Clarify and extend the "git diff" format documentation

Move the similarity and dissimilarity index header description closer to
where those extended headers are described.

Describe and/or clarify the format used for file modes, pathnames, and
the index header.

Document that all "old" files refer to the state before applying the
*entire* output, and all "new" files refer to the state thereafter.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt
index 8f9a2412fd44c80f2bf8d63271e2897ebeb3ddeb..3ac2beac6229955dc2534c428238c3d5ff57d25d 100644 (file)
--- a/Documentation/diff-generate-patch.txt
+++ b/Documentation/diff-generate-patch.txt
@@ -9,16 +9,15 @@ patch file.  You can customize the creation of such patches via the
 GIT_EXTERNAL_DIFF and the GIT_DIFF_OPTS environment variables.
 
 What the -p option produces is slightly different from the traditional
 GIT_EXTERNAL_DIFF and the GIT_DIFF_OPTS environment variables.
 
 What the -p option produces is slightly different from the traditional

-diff format.
+diff format:

 
 

-1.   It is preceded with a "git diff" header, that looks like
-     this:
+1.   It is preceded with a "git diff" header that looks like this:

 
        diff --git a/file1 b/file2
 +
 The `a/` and `b/` filenames are the same unless rename/copy is
 involved.  Especially, even for a creation or a deletion,
 
        diff --git a/file1 b/file2
 +
 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.

 +
 When rename/copy is involved, `file1` and `file2` show the
 name of the source file of the rename/copy and the name of
 +
 When rename/copy is involved, `file1` and `file2` show the
 name of the source file of the rename/copy and the name of


@@ -37,18 +36,39 @@ the file that rename/copy produces, respectively.
        similarity index <number>
        dissimilarity index <number>
        index <hash>..<hash> <mode>
        similarity index <number>
        dissimilarity index <number>
        index <hash>..<hash> <mode>

-
-3.  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.
-
++
+File modes are printed as 6-digit octal numbers including the file type
+and file permission bits.
++
+Path names in extended headers do not include the `a/` and `b/` prefixes.
++

 The similarity index is the percentage of unchanged lines, and
 the dissimilarity index is the percentage of changed lines.  It
 is a rounded down integer, followed by a percent sign.  The
 similarity index value of 100% is thus reserved for two equal
 files, while 100% dissimilarity means that no line from the old
 file made it into the new one.
 The similarity index is the percentage of unchanged lines, and
 the dissimilarity index is the percentage of changed lines.  It
 is a rounded down integer, followed by a percent sign.  The
 similarity index value of 100% is thus reserved for two equal
 files, while 100% dissimilarity means that no line from the old
 file made it into the new one.

++
+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
+    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
+    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:
+
+      diff --git a/a b/b
+      rename from a
+      rename to b
+      diff --git a/b b/a
+      rename from b
+      rename to a

 
 
 combined diff format
 
 
 combined diff format