Documentation: publicize hints for sending patches with GMail

[git] / Documentation / git-format-patch.txt

git-format-patch(1)
===================

NAME
----
git-format-patch - Prepare patches for e-mail submission


SYNOPSIS
--------
[verse]
'git format-patch' [-k] [(-o|--output-directory) <dir> | --stdout]
                   [--no-thread | --thread[=<style>]]
                   [(--attach|--inline)[=<boundary>] | --no-attach]
                   [-s | --signoff]
                   [--signature=<signature> | --no-signature]
                   [-n | --numbered | -N | --no-numbered]
                   [--start-number <n>] [--numbered-files]
                   [--in-reply-to=Message-Id] [--suffix=.<sfx>]
                   [--ignore-if-in-upstream]
                   [--subject-prefix=Subject-Prefix]
                   [--to=<email>] [--cc=<email>]
                   [--cover-letter]
                   [<common diff options>]
                   [ <since> | <revision range> ]

DESCRIPTION
-----------

Prepare each commit with its patch in
one file per commit, formatted to resemble UNIX mailbox format.
The output of this command is convenient for e-mail submission or
for use with 'git am'.

There are two ways to specify which commits to operate on.

1. A single commit, <since>, specifies that the commits leading
   to the tip of the current branch that are not in the history
   that leads to the <since> to be output.

2. Generic <revision range> expression (see "SPECIFYING
   REVISIONS" section in linkgit:gitrevisions[7]) means the
   commits in the specified range.

The first rule takes precedence in the case of a single <commit>.  To
apply the second rule, i.e., format everything since the beginning of
history up until <commit>, use the '\--root' option: `git format-patch
\--root <commit>`.  If you want to format only <commit> itself, you
can do this with `git format-patch -1 <commit>`.

By default, each output file is numbered sequentially from 1, and uses the
first line of the commit message (massaged for pathname safety) as
the filename. With the `--numbered-files` option, the output file names
will only be numbers, without the first line of the commit appended.
The names of the output files are printed to standard
output, unless the `--stdout` option is specified.

If `-o` is specified, output files are created in <dir>.  Otherwise
they are created in the current working directory.

By default, the subject of a single patch is "[PATCH] First Line" and
the subject when multiple patches are output is "[PATCH n/m] First
Line". To force 1/1 to be added for a single patch, use `-n`.  To omit
patch numbers from the subject, use `-N`.

If given `--thread`, `git-format-patch` will generate `In-Reply-To` and
`References` headers to make the second and subsequent patch mails appear
as replies to the first mail; this also generates a `Message-Id` header to
reference.

OPTIONS
-------
:git-format-patch: 1
include::diff-options.txt[]

-<n>::
        Prepare patches from the topmost <n> commits.

-o <dir>::
--output-directory <dir>::
        Use <dir> to store the resulting files, instead of the
        current working directory.

-n::
--numbered::
        Name output in '[PATCH n/m]' format, even with a single patch.

-N::
--no-numbered::
        Name output in '[PATCH]' format.

--start-number <n>::
        Start numbering the patches at <n> instead of 1.

--numbered-files::
        Output file names will be a simple number sequence
        without the default first line of the commit appended.

-k::
--keep-subject::
        Do not strip/add '[PATCH]' from the first line of the
        commit log message.

-s::
--signoff::
        Add `Signed-off-by:` line to the commit message, using
        the committer identity of yourself.

--stdout::
        Print all commits to the standard output in mbox format,
        instead of creating a file for each one.

--attach[=<boundary>]::
        Create multipart/mixed attachment, the first part of
        which is the commit message and the patch itself in the
        second part, with `Content-Disposition: attachment`.

--no-attach::
        Disable the creation of an attachment, overriding the
        configuration setting.

--inline[=<boundary>]::
        Create multipart/mixed attachment, the first part of
        which is the commit message and the patch itself in the
        second part, with `Content-Disposition: inline`.

--thread[=<style>]::
--no-thread::
        Controls addition of `In-Reply-To` and `References` headers to
        make the second and subsequent mails appear as replies to the
        first.  Also controls generation of the `Message-Id` header to
        reference.
+
The optional <style> argument can be either `shallow` or `deep`.
'shallow' threading makes every mail a reply to the head of the
series, where the head is chosen from the cover letter, the
`\--in-reply-to`, and the first patch mail, in this order.  'deep'
threading makes every mail a reply to the previous one.
+
The default is `--no-thread`, unless the 'format.thread' configuration
is set.  If `--thread` is specified without a style, it defaults to the
style specified by 'format.thread' if any, or else `shallow`.
+
Beware that the default for 'git send-email' is to thread emails
itself.  If you want `git format-patch` to take care of threading, you
will want to ensure that threading is disabled for `git send-email`.

--in-reply-to=Message-Id::
        Make the first mail (or all the mails with `--no-thread`) appear as a
        reply to the given Message-Id, which avoids breaking threads to
        provide a new patch series.

--ignore-if-in-upstream::
        Do not include a patch that matches a commit in
        <until>..<since>.  This will examine all patches reachable
        from <since> but not from <until> and compare them with the
        patches being generated, and any patch that matches is
        ignored.

