howto/maintain-git.html

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 441 <body class="article">
 442 <div id="header">
 443 <h1>How to maintain Git</h1>
 444 <div class="details">
 445 <span id="revdate">2024-08-15</span>
 446 </div>
 447 </div>
 448 <div id="content">
 449 <div class="sect1">
 450 <h2 id="_activities">Activities</h2>
 451 <div class="sectionbody">
 452 <div class="paragraph">
 453 <p>The maintainer&#8217;s Git time is spent on three activities.</p>
 454 </div>
 455 <div class="ulist">
 456 <ul>
 457 <li>
 458 <p>Communication (45%)</p>
 459 <div class="literalblock">
 460 <div class="content">
 461 <pre>Mailing list discussions on general design, fielding user
 462 questions, diagnosing bug reports; reviewing, commenting on,
 463 suggesting alternatives to, and rejecting patches.</pre>
 464 </div>
 465 </div>
 466 </li>
 467 <li>
 468 <p>Integration (50%)</p>
 469 <div class="literalblock">
 470 <div class="content">
 471 <pre>Applying new patches from the contributors while spotting and
 472 correcting minor mistakes, shuffling the integration and
 473 testing branches, pushing the results out, cutting the
 474 releases, and making announcements.</pre>
 475 </div>
 476 </div>
 477 </li>
 478 <li>
 479 <p>Own development (5%)</p>
 480 <div class="literalblock">
 481 <div class="content">
 482 <pre>Scratching my own itch and sending proposed patch series out.</pre>
 483 </div>
 484 </div>
 485 </li>
 486 </ul>
 487 </div>
 488 </div>
 489 </div>
 490 <div class="sect1">
 491 <h2 id="_the_policy">The Policy</h2>
 492 <div class="sectionbody">
 493 <div class="paragraph">
 494 <p>The policy on Integration is informally mentioned in "A Note
 495 from the maintainer" message, which is periodically posted to
 496 the mailing list after each feature release is made:</p>
 497 </div>
 498 <div class="ulist">
 499 <ul>
 500 <li>
 501 <p>Feature releases are numbered as vX.Y.0 and are meant to
 502 contain bugfixes and enhancements in any area, including
 503 functionality, performance and usability, without regression.</p>
 504 </li>
 505 <li>
 506 <p>Maintenance releases are numbered as vX.Y.Z (0 &lt; Z) and are meant
 507 to contain only bugfixes for the corresponding vX.Y.0 feature
 508 release and earlier maintenance releases vX.Y.W (W &lt; Z).</p>
 509 </li>
 510 <li>
 511 <p>The <em>master</em> branch is used to prepare for the next feature
 512 release. In other words, at some point, the tip of <em>master</em>
 513 branch is tagged as vX.(Y+1).0, when vX.Y.0 is the latest
 514 feature release.</p>
 515 </li>
 516 <li>
 517 <p><em>maint</em> branch is used to prepare for the next maintenance
 518 release.  After the feature release vX.Y.0 is made, the tip
 519 of <em>maint</em> branch is set to that release, and bugfixes will
 520 accumulate on the branch, and at some point, the tip of the
 521 branch is tagged with vX.Y.1, vX.Y.2, and so on.</p>
 522 </li>
 523 <li>
 524 <p><em>next</em> branch is used to publish changes (both enhancements
 525 and fixes) that (1) have worthwhile goal, (2) are in a fairly
 526 good shape suitable for everyday use, (3) but have not yet
 527 demonstrated to be regression free.  Reviews from contributors on
 528 the mailing list help to make the determination.  After a topic
 529 is merged to <em>next</em>, it is tested for at least 7 calendar days
 530 before getting merged to <em>master</em>.</p>
 531 </li>
 532 <li>
 533 <p><em>seen</em> branch is used to publish other proposed changes that do
 534 not yet pass the criteria set for <em>next</em> (see above).</p>
 535 </li>
 536 <li>
 537 <p>The tips of <em>master</em> and <em>maint</em> branches will not be rewound to
 538 allow people to build their own customization on top of them.
