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Once someone has their own branch of a project, they can make
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and commit changes in parallel to any development proceeding
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on the original branch. Pretty soon though, these independent
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lines of development will need to be combined again. This
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process is known as *merging*.
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To incorporate changes from another branch, use the ``merge`` command.
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If no URL is given, a default is used, initially the branch this branch
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For example, if Bill made a branch from Mary's work, he can merge her
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subsequent changes by simply typing this::
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On the other hand, Mary might want to merge into her branch the work Bill
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has done in his. In this case, she needs to explicitly give the URL the
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bzr merge sftp://mary@bill-laptop/cool-repo/cool-trunk
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This sets the default merge branch if one is not already set. To change the
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default after it is set, use the ``--remember`` option.
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How does merging work?
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----------------------
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A variety of algorithms exist for merging changes. Bazaar's
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default algorithm is a variation of *3-way merging* which
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works as follows. Given an ancestor A and two branches B and C,
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the following table provides the rules used.
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=== === === ========================
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=== === === ========================
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=== === === ========================
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Note that some merges can only be completed with the assistance
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of a human. Details on how to resolve these are given in
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`Resolving conflicts`_.
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After any conflicts are resolved, the merge needs to be committed.
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bzr commit -m "Merged Mary's changes"
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Even if there are no conflicts, an explicit commit is still required.
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Unlike some other tools, this is considered a feature in Bazaar.
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A clean merge is not necessarily a good merge so making the commit
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a separate explicit step allows you to run your test suite first to
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verify all is good. If problems are found, you should correct them
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before committing the merge or throw the merge away using ``revert``.
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One of the most important features of Bazaar is distributed,
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high quality *merge tracking*.
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In other words, Bazaar remembers what has been merged already and
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uses that information to intelligently choose the best ancestor for
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a merge, minimizing the number and size of conflicts.
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If you are a refugee from many other VCS tools, it can be really
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hard to "unlearn" the *please-let-me-avoid-merging-at-any-cost* habit.
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Bazaar lets you safely merge as often as you like with other people.
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By working in a peer-to-peer manner when it makes sense to do so, you
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also avoid using a central branch as an "integration swamp", keeping
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its quality higher. When the change you're collaborating on is
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truly ready for wider sharing, that's the time to merge and commit
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it to a central branch, not before.
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Merging that Just Works truly can change how developers work together.
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doc/en/user-guide/merging_changes.txt
