Documentation/howto/maintain-git.txt

From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 21 Nov 2007 16:32:55 -0800
Subject: Addendum to "MaintNotes"
Abstract: Imagine that git development is racing along as usual, when our friendly
 neighborhood maintainer is struck down by a wayward bus. Out of the
 hordes of suckers (loyal developers), you have been tricked (chosen) to
 step up as the new maintainer. This howto will show you "how to" do it.

The maintainer's git time is spent on three activities.

 - Communication (60%)

   Mailing list discussions on general design, fielding user
   questions, diagnosing bug reports; reviewing, commenting on,
   suggesting alternatives to, and rejecting patches.

 - Integration (30%)

   Applying new patches from the contributors while spotting and
   correcting minor mistakes, shuffling the integration and
   testing branches, pushing the results out, cutting the
   releases, and making announcements.

 - Own development (10%)

   Scratching my own itch and sending proposed patch series out.

The policy on Integration is informally mentioned in "A Note
from the maintainer" message, which is periodically posted to
this mailing list after each feature release is made.

The policy.

 - Feature releases are numbered as vX.Y.Z and are meant to
   contain bugfixes and enhancements in any area, including
   functionality, performance and usability, without regression.

 - Maintenance releases are numbered as vX.Y.Z.W and are meant
   to contain only bugfixes for the corresponding vX.Y.Z feature
   release and earlier maintenance releases vX.Y.Z.V (V < W).

 - 'master' branch is used to prepare for the next feature
   release. In other words, at some point, the tip of 'master'
   branch is tagged with vX.Y.Z.

 - 'maint' branch is used to prepare for the next maintenance
   release.  After the feature release vX.Y.Z is made, the tip
   of 'maint' branch is set to that release, and bugfixes will
   accumulate on the branch, and at some point, the tip of the
   branch is tagged with vX.Y.Z.1, vX.Y.Z.2, and so on.

 - 'next' branch is used to publish changes (both enhancements
   and fixes) that (1) have worthwhile goal, (2) are in a fairly
   good shape suitable for everyday use, (3) but have not yet
   demonstrated to be regression free.  New changes are tested
   in 'next' before merged to 'master'.

 - 'pu' branch is used to publish other proposed changes that do
   not yet pass the criteria set for 'next'.

 - The tips of 'master', 'maint' and 'next' branches will always
   fast forward, to allow people to build their own
   customization on top of them.

 - Usually 'master' contains all of 'maint', 'next' contains all
   of 'master' and 'pu' contains all of 'next'.

 - The tip of 'master' is meant to be more stable than any
   tagged releases, and the users are encouraged to follow it.

 - The 'next' branch is where new action takes place, and the
   users are encouraged to test it so that regressions and bugs
   are found before new topics are merged to 'master'.


A typical git day for the maintainer implements the above policy
by doing the following:

 - Scan mailing list and #git channel log.  Respond with review
   comments, suggestions etc.  Kibitz.  Collect potentially
   usable patches from the mailing list.  Patches about a single
   topic go to one mailbox (I read my mail in Gnus, and type
   \C-o to save/append messages in files in mbox format).

 - Review the patches in the saved mailboxes.  Edit proposed log
   message for typofixes and clarifications, and add Acks
   collected from the list.  Edit patch to incorporate "Oops,
   that should have been like this" fixes from the discussion.

 - Classify the collected patches and handle 'master' and
   'maint' updates:

   - Obviously correct fixes that pertain to the tip of 'maint'
     are directly applied to 'maint'.

   - Obviously correct fixes that pertain to the tip of 'master'
     are directly applied to 'master'.

   This step is done with "git am".

     $ git checkout master    ;# or "git checkout maint"
     $ git am -3 -s mailbox
     $ make test

 - Merge downwards (maint->master):

     $ git checkout master
     $ git merge maint
     $ make test

 - Review the last issue of "What's cooking" message, review the
   topics scheduled for merging upwards (topic->master and
   topic->maint), and merge.

     $ git checkout master    ;# or "git checkout maint"
     $ git merge ai/topic     ;# or "git merge ai/maint-topic"
     $ git log -p ORIG_HEAD.. ;# final review
     $ git diff ORIG_HEAD..   ;# final review
     $ make test              ;# final review
     $ git branch -d ai/topic ;# or "git branch -d ai/maint-topic"

 - Merge downwards (maint->master) if needed:

     $ git checkout master
     $ git merge maint
     $ make test

 - Merge downwards (master->next) if needed:

     $ git checkout next
     $ git merge master
     $ make test

 - Handle the remaining patches:

   - Anything unobvious that is applicable to 'master' (in other
     words, does not depend on anything that is still in 'next'
     and not in 'master') is applied to a new topic branch that
     is forked from the tip of 'master'.  This includes both
     enhancements and unobvious fixes to 'master'.  A topic
     branch is named as ai/topic where "ai" is typically
     author's initial and "topic" is a descriptive name of the
     topic (in other words, "what's the series is about").

