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1 From: Junio C Hamano <email@example.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.
8 Content-type: text/asciidoc
10 How to maintain Git
16 The maintainer's Git time is spent on three activities.
18 - Communication (45%)
20 Mailing list discussions on general design, fielding user
21 questions, diagnosing bug reports; reviewing, commenting on,
22 suggesting alternatives to, and rejecting patches.
24 - Integration (50%)
26 Applying new patches from the contributors while spotting and
27 correcting minor mistakes, shuffling the integration and
28 testing branches, pushing the results out, cutting the
29 releases, and making announcements.
31 - Own development (5%)
33 Scratching my own itch and sending proposed patch series out.
35 The Policy
38 The policy on Integration is informally mentioned in "A Note
39 from the maintainer" message, which is periodically posted to
40 this mailing list after each feature release is made.
42 - Feature releases are numbered as vX.Y.0 and are meant to
43 contain bugfixes and enhancements in any area, including
44 functionality, performance and usability, without regression.
46 - One release cycle for a feature release is expected to last for
47 eight to ten weeks.
49 - Maintenance releases are numbered as vX.Y.Z and are meant
50 to contain only bugfixes for the corresponding vX.Y.0 feature
51 release and earlier maintenance releases vX.Y.W (W < Z).
53 - 'master' branch is used to prepare for the next feature
54 release. In other words, at some point, the tip of 'master'
55 branch is tagged with vX.Y.0.
57 - 'maint' branch is used to prepare for the next maintenance
58 release. After the feature release vX.Y.0 is made, the tip
59 of 'maint' branch is set to that release, and bugfixes will
60 accumulate on the branch, and at some point, the tip of the
61 branch is tagged with vX.Y.1, vX.Y.2, and so on.
63 - 'next' branch is used to publish changes (both enhancements
64 and fixes) that (1) have worthwhile goal, (2) are in a fairly
65 good shape suitable for everyday use, (3) but have not yet
66 demonstrated to be regression free. New changes are tested
67 in 'next' before merged to 'master'.
69 - 'pu' branch is used to publish other proposed changes that do
70 not yet pass the criteria set for 'next'.
72 - The tips of 'master' and 'maint' branches will not be rewound to
73 allow people to build their own customization on top of them.
74 Early in a new development cycle, 'next' is rewound to the tip of
75 'master' once, but otherwise it will not be rewound until the end
76 of the cycle.
78 - Usually 'master' contains all of 'maint' and 'next' contains all
79 of 'master'. 'pu' contains all the topics merged to 'next', but
80 is rebuilt directly on 'master'.
82 - The tip of 'master' is meant to be more stable than any
83 tagged releases, and the users are encouraged to follow it.
85 - The 'next' branch is where new action takes place, and the
86 users are encouraged to test it so that regressions and bugs
87 are found before new topics are merged to 'master'.
89 Note that before v1.9.0 release, the version numbers used to be
90 structured slightly differently. vX.Y.Z were feature releases while
91 vX.Y.Z.W were maintenance releases for vX.Y.Z.
94 A Typical Git Day
97 A typical Git day for the maintainer implements the above policy
98 by doing the following:
100 - Scan mailing list. Respond with review comments, suggestions
101 etc. Kibitz. Collect potentially usable patches from the
102 mailing list. Patches about a single topic go to one mailbox (I
103 read my mail in Gnus, and type \C-o to save/append messages in
104 files in mbox format).
106 - Write his own patches to address issues raised on the list but
107 nobody has stepped up solving. Send it out just like other
108 contributors do, and pick them up just like patches from other
109 contributors (see above).
111 - Review the patches in the saved mailboxes. Edit proposed log
112 message for typofixes and clarifications, and add Acks
113 collected from the list. Edit patch to incorporate "Oops,
114 that should have been like this" fixes from the discussion.
