admin/notes/bzr

   1 NOTES ON COMMITTING TO EMACS'S BAZAAR REPO    -*- outline -*-
   2
   3 * Install changes only on one branch, let them get merged elsewhere if needed.
   4 In particular, install bug-fixes only on the release branch (if there
   5 is one) and let them get synced to the trunk; do not install them by
   6 hand on the trunk as well.  E.g. if there is an active "emacs-23" branch
   7 and you have a bug-fix appropriate for the next Emacs-23.x release,
   8 install it only on the emacs-23 branch, not on the trunk as well.
   9
  10 Installing things manually into more than one branch makes merges more
  11 difficult.
  12
  13 http://lists.gnu.org/archive/html/emacs-devel/2010-03/msg01124.html
  14
  15 The exception is, if you know that the change will be difficult to
  16 merge to the trunk (eg because the trunk code has changed a lot).
  17 In that case, it's helpful if you can apply the change to both trunk
  18 and branch yourself (when committing the branch change, indicate
  19 in the commit log that it should not be merged to the trunk; see below).
  20
  21 * Backporting a bug-fix from the trunk to a branch (e.g. "emacs-23").
  22 Indicate in the commit log that there is no need to merge the commit
  23 to the trunk.  Anything that matches `bzrmerge-skip-regexp' will do;
  24 eg start the commit message with "Backport:".  This is helpful for the
  25 person merging the release branch to the trunk.
  26
  27 http://lists.gnu.org/archive/html/emacs-devel/2010-05/msg00262.html
  28
  29 * Installing changes from your personal branches.
  30 If your branch has only a single commit, or many different real
  31 commits, it is fine to do a merge.  If your branch has only a very
  32 small number of "real" commits, but several "merge from trunks", it is
  33 preferred that you take your branch's diff, apply it to the trunk, and
  34 commit directly, not merge.  This keeps the history cleaner.
  35
  36 In general, when working on some feature in a separate branch, it is
  37 preferable not to merge from trunk until you are done with the
  38 feature.  Unless you really need some change that was done on the
  39 trunk while you were developing on the branch, you don't really need
  40 those merges; just merge once, when you are done with the feature, and
  41 Bazaar will take care of the rest.  Bazaar is much better in this than
  42 CVS, so interim merges are unnecessary.
  43
  44 Or use shelves; or rebase; or do something else.  See the thread for
  45 yet another fun excursion into the exciting world of version control.
  46
  47 http://lists.gnu.org/archive/html/emacs-devel/2010-04/msg00086.html
  48
  49 * Installing changes from gnulib
  50 Some of the files in Emacs are copied from gnulib.  To synchronize
  51 these files from the version of gnulib that you have checked out into
  52 a sibling directory of your branch, type "make sync-from-gnulib"; this
  53 will check out the latest version of gnulib if there is no sibling
  54 directory already.  It is a good idea to run "bzr status" afterwards,
  55 so that if a gnulib module added a file, you can record the new file
  56 using "bzr add".  After synchronizing from gnulib, do a "make" in the
  57 usual way.
  58
  59 To change the set of gnulib modules, change the GNULIB_MODULES
  60 variable in the top-level Makefile.in, and then run:
  61
  62   ./config.status
  63   make sync-from-gnulib
  64   bzr status
  65
  66 The last command will mention files that may need to be added using
  67 "bzr add".  If you remove a gnulib module, or if a gnulib module
  68 removes a file, then remove the corresponding files by hand.
  69
  70 * How to merge changes from emacs-23 to trunk
  71
  72 The following description uses bound branches, presumably it works in
  73 a similar way with unbound ones.
  74
  75 0) (First time only) Get the bzr changelog_merge plugin
  76 (this will be included by default in bzr 2.4 onwards):
  77
  78 cd ~/.bazaar/plugins
  79 # The following is an improved version of: lp:bzr-changelog-merge
  80 bzr branch lp:~spiv/bzr-changelog-merge/non-head-edits-723968
  81 mv bzr-changelog-merge changelog_merge
  82
  83 This should make merging ChangeLogs smoother.  It merges new entries
  84 to the top of the file, rather than trying to fit them in mid-way
  85 through.  Newer versions of the plugin should also be able to deal
  86 with changes to *old* ChangeLog entries, that should not be floated to
  87 the head of the file (see launchpad#723968).
