\n`, `\"` and `\\`, respectively.
If there is need for such substitution then the whole
pathname is put in double quotes.
-4. All the `file1` files in the output refer to files before the
+5. All the `file1` files in the output refer to files before the
commit, and all the `file2` files refer to files after the commit.
It is incorrect to apply each change to each file sequentially. For
example, this patch will swap a and b:
@@ -133,14 +143,14 @@ information about detected contents movement (renames and
copying detection) are designed to work with diff of two
<tree-ish> and are not used by combined diff format.
-3. It is followed by two-line from-file/to-file header
+3. It is followed by a two-line from-file/to-file header similar to the
+ traditional 'unified' diff format header:
- --- a/file
- +++ b/file
+ --- a/file1
+ +++ b/file2
+
-Similar to two-line header for traditional 'unified' diff
-format, `/dev/null` is used to signal created or deleted
-files.
+To signal created or deleted files, `/dev/null` is used instead of `a/file1`
+or `b/file2`.
4. Chunk header format is modified to prevent people from
accidentally feeding it to `patch -p1`. Combined diff format
next prev parent reply other threads:[~2010-10-14 12:40 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-06 16:23 [PATCH] Improve the "diff --git" format documentation Andreas Gruenbacher
2010-10-06 17:22 ` Junio C Hamano
2010-10-06 23:03 ` Andreas Gruenbacher
2010-10-11 13:14 ` Andreas Gruenbacher
2010-10-14 1:55 ` Junio C Hamano
2010-10-14 1:55 ` Junio C Hamano
2010-10-14 10:53 ` Andreas Gruenbacher
2010-10-14 12:39 ` Andreas Gruenbacher [this message]
2010-10-14 16:16 ` Jonathan Nieder
2010-10-17 4:43 ` Junio C Hamano
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