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diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt index 3c08a6f7db..9c9618cead 100644 --- a/Documentation/git-merge.txt +++ b/Documentation/git-merge.txt @@ -9,146 +9,285 @@ git-merge - Join two or more development histories together SYNOPSIS -------- [verse] -'git-merge' [-n] [--no-commit] [--squash] [-s <strategy>]... - -m=<msg> <remote> <remote>... +'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]... + [--[no-]rerere-autoupdate] [-m <msg>] <commit>... +'git merge' <msg> HEAD <commit>... DESCRIPTION ----------- -This is the top-level interface to the merge machinery -which drives multiple merge strategy scripts. +Incorporates changes from the named commits (since the time their +histories diverged from the current branch) into the current +branch. This command is used by 'git pull' to incorporate changes +from another repository and can be used by hand to merge changes +from one branch into another. + +Assume the following history exists and the current branch is +"`master`": + +------------ + A---B---C topic + / + D---E---F---G master +------------ + +Then "`git merge topic`" will replay the changes made on the +`topic` branch since it diverged from `master` (i.e., `E`) until +its current commit (`C`) on top of `master`, and record the result +in a new commit along with the names of the two parent commits and +a log message from the user describing the changes. + +------------ + A---B---C topic + / \ + D---E---F---G---H master +------------ + +The second syntax (<msg> `HEAD` <commit>...) is supported for +historical reasons. Do not use it from the command line or in +new scripts. It is the same as `git merge -m <msg> <commit>...`. + +*Warning*: Running 'git merge' with uncommitted changes is +discouraged: while possible, it leaves you in a state that is hard to +back out of in the case of a conflict. OPTIONS ------- include::merge-options.txt[] -<msg>:: - The commit message to be used for the merge commit (in case - it is created). The `git-fmt-merge-msg` script can be used - to give a good default for automated `git-merge` invocations. - -<head>:: - Our branch head commit. This has to be `HEAD`, so new - syntax does not require it - -<remote>:: - Other branch head merged into our branch. You need at - least one <remote>. Specifying more than one <remote> - obviously means you are trying an Octopus. - -include::merge-strategies.txt[] - - -If you tried a merge which resulted in a complex conflicts and -would want to start over, you can recover with -gitlink:git-reset[1]. - - -HOW MERGE WORKS ---------------- - -A merge is always between the current `HEAD` and one or more -remote branch heads, and the index file must exactly match the -tree of `HEAD` commit (i.e. the contents of the last commit) when -it happens. In other words, `git-diff --cached HEAD` must -report no changes. - -[NOTE] -This is a bit of lie. In certain special cases, your index are -allowed to be different from the tree of `HEAD` commit. The most -notable case is when your `HEAD` commit is already ahead of what -is being merged, in which case your index can have arbitrary -difference from your `HEAD` commit. Otherwise, your index entries -are allowed have differences from your `HEAD` commit that match -the result of trivial merge (e.g. you received the same patch -from external source to produce the same result as what you are -merging). For example, if a path did not exist in the common -ancestor and your head commit but exists in the tree you are -merging into your repository, and if you already happen to have -that path exactly in your index, the merge does not have to -fail. - -Otherwise, merge will refuse to do any harm to your repository -(that is, it may fetch the objects from remote, and it may even -update the local branch used to keep track of the remote branch -with `git pull remote rbranch:lbranch`, but your working tree, -`.git/HEAD` pointer and index file are left intact). - -You may have local modifications in the working tree files. In -other words, `git-diff` is allowed to report changes. -However, the merge uses your working tree as the working area, -and in order to prevent the merge operation from losing such -changes, it makes sure that they do not interfere with the -merge. Those complex tables in read-tree documentation define -what it means for a path to "interfere with the merge". And if -your local modifications interfere with the merge, again, it -stops before touching anything. - -So in the above two "failed merge" case, you do not have to -worry about loss of data --- you simply were not ready to do -a merge, so no merge happened at all. You may want to finish -whatever you were in the middle of doing, and retry the same -pull after you are done and ready. - -When things cleanly merge, these things happen: - -1. the results are updated both in the index file and in your - working tree, -2. index file is written out as a tree, -3. the tree gets committed, and -4. the `HEAD` pointer gets advanced. - -Because of 2., we require that the original state of the index -file to match exactly the current `HEAD` commit; otherwise we -will write out your local