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3ae854c356
Morten Welinder says examples of resetting is really about recovering from botched commit/pulls. I agree that pointers from commands that cause a reset to be needed in the first place would be very helpful. Also reset examples did not mention "pull/merge" cases. Signed-off-by: Junio C Hamano <junkio@cox.net>
158 lines
5.3 KiB
Text
158 lines
5.3 KiB
Text
git-merge(1)
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============
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NAME
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----
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git-merge - Grand Unified Merge Driver
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SYNOPSIS
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--------
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'git-merge' [-n] [--no-commit] [-s <strategy>]... <msg> <head> <remote> <remote>...
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DESCRIPTION
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-----------
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This is the top-level user interface to the merge machinery
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which drives multiple merge strategy scripts.
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OPTIONS
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-------
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include::merge-options.txt[]
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<msg>::
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The commit message to be used for the merge commit (in case
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it is created). The `git-fmt-merge-msg` script can be used
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to give a good default for automated `git-merge` invocations.
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<head>::
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our branch head commit.
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<remote>::
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other branch head merged into our branch. You need at
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least one <remote>. Specifying more than one <remote>
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obviously means you are trying an Octopus.
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include::merge-strategies.txt[]
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If you tried a merge which resulted in a complex conflicts and
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would want to start over, you can recover with
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gitlink:git-reset[1].
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HOW MERGE WORKS
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---------------
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A merge is always between the current `HEAD` and one or more
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remote branch heads, and the index file must exactly match the
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tree of `HEAD` commit (i.e. the contents of the last commit) when
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it happens. In other words, `git-diff --cached HEAD` must
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report no changes.
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[NOTE]
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This is a bit of lie. In certain special cases, your index are
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allowed to be different from the tree of `HEAD` commit. The most
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notable case is when your `HEAD` commit is already ahead of what
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is being merged, in which case your index can have arbitrary
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difference from your `HEAD` commit. Otherwise, your index entries
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are allowed have differences from your `HEAD` commit that match
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the result of trivial merge (e.g. you received the same patch
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from external source to produce the same result as what you are
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merging). For example, if a path did not exist in the common
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ancestor and your head commit but exists in the tree you are
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merging into your repository, and if you already happen to have
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that path exactly in your index, the merge does not have to
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fail.
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Otherwise, merge will refuse to do any harm to your repository
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(that is, it may fetch the objects from remote, and it may even
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update the local branch used to keep track of the remote branch
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with `git pull remote rbranch:lbranch`, but your working tree,
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`.git/HEAD` pointer and index file are left intact).
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You may have local modifications in the working tree files. In
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other words, `git-diff` is allowed to report changes.
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However, the merge uses your working tree as the working area,
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and in order to prevent the merge operation from losing such
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changes, it makes sure that they do not interfere with the
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merge. Those complex tables in read-tree documentation define
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what it means for a path to "interfere with the merge". And if
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your local modifications interfere with the merge, again, it
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stops before touching anything.
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So in the above two "failed merge" case, you do not have to
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worry about lossage of data --- you simply were not ready to do
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a merge, so no merge happened at all. You may want to finish
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whatever you were in the middle of doing, and retry the same
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pull after you are done and ready.
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When things cleanly merge, these things happen:
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1. the results are updated both in the index file and in your
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working tree,
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2. index file is written out as a tree,
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3. the tree gets committed, and
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4. the `HEAD` pointer gets advanced.
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Because of 2., we require that the original state of the index
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file to match exactly the current `HEAD` commit; otherwise we
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will write out your local changes already registered in your
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index file along with the merge result, which is not good.
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Because 1. involves only the paths different between your
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branch and the remote branch you are pulling from during the
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merge (which is typically a fraction of the whole tree), you can
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have local modifications in your working tree as long as they do
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not overlap with what the merge updates.
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When there are conflicts, these things happen:
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1. `HEAD` stays the same.
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2. Cleanly merged paths are updated both in the index file and
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in your working tree.
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3. For conflicting paths, the index file records up to three
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versions; stage1 stores the version from the common ancestor,
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stage2 from `HEAD`, and stage3 from the remote branch (you
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can inspect the stages with `git-ls-files -u`). The working
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tree files have the result of "merge" program; i.e. 3-way
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merge result with familiar conflict markers `<<< === >>>`.
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4. No other changes are done. In particular, the local
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modifications you had before you started merge will stay the
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same and the index entries for them stay as they were,
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i.e. matching `HEAD`.
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After seeing a conflict, you can do two things:
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* Decide not to merge. The only clean-up you need are to reset
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the index file to the `HEAD` commit to reverse 2. and to clean
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up working tree changes made by 2. and 3.; `git-reset` can
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be used for this.
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* Resolve the conflicts. `git-diff` would report only the
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conflicting paths because of the above 2. and 3.. Edit the
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working tree files into a desirable shape, `git-update-index`
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them, to make the index file contain what the merge result
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should be, and run `git-commit` to commit the result.
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SEE ALSO
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--------
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gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1]
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Author
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------
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Written by Junio C Hamano <junkio@cox.net>
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Documentation
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--------------
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Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
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GIT
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---
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Part of the gitlink:git[7] suite
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