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completions | ||
doc/presentations/GitMerge-2013 | ||
t | ||
.gitignore | ||
COPYING | ||
gitimerge.py | ||
imerge.css | ||
MANIFEST.in | ||
README.md | ||
setup.py | ||
TODO.md | ||
tox.ini |
git-imerge -- incremental merge and rebase for Git
Perform a merge between two branches incrementally. If conflicts are encountered, figure out exactly which pairs of commits conflict, and present the user with one pairwise conflict at a time for resolution.
git-imerge
has two primary design goals:
-
Reduce the pain of resolving merge conflicts to its unavoidable minimum, by finding and presenting the smallest possible conflicts: those between the changes introduced by one commit from each branch.
-
Allow a merge to be saved, tested, interrupted, published, and collaborated on while it is in progress.
I think that it is easiest to understand the concept of incremental merging visually, and therefore I recommend the video of my git-imerge presentation from the GitMerge 2013 conference (20 min) as a good place to start. The full slides for that talk are available in this repository under doc/presentations/GitMerge-2013
. At the same conference, I was interviewed about git-imerge
by Thomas Ferris Nicolaisen for his GitMinutes Podcast #12.
To learn how to use the git-imerge
tool itself, I suggest the blog article git-imerge: A Practical Introduction and also typing git-imerge --help
and git-imerge SUBCOMMAND --help
. If you want more information, the theory and benefits of incremental merging are described in minute detail in a series of blog articles [1], as are the benefits of retaining history when doing a rebase [2].
Multiple incremental merges can be in progress at the same time. Each incremental merge has a name, and its progress is recorded in the Git repository as references under refs/imerge/NAME
. The current state of an incremental merge can be visualized using the diagram
command.
An incremental merge can be interrupted and resumed arbitrarily, or even pushed to a server to allow somebody else to work on it.
git-imerge
comes with a Bash completion script, completions/git-imerge
, which is installed automatically when installing git-imerge
.
Requirements
git-imerge
requires:
-
A Python interpreter; either
-
Python 3.x, version 3.3 or later.
-
Python 2.x, version 2.6 or later. If you are using Python 2.6.x, then you have to install the
argparse
module yourself, as it was only added to the standard library in Python 2.7.
-
-
A recent version of Git.
Bash completion requires Git's completion being available.
Installation
git-imerge
is available on PyPI_, so you can install it with pip
:
$ pip install git-imerge
or using setup.py
if you have downloaded the source package locally:
$ python setup.py install
Instructions
To start a merge or rebase operation using git-imerge
, you use commands that are similar to the corresponding git
commands:
git-imerge command |
git analogue |
Effect |
---|---|---|
git-imerge merge BRANCH |
git merge BRANCH |
Merge BRANCH into the current branch |
git-imerge rebase BRANCH |
git rebase BRANCH |
Rebase the current branch on top of BRANCH |
git-imerge revert COMMIT |
git revert COMMIT |
Add a new commit that undoes the effect of COMMIT |
git-imerge revert COMMIT1..COMMIT2 |
git revert COMMIT1..COMMIT2 |
Add new commits that undo the effects of COMMIT1..COMMIT2 |
git-imerge drop COMMIT |
git rebase --onto COMMIT^ COMMIT |
Entirely delete commit COMMIT from the history of the current branch |
git-imerge drop COMMIT1..COMMIT2 |
git rebase --onto COMMIT1 COMMIT2 |
Entirely delete commits COMMIT1..COMMIT2 from the history of the current branch |
git-imerge drop
is also analogous to running git rebase --interactive
, then deleting the specified commit(s) from the history. Both the drop
and the revert
subcommands are included in git-imerge because the equivalent git operations can conflict, so they both can benefit from using the incremental merge approach.)
A few more options are available if you start the incremental merge using git imerge start
:
$ git-imerge start --name=NAME --goal=GOAL [--first-parent] BRANCH
where
-
NAME
is the name for this merge (and also the default name of the branch to which the results will be saved). -
GOAL
describes how you want to simplify the results (see next section).