 539 Early in a new development cycle, <em>next</em> is rewound to the tip of
 540 <em>master</em> once, but otherwise it will not be rewound until the end
 541 of the cycle.</p>
 542 </li>
 543 <li>
 544 <p>Usually <em>master</em> contains all of <em>maint</em> and <em>next</em> contains all
 545 of <em>master</em>.  <em>seen</em> contains all the topics merged to <em>next</em>, but
 546 is rebuilt directly on <em>master</em>.</p>
 547 </li>
 548 <li>
 549 <p>The tip of <em>master</em> is meant to be more stable than any
 550 tagged releases, and the users are encouraged to follow it.</p>
 551 </li>
 552 <li>
 553 <p>The <em>next</em> branch is where new action takes place, and the
 554 users are encouraged to test it so that regressions and bugs
 555 are found before new topics are merged to <em>master</em>.</p>
 556 </li>
 557 <li>
 558 <p>When a problem is found in a topic in <em>next</em>, the topic is marked
 559 not to be merged to <em>master</em>.  Follow-up patches are discussed on
 560 the mailing list and applied to the topic after being reviewed and
 561 then the topic is merged (again) to <em>next</em>.  After going through
 562 the usual testing in <em>next</em>, the entire (fixed) topic is merged
 563 to <em>master</em>.</p>
 564 </li>
 565 <li>
 566 <p>One release cycle for a feature release is expected to last for
 567 eight to ten weeks.  A few "release candidate" releases are
 568 expected to be tagged about a week apart before the final
 569 release, and a "preview" release is tagged about a week before
 570 the first release candidate gets tagged.</p>
 571 </li>
 572 <li>
 573 <p>After the preview release is tagged, topics that were well
 574 reviewed may be merged to <em>master</em> before spending the usual 7
 575 calendar days in <em>next</em>, with the expectation that any bugs in
 576 them can be caught and fixed in the release candidates before
 577 the final release.</p>
 578 </li>
 579 <li>
 580 <p>After the first release candidate is tagged, the contributors are
 581 strongly encouraged to focus on finding and fixing new regressions
 582 introduced during the cycle, over addressing old bugs and any new
 583 features.  Topics stop getting merged down from <em>next</em> to <em>master</em>,
 584 and new topics stop getting merged to <em>next</em>. Unless they are fixes
 585 to new regressions in the cycle, that is.</p>
 586 </li>
 587 <li>
 588 <p>Soon after a feature release is made, the tip of <em>maint</em> gets
 589 fast-forwarded to point at the release.  Topics that have been
 590 kept in <em>next</em> are merged down to <em>master</em> and a new development
 591 cycle starts.</p>
 592 </li>
 593 </ul>
 594 </div>
 595 <div class="paragraph">
 596 <p>Note that before v1.9.0 release, the version numbers used to be
 597 structured slightly differently.  vX.Y.Z were feature releases while
 598 vX.Y.Z.W were maintenance releases for vX.Y.Z.</p>
 599 </div>
 600 </div>
 601 </div>
 602 <div class="sect1">
 603 <h2 id="_a_typical_git_day">A Typical Git Day</h2>
 604 <div class="sectionbody">
 605 <div class="paragraph">
 606 <p>A typical Git day for the maintainer implements the above policy
 607 by doing the following:</p>
 608 </div>
 609 <div class="ulist">
 610 <ul>
 611 <li>
 612 <p>Scan mailing list.  Respond with review comments, suggestions
 613 etc.  Kibitz.  Collect potentially usable patches from the
 614 mailing list.  Patches about a single topic go to one mailbox (I
 615 read my mail in Gnus, and type \C-o to save/append messages in
 616 files in mbox format).</p>
 617 </li>
 618 <li>
 619 <p>Write his own patches to address issues raised on the list but
 620 nobody has stepped up to solve.  Send it out just like other
 621 contributors do, and pick them up just like patches from other
 622 contributors (see above).</p>
 623 </li>
 624 <li>
 625 <p>Review the patches in the saved mailboxes.  Edit proposed log
 626 message for typofixes and clarifications, and add Acks
 627 collected from the list.  Edit patch to incorporate "Oops,
 628 that should have been like this" fixes from the discussion.</p>
 629 </li>
 630 <li>
 631 <p>Classify the collected patches and handle <em>master</em> and
 632 <em>maint</em> updates:</p>
