1 From: Junio C Hamano <gitster@pobox.com>
2 Date: Wed, 21 Nov 2007 16:32:55 -0800
3 Subject: Addendum to "MaintNotes"
4 Abstract: Imagine that git development is racing along as usual, when our friendly
5 neighborhood maintainer is struck down by a wayward bus. Out of the
6 hordes of suckers (loyal developers), you have been tricked (chosen) to
7 step up as the new maintainer. This howto will show you "how to" do it.
9 The maintainer's git time is spent on three activities.
13 Mailing list discussions on general design, fielding user
14 questions, diagnosing bug reports; reviewing, commenting on,
15 suggesting alternatives to, and rejecting patches.
19 Applying new patches from the contributors while spotting and
20 correcting minor mistakes, shuffling the integration and
21 testing branches, pushing the results out, cutting the
22 releases, and making announcements.
24 - Own development (5%)
26 Scratching my own itch and sending proposed patch series out.
28 The policy on Integration is informally mentioned in "A Note
29 from the maintainer" message, which is periodically posted to
30 this mailing list after each feature release is made.
34 - Feature releases are numbered as vX.Y.Z and are meant to
35 contain bugfixes and enhancements in any area, including
36 functionality, performance and usability, without regression.
38 - One release cycle for a feature release is expected to last for
41 - Maintenance releases are numbered as vX.Y.Z.W and are meant
42 to contain only bugfixes for the corresponding vX.Y.Z feature
43 release and earlier maintenance releases vX.Y.Z.V (V < W).
45 - 'master' branch is used to prepare for the next feature
46 release. In other words, at some point, the tip of 'master'
47 branch is tagged with vX.Y.Z.
49 - 'maint' branch is used to prepare for the next maintenance
50 release. After the feature release vX.Y.Z is made, the tip
51 of 'maint' branch is set to that release, and bugfixes will
52 accumulate on the branch, and at some point, the tip of the
53 branch is tagged with vX.Y.Z.1, vX.Y.Z.2, and so on.
55 - 'next' branch is used to publish changes (both enhancements
56 and fixes) that (1) have worthwhile goal, (2) are in a fairly
57 good shape suitable for everyday use, (3) but have not yet
58 demonstrated to be regression free. New changes are tested
59 in 'next' before merged to 'master'.
61 - 'pu' branch is used to publish other proposed changes that do
62 not yet pass the criteria set for 'next'.
64 - The tips of 'master' and 'maint' branches will not be rewound to
65 allow people to build their own customization on top of them.
66 Early in a new development cycle, 'next' is rewound to the tip of
67 'master' once, but otherwise it will not be rewound until the end
70 - Usually 'master' contains all of 'maint' and 'next' contains all
71 of 'master'. 'pu' contains all the topics merged to 'next', but
72 is rebuilt directly on 'master'.
74 - The tip of 'master' is meant to be more stable than any
75 tagged releases, and the users are encouraged to follow it.
77 - The 'next' branch is where new action takes place, and the
78 users are encouraged to test it so that regressions and bugs
79 are found before new topics are merged to 'master'.
82 A typical git day for the maintainer implements the above policy
83 by doing the following:
85 - Scan mailing list. Respond with review comments, suggestions
86 etc. Kibitz. Collect potentially usable patches from the
87 mailing list. Patches about a single topic go to one mailbox (I
88 read my mail in Gnus, and type \C-o to save/append messages in
89 files in mbox format).
91 - Write his own patches to address issues raised on the list but
92 nobody has stepped up solving. Send it out just like other
93 contributors do, and pick them up just like patches from other
94 contributors (see above).
96 - Review the patches in the saved mailboxes. Edit proposed log
97 message for typofixes and clarifications, and add Acks
98 collected from the list. Edit patch to incorporate "Oops,
99 that should have been like this" fixes from the discussion.
101 - Classify the collected patches and handle 'master' and
104 - Obviously correct fixes that pertain to the tip of 'maint'
105 are directly applied to 'maint'.
107 - Obviously correct fixes that pertain to the tip of 'master'
108 are directly applied to 'master'.
110 - Other topics are not handled in this step.
112 This step is done with "git am".
114 $ git checkout master ;# or "git checkout maint"
115 $ git am -sc3 mailbox
118 In practice, almost no patch directly goes to 'master' or
121 - Review the last issue of "What's cooking" message, review the
122 topics ready for merging (topic->master and topic->maint). Use
123 "Meta/cook -w" script (where Meta/ contains a checkout of the
124 'todo' branch) to aid this step.
126 And perform the merge. Use "Meta/Reintegrate -e" script (see
127 later) to aid this step.
