git/Documentation/diff-generate-patch.txt
Jeff King 6cf378f0cb docs: stop using asciidoc no-inline-literal
In asciidoc 7, backticks like `foo` produced a typographic
effect, but did not otherwise affect the syntax. In asciidoc
8, backticks introduce an "inline literal" inside which markup
is not interpreted. To keep compatibility with existing
documents, asciidoc 8 has a "no-inline-literal" attribute to
keep the old behavior. We enabled this so that the
documentation could be built on either version.

It has been several years now, and asciidoc 7 is no longer
in wide use. We can now decide whether or not we want
inline literals on their own merits, which are:

  1. The source is much easier to read when the literal
     contains punctuation. You can use `master~1` instead
     of `master{tilde}1`.

  2. They are less error-prone. Because of point (1), we
     tend to make mistakes and forget the extra layer of
     quoting.

This patch removes the no-inline-literal attribute from the
Makefile and converts every use of backticks in the
documentation to an inline literal (they must be cleaned up,
or the example above would literally show "{tilde}" in the
output).

Problematic sites were found by grepping for '`.*[{\\]' and
examined and fixed manually. The results were then verified
by comparing the output of "html2text" on the set of
generated html pages. Doing so revealed that in addition to
making the source more readable, this patch fixes several
formatting bugs:

  - HTML rendering used the ellipsis character instead of
    literal "..." in code examples (like "git log A...B")

  - some code examples used the right-arrow character
    instead of '->' because they failed to quote

  - api-config.txt did not quote tilde, and the resulting
    HTML contained a bogus snippet like:

      <tt><sub></tt> foo <tt></sub>bar</tt>

    which caused some parsers to choke and omit whole
    sections of the page.

  - git-commit.txt confused ``foo`` (backticks inside a
    literal) with ``foo'' (matched double-quotes)

  - mentions of `A U Thor <author@example.com>` used to
    erroneously auto-generate a mailto footnote for
    author@example.com

  - the description of --word-diff=plain incorrectly showed
    the output as "[-removed-] and {added}", not "{+added+}".

  - using "prime" notation like:

      commit `C` and its replacement `C'`

    confused asciidoc into thinking that everything between
    the first backtick and the final apostrophe were meant
    to be inside matched quotes

  - asciidoc got confused by the escaping of some of our
    asterisks. In particular,

      `credential.\*` and `credential.<url>.\*`

    properly escaped the asterisk in the first case, but
    literally passed through the backslash in the second
    case.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2012-04-26 13:19:06 -07:00

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Generating patches with -p
--------------------------
When "git-diff-index", "git-diff-tree", or "git-diff-files" are run
with a '-p' option, "git diff" without the '--raw' option, or
"git log" with the "-p" option, they
do not produce the output described above; instead they produce a
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
diff format:
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,
`/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
the file that rename/copy produces, respectively.
2. It is followed by one or more extended header lines:
old mode <mode>
new mode <mode>
deleted file mode <mode>
new file mode <mode>
copy from <path>
copy to <path>
rename from <path>
rename to <path>
similarity index <number>
dissimilarity index <number>
index <hash>..<hash> <mode>
+
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 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
--------------------
Any diff-generating command can take the `-c` or `--cc` option to
produce a 'combined diff' when showing a merge. This is the default
format when showing merges with linkgit:git-diff[1] or
linkgit:git-show[1]. Note also that you can give the `-m' option to any
of these commands to force generation of diffs with individual parents
of a merge.
A 'combined diff' format looks like this:
------------
diff --combined describe.c
index fabadb8,cc95eb0..4866510
--- a/describe.c
+++ b/describe.c
@@@ -98,20 -98,12 +98,20 @@@
return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;
}
- static void describe(char *arg)
-static void describe(struct commit *cmit, int last_one)
++static void describe(char *arg, int last_one)
{
+ unsigned char sha1[20];
+ struct commit *cmit;
struct commit_list *list;
static int initialized = 0;
struct commit_name *n;
+ if (get_sha1(arg, sha1) < 0)
+ usage(describe_usage);
+ cmit = lookup_commit_reference(sha1);
+ if (!cmit)
+ usage(describe_usage);
+
if (!initialized) {
initialized = 1;
for_each_ref(get_name);
------------
1. It is preceded with a "git diff" header, that looks like
this (when '-c' option is used):
diff --combined file
+
or like this (when '--cc' option is used):
diff --cc file
2. It is followed by one or more extended header lines
(this example shows a merge with two parents):
index <hash>,<hash>..<hash>
mode <mode>,<mode>..<mode>
new file mode <mode>
deleted file mode <mode>,<mode>
+
The `mode <mode>,<mode>..<mode>` line appears only if at least one of
the <mode> is different from the rest. Extended headers with
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
--- a/file
+++ b/file
+
Similar to two-line header for traditional 'unified' diff
format, `/dev/null` is used to signal created or deleted
files.
4. Chunk header format is modified to prevent people from
accidentally feeding it to `patch -p1`. Combined diff format
was created for review of merge commit changes, and was not
meant for apply. The change is similar to the change in the
extended 'index' header:
@@@ <from-file-range> <from-file-range> <to-file-range> @@@
+
There are (number of parents + 1) `@` characters in the chunk
header for combined diff format.
Unlike the traditional 'unified' diff format, which shows two
files A and B with a single column that has `-` (minus --
appears in A but removed in B), `+` (plus -- missing in A but
added to B), or `" "` (space -- unchanged) prefix, this format
compares two or more files file1, file2,... with one file X, and
shows how X differs from each of fileN. One column for each of
fileN is prepended to the output line to note how X's line is
different from it.
A `-` character in the column N means that the line appears in
fileN but it does not appear in the result. A `+` character
in the column N means that the line appears in the result,
and fileN does not have that line (in other words, the line was
added, from the point of view of that parent).
In the above example output, the function signature was changed
from both files (hence two `-` removals from both file1 and
file2, plus `++` to mean one line that was added does not appear
in either file1 nor file2). Also eight other lines are the same
from file1 but do not appear in file2 (hence prefixed with `+`).
When shown by `git diff-tree -c`, it compares the parents of a
merge commit with the merge result (i.e. file1..fileN are the
parents). When shown by `git diff-files -c`, it compares the
two unresolved merge parents with the working tree file
(i.e. file1 is stage 2 aka "our version", file2 is stage 3 aka
"their version").