 633 </li>
 634 <li>
 635 <p>Obviously correct fixes that pertain to the tip of <em>maint</em>
 636 are directly applied to <em>maint</em>.</p>
 637 </li>
 638 <li>
 639 <p>Obviously correct fixes that pertain to the tip of <em>master</em>
 640 are directly applied to <em>master</em>.</p>
 641 </li>
 642 <li>
 643 <p>Other topics are not handled in this step.</p>
 644 <div class="literalblock">
 645 <div class="content">
 646 <pre>This step is done with "git am".</pre>
 647 </div>
 648 </div>
 649 <div class="literalblock">
 650 <div class="content">
 651 <pre>$ git checkout master    ;# or "git checkout maint"
 652 $ git am -sc3 mailbox
 653 $ make test</pre>
 654 </div>
 655 </div>
 656 <div class="literalblock">
 657 <div class="content">
 658 <pre>In practice, almost no patch directly goes to 'master' or
 659 'maint'.</pre>
 660 </div>
 661 </div>
 662 </li>
 663 <li>
 664 <p>Review the last issue of "What&#8217;s cooking" message, review the
 665 topics ready for merging (topic&#8594;master and topic&#8594;maint).  Use
 666 "Meta/cook -w" script (where Meta/ contains a checkout of the
 667 <em>todo</em> branch) to aid this step.</p>
 668 <div class="literalblock">
 669 <div class="content">
 670 <pre>And perform the merge.  Use "Meta/Reintegrate -e" script (see
 671 later) to aid this step.</pre>
 672 </div>
 673 </div>
 674 <div class="literalblock">
 675 <div class="content">
 676 <pre>$ Meta/cook -w last-issue-of-whats-cooking.mbox</pre>
 677 </div>
 678 </div>
 679 <div class="literalblock">
 680 <div class="content">
 681 <pre>$ git checkout master    ;# or "git checkout maint"
 682 $ echo ai/topic | Meta/Reintegrate -e ;# "git merge ai/topic"
 683 $ git log -p ORIG_HEAD.. ;# final review
 684 $ git diff ORIG_HEAD..   ;# final review
 685 $ make test              ;# final review</pre>
 686 </div>
 687 </div>
 688 </li>
 689 <li>
 690 <p>Handle the remaining patches:</p>
 691 </li>
 692 <li>
 693 <p>Anything unobvious that is applicable to <em>master</em> (in other
 694 words, does not depend on anything that is still in <em>next</em>
 695 and not in <em>master</em>) is applied to a new topic branch that
 696 is forked from the tip of <em>master</em> (or the last feature release,
 697 which is a bit older than <em>master</em>).  This includes both
 698 enhancements and unobvious fixes to <em>master</em>.  A topic
 699 branch is named as ai/topic where "ai" is two-letter string
 700 named after author&#8217;s initial and "topic" is a descriptive name
 701 of the topic (in other words, "what&#8217;s the series is about").</p>
 702 </li>
 703 <li>
 704 <p>An unobvious fix meant for <em>maint</em> is applied to a new
 705 topic branch that is forked from the tip of <em>maint</em> (or the
 706 oldest and still relevant maintenance branch).  The
 707 topic may be named as ai/maint-topic.</p>
 708 </li>
 709 <li>
 710 <p>Changes that pertain to an existing topic are applied to
 711 the branch, but:</p>
 712 </li>
 713 <li>
 714 <p>obviously correct ones are applied first;</p>
 715 </li>
 716 <li>
 717 <p>questionable ones are discarded or applied to near the tip;</p>
 718 </li>
 719 <li>
 720 <p>Replacement patches to an existing topic are accepted only
 721 for commits not in <em>next</em>.</p>
 722 <div class="literalblock">
 723 <div class="content">
 724 <pre>The initial round is done with:</pre>
 725 </div>
 726 </div>
 727 <div class="literalblock">
 728 <div class="content">
 729 <pre>$ git checkout ai/topic ;# or "git checkout -b ai/topic master"
 730 $ git am -sc3 --whitespace=warn mailbox</pre>
 731 </div>
 732 </div>
 733 <div class="literalblock">
 734 <div class="content">
 735 <pre>and replacing an existing topic with subsequent round is done with:</pre>
 736 </div>
 737 </div>
 738 <div class="literalblock">
 739 <div class="content">
 740 <pre>$ git checkout master...ai/topic ;# try to reapply to the same base
 741 $ git am -sc3 --whitespace=warn mailbox</pre>
 742 </div>
 743 </div>
 744 <div class="literalblock">
 745 <div class="content">
 746 <pre>to prepare the new round on a detached HEAD, and then</pre>
 747 </div>
 748 </div>
 749 <div class="literalblock">
 750 <div class="content">
 751 <pre>$ git range-diff @{-1}...