129 $ Meta/cook -w last-issue-of-whats-cooking.mbox
131 $ git checkout master ;# or "git checkout maint"
132 $ echo ai/topic | Meta/Reintegrate -e ;# "git merge ai/topic"
133 $ git log -p ORIG_HEAD.. ;# final review
134 $ git diff ORIG_HEAD.. ;# final review
135 $ make test ;# final review
137 - Handle the remaining patches:
139 - Anything unobvious that is applicable to 'master' (in other
140 words, does not depend on anything that is still in 'next'
141 and not in 'master') is applied to a new topic branch that
142 is forked from the tip of 'master'. This includes both
143 enhancements and unobvious fixes to 'master'. A topic
144 branch is named as ai/topic where "ai" is two-letter string
145 named after author's initial and "topic" is a descriptive name
146 of the topic (in other words, "what's the series is about").
148 - An unobvious fix meant for 'maint' is applied to a new
149 topic branch that is forked from the tip of 'maint'. The
150 topic is named as ai/maint-topic.
152 - Changes that pertain to an existing topic are applied to
155 - obviously correct ones are applied first;
157 - questionable ones are discarded or applied to near the tip;
159 - Replacement patches to an existing topic are accepted only
160 for commits not in 'next'.
162 The above except the "replacement" are all done with:
164 $ git checkout ai/topic ;# or "git checkout -b ai/topic master"
165 $ git am -sc3 mailbox
167 while patch replacement is often done by:
169 $ git format-patch ai/topic~$n..ai/topic ;# export existing
171 then replace some parts with the new patch, and reapplying:
173 $ git checkout ai/topic
174 $ git reset --hard ai/topic~$n
175 $ git am -sc3 -s 000*.txt
177 The full test suite is always run for 'maint' and 'master'
178 after patch application; for topic branches the tests are run
181 - Merge maint to master as needed:
183 $ git checkout master
187 - Merge master to next as needed:
193 - Review the last issue of "What's cooking" again and see if topics
194 that are ready to be merged to 'next' are still in good shape
195 (e.g. has there any new issue identified on the list with the
198 - Prepare 'jch' branch, which is used to represent somewhere
199 between 'master' and 'pu' and often is slightly ahead of 'next'.
201 $ Meta/Reintegrate master..pu >Meta/redo-jch.sh
203 The result is a script that lists topics to be merged in order to
204 rebuild 'pu' as the input to Meta/Reintegrate script. Remove
205 later topics that should not be in 'jch' yet. Add a line that
206 consists of '###' before the name of the first topic in the output
207 that should be in 'jch' but not in 'next' yet.
209 - Now we are ready to start merging topics to 'next'. For each
210 branch whose tip is not merged to 'next', one of three things can
213 - The commits are all next-worthy; merge the topic to next;
214 - The new parts are of mixed quality, but earlier ones are
215 next-worthy; merge the early parts to next;
216 - Nothing is next-worthy; do not do anything.
218 This step is aided with Meta/redo-jch.sh script created earlier.
219 If a topic that was already in 'next' gained a patch, the script
220 would list it as "ai/topic~1". To include the new patch to the
221 updated 'next', drop the "~1" part; to keep it excluded, do not
222 touch the line. If a topic that was not in 'next' should be
223 merged to 'next', add it at the end of the list. Then:
225 $ git checkout -B jch master
226 $ Meta/redo-jch.sh -c1
228 to rebuild the 'jch' branch from scratch. "-c1" tells the script
229 to stop merging at the '###' line you added earlier.
231 At this point, build-test the result. It may reveal semantic
232 conflicts (e.g. a topic renamed a variable, another added a new
233 reference to the variable under its old name), in which case
234 prepare an appropriate merge-fix first (see appendix), and
235 rebuild the 'jch' branch from scratch, starting at the tip of
238 Then do the same to 'next'
241 $ sh Meta/redo-jch.sh -c1 -e
243 The "-e" option allows the merge message that comes from the
244 history of the topic and the comments in the "What's cooking" to
245 be edited. The resulting tree should match 'jch' as the same set
246 of topics are merged on 'master'; otherwise there is a mismerge.
247 Investigate why and do not proceed until the mismerge is found
252 When all is well, clean up the redo-jch.sh script with
254 $ sh Meta/redo-jch.sh -u
256 This removes topics listed in the script that have already been
257 merged to 'master'. This unfortunately loses the "###" marker,
258 so add it again to the appropriate place.
262 $ Meta/Reintegrate master..pu >Meta/redo-pu.sh
264 Edit the result by adding new topics that are not still in 'pu'
267 $ git checkout -B pu jch
270 When all is well, clean up the redo-pu.sh script with
272 $ sh Meta/redo-pu.sh -u
274 Double check by running
276 $ git branch --no-merged pu
278 to see there is no unexpected leftover topics.
280 At this point, build-test the result for semantic conflicts, and
281 if there are, prepare an appropriate merge-fix first (see
282 appendix), and rebuild the 'pu' branch from scratch, starting at
285 - Update "What's cooking" message to review the updates to
286 existing topics, newly added topics and graduated topics.
288 This step is helped with Meta/cook script.
292 This script inspects the history between master..pu, finds tips
293 of topic branches, compares what it found with the current
294 contents in Meta/whats-cooking.txt, and updates that file.