116 - Classify the collected patches and handle 'master' and
117 'maint' updates:
119 - Obviously correct fixes that pertain to the tip of 'maint'
120 are directly applied to 'maint'.
122 - Obviously correct fixes that pertain to the tip of 'master'
123 are directly applied to 'master'.
125 - Other topics are not handled in this step.
127 This step is done with "git am".
129 $ git checkout master ;# or "git checkout maint"
130 $ git am -sc3 mailbox
131 $ make test
133 In practice, almost no patch directly goes to 'master' or
136 - Review the last issue of "What's cooking" message, review the
137 topics ready for merging (topic->master and topic->maint). Use
138 "Meta/cook -w" script (where Meta/ contains a checkout of the
139 'todo' branch) to aid this step.
141 And perform the merge. Use "Meta/Reintegrate -e" script (see
142 later) to aid this step.
144 $ Meta/cook -w last-issue-of-whats-cooking.mbox
146 $ git checkout master ;# or "git checkout maint"
147 $ echo ai/topic | Meta/Reintegrate -e ;# "git merge ai/topic"
148 $ git log -p ORIG_HEAD.. ;# final review
149 $ git diff ORIG_HEAD.. ;# final review
150 $ make test ;# final review
152 - Handle the remaining patches:
154 - Anything unobvious that is applicable to 'master' (in other
155 words, does not depend on anything that is still in 'next'
156 and not in 'master') is applied to a new topic branch that
157 is forked from the tip of 'master'. This includes both
158 enhancements and unobvious fixes to 'master'. A topic
159 branch is named as ai/topic where "ai" is two-letter string
160 named after author's initial and "topic" is a descriptive name
161 of the topic (in other words, "what's the series is about").
163 - An unobvious fix meant for 'maint' is applied to a new
164 topic branch that is forked from the tip of 'maint'. The
165 topic is named as ai/maint-topic.
167 - Changes that pertain to an existing topic are applied to
168 the branch, but:
170 - obviously correct ones are applied first;
172 - questionable ones are discarded or applied to near the tip;
174 - Replacement patches to an existing topic are accepted only
175 for commits not in 'next'.
177 The above except the "replacement" are all done with:
179 $ git checkout ai/topic ;# or "git checkout -b ai/topic master"
180 $ git am -sc3 mailbox
182 while patch replacement is often done by:
184 $ git format-patch ai/topic~$n..ai/topic ;# export existing
186 then replace some parts with the new patch, and reapplying:
188 $ git checkout ai/topic
189 $ git reset --hard ai/topic~$n
190 $ git am -sc3 -s 000*.txt
192 The full test suite is always run for 'maint' and 'master'
193 after patch application; for topic branches the tests are run
194 as time permits.
196 - Merge maint to master as needed:
198 $ git checkout master
199 $ git merge maint
200 $ make test
202 - Merge master to next as needed:
204 $ git checkout next
205 $ git merge master
206 $ make test
208 - Review the last issue of "What's cooking" again and see if topics
209 that are ready to be merged to 'next' are still in good shape
210 (e.g. has there any new issue identified on the list with the
213 - Prepare 'jch' branch, which is used to represent somewhere
214 between 'master' and 'pu' and often is slightly ahead of 'next'.
216 $ Meta/Reintegrate master..pu >Meta/redo-jch.sh
218 The result is a script that lists topics to be merged in order to
219 rebuild 'pu' as the input to Meta/Reintegrate script. Remove
220 later topics that should not be in 'jch' yet. Add a line that
221 consists of '### match next' before the name of the first topic
222 in the output that should be in 'jch' but not in 'next' yet.
224 - Now we are ready to start merging topics to 'next'. For each
225 branch whose tip is not merged to 'next', one of three things can
228 - The commits are all next-worthy; merge the topic to next;
229 - The new parts are of mixed quality, but earlier ones are
230 next-worthy; merge the early parts to next;
231 - Nothing is next-worthy; do not do anything.