 752 $ git diff @{-1}</pre>
 753 </div>
 754 </div>
 755 <div class="literalblock">
 756 <div class="content">
 757 <pre>to double check what changed since the last round, and finally</pre>
 758 </div>
 759 </div>
 760 <div class="literalblock">
 761 <div class="content">
 762 <pre>$ git checkout -B @{-1}</pre>
 763 </div>
 764 </div>
 765 <div class="literalblock">
 766 <div class="content">
 767 <pre>to conclude (the last step is why a topic already in 'next' is
 768 not replaced but updated incrementally).</pre>
 769 </div>
 770 </div>
 771 <div class="literalblock">
 772 <div class="content">
 773 <pre>Whether it is the initial round or a subsequent round, the topic
 774 may not build even in isolation, or may break the build when
 775 merged to integration branches due to bugs.  There may already
 776 be obvious and trivial improvements suggested on the list.  The
 777 maintainer often adds an extra commit, with "SQUASH???" in its
 778 title, to fix things up, before publishing the integration
 779 branches to make it usable by other developers for testing.
 780 These changes are what the maintainer is not 100% committed to
 781 (trivial typofixes etc. are often squashed directly into the
 782 patches that need fixing, without being applied as a separate
 783 "SQUASH???" commit), so that they can be removed easily as needed.
 784 The expectation is that the original author will make corrections
 785 in a reroll.</pre>
 786 </div>
 787 </div>
 788 </li>
 789 <li>
 790 <p>By now, new topic branches are created and existing topic
 791 branches are updated.  The integration branches <em>next</em>, <em>jch</em>,
 792 and <em>seen</em> need to be updated to contain them.</p>
 793 </li>
 794 <li>
 795 <p>If there are topics that have been merged to <em>master</em> and should
 796 be merged to <em>maint</em>, merge them to <em>maint</em>, and update the
 797 release notes to the next maintenance release.</p>
 798 </li>
 799 <li>
 800 <p>Review the latest issue of "What&#8217;s cooking" again.  Are topics
 801 that have been sufficiently long in <em>next</em> ready to be merged to
 802 <em>master</em>?  Are topics we saw earlier and are in <em>seen</em> now got
 803 positive reviews and are ready to be merged to <em>next</em>?</p>
 804 </li>
 805 <li>
 806 <p>If there are topics that have been cooking in <em>next</em> long enough
 807 and should be merged to <em>master</em>, merge them to <em>master</em>, and
 808 update the release notes to the next feature release.</p>
 809 </li>
 810 <li>
 811 <p>If there were patches directly made on <em>maint</em>, merge <em>maint</em> to
 812 <em>master</em>; make sure that the result is what you want.</p>
 813 <div class="literalblock">
 814 <div class="content">
 815 <pre>$ git checkout master
 816 $ git merge -m "Sync with 'maint'" --no-log maint
 817 $ git log -p --first-parent ORIG_HEAD..