changes already registered in your -index file along with the merge result, which is not good. -Because 1. involves only the paths different between your -branch and the remote branch you are pulling from during the -merge (which is typically a fraction of the whole tree), you can -have local modifications in your working tree as long as they do -not overlap with what the merge updates. - -When there are conflicts, these things happen: - -1. `HEAD` stays the same. - -2. Cleanly merged paths are updated both in the index file and +-m <msg>:: + Set the commit message to be used for the merge commit (in + case one is created). The 'git fmt-merge-msg' command can be + used to give a good default for automated 'git merge' + invocations. + +--rerere-autoupdate:: +--no-rerere-autoupdate:: + Allow the rerere mechanism to update the index with the + result of auto-conflict resolution if possible. + +<commit>...:: + Commits, usually other branch heads, to merge into our branch. + You need at least one <commit>. Specifying more than one + <commit> obviously means you are trying an Octopus. + + +PRE-MERGE CHECKS +---------------- + +Before applying outside changes, you should get your own work in +good shape and committed locally, so it will not be clobbered if +there are conflicts. See also linkgit:git-stash[1]. +'git pull' and 'git merge' will stop without doing anything when +local uncommitted changes overlap with files that 'git pull'/'git +merge' may need to update. + +To avoid recording unrelated changes in the merge commit, +'git pull' and 'git merge' will also abort if there are any changes +registered in the index relative to the `HEAD` commit. (One +exception is when the changed index entries are in the state that +would result from the merge already.) + +If all named commits are already ancestors of `HEAD`, 'git merge' +will exit early with the message "Already up-to-date." + +FAST-FORWARD MERGE +------------------ + +Often the current branch head is an ancestor of the named commit. +This is the most common case especially when invoked from 'git +pull': you are tracking an upstream repository, you have committed +no local changes, and now you want to update to a newer upstream +revision. In this case, a new commit is not needed to store the +combined history; instead, the `HEAD` (along with the index) is +updated to point at the named commit, without creating an extra +merge commit. + +This behavior can be suppressed with the `--no-ff` option. + +TRUE MERGE +---------- + +Except in a fast-forward merge (see above), the branches to be +merged must be tied together by a merge commit that has both of them +as its parents. + +A merged version reconciling the changes from all branches to be +merged is committed, and your `HEAD`, index, and working tree are +updated to it. It is possible to have modifications in the working +tree as long as they do not overlap; the update will preserve them. + +When it is not obvious how to reconcile the changes, the following +happens: + +1. The `HEAD` pointer stays the same. +2. The `MERGE_HEAD` ref is set to point to the other branch head. +3. Paths that merged cleanly are updated both in the index file and in your working tree. - -3. For conflicting paths, the index file records up to three - versions; stage1 stores the version from the common ancestor, - stage2 from `HEAD`, and stage3 from the remote branch (you - can inspect the stages with `git-ls-files -u`). The working - tree files have the result of "merge" program; i.e. 3-way - merge result with familiar conflict markers `<<< === >>>`. - -4. No other changes are done. In particular, the local +4. For conflicting paths, the index file records up to three + versions: stage 1 stores the version from the common ancestor, + stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you + can inspect the stages with `git ls-files -u`). The working + tree files contain the result of the "merge" program; i.e. 3-way + merge results with familiar conflict markers `<<<` `===` `>>>`. +5. No other changes are made. In particular, the local modifications you had before you started merge will stay the same and the index entries for them stay as they were, i.e. matching `HEAD`. +If you tried a merge which resulted in complex conflicts and +want to start over, you can recover with `git reset --merge`. + +HOW CONFLICTS ARE PRESENTED +--------------------------- + +During a merge, the working tree files are updated to reflect the result +of the merge. Among the changes made to the common ancestor's version, +non-overlapping ones (that is, you changed an area of the file while the +other side left that area intact, or vice versa) are incorporated in the +final result verbatim. When both sides made changes to the same area, +however, git cannot randomly pick one side over the other, and asks you to +resolve it by leaving what both sides did to that area. + +By default, git uses the same style as that is used by "merge" program +from the RCS suite to present such a conflicted hunk, like this: + +------------ +Here are lines that are either unchanged from the common +ancestor, or cleanly resolved because only one side changed. +<<<<<<< yours:sample.txt +Conflict resolution is hard; +let's go shopping. +======= +Git makes conflict resolution easy. +>>>>>>> theirs:sample.txt +And here is another line that is cleanly resolved or unmodified. +------------ + +The area where a pair of conflicting changes happened is marked with markers +`<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======` +is typically your side, and the part afterwards is typically their side. + +The default format does not show what the original said in the conflicting +area. You cannot tell how many lines are deleted and replaced with +Barbie's remark on your side. The only thing you can tell is that your +side wants to say it is hard and you'd prefer to go shopping, while the +other side wants to claim it is easy. + +An alternative style can be used by setting the "merge.conflictstyle" +configuration variable to "diff3". In "diff3" style, the above conflict +may look like this: + +------------ +Here are lines that are either unchanged from the common +ancestor, or cleanly resolved because only one side changed. +<<<<<<< yours:sample.txt +Conflict resolution is hard; +let's go shopping. +||||||| +Conflict resolution is hard. +======= +Git makes conflict resolution easy. +>>>>>>> theirs:sample.txt +And here is another line that is cleanly resolved or unmodified. +------------ + +In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses +another `|||||||` marker that is followed by the original text. You can +tell that the original just stated a fact, and your side simply gave in to +that statement and gave up, while the other side tried to have a more +positive attitude. You can sometimes come up with a better resolution by +viewing the original. + + +HOW TO RESOLVE CONFLICTS +------------------------ + After seeing a conflict, you can do two things: - * Decide not to merge. The only clean-up you need are to reset + * Decide not to merge. The only clean-ups you need are to reset the index file to the `HEAD` commit to reverse 2. and to clean - up working tree changes made by 2. and 3.; `git-reset` can + up working tree changes made by 2. and 3.; `git-reset --hard` can be used for this. - * Resolve the conflicts. `git-diff` would report only the - conflicting paths because of the above 2. and 3.. Edit the - working tree files into a desirable shape, `git-update-index` - them, to make the index file contain what the merge result - should be, and run `git-commit` to commit the result. + * Resolve the conflicts. Git will mark the conflicts in + the working tree. Edit the files into shape and + 'git add' them to the index. Use 'git commit' to seal the deal. +You can work through the conflict with a number of tools: -SEE ALSO + * Use a mergetool. `git mergetool` to launch a graphical + mergetool which will work you through the merge. + + * Look at the diffs. `git diff` will show a three-way diff, + highlighting changes from both the `HEAD` and `MERGE_HEAD` + versions. + + * Look at the diffs from each branch. `git log --merge -p <path>` + will show diffs first for the `HEAD` version and then the + `MERGE_HEAD` version. + + * Look at the originals. `git show :1:filename` shows the + common ancestor, `git show :2:filename` shows the `HEAD` + version, and `git show :3:filename` shows the `MERGE_HEAD` + version. + + +EXAMPLES -------- -gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1] +* Merge branches `fixes` and `enhancements` on top of + the current branch, making an octopus merge: ++ +------------------------------------------------ +$ git merge fixes enhancements +------------------------------------------------ + +* Merge branch `obsolete` into the current branch, using `ours` + merge strategy: ++ +------------------------------------------------ +$ git merge -s ours obsolete +------------------------------------------------ + +* Merge branch `maint` into the current branch, but do not make + a new commit automatically: ++ +------------------------------------------------ +$ git merge --no-commit maint +------------------------------------------------ ++ +This can be used when you want to include further changes to the +merge, or want to write your own merge commit message. ++ +You should refrain from abusing this option to sneak substantial +changes into a merge commit. Small fixups like bumping +release/version name would be acceptable. + + +include::merge-strategies.txt[] + +CONFIGURATION +------------- +include::merge-config.txt[] + +branch.<name>.mergeoptions:: + Sets default options for merging into branch <name>. The syntax and + supported options are the same as those of 'git merge', but option + values containing whitespace characters are currently not supported. + +SEE ALSO +-------- +linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1], +linkgit:gitattributes[5], +linkgit:git-reset[1], +linkgit:git-diff[1], linkgit:git-ls-files[1], +linkgit:git-add[1], linkgit:git-rm[1], +linkgit:git-mergetool[1] Author ------ -Written by Junio C Hamano <junkio@cox.net> +Written by Junio C Hamano <gitster@pobox.com> Documentation @@ -157,4 +296,4 @@ Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>. GIT --- -Part of the gitlink:git[7] suite +Part of the linkgit:git[1] suite |