5
There should be one merge command which does the right thing, and
6
which is called 'merge'.
8
The merge command pulls a changeset or a range of changesets into your
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tree. It knows what changes have already been integrated and avoids
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There should be some intelligence about working out what changes have
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The tool intelligently chooses (or perhaps synthesizes) an ancestor
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and two trees to merge. These are then intelligently merged.
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Merge should refuse to run (unless forced) if there are any
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uncommitted changes in your tree beforehand. This has two purposes:
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if you mess up the merge you won't lose anything important; secondly
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this makes it more likely that the merge will be relatively pure.
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It is a good idea to commit as soon as a merge is complete and
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satisfactorily resolved, so as to protect the work you did in the
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merge and to keep it separate from later development. (Mark suggests
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an option to automatically commit when the merge is complete.)
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bzr records what branches have been merged so far. This is useful as
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historical information and also for later choosing a merge ancestor.
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For each revision we record all the other revisions which have come
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into this tree, either by being completely merged or as cherry-picks.
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(This design is similar to the PatchLogPruning__ draft from baz.)
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__ http://wiki.gnuarch.org/PatchLogPruning
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This list of merged revisions is generally append-only, but can be
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reduced if changes are taken back out. Changes can be
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anti-cherry-picked, which causes any successors to change from being
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fully-merged to being cherry-picked.
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The list of merged patches is stored delta-compressed.
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``tla update`` performs a useful but slightly subtle change: it pulls
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in only changes that have been made on the other branch since you last
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merged. That is to say, it sets the merge basis as the most recent
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merged-from point on the other branch.
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This means that any changes which were taken from your branch into the
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other and then reversed or modified will not be reversed. Those
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changes will always be considered as new in your branch and will have
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The basic idea of a merge that only brings in remote work and doesn't
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revert your own changes is good. It could be handled by a three way
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merge with a specified version but perhaps there is a better way.
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Merge is conducted at two levels: merging the tree shape, and merging
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the file contents. Merging the tree shape means accounting for
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renames, adds, deletes, etc. This is almost the same as merging the
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two inventories, but we need to do a smart merge on them to enforce
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structural invariants.
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Some tools insist that you complete the entire merge while the
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``merge`` command is running; you cannot exit the program or restart
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the computer because state is held in memory. We should avoid that.
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At least when the tool is waiting for user input it should have
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written everything to disk sufficient to pick up and continue the
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merge from that point.
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This suggests that there should be a command to continue a merge;
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perhaps ``bzr resolve`` should look for any unresolved changes and
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start resolving them. ``bzr merge`` can (by default) automatically
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One hard aspect is transformation of the tree state such as renames,
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directory creation, etc. This might include files swapping place,
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etc. We would like to do atomically but cannot.
103
If a merge has been begun but not committed then ``bzr revert`` should
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put everything back as it was in the previous revision. This includes
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resetting the tree state and texts, and also clearing the list of
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pending-merged revisions.
113
It should be possible to download all the data necessary to do a merge
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from a remote branch, then disconnect and complete the merge. It
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should be possible to interrupt and continue the merge during this
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This implies that all the data is pulled down and stored somewhere
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locally before the actual merge begins. It could be pulled either
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into the revision history on non-trunk revisions, or into temporary
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It seems useful to move all revisions and texts from the other branch
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into the storage of this branch, in concordance with the general idea
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of every branch moving towards complete knowledge. This allows the
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most options for an offline merge, and also for later looking back to
127
see what was merged in and what decisions were made during the merge.
134
What does cherry-picking mean here? It means we merged the changes
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from a revision relative to its predecessor? But what if we actually
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want to merge the delta relative to something else? Can that be
143
ddaa says perhaps we should have three states: with respect to a
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branch any foreign revision can be *merged*, *not-merged*, or *rejected*.
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The difference between *not-merged* and *rejected* is that not-merged
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patches will try to merge in when you next sync from their
147
branch, whereas rejected changes will not.
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'rejected' seems technically equivalent to it merged with the text
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changes not present. But perhaps there should be something more?
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Bitkeeper has the very interesting feature of *excluded* changesets,
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where something previously committed to or merged into this branch is
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treated as if it never occurred. Because of their representation of
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changes as a weave they can do this without dependency problems on
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Although the later changes will not mechanically conflict, there is of
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course no guarantee that excluding the patch will generate anything
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Cool though this is, it seems that few people understand it well
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enough to use it confidently. It complicates the merge algorithms and
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seems to have been a source of some bugs. It may be better just to
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apply a reversed patch.
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Each revision has a pointer to two sets, represented as lists of
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* ``merged-revisions``
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* ``picked-revisions``
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When a branch is merged in, its revision history plus merged-revisions
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are added to the merged-revisions file. When changes are
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cherry-picked in they are added to the picked-revisions.
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These lists are stored in the text store and their sha1 and id is
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stored in the revision.
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While a merge is underway, these are stored in
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``.bzr/pending-merged-revisions`` and
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``.bzr/pending-picked-revisions``.
added
removed
doc/merge.txt