 818 $ make test</pre>
 819 </div>
 820 </div>
 821 </li>
 822 <li>
 823 <p>Prepare to update the <em>jch</em> branch, which is used to represent
 824 somewhere between <em>master</em> and <em>seen</em> and often is slightly ahead
 825 of <em>next</em>, and the <em>seen</em> branch, which is used to hold the rest.</p>
 826 <div class="literalblock">
 827 <div class="content">
 828 <pre>$ Meta/Reintegrate master..jch &gt;Meta/redo-jch.sh</pre>
 829 </div>
 830 </div>
 831 <div class="literalblock">
 832 <div class="content">
 833 <pre>The result is a script that lists topics to be merged in order to
 834 rebuild the current 'jch'.  Do the same for 'seen'.</pre>
 835 </div>
 836 </div>
 837 </li>
 838 <li>
 839 <p>Review the Meta/redo-jch.sh and Meta/redo-seen.sh scripts.  The
 840 former should have a line <em><mark>#</mark> match next</em>---the idea is that
 841 merging the topics listed before the line on top of <em>master</em>
 842 should result in a tree identical to that of <em>next</em>.</p>
 843 </li>
 844 <li>
 845 <p>As newly created topics are usually merged near the tip of
 846 <em>seen</em>, add them to the end of the Meta/redo-seen.sh script.
 847 Among the topics that were in <em>seen</em>, there may be ones that
 848 are not quite ready for <em>next</em> but are getting there.  Move
 849 them from Meta/redo-seen.sh to the end of Meta/redo-jch.sh.
 850 The expectation is that you&#8217;d use <em>jch</em> as your daily driver
 851 as the first guinea pig, so you should choose carefully.</p>
 852 </li>
 853 <li>
 854 <p>Now we are ready to start rebuilding <em>jch</em> and merging topics to
 855 <em>next</em>.  For each branch whose tip is not merged to <em>next</em>, one
 856 of three things can happen:</p>
 857 </li>
 858 <li>
 859 <p>The commits are all next-worthy; merge the topic to next;</p>
 860 </li>
 861 <li>
 862 <p>The new parts are of mixed quality, but earlier ones are
 863 next-worthy; merge the early parts to next;</p>
 864 </li>
 865 <li>
 866 <p>Nothing is next-worthy; do not do anything.</p>
 867 <div class="literalblock">
 868 <div class="content">
 869 <pre>This step is aided with Meta/redo-jch.sh script created earlier.
 870 If a topic that was already in 'next' gained a patch, the script
 871 would list it as "ai/topic~1".  To include the new patch to the
 872 updated 'next', drop the "~1" part; to keep it excluded, do not
 873 touch the line.</pre>
 874 </div>
 875 </div>
 876 <div class="literalblock">
 877 <div class="content">
 878 <pre>If a topic that was not in 'next' should be merged to 'next', add
 879 it before the '### match next' line.  Then:</pre>
 880 </div>
 881 </div>
 882 <div class="literalblock">
 883 <div class="content">
 884 <pre>$ git checkout --detach master
 885 $ sh Meta/redo-jch.sh -c1</pre>
 886 </div>
 887 </div>
 888 <div class="literalblock">
 889 <div class="content">
 890 <pre>to rebuild the 'jch' branch from scratch.  "-c1" tells the script
 891 to stop merging at the first line that begins with '###'
 892 (i.e. the "### match next" line you added earlier).</pre>
 893 </div>
 894 </div>
 895 <div class="literalblock">
 896 <div class="content">
 897 <pre>At this point, build-test the result.  It may reveal semantic
 898 conflicts (e.g. a topic renamed a variable, another added a new
 899 reference to the variable under its old name), in which case
 900 prepare an appropriate merge-fix first (see appendix), and
 901 rebuild the 'jch' branch from scratch, starting at the tip of
 902 'master', this time without using "-c1" to merge all topics.</pre>
 903 </div>
 904 </div>
 905 <div class="literalblock">
 906 <div class="content">
 907 <pre>Then do the same to 'next'.</pre>
 908 </div>
 909 </div>
 910 <div class="literalblock">
 911 <div class="content">