--subject-prefix=<Subject-Prefix>::
        Instead of the standard '[PATCH]' prefix in the subject
        line, instead use '[<Subject-Prefix>]'. This
        allows for useful naming of a patch series, and can be
        combined with the `--numbered` option.

--to=<email>::
        Add a `To:` header to the email headers. This is in addition
        to any configured headers, and may be used multiple times.

--cc=<email>::
        Add a `Cc:` header to the email headers. This is in addition
        to any configured headers, and may be used multiple times.

--add-header=<header>::
        Add an arbitrary header to the email headers.  This is in addition
        to any configured headers, and may be used multiple times.
        For example, `--add-header="Organization: git-foo"`

--cover-letter::
        In addition to the patches, generate a cover letter file
        containing the shortlog and the overall diffstat.  You can
        fill in a description in the file before sending it out.

--[no]-signature=<signature>::
        Add a signature to each message produced. Per RFC 3676 the signature
        is separated from the body by a line with '-- ' on it. If the
        signature option is omitted the signature defaults to the git version
        number.

--suffix=.<sfx>::
        Instead of using `.patch` as the suffix for generated
        filenames, use specified suffix.  A common alternative is
        `--suffix=.txt`.  Leaving this empty will remove the `.patch`
        suffix.
+
Note that the leading character does not have to be a dot; for example,
you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.

--no-binary::
        Do not output contents of changes in binary files, instead
        display a notice that those files changed.  Patches generated
        using this option cannot be applied properly, but they are
        still useful for code review.

--root::
        Treat the revision argument as a <revision range>, even if it
        is just a single commit (that would normally be treated as a
        <since>).  Note that root commits included in the specified
        range are always formatted as creation patches, independently
        of this flag.

CONFIGURATION
-------------
You can specify extra mail header lines to be added to each message,
defaults for the subject prefix and file suffix, number patches when
outputting more than one patch, add "To" or "Cc:" headers, configure
attachments, and sign off patches with configuration variables.

------------
[format]
        headers = "Organization: git-foo\n"
        subjectprefix = CHANGE
        suffix = .txt
        numbered = auto
        to = <email>
        cc = <email>
        attach [ = mime-boundary-string ]
        signoff = true
------------


DISCUSSION
----------

The patch produced by 'git format-patch' is in UNIX mailbox format,
with a fixed "magic" time stamp to indicate that the file is output
from format-patch rather than a real mailbox, like so:

------------
From 8f72bad1baf19a53459661343e21d6491c3908d3 Mon Sep 17 00:00:00 2001
From: Tony Luck <tony.luck@intel.com>
Date: Tue, 13 Jul 2010 11:42:54 -0700
Subject: [PATCH] =?UTF-8?q?[IA64]=20Put=20ia64=20config=20files=20on=20the=20?=
 =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig=20diet?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

arch/arm config files were slimmed down using a python script
(See commit c2330e286f68f1c408b4aa6515ba49d57f05beae comment)

Do the same for ia64 so we can have sleek & trim looking
...
------------

Typically it will be placed in a MUA's drafts folder, edited to add
timely commentary that should not go in the changelog after the three
dashes, and then sent as a message whose body, in our example, starts
with "arch/arm config files were...".  On the receiving end, readers
can save interesting patches in a UNIX mailbox and apply them with
linkgit:git-am[1].

When a patch is part of an ongoing discussion, the patch generated by
'git format-patch' can be tweaked to take advantage of the 'git am
--scissors' feature.  After your response to the discussion comes a
line that consists solely of "`-- >8 --`" (scissors and perforation),
followed by the patch with unnecessary header fields removed:

------------
...
> So we should do such-and-such.

Makes sense to me.  How about this patch?

-- >8 --
Subject: [IA64] Put ia64 config files on the Uwe Kleine-König diet

arch/arm config files were slimmed down using a python script
...
------------

When sending a patch this way, most often you are sending your own
patch, so in addition to the "`From $SHA1 $magic_timestamp`" marker you
should omit `From:` and `Date:` lines from the patch file.  The patch
title is likely to be different from the subject of the discussion the
patch is in response to, so it is likely that you would want to keep
the Subject: line, like the example above.

Checking for patch corruption
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Many mailers if not set up properly will corrupt whitespace.  Here are
two common types of corruption:

* Empty context lines that do not have _any_ whitespace.

* Non-empty context lines that have one extra whitespace at the
  beginning.

One way to test if your MUA is set up correctly is:

* Send the patch to yourself, exactly the way you would, except
  with To: and Cc: lines that do not contain the list and
  maintainer address.

* Save that patch to a file in UNIX mailbox format.  Call it a.patch,
  say.

* Apply it:

    $ git fetch <project> master:test-apply
    $ git checkout test-apply
    $ git reset --hard
    $ git am a.patch

If it does not apply correctly, there can be various reasons.

* The patch itself does not apply cleanly.  That is _bad_ but
  does not have much to do with your MUA.  You might want to rebase
  the patch with linkgit:git-rebase[1] before regenerating it in
  this case.

