emacs/admin/notes/git-workflow

Setting up and using git for normal, simple bugfixing
=====================================================

If you haven't configured git before you should first do:

git config --global user.name "Frank Chu"
git config --global user.email "fchu@example.com"
git config --global transfer.fsckObjects true

(See the thread "Recommend these .gitconfig settings for git integrity."
[https://lists.gnu.org/r/emacs-devel/2016-01/threads.html#01802]
for more details about why that last line is there.)

Initial setup
=============

Then we want to clone the repository.  We normally want to have both
the current master and (if there is one) the active release branch
(eg emacs-27).

mkdir ~/emacs
cd ~/emacs
git clone <membername>@git.sv.gnu.org:/srv/git/emacs.git master
cd master
git config push.default current
git worktree add ../emacs-27 emacs-27

You now have both branches conveniently accessible, and you can do
"git pull" in them once in a while to keep updated.


Fixing bugs
===========

You edit the files in either branch, 'M-x vc-dir', and check in your
changes.  Then you need to push the data to the main repository.  This
will usually fail, since somebody else has pushed other changes in the
meantime.  To fix this, say

git pull --rebase

which will update your repository, and then re-apply your changes on
top of that.  Then say

git push


Sending patches
===============

If you lack push access or would like feedback before pushing a patch,
you commit your change locally and then send a patch file as a bug report
as described in ../../CONTRIBUTE.


Backporting to release branch
=============================

If you have applied a fix to the master, but then decide that it should
be applied to the release branch, too, then

cd ~/emacs/master
git log

and find the commit you're looking for.  Then find the commit ID,
which will look like

commit 958b768a6534ae6e77a8547a56fc31b46b63710b

cd ~/emacs/emacs-27
git cherry-pick -xe 958b768a6534ae6e77a8547a56fc31b46b63710b

and add "Backport:" to the commit string.  Then

git push


Reverting on release branch
===========================

If a commit is made to the release branch, and then it is later
decided that this change should only be on the master branch, the
simplest way to handle this is to revert the commit on the release
branch, and include in the associated log entry "do not merge to master".
(Otherwise, the reversion may get merged to master, and inadvertently
clobber the change on master if it has been manually made there.)


Merging release branch to the master
====================================

It is recommended to use the file gitmerge.el in the admin directory
for merging the release branch into 'master'.  It will take care of many
things which would otherwise have to be done manually, like ignoring
commits that should not land in master, fixing up ChangeLogs and
automatically dealing with certain types of conflicts.  If you really
want to, you can do the merge manually, but then you're on your own.
If you still choose to do that, make absolutely sure that you *always*
use the 'merge' command to transport commits from the release branch to
'master'.  *Never* use 'cherry-pick'!  If you don't know why, then you
shouldn't manually do the merge in the first place; just use
gitmerge.el instead.

How to use gitmerge.el:

Enter the Emacs repository, checkout 'master' and make sure it's
up-to-date by doing a pull.  Then start Emacs with

  emacs -l admin/gitmerge.el -f gitmerge

You'll be asked for the branch to merge, which will default to
(eg) 'origin/emacs-27', which you should accept.  Merging a local tracking
branch is discouraged, since it might not be up-to-date, or worse,
contain commits from you which are not yet pushed upstream.

You will now see the list of commits from the release branch that are not yet
merged to 'master'.  You might also see commits that are already
marked for "skipping", which means that they will be merged with a
different merge strategy ('ours'), which will effectively ignore the
commit's diff while still being seen as merged, so it won't turn up
again in future merges.  Recognizing these kinds of commits is done
with a simple regexp searching the log for strings like 'backport' or
'merge', so you'll probably see false positives as well as false
negatives.  Carefully go through the commits, investigate them by
hitting 'l', 'd' and 'f', and mark or unmark them for skipping with
's'.  When you're done, hit 'm' to start the merge.

You'll likely get conflicts during the process which cannot be dealt
with automatically.  In that case, the merge will stop and show you
the list of conflicted files.  Resolve those conflicts as usual using
smerge and restart gitmerge (remember to enter the repository when
doing that).  You don't have to 'add' the resolved files and 'commit'
the resulting merge, but if you really want to, feel free to do that.
Note you can also resume gitmerge in a new Emacs session, since the
current state will be saved to disk.

When everything's done, look hard at the resulting merge.  Skipping
commits requires separate merges, so don't be surprised to see more
than one merge commit.  If you're happy, push.

Warnings about X11 forwarding
=============================

If you get warnings like

Warning: No xauth data; using fake authentication data for X11 forwarding.
X11 forwarding request failed on channel 0

when pulling or pushing data, add the following to the start of
~/.ssh/config:

Host git.sv.gnu.org
   ForwardX11 no