   - An unobvious fix meant for 'maint' is applied to a new
     topic branch that is forked from the tip of 'maint'.  The
     topic is named as ai/maint-topic.

   - Changes that pertain to an existing topic are applied to
     the branch, but:

     - obviously correct ones are applied first;

     - questionable ones are discarded or applied to near the tip;

   - Replacement patches to an existing topic are accepted only
     for commits not in 'next'.

   The above except the "replacement" are all done with:

     $ git am -3 -s mailbox

   while patch replacement is often done by:

     $ git format-patch ai/topic~$n..ai/topic ;# export existing

   then replace some parts with the new patch, and reapplying:

     $ git reset --hard ai/topic~$n
     $ git am -3 -s 000*.txt

   The full test suite is always run for 'maint' and 'master'
   after patch application; for topic branches the tests are run
   as time permits.

 - Update "What's cooking" message to review the updates to
   existing topics, newly added topics and graduated topics.

   This step is helped with Meta/UWC script (where Meta/ contains
   a checkout of the 'todo' branch).

 - Merge topics to 'next'.  For each branch whose tip is not
   merged to 'next', one of three things can happen:

   - The commits are all next-worthy; merge the topic to next:

     $ git checkout next
     $ git merge ai/topic     ;# or "git merge ai/maint-topic"
     $ make test

   - The new parts are of mixed quality, but earlier ones are
     next-worthy; merge the early parts to next:

     $ git checkout next
     $ git merge ai/topic~2   ;# the tip two are dubious
     $ make test

   - Nothing is next-worthy; do not do anything.

 - Rebase topics that do not have any commit in next yet.  This
   step is optional but sometimes is worth doing when an old
   series that is not in next can take advantage of low-level
   framework change that is merged to 'master' already.

     $ git rebase master ai/topic

   This step is helped with Meta/git-topic.perl script to
   identify which topic is rebaseable.  There also is a
   pre-rebase hook to make sure that topics that are already in
   'next' are not rebased beyond the merged commit.

 - Rebuild "pu" to merge the tips of topics not in 'next'.

     $ git checkout pu
     $ git reset --hard next
     $ git merge ai/topic     ;# repeat for all remaining topics
     $ make test

   This step is helped with Meta/PU script

 - Push four integration branches to a private repository at
   k.org and run "make test" on all of them.

 - Push four integration branches to /pub/scm/git/git.git at
   k.org.  This triggers its post-update hook which:

    (1) runs "git pull" in $HOME/git-doc/ repository to pull
        'master' just pushed out;

    (2) runs "make doc" in $HOME/git-doc/, install the generated
        documentation in staging areas, which are separate
        repositories that have html and man branches checked
        out.

    (3) runs "git commit" in the staging areas, and run "git
        push" back to /pub/scm/git/git.git/ to update the html
        and man branches.

    (4) installs generated documentation to /pub/software/scm/git/docs/
        to be viewed from http://www.kernel.org/

 - Fetch html and man branches back from k.org, and push four
   integration branches and the two documentation branches to
   repo.or.cz


Some observations to be made.

 * Each topic is tested individually, and also together with
   other topics cooking in 'next'.  Until it matures, none part
   of it is merged to 'master'.

 * A topic already in 'next' can get fixes while still in
   'next'.  Such a topic will have many merges to 'next' (in
   other words, "git log --first-parent next" will show many
   "Merge ai/topic to next" for the same topic.

 * An unobvious fix for 'maint' is cooked in 'next' and then
   merged to 'master' to make extra sure it is Ok and then
   merged to 'maint'.

 * Even when 'next' becomes empty (in other words, all topics
   prove stable and are merged to 'master' and "git diff master
   next" shows empty), it has tons of merge commits that will
   never be in 'master'.

 * In principle, "git log --first-parent master..next" should
   show nothing but merges (in practice, there are fixup commits
   and reverts that are not merges).

 * Commits near the tip of a topic branch that are not in 'next'
   are fair game to be discarded, replaced or rewritten.
   Commits already merged to 'next' will not be.

 * Being in the 'next' branch is not a guarantee for a topic to
   be included in the next feature release.  Being in the
   'master' branch typically is.