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c0be8aa06b
The git-merge documentation's "HOW MERGE WORKS" section is confusingly composed and actually omits the most interesting part, the merging of the arguments into HEAD itself, surprisingly not actually mentioning the fast-forward merge anywhere. This patch replaces the "[NOTE]" screenful of highly technical details by a single sentence summing up the interesting information, and instead explains how are the arguments compared with HEAD and the three possible inclusion states that are named "Already up-to-date", "Fast-forward" and "True merge". It also makes it clear that the rest of the section talks only about the true merge situation, and slightly expands the talk on solving conflicts. Junio initiated the removal of the Note screenful altogether and offered many stylistical fixes. Signed-off-by: Petr Baudis <pasky@suse.cz> Signed-off-by: Junio C Hamano <gitster@pobox.com>
157 lines
5.1 KiB
Text
157 lines
5.1 KiB
Text
git-merge(1)
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============
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NAME
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----
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git-merge - Join two or more development histories together
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SYNOPSIS
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--------
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[verse]
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'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
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[-m <msg>] <remote> <remote>...
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'git merge' <msg> HEAD <remote>...
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DESCRIPTION
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-----------
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This is the top-level interface to the merge machinery
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which drives multiple merge strategy scripts.
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The second syntax (<msg> `HEAD` <remote>) is supported for
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historical reasons. Do not use it from the command line or in
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new scripts. It is the same as `git merge -m <msg> <remote>`.
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OPTIONS
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-------
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include::merge-options.txt[]
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-m <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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<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 'git-reset'.
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CONFIGURATION
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-------------
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include::merge-config.txt[]
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branch.<name>.mergeoptions::
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Sets default options for merging into branch <name>. The syntax and
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supported options are equal to that of 'git-merge', but option values
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containing whitespace characters are currently not supported.
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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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commits (usually, branch head or tag), and the index file must
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match the tree of `HEAD` commit (i.e. the contents of the last commit)
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when it starts out. In other words, `git diff --cached HEAD` must
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report no changes. (One exception is when the changed index
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entries are already in the same state that would result from
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the merge anyway.)
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Three kinds of merge can happen:
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* The merged commit is already contained in `HEAD`. This is the
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simplest case, called "Already up-to-date."
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* `HEAD` is already contained in the merged commit. This is the
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most common case especially when involved through 'git pull':
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you are tracking an upstream repository, committed no local
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changes and now you want to update to a newer upstream revision.
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Your `HEAD` (and the index) is updated to at point the merged
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commit, without creating an extra merge commit. This is
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called "Fast-forward".
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* Both the merged commit and `HEAD` are independent and must be
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tied together by a merge commit that has them both as its parents.
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The rest of this section describes this "True merge" case.
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The chosen merge strategy merges the two commits into a single
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new source tree.
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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 --hard' 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.
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Edit the working tree files into a desirable shape
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('git mergetool' can ease this task), 'git-add' or 'git-rm'
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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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linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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linkgit:gitattributes[5],
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linkgit:git-reset[1],
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linkgit:git-diff[1], linkgit:git-ls-files[1],
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linkgit:git-add[1], linkgit:git-rm[1],
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linkgit:git-mergetool[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 linkgit:git[1] suite
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