 912 <pre>$ git checkout next
 913 $ sh Meta/redo-jch.sh -c1 -e</pre>
 914 </div>
 915 </div>
 916 <div class="literalblock">
 917 <div class="content">
 918 <pre>The "-e" option allows the merge message that comes from the
 919 history of the topic and the comments in the "What's cooking" to
 920 be edited.  The resulting tree should match 'jch^{/^### match next'}'
 921 as the same set of topics are merged on 'master'; otherwise there
 922 is a mismerge. Investigate why and do not proceed until the mismerge
 923 is found and rectified.</pre>
 924 </div>
 925 </div>
 926 <div class="literalblock">
 927 <div class="content">
 928 <pre>If 'master' was updated before you started redoing 'next', then</pre>
 929 </div>
 930 </div>
 931 <div class="literalblock">
 932 <div class="content">
 933 <pre>$ git diff 'jch^{/^### match next}' next</pre>
 934 </div>
 935 </div>
 936 <div class="literalblock">
 937 <div class="content">
 938 <pre>would show differences that went into 'master' (which 'jch' has,
 939 but 'next' does not yet---often it is updates to the release
 940 notes).  Merge 'master' back to 'next' if that is the case.</pre>
 941 </div>
 942 </div>
 943 <div class="literalblock">
 944 <div class="content">
 945 <pre>$ git merge -m "Sync with 'master'" --no-log master</pre>
 946 </div>
 947 </div>
 948 <div class="literalblock">
 949 <div class="content">
 950 <pre>When all is well, clean up the redo-jch.sh script with</pre>
 951 </div>
 952 </div>
 953 <div class="literalblock">
 954 <div class="content">
 955 <pre>$ sh Meta/redo-jch.sh -u</pre>
 956 </div>
 957 </div>
 958 <div class="literalblock">
 959 <div class="content">
 960 <pre>This removes topics listed in the script that have already been
 961 merged to 'master'.  This may lose '### match next' marker;
 962 add it again to the appropriate place when it happens.</pre>
 963 </div>
 964 </div>
 965 </li>
 966 <li>
 967 <p>Rebuild <em>seen</em> on top of <em>jch</em>.</p>
 968 <div class="literalblock">
 969 <div class="content">
 970 <pre>$ git checkout -B seen jch
 971 $ sh Meta/redo-seen.sh</pre>
 972 </div>
 973 </div>
 974 <div class="literalblock">
 975 <div class="content">
 976 <pre>When all is well, clean up the redo-seen.sh script with</pre>
 977 </div>
 978 </div>
 979 <div class="literalblock">
 980 <div class="content">
 981 <pre>$ sh Meta/redo-seen.sh -u</pre>
 982 </div>
 983 </div>
 984 <div class="literalblock">
 985 <div class="content">
 986 <pre>Double check by running</pre>
 987 </div>
 988 </div>
 989 <div class="literalblock">
 990 <div class="content">
 991 <pre>$ git branch --no-merged seen '??/*'</pre>
 992 </div>
 993 </div>
 994 <div class="literalblock">
 995 <div class="content">
 996 <pre>to see there is no unexpected leftover topics.</pre>
 997 </div>
 998 </div>
 999 <div class="literalblock">
1000 <div class="content">
1001 <pre>At this point, build-test the result for semantic conflicts, and
1002 if there are, prepare an appropriate merge-fix first (see
1003 appendix), and rebuild the 'seen' branch from scratch, starting at
1004 the tip of 'jch'.</pre>
1005 </div>
1006 </div>
1007 </li>
1008 <li>
1009 <p>Update "What&#8217;s cooking" message to review the updates to
1010 existing topics, newly added topics and graduated topics.</p>
1011 <div class="literalblock">
1012 <div class="content">
1013 <pre>This step is helped with Meta/cook script.</pre>
1014 </div>
1015 </div>
1016 <div class="literalblock">
1017 <div class="content">
1018 <pre>$ Meta/cook</pre>
1019 </div>
1020 </div>
1021 <div class="literalblock">
1022 <div class="content">
1023 <pre>This script inspects the history between master..seen, finds tips
1024 of topic branches, compares what it found with the current
1025 contents in Meta/whats-cooking.txt, and updates that file.