* The MUA corrupted your patch; "am" would complain that
  the patch does not apply.  Look in the .git/rebase-apply/ subdirectory and
  see what 'patch' file contains and check for the common
  corruption patterns mentioned above.

* While at it, check the 'info' and 'final-commit' files as well.
  If what is in 'final-commit' is not exactly what you would want to
  see in the commit log message, it is very likely that the
  receiver would end up hand editing the log message when applying
  your patch.  Things like "Hi, this is my first patch.\n" in the
  patch e-mail should come after the three-dash line that signals
  the end of the commit message.

MUA-SPECIFIC HINTS
------------------
Here are some hints on how to successfully submit patches inline using
various mailers.

GMail
~~~~~
GMail does not have any way to turn off line wrapping in the web
interface, so it will mangle any emails that you send.  You can however
use "git send-email" and send your patches through the GMail SMTP server, or
use any IMAP email client to connect to the google IMAP server and forward
the emails through that.

For hints on using 'git send-email' to send your patches through the
GMail SMTP server, see the EXAMPLE section of linkgit:git-send-email[1].

For hints on submission using the IMAP interface, see the EXAMPLE
section of linkgit:git-imap-send[1].

Thunderbird
~~~~~~~~~~~
By default, Thunderbird will both wrap emails as well as flag
them as being 'format=flowed', both of which will make the
resulting email unusable by git.

There are two different approaches.  One approach is to configure
Thunderbird to not mangle patches.  The second approach is to use
an external editor to keep Thunderbird from mangling the patches.

Approach #1 (configuration)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Three steps:

1. Configure your mail server composition as plain text:
   Edit...Account Settings...Composition & Addressing,
   uncheck "Compose Messages in HTML".

2. Configure your general composition window to not wrap.
+
In Thunderbird 2:
Edit..Preferences..Composition, wrap plain text messages at 0
+
In Thunderbird 3:
Edit..Preferences..Advanced..Config Editor.  Search for
"mail.wrap_long_lines".
Toggle it to make sure it is set to `false`.

3. Disable the use of format=flowed:
Edit..Preferences..Advanced..Config Editor.  Search for
"mailnews.send_plaintext_flowed".
Toggle it to make sure it is set to `false`.

After that is done, you should be able to compose email as you
otherwise would (cut + paste, 'git format-patch' | 'git imap-send', etc),
and the patches will not be mangled.

Approach #2 (external editor)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The following Thunderbird extensions are needed:
AboutConfig from http://aboutconfig.mozdev.org/ and
External Editor from http://globs.org/articles.php?lng=en&pg=8

1. Prepare the patch as a text file using your method of choice.

2. Before opening a compose window, use Edit->Account Settings to
   uncheck the "Compose messages in HTML format" setting in the
   "Composition & Addressing" panel of the account to be used to
   send the patch.

3. In the main Thunderbird window, 'before' you open the compose
   window for the patch, use Tools->about:config to set the
   following to the indicated values:
+
----------
        mailnews.send_plaintext_flowed  => false
        mailnews.wraplength             => 0
----------

4. Open a compose window and click the external editor icon.

5. In the external editor window, read in the patch file and exit
   the editor normally.

Side note: it may be possible to do step 2 with
about:config and the following settings but no one's tried yet.

----------
        mail.html_compose                       => false
        mail.identity.default.compose_html      => false
        mail.identity.id?.compose_html          => false
----------

There is a script in contrib/thunderbird-patch-inline which can help
you include patches with Thunderbird in an easy way. To use it, do the
steps above and then use the script as the external editor.

KMail
~~~~~
This should help you to submit patches inline using KMail.

1. Prepare the patch as a text file.

2. Click on New Mail.

3. Go under "Options" in the Composer window and be sure that
   "Word wrap" is not set.

4. Use Message -> Insert file... and insert the patch.

5. Back in the compose window: add whatever other text you wish to the
   message, complete the addressing and subject fields, and press send.


EXAMPLES
--------

* Extract commits between revisions R1 and R2, and apply them on top of
the current branch using 'git am' to cherry-pick them:
+
------------
$ git format-patch -k --stdout R1..R2 | git am -3 -k
------------

* Extract all commits which are in the current branch but not in the
origin branch:
+
------------
$ git format-patch origin
------------
+
For each commit a separate file is created in the current directory.

* Extract all commits that lead to 'origin' since the inception of the
project:
+
------------
$ git format-patch --root origin
------------

* The same as the previous one:
+
------------
$ git format-patch -M -B origin
------------
+
Additionally, it detects and handles renames and complete rewrites
intelligently to produce a renaming patch.  A renaming patch reduces
the amount of text output, and generally makes it easier to review.
Note that non-git "patch" programs won't understand renaming patches, so
use it only when you know the recipient uses git to apply your patch.

* Extract three topmost commits from the current branch and format them
as e-mailable patches:
+
------------
$ git format-patch -3
------------

SEE ALSO
--------
linkgit:git-am[1], linkgit:git-send-email[1]

GIT
---
Part of the linkgit:git[1] suite