After the incremental merge is started, you will be presented with any conflicts that have to be resolved. The basic procedure is similar to performing an incremental merge using git
:
while not done:
<fix the conflict that is presented to you>
<"git add" the files that you changed>
git-imerge continue
When you have resolved all of the conflicts, you finish the incremental merge by typing:
git-imerge finish
That should be enough to get you going. All of these subcommands have additional options; to learn about them type:
git-imerge --help
git-imerge SUBCMD --help
Simplifying results
When the incremental merge is finished, you can simplify its results in various ways before recording it in your project's permanent history by using either the finish
or simplify
command. The "goal" of the incremental merge can be one of the following:
-
merge
— keep only a simple merge of the second branch into the first branch, discarding all intermediate merges. The end result is similar to what you would get fromgit checkout BRANCH1 git merge BRANCH2
-
rebase
— keep the versions of the commits from the second branch rebased onto the first branch. The end result is similar to what you would get fromgit checkout BRANCH2 git rebase BRANCH1
-
rebase-with-history
— likerebase
, except that it retains the old versions of the rebased commits in the history. It is equivalent to merging the commits fromBRANCH2
intoBRANCH1
, one commit at a time. In other words, it transforms this:o---o---o---o BRANCH1 \ A---B---C---D BRANCH2
into this:
o---o---o---o---A'--B'--C'--D' NEW_BRANCH \ / / / / --------A---B---C---D
It is safe to rebase an already-published branch using this approach. See [2] for more information.
-
full
— don't simplify the incremental merge at all: do all of the intermediate merges and retain them all in the permanent history. In other words, it transforms this:o---o---1---2---3 BRANCH1 \ A---B---C---D BRANCH2
into this:
o---o---1---2---3 \ \ \ \ A---A1--A2--A3 \ \ \ \ B---B1--B2--B3 \ \ \ \ C---C1--C2--C3 \ \ \ \ D---D1--D2--D3 NEW_BRANCH
This approach retains the complete history and ancestry information, which gives the maximum flexibility for conducting future merges. On the other hand, it clutters up the permanent Git history considerably.
-
border
— this experimental goal retains the rebase ofBRANCH2
ontoBRANCH1
and also the rebase ofBRANCH1
ontoBRANCH2
, plus a merge commit that includes both branches. In other words, it transforms this:o---o---1---2---3 BRANCH1 \ A---B---C---D BRANCH2
into this:
o---o---1---2---3 \ \ A A2 \ \ B B2 \ \ C C2 \ \ D---D1--D2--D3 NEW_BRANCH
This approach leaves more history than a simple merge or rebase, possibly making future merges easier.
-
border-with-history
— this experimental goal retains therebase-with-history of
BRANCH2
ontoBRANCH1
and also the rebase (without history) ofBRANCH1
ontoBRANCH2
, plus a merge commit that includes both branches. In other words, it transforms this:o---o---1---2---3 BRANCH1 \ A---B---C---D BRANCH2
into this:
o---o---1---2---3 \ \ A-----------A3 \ \ B-----------B3 \ \ C-----------C3 \ \ D---D1--D2--D3 NEW_BRANCH
This approach leaves more history and ancestry information than a simple merge or rebase, possibly making future merges easier.
-
border-with-history2
— this experimental goal retains therebase-with-history
ofBRANCH1
ontoBRANCH2
and also therebase-with-history
ofBRANCH2
ontoBRANCH1
, plus a merge commit that includes both branches. In other words, it transforms this:o---o---1---2---3 BRANCH1 \ A---B---C---D BRANCH2
into this:
o---o---1---2---3 \ \ \ \ A--- --- ---A3 \ \ \ \ B--- --- ---B3 \ \ \ \ C--- --- ---C3 \ \ \ \ D---D1--D2--D3 NEW_BRANCH
This approach leaves more history and ancestry information than a simple merge or rebase, possibly making future merges easier.