  88
  89 Maybe the default Emacs behavior without this plugin is better,
  90 though, it's not clear yet.
  91
  92 1) Get clean, up-to-date copies of the emacs-23 and trunk branches.
  93 Check for any uncommitted changes with bzr status.
  94
  95 2) M-x cd /path/to/trunk
  96
  97 The first time only, do this:
  98 cd .bzr/branch
  99 Add the following line to branch.conf:
 100 changelog_merge_files = ChangeLog
 101
 102 3) load admin/bzrmerge.el
 103
 104 4) M-x bzrmerge RET /path/to/emacs-23 RET
 105
 106 It will prompt about revisions that should be skipped, based on the
 107 regexp in bzrmerge-missing.  If there are more revisions that you know
 108 need skipping, you'll have to do that by hand.
 109
 110 5) It will stop if there are any conflicts.  Resolve them.
 111 Using smerge-mode, there are menu items to skip to the next conflict,
 112 and to take either the trunk, branch, or both copies.
 113
 114 6) After resolving all conflicts, you might need to run the bzmerge
 115 command again if there are more revisions still to merge.
 116
 117 Do not commit (or exit Emacs) until you have run bzrmerge to completion.
 118
 119 Before committing, check bzr status and bzr diff output.
 120 If you have run bzrmerge enough times, the "pending merge tip" in bzr
 121 status should be the last revision from the emacs-23 branch, and
 122 bzr status -v should show all the revisions you expect to merge.
 123
 124 (Note that it will also show "skipped" revisions.  This is expected,
 125 and is due to a technical limitation of bzr.  The log data for those
 126 revisions gets merged, the actual changes themselves do not.
 127 http://lists.gnu.org/archive/html/emacs-devel/2011-01/msg00609.html )
 128
 129 In particular, check the ChangeLog entries (eg in case too many
 130 entries have been included or whitespace between entries needs fixing).
 131 bzrmerge tries to fix up the dates to today's date, but it only does
 132 this where there are conflicts.  If you used the changelog_merge plugin,
 133 there won't be any conflicts, and (at time of writing) you will need
 134 to adjust dates by hand.  In any case, if someone made multiple
 135 ChangeLog entries on different days in the branch, you may wish to
 136 collapse them all to a single entry for that author in the trunk
 137 (because in the trunk they all appear under the same date).
 138 Obviously, if there are multiple changes to the same file by different
 139 authors, don't break the logical ordering in doing this.
 140
 141 Notes:
 142
 143 1) A lot that was in tramp.el in emacs-23 has moved to tramp-sh.el in
 144 the trunk.  If you end up with a conflict in tramp.el, the changes may
 145 need to go to tramp-sh.el instead.  Remember to update the file name in
 146 the ChangeLog.
 147
 148 2) If a file is modified in emacs-23, and deleted in the trunk, you
 149 get a "contents conflict".  Assuming the changes don't need to be in
 150 the trunk at all, use `bzr resolve path/to/file --take-this' to keep the
 151 trunk version.  Prior to bzr 2.2.3, this may fail.  You can just
 152 delete the .OTHER etc files by hand and use bzr resolve path/to/file.
 153
 154 3) Conflicts in autoload md5sums in comments.  Strictly speaking, the
 155 right thing to do is merge everything else, resolve the conflict by
 156 choosing either the trunk or branch version, then run `make -C lisp
 157 autoloads' to update the md5sums to the correct trunk value before
 158 committing.
 159
 160 * Re-adding a file that has been removed from the repository
 161
 162 It's easy to get this wrong. Let's suppose you've done:
 163
 164 bzr remove file; bzr commit
 165
 166 and now, sometime later, you realize this was a mistake and file needs
 167 to be brought back.  DON'T just do:
 168
 169 bzr add file; bzr commit
 170
 171 This restores file, but without its history (`bzr log file' will be
 172 very short).  This is because file gets re-added with a new file-id
 173 (use `bzr file-id file' to see the id).
 174
 175 Insteading of adding the file, try:
 176
 177 bzr revert -rN file; bzr commit
 178
 179 where revision N+1 is the one where file was removed.
 180
 181 You could also try `bzr add --file-ids-from', if you have a copy of
 182 another branch where file still exists.