1026 Topics not listed in the file but are found in master..seen are
1027 added to the "New topics" section, topics listed in the file that
1028 are no longer found in master..seen are moved to the "Graduated to
1029 master" section, and topics whose commits changed their states
1030 (e.g. used to be only in 'seen', now merged to 'next') are updated
1031 with change markers "&lt;&lt;" and "&gt;&gt;".</pre>
1032 </div>
1033 </div>
1034 <div class="literalblock">
1035 <div class="content">
1036 <pre>Look for lines enclosed in "&lt;&lt;" and "&gt;&gt;"; they hold contents from
1037 old file that are replaced by this integration round.  After
1038 verifying them, remove the old part.  Review the description for
1039 each topic and update its doneness and plan as needed.  To review
1040 the updated plan, run</pre>
1041 </div>
1042 </div>
1043 <div class="literalblock">
1044 <div class="content">
1045 <pre>$ Meta/cook -w</pre>
1046 </div>
1047 </div>
1048 <div class="literalblock">
1049 <div class="content">
1050 <pre>which will pick up comments given to the topics, such as "Will
1051 merge to 'next'", etc. (see Meta/cook script to learn what kind
1052 of phrases are supported).</pre>
1053 </div>
1054 </div>
1055 </li>
1056 <li>
1057 <p>Compile, test and install all four (five) integration branches;
1058 Meta/Dothem script may aid this step.</p>
1059 </li>
1060 <li>
1061 <p>Format documentation if the <em>master</em> branch was updated;
1062 Meta/dodoc.sh script may aid this step.</p>
1063 </li>
1064 <li>
1065 <p>Push the integration branches out to public places; Meta/pushall
1066 script may aid this step.</p>
1067 </li>
1068 </ul>
1069 </div>
1070 </div>
1071 </div>
1072 <div class="sect1">
1073 <h2 id="_observations">Observations</h2>
1074 <div class="sectionbody">
1075 <div class="paragraph">
1076 <p>Some observations to be made.</p>
1077 </div>
1078 <div class="ulist">
1079 <ul>
1080 <li>
1081 <p>Each topic is tested individually, and also together with other
1082 topics cooking first in <em>seen</em>, then in <em>jch</em> and then in <em>next</em>.
1083 Until it matures, no part of it is merged to <em>master</em>.</p>
1084 </li>
1085 <li>
1086 <p>A topic already in <em>next</em> can get fixes while still in
1087 <em>next</em>.  Such a topic will have many merges to <em>next</em> (in
1088 other words, "git log --first-parent next" will show many
1089 "Merge branch <em>ai/topic</em> to next" for the same topic.</p>
1090 </li>
1091 <li>
1092 <p>An unobvious fix for <em>maint</em> is cooked in <em>next</em> and then
1093 merged to <em>master</em> to make extra sure it is Ok and then
1094 merged to <em>maint</em>.</p>
1095 </li>
1096 <li>
1097 <p>Even when <em>next</em> becomes empty (in other words, all topics
1098 prove stable and are merged to <em>master</em> and "git diff master
1099 next" shows empty), it has tons of merge commits that will
1100 never be in <em>master</em>.</p>
1101 </li>
1102 <li>
1103 <p>In principle, "git log --first-parent master..next" should
1104 show nothing but merges (in practice, there are fixup commits
1105 and reverts that are not merges).</p>
1106 </li>
1107 <li>
1108 <p>Commits near the tip of a topic branch that are not in <em>next</em>
1109 are fair game to be discarded, replaced or rewritten.
1110 Commits already merged to <em>next</em> will not be.</p>
1111 </li>
1112 <li>
1113 <p>Being in the <em>next</em> branch is not a guarantee for a topic to
1114 be included in the next feature release.  Being in the
1115 <em>master</em> branch typically is.</p>
1116 </li>
1117 <li>
1118 <p>Due to the nature of "SQUASH???" fix-ups, if the original author
1119 agrees with the suggested changes, it is OK to squash them to
1120 appropriate patches in the next round (when the suggested change
1121 is small enough, the author should not even bother with
1122 "Helped-by").  It is also OK to drop them from the next round
1123 when the original author does not agree with the suggestion, but
1124 the author is expected to say why somewhere in the discussion.</p>
1125 </li>
1126 </ul>
1127 </div>
1128 </div>
1129 </div>
1130 <div class="sect1">
1131 <h2 id="_appendix">Appendix</h2>
1132 <div class="sectionbody">
1133 <div class="sect2">
1134 <h3 id="_preparing_a_merge_fix">Preparing a "merge-fix"</h3>
1135 <div class="paragraph">
1136 <p>A merge of two topics may not textually conflict but still have
1137 conflict at the semantic level. A classic example is for one topic
1138 to rename a variable and all its uses, while another topic adds a
1139 new use of the variable under its old name. When these two topics
1140 are merged together, the reference to the variable newly added by
1141 the latter topic will still use the old name in the result.</p>
1142 </div>
1143 <div class="paragraph">
1144 <p>The Meta/Reintegrate script that is used by redo-jch and redo-seen
1145 scripts implements a crude but usable way to work around this issue.