Technical notes
Suspending/resuming
When git-imerge
needs to ask the user to do a merge manually, it creates a temporary branch refs/heads/imerge/NAME
to hold the result. If you want to suspend an incremental merge to do something else before continuing, all you need to do is abort any pending merge using git merge --abort
and switch to your other branch. When you are ready to resume the incremental merge, just type git imerge continue
.
If you need to completely abort an in-progress incremental merge, first remove the temporary branches git-imerge
creates using git-imerge remove
, then checkout the branch you were in before you started the incremental merge with git checkout ORIGINAL_BRANCH
.
Storage
git-imerge
records all of the intermediate state about an incremental merge in the Git object database as a bunch of references under refs/imerge/NAME
, where NAME
is the name of the imerge:
-
refs/imerge/NAME/state
points to a blob that describes the current state of the imerge in JSON format; for example,-
The tips of the two branches that are being merged
-
The current "blocker" merges (merges that the user will have to do by hand), if any
-
The simplification goal
-
The name of the branch to which the result will be written.
-
-
refs/imerge/NAME/manual/I-J
andrefs/imerge/NAME/auto/I-J
refer to the manual and automatic merge commits, respectively, that have been done so far as part of the incremental merge.I
andJ
are integers indicating the location(I,J)
of the merge in the incremental merge diagram.
Transferring an in-progress imerge between repositories
It might sometimes be convenient to transfer an in-progress incremental merge from one Git repository to another. For example, you might want to make a backup of the current state, or continue an imerge at home that you started at work, or ask a colleague to do a particular pairwise merge for you. Since all of the imerge state is stored in the Git object database, this can be done by pushing/fetching the references named in the previous section. For example,
$ git push --prune origin +refs/imerge/NAME/*:refs/imerge/NAME/*
or
$ git fetch --prune origin +refs/imerge/NAME/*:refs/imerge/NAME/*
Please note that these commands overwrite any state that already existed in the destination repository. There is currently no support for combining the work done by two people in parallel on an incremental merge, so for now you'll just have to take turns.
Interaction with git rerere
git rerere
is a nice tool that records how you resolve merge conflicts, and if it sees the same conflict again it tries to automatically reuse the same resolution.
Since git-imerge
attempts so many similar test merges, it is easy to imagine rerere
getting confused. Moreover, git-imerge
relies on a merge resolving (or not resolving) consistently if it is carried out more than once. Having rerere
store extra information behind the scenes could therefore confuse git-imerge
.
Indeed, in testing it appeared that during incremental merges, the interaction of git-imerge
with rerere
was sometimes causing merge conflicts to be resolved incorrectly. Therefore, git-imerge
explicitly turns rerere off temporarily whenever it runs any git
commands.
Log messages for pairwise merge commits
When git imerge continue
or git imerge record
finds a resolved merge in the working tree, it commits that merge then incorporates it into the incremental merge. Usually it just uses Git's autogenerated commit message for such commits. If you want to be prompted to edit such commit messages, you can either specify --edit
on the command line or change the default in your configuration:
$ git config --global imerge.editmergemessages true
Testing
git-imerge
uses tox
to run tests. To run the test suite with the system's default Python:
$ tox
To run with a specific Python version, such as 3.7, pass the -e
argument to tox
:
$ tox -e py37
License
git-imerge
is released as open-source software under the GNU General Public License (GPL), version 2 or later. See file COPYING
for more information.
References
- https://softwareswirl.blogspot.com/2012/12/the-conflict-frontier-of-nightmare-merge.html
- https://softwareswirl.blogspot.com/2012/12/mapping-merge-conflict-frontier.html
- https://softwareswirl.blogspot.com/2012/12/real-world-conflict-diagrams.html
- https://softwareswirl.blogspot.com/2013/05/git-incremental-merge.html
- https://softwareswirl.blogspot.com/2013/05/one-merge-to-rule-them-all.html
- https://softwareswirl.blogspot.com/2013/05/incremental-merge-vs-direct-merge-vs.html
- https://softwareswirl.blogspot.com/2013/05/git-imerge-practical-introduction.html