git-pack-objects: cache small deltas between big objects

[git/jrn.git] / Documentation / SubmittingPatches

Checklist (and a short version for the impatient):

        Commits:

        - make commits of logical units
        - check for unnecessary whitespace with "git diff --check"
          before committing
        - do not check in commented out code or unneeded files
        - provide a meaningful commit message
        - the first line of the commit message should be a short
          description and should skip the full stop
        - if you want your work included in git.git, add a
          "Signed-off-by: Your Name <your@email.com>" line to the
          commit message (or just use the option "-s" when
          committing) to confirm that you agree to the Developer's
          Certificate of Origin

        Patch:

        - use "git format-patch -M" to create the patch
        - send your patch to <git@vger.kernel.org>. If you use
          git-send-email(1), please test it first by sending
          email to yourself.
        - do not PGP sign your patch
        - do not attach your patch, but read in the mail
          body, unless you cannot teach your mailer to
          leave the formatting of the patch alone.
        - be careful doing cut & paste into your mailer, not to
          corrupt whitespaces.
        - provide additional information (which is unsuitable for
          the commit message) between the "---" and the diffstat
        - send the patch to the list _and_ the maintainer
        - if you change, add, or remove a command line option or
          make some other user interface change, the associated
          documentation should be updated as well.

Long version:

I started reading over the SubmittingPatches document for Linux
kernel, primarily because I wanted to have a document similar to
it for the core GIT to make sure people understand what they are
doing when they write "Signed-off-by" line.

But the patch submission requirements are a lot more relaxed
here on the technical/contents front, because the core GIT is
thousand times smaller ;-).  So here is only the relevant bits.


(1) Make separate commits for logically separate changes.

Unless your patch is really trivial, you should not be sending
out a patch that was generated between your working tree and
your commit head.  Instead, always make a commit with complete
commit message and generate a series of patches from your
repository.  It is a good discipline.

Describe the technical detail of the change(s).

If your description starts to get too long, that's a sign that you
probably need to split up your commit to finer grained pieces.

Oh, another thing.  I am picky about whitespaces.  Make sure your
changes do not trigger errors with the sample pre-commit hook shipped
in templates/hooks--pre-commit.  To help ensure this does not happen,
run git diff --check on your changes before you commit.


(1a) Try to be nice to older C compilers

We try to support wide range of C compilers to compile
git with. That means that you should not use C99 initializers, even
if a lot of compilers grok it.

Also, variables have to be declared at the beginning of the block
(you can check this with gcc, using the -Wdeclaration-after-statement
option).

Another thing: NULL pointers shall be written as NULL, not as 0.


(2) Generate your patch using git tools out of your commits.

git based diff tools (git, Cogito, and StGIT included) generate
unidiff which is the preferred format.

You do not have to be afraid to use -M option to "git diff" or
"git format-patch", if your patch involves file renames.  The
receiving end can handle them just fine.

Please make sure your patch does not include any extra files
which do not belong in a patch submission.  Make sure to review
your patch after generating it, to ensure accuracy.  Before
sending out, please make sure it cleanly applies to the "master"
branch head.  If you are preparing a work based on "next" branch,
that is fine, but please mark it as such.


(3) Sending your patches.

People on the git mailing list need to be able to read and
comment on the changes you are submitting.  It is important for
a developer to be able to "quote" your changes, using standard
e-mail tools, so that they may comment on specific portions of
your code.  For this reason, all patches should be submitted
"inline".  WARNING: Be wary of your MUAs word-wrap
corrupting your patch.  Do not cut-n-paste your patch; you can
lose tabs that way if you are not careful.

It is a common convention to prefix your subject line with
[PATCH].  This lets people easily distinguish patches from other
e-mail discussions.

"git format-patch" command follows the best current practice to
format the body of an e-mail message.  At the beginning of the
patch should come your commit message, ending with the
Signed-off-by: lines, and a line that consists of three dashes,
followed by the diffstat information and the patch itself.  If
you are forwarding a patch from somebody else, optionally, at
the beginning of the e-mail message just before the commit
message starts, you can put a "From: " line to name that person.

You often want to add additional explanation about the patch,
other than the commit message itself.  Place such "cover letter"
material between the three dash lines and the diffstat.

Do not attach the patch as a MIME attachment, compressed or not.
Do not let your e-mail client send quoted-printable.  Do not let
your e-mail client send format=flowed which would destroy
whitespaces in your patches. Many
popular e-mail applications will not always transmit a MIME
attachment as plain text, making it impossible to comment on
your code.  A MIME attachment also takes a bit more time to
process.  This does not decrease the likelihood of your
MIME-attached change being accepted, but it makes it more likely
that it will be postponed.

Exception:  If your mailer is mangling patches then someone may ask
you to re-send them using MIME, that is OK.

Do not PGP sign your patch, at least for now.  Most likely, your
maintainer or other people on the list would not have your PGP
key and would not bother obtaining it anyway.  Your patch is not
judged by who you are; a good patch from an unknown origin has a
far better chance of being accepted than a patch from a known,
respected origin that is done poorly or does incorrect things.

If you really really really really want to do a PGP signed
patch, format it as "multipart/signed", not a text/plain message
that starts with '-----BEGIN PGP SIGNED MESSAGE-----'.  That is
not a text/plain, it's something else.

Note that your maintainer does not necessarily read everything
on the git mailing list.  If your patch is for discussion first,
send it "To:" the mailing list, and optionally "cc:" him.  If it
is trivially correct or after the list reached a consensus, send
it "To:" the maintainer and optionally "cc:" the list.

Also note that your maintainer does not actively involve himself in
maintaining what are in contrib/ hierarchy.  When you send fixes and
enhancements to them, do not forget to "cc: " the person who primarily
worked on that hierarchy in contrib/.