295 Topics not listed in the file but are found in master..pu are
296 added to the "New topics" section, topics listed in the file that
297 are no longer found in master..pu are moved to the "Graduated to
298 master" section, and topics whose commits changed their states
299 (e.g. used to be only in 'pu', now merged to 'next') are updated
300 with change markers "<<" and ">>".
302 Look for lines enclosed in "<<" and ">>"; they hold contents from
303 old file that are replaced by this integration round. After
304 verifying them, remove the old part. Review the description for
305 each topic and update its doneness and plan as needed. To review
306 the updated plan, run
310 which will pick up comments given to the topics, such as "Will
311 merge to 'next'", etc. (see Meta/cook script to learn what kind
312 of phrases are supported).
314 - Compile, test and install all four (five) integration branches;
315 Meta/Dothem script may aid this step.
317 - Format documentation if the 'master' branch was updated;
318 Meta/dodoc.sh script may aid this step.
320 - Push the integration branches out to public places; Meta/pushall
321 script may aid this step.
323 Some observations to be made.
325 * Each topic is tested individually, and also together with other
326 topics cooking first in 'pu', then in 'jch' and then in 'next'.
327 Until it matures, no part of it is merged to 'master'.
329 * A topic already in 'next' can get fixes while still in
330 'next'. Such a topic will have many merges to 'next' (in
331 other words, "git log --first-parent next" will show many
332 "Merge branch 'ai/topic' to next" for the same topic.
334 * An unobvious fix for 'maint' is cooked in 'next' and then
335 merged to 'master' to make extra sure it is Ok and then
338 * Even when 'next' becomes empty (in other words, all topics
339 prove stable and are merged to 'master' and "git diff master
340 next" shows empty), it has tons of merge commits that will
341 never be in 'master'.
343 * In principle, "git log --first-parent master..next" should
344 show nothing but merges (in practice, there are fixup commits
345 and reverts that are not merges).
347 * Commits near the tip of a topic branch that are not in 'next'
348 are fair game to be discarded, replaced or rewritten.
349 Commits already merged to 'next' will not be.
351 * Being in the 'next' branch is not a guarantee for a topic to
352 be included in the next feature release. Being in the
353 'master' branch typically is.
358 Preparing a "merge-fix"
360 A merge of two topics may not textually conflict but still have
361 conflict at the semantic level. A classic example is for one topic
362 to rename an variable and all its uses, while another topic adds a
363 new use of the variable under its old name. When these two topics
364 are merged together, the reference to the variable newly added by
365 the latter topic will still use the old name in the result.
367 The Meta/Reintegrate script that is used by redo-jch and redo-pu
368 scripts implements a crude but usable way to work this issue around.
369 When the script merges branch $X, it checks if "refs/merge-fix/$X"
370 exists, and if so, the effect of it is squashed into the result of
371 the mechanical merge. In other words,
373 $ echo $X | Meta/Reintegrate
375 is roughly equivalent to this sequence:
377 $ git merge --rerere-autoupdate $X
379 $ git cherry-pick -n refs/merge-fix/$X
382 The goal of this "prepare a merge-fix" step is to come up with a
383 commit that can be squashed into a result of mechanical merge to
384 correct semantic conflicts.
386 After finding that the result of merging branch "ai/topic" to an
387 integration branch had such a semantic conflict, say pu~4, check the
388 problematic merge out on a detached HEAD, edit the working tree to
389 fix the semantic conflict, and make a separate commit to record the
393 $ git show -s --pretty=%s ;# double check
394 Merge branch 'ai/topic' to pu
396 $ git commit -m 'merge-fix/ai/topic' -a
398 Then make a reference "refs/merge-fix/ai/topic" to point at this
401 $ git update-ref refs/merge-fix/ai/topic HEAD
403 Then double check the result by asking Meta/Reintegrate to redo the
406 $ git checkout pu~5 ;# the parent of the problem merge
407 $ echo ai/topic | Meta/Reintegrate
410 This time, because you prepared refs/merge-fix/ai/topic, the
411 resulting merge should have been tweaked to include the fix for the
414 Note that this assumes that the order in which conflicting branches
415 are merged does not change. If the reason why merging ai/topic
416 branch needs this merge-fix is because another branch merged earlier
417 to the integration branch changed the underlying assumption ai/topic
418 branch made (e.g. ai/topic branch added a site to refer to a
419 variable, while the other branch renamed that variable and adjusted
420 existing use sites), and if you changed redo-jch (or redo-pu) script
421 to merge ai/topic branch before the other branch, then the above
422 merge-fix should not be applied while merging ai/topic, but should
423 instead be applied while merging the other branch. You would need
424 to move the fix to apply to the other branch, perhaps like this:
427 $ git update-ref $mf/$the_other_branch $mf/ai/topic
428 $ git update-ref -d $mf/ai/topic