233 This step is aided with Meta/redo-jch.sh script created earlier.
234 If a topic that was already in 'next' gained a patch, the script
235 would list it as "ai/topic~1". To include the new patch to the
236 updated 'next', drop the "~1" part; to keep it excluded, do not
237 touch the line. If a topic that was not in 'next' should be
238 merged to 'next', add it at the end of the list. Then:
240 $ git checkout -B jch master
241 $ Meta/redo-jch.sh -c1
243 to rebuild the 'jch' branch from scratch. "-c1" tells the script
244 to stop merging at the first line that begins with '###'
245 (i.e. the "### match next" line you added earlier).
247 At this point, build-test the result. It may reveal semantic
248 conflicts (e.g. a topic renamed a variable, another added a new
249 reference to the variable under its old name), in which case
250 prepare an appropriate merge-fix first (see appendix), and
251 rebuild the 'jch' branch from scratch, starting at the tip of
254 Then do the same to 'next'
256 $ git checkout next
257 $ sh Meta/redo-jch.sh -c1 -e
259 The "-e" option allows the merge message that comes from the
260 history of the topic and the comments in the "What's cooking" to
261 be edited. The resulting tree should match 'jch' as the same set
262 of topics are merged on 'master'; otherwise there is a mismerge.
263 Investigate why and do not proceed until the mismerge is found
264 and rectified.
266 $ git diff jch next
268 When all is well, clean up the redo-jch.sh script with
270 $ sh Meta/redo-jch.sh -u
272 This removes topics listed in the script that have already been
273 merged to 'master'. This may lose '### match next' marker;
274 add it again to the appropriate place when it happens.
276 - Rebuild 'pu'.
278 $ Meta/Reintegrate master..pu >Meta/redo-pu.sh
280 Edit the result by adding new topics that are not still in 'pu'
281 in the script. Then
283 $ git checkout -B pu jch
284 $ sh Meta/redo-pu.sh
286 When all is well, clean up the redo-pu.sh script with
288 $ sh Meta/redo-pu.sh -u
290 Double check by running
292 $ git branch --no-merged pu
294 to see there is no unexpected leftover topics.
296 At this point, build-test the result for semantic conflicts, and
297 if there are, prepare an appropriate merge-fix first (see
298 appendix), and rebuild the 'pu' branch from scratch, starting at
299 the tip of 'jch'.
301 - Update "What's cooking" message to review the updates to
302 existing topics, newly added topics and graduated topics.
304 This step is helped with Meta/cook script.
306 $ Meta/cook
308 This script inspects the history between master..pu, finds tips
309 of topic branches, compares what it found with the current
310 contents in Meta/whats-cooking.txt, and updates that file.
311 Topics not listed in the file but are found in master..pu are
312 added to the "New topics" section, topics listed in the file that
313 are no longer found in master..pu are moved to the "Graduated to
314 master" section, and topics whose commits changed their states
315 (e.g. used to be only in 'pu', now merged to 'next') are updated
316 with change markers "<<" and ">>".
318 Look for lines enclosed in "<<" and ">>"; they hold contents from
319 old file that are replaced by this integration round. After
320 verifying them, remove the old part. Review the description for
321 each topic and update its doneness and plan as needed. To review
322 the updated plan, run
324 $ Meta/cook -w
326 which will pick up comments given to the topics, such as "Will
327 merge to 'next'", etc. (see Meta/cook script to learn what kind
328 of phrases are supported).
330 - Compile, test and install all four (five) integration branches;
331 Meta/Dothem script may aid this step.
333 - Format documentation if the 'master' branch was updated;
334 Meta/dodoc.sh script may aid this step.
336 - Push the integration branches out to public places; Meta/pushall
337 script may aid this step.
342 Some observations to be made.
344 * Each topic is tested individually, and also together with other
345 topics cooking first in 'pu', then in 'jch' and then in 'next'.