(4) Sign your work

To improve tracking of who did what, we've borrowed the
"sign-off" procedure from the Linux kernel project on patches
that are being emailed around.  Although core GIT is a lot
smaller project it is a good discipline to follow it.

The sign-off is a simple line at the end of the explanation for
the patch, which certifies that you wrote it or otherwise have
the right to pass it on as a open-source patch.  The rules are
pretty simple: if you can certify the below:

        Developer's Certificate of Origin 1.1

        By making a contribution to this project, I certify that:

        (a) The contribution was created in whole or in part by me and I
            have the right to submit it under the open source license
            indicated in the file; or

        (b) The contribution is based upon previous work that, to the best
            of my knowledge, is covered under an appropriate open source
            license and I have the right under that license to submit that
            work with modifications, whether created in whole or in part
            by me, under the same open source license (unless I am
            permitted to submit under a different license), as indicated
            in the file; or

        (c) The contribution was provided directly to me by some other
            person who certified (a), (b) or (c) and I have not modified
            it.

        (d) I understand and agree that this project and the contribution
            are public and that a record of the contribution (including all
            personal information I submit with it, including my sign-off) is
            maintained indefinitely and may be redistributed consistent with
            this project or the open source license(s) involved.

then you just add a line saying

        Signed-off-by: Random J Developer <random@developer.example.org>

This line can be automatically added by git if you run the git-commit
command with the -s option.

Some people also put extra tags at the end.  They'll just be ignored for
now, but you can do this to mark internal company procedures or just
point out some special detail about the sign-off.


------------------------------------------------
MUA specific hints

Some of patches I receive or pick up from the list share common
patterns of breakage.  Please make sure your MUA is set up
properly not to corrupt whitespaces.  Here are two common ones
I have seen:

* Empty context lines that do not have _any_ whitespace.

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

One test you could do yourself if your MUA is set up correctly is:

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

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

* Try to apply to the tip of the "master" branch from the
  git.git public repository:

    $ git fetch http://kernel.org/pub/scm/git/git.git master:test-apply
    $ git checkout test-apply
    $ git reset --hard
    $ git applymbox a.patch

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

* Your patch itself does not apply cleanly.  That is _bad_ but
  does not have much to do with your MUA.  Please rebase the
  patch appropriately.

* Your MUA corrupted your patch; applymbox would complain that
  the patch does not apply.  Look at .dotest/ subdirectory and
  see what 'patch' file contains and check for the common
  corruption patterns mentioned above.

* While you are at it, check what are in '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 your maintainer would end up
  hand editing the log message when he applies your patch.
  Things like "Hi, this is my first patch.\n", if you really
  want to put in the patch e-mail, should come after the
  three-dash line that signals the end of the commit message.


Pine
----

(Johannes Schindelin)

I don't know how many people still use pine, but for those poor
souls it may be good to mention that the quell-flowed-text is
needed for recent versions.

... the "no-strip-whitespace-before-send" option, too. AFAIK it
was introduced in 4.60.

(Linus Torvalds)

And 4.58 needs at least this.

---
diff-tree 8326dd8350be64ac7fc805f6563a1d61ad10d32c (from e886a61f76edf5410573e92e38ce22974f9c40f1)
Author: Linus Torvalds <torvalds@g5.osdl.org>
Date:   Mon Aug 15 17:23:51 2005 -0700

    Fix pine whitespace-corruption bug

    There's no excuse for unconditionally removing whitespace from
    the pico buffers on close.

diff --git a/pico/pico.c b/pico/pico.c
--- a/pico/pico.c
+++ b/pico/pico.c
@@ -219,7 +219,9 @@ PICO *pm;
            switch(pico_all_done){      /* prepare for/handle final events */
              case COMP_EXIT :          /* already confirmed */
                packheader();
+#if 0
                stripwhitespace();
+#endif
                c |= COMP_EXIT;
                break;
 

(Daniel Barkalow)

> A patch to SubmittingPatches, MUA specific help section for
> users of Pine 4.63 would be very much appreciated.

Ah, it looks like a recent version changed the default behavior to do the
right thing, and inverted the sense of the configuration option. (Either
that or Gentoo did it.) So you need to set the
"no-strip-whitespace-before-send" option, unless the option you have is
"strip-whitespace-before-send", in which case you should avoid checking
it.


Thunderbird
-----------

(A Large Angry SCM)

Here are some hints on how to successfully submit patches inline using
Thunderbird.

This recipe appears to work with the current [*1*] Thunderbird from Suse.

The following Thunderbird extensions are needed:
        AboutConfig 0.5
                http://aboutconfig.mozdev.org/
        External Editor 0.7.2
                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. [*2*]

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.

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

7) Optionally, undo the about:config/account settings changes made in
steps 2 & 3.


[Footnotes]
*1* Version 1.0 (20041207) from the MozillaThunderbird-1.0-5 rpm of Suse
9.3 professional updates.

*2* It may be possible to do this with about:config and the following
settings but I haven't tried, yet.
        mail.html_compose                       => false
        mail.identity.default.compose_html      => false
        mail.identity.id?.compose_html          => false


Gnus
----

'|' in the *Summary* buffer can be used to pipe the current
message to an external program, and this is a handy way to drive
"git am".  However, if the message is MIME encoded, what is
piped into the program is the representation you see in your
*Article* buffer after unwrapping MIME.  This is often not what
you would want for two reasons.  It tends to screw up non ASCII
characters (most notably in people's names), and also
whitespaces (fatal in patches).  Running 'C-u g' to display the
message in raw form before using '|' to run the pipe can work
this problem around.


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.