1146 When the script merges branch $X, it checks if "refs/merge-fix/$X"
1147 exists, and if so, the effect of it is squashed into the result of
1148 the mechanical merge.  In other words,</p>
1149 </div>
1150 <div class="literalblock">
1151 <div class="content">
1152 <pre>$ echo $X | Meta/Reintegrate</pre>
1153 </div>
1154 </div>
1155 <div class="paragraph">
1156 <p>is roughly equivalent to this sequence:</p>
1157 </div>
1158 <div class="literalblock">
1159 <div class="content">
1160 <pre>$ git merge --rerere-autoupdate $X
1161 $ git commit
1162 $ git cherry-pick -n refs/merge-fix/$X
1163 $ git commit --amend</pre>
1164 </div>
1165 </div>
1166 <div class="paragraph">
1167 <p>The goal of this "prepare a merge-fix" step is to come up with a
1168 commit that can be squashed into a result of mechanical merge to
1169 correct semantic conflicts.</p>
1170 </div>
1171 <div class="paragraph">
1172 <p>After finding that the result of merging branch "ai/topic" to an
1173 integration branch had such a semantic conflict, say seen~4, check the
1174 problematic merge out on a detached HEAD, edit the working tree to
1175 fix the semantic conflict, and make a separate commit to record the
1176 fix-up:</p>
1177 </div>
1178 <div class="literalblock">
1179 <div class="content">
1180 <pre>$ git checkout seen~4
1181 $ git show -s --pretty=%s ;# double check
1182 Merge branch 'ai/topic' to seen
1183 $ edit
1184 $ git commit -m 'merge-fix/ai/topic' -a</pre>
1185 </div>
1186 </div>
1187 <div class="paragraph">
1188 <p>Then make a reference "refs/merge-fix/ai/topic" to point at this
1189 result:</p>
1190 </div>
1191 <div class="literalblock">
1192 <div class="content">
1193 <pre>$ git update-ref refs/merge-fix/ai/topic HEAD</pre>
1194 </div>
1195 </div>
1196 <div class="paragraph">
1197 <p>Then double check the result by asking Meta/Reintegrate to redo the
1198 merge:</p>
1199 </div>
1200 <div class="literalblock">
1201 <div class="content">
1202 <pre>$ git checkout seen~5 ;# the parent of the problem merge
1203 $ echo ai/topic | Meta/Reintegrate
1204 $ git diff seen~4</pre>
1205 </div>
1206 </div>
1207 <div class="paragraph">
1208 <p>This time, because you prepared refs/merge-fix/ai/topic, the
1209 resulting merge should have been tweaked to include the fix for the
1210 semantic conflict.</p>
1211 </div>
1212 <div class="paragraph">
1213 <p>Note that this assumes that the order in which conflicting branches
1214 are merged does not change.  If the reason why merging ai/topic
1215 branch needs this merge-fix is because another branch merged earlier
1216 to the integration branch changed the underlying assumption ai/topic
1217 branch made (e.g. ai/topic branch added a site to refer to a
1218 variable, while the other branch renamed that variable and adjusted
1219 existing use sites), and if you changed redo-jch (or redo-seen) script
1220 to merge ai/topic branch before the other branch, then the above
1221 merge-fix should not be applied while merging ai/topic, but should
1222 instead be applied while merging the other branch.  You would need
1223 to move the fix to apply to the other branch, perhaps like this:</p>
1224 </div>
1225 <div class="literalblock">
1226 <div class="content">
1227 <pre>$ mf=refs/merge-fix
1228 $ git update-ref $mf/$the_other_branch $mf/ai/topic
1229 $ git update-ref -d $mf/ai/topic</pre>
1230 </div>
1231 </div>
1232 </div>
1233 </div>
1234 </div>
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