346 Until it matures, no part of it is merged to 'master'.
348 * A topic already in 'next' can get fixes while still in
349 'next'. Such a topic will have many merges to 'next' (in
350 other words, "git log --first-parent next" will show many
351 "Merge branch 'ai/topic' to next" for the same topic.
353 * An unobvious fix for 'maint' is cooked in 'next' and then
354 merged to 'master' to make extra sure it is Ok and then
355 merged to 'maint'.
357 * Even when 'next' becomes empty (in other words, all topics
358 prove stable and are merged to 'master' and "git diff master
359 next" shows empty), it has tons of merge commits that will
360 never be in 'master'.
362 * In principle, "git log --first-parent master..next" should
363 show nothing but merges (in practice, there are fixup commits
364 and reverts that are not merges).
366 * Commits near the tip of a topic branch that are not in 'next'
367 are fair game to be discarded, replaced or rewritten.
368 Commits already merged to 'next' will not be.
370 * Being in the 'next' branch is not a guarantee for a topic to
371 be included in the next feature release. Being in the
372 'master' branch typically is.
378 Preparing a "merge-fix"
381 A merge of two topics may not textually conflict but still have
382 conflict at the semantic level. A classic example is for one topic
383 to rename an variable and all its uses, while another topic adds a
384 new use of the variable under its old name. When these two topics
385 are merged together, the reference to the variable newly added by
386 the latter topic will still use the old name in the result.
388 The Meta/Reintegrate script that is used by redo-jch and redo-pu
389 scripts implements a crude but usable way to work this issue around.
390 When the script merges branch $X, it checks if "refs/merge-fix/$X"
391 exists, and if so, the effect of it is squashed into the result of
392 the mechanical merge. In other words,
394 $ echo $X | Meta/Reintegrate
396 is roughly equivalent to this sequence:
398 $ git merge --rerere-autoupdate $X
399 $ git commit
400 $ git cherry-pick -n refs/merge-fix/$X
401 $ git commit --amend
403 The goal of this "prepare a merge-fix" step is to come up with a
404 commit that can be squashed into a result of mechanical merge to
405 correct semantic conflicts.
407 After finding that the result of merging branch "ai/topic" to an
408 integration branch had such a semantic conflict, say pu~4, check the
409 problematic merge out on a detached HEAD, edit the working tree to
410 fix the semantic conflict, and make a separate commit to record the
413 $ git checkout pu~4
414 $ git show -s --pretty=%s ;# double check
415 Merge branch 'ai/topic' to pu
416 $ edit
417 $ git commit -m 'merge-fix/ai/topic' -a
419 Then make a reference "refs/merge-fix/ai/topic" to point at this
422 $ git update-ref refs/merge-fix/ai/topic HEAD
424 Then double check the result by asking Meta/Reintegrate to redo the
427 $ git checkout pu~5 ;# the parent of the problem merge
428 $ echo ai/topic | Meta/Reintegrate
429 $ git diff pu~4
431 This time, because you prepared refs/merge-fix/ai/topic, the
432 resulting merge should have been tweaked to include the fix for the
433 semantic conflict.
435 Note that this assumes that the order in which conflicting branches
436 are merged does not change. If the reason why merging ai/topic
437 branch needs this merge-fix is because another branch merged earlier
438 to the integration branch changed the underlying assumption ai/topic
439 branch made (e.g. ai/topic branch added a site to refer to a
440 variable, while the other branch renamed that variable and adjusted
441 existing use sites), and if you changed redo-jch (or redo-pu) script
442 to merge ai/topic branch before the other branch, then the above
443 merge-fix should not be applied while merging ai/topic, but should
444 instead be applied while merging the other branch. You would need
445 to move the fix to apply to the other branch, perhaps like this:
447 $ mf=refs/merge-fix
448 $ git update-ref $mf/$the_other_branch $mf/ai/topic
449 $ git update-ref -d $mf/ai/topic