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Diffstat (limited to 'Documentation/git-rebase.txt')
| -rw-r--r-- | Documentation/git-rebase.txt | 146 |
1 files changed, 134 insertions, 12 deletions
diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt index 59c1b02..c8ad86a 100644 --- a/Documentation/git-rebase.txt +++ b/Documentation/git-rebase.txt @@ -9,7 +9,7 @@ SYNOPSIS -------- [verse] 'git rebase' [-i | --interactive] [-v | --verbose] [-m | --merge] - [-s <strategy> | --strategy=<strategy>] + [-s <strategy> | --strategy=<strategy>] [--no-verify] [-C<n>] [ --whitespace=<option>] [-p | --preserve-merges] [--onto <newbase>] <upstream> [<branch>] 'git rebase' --continue | --skip | --abort @@ -92,7 +92,7 @@ branch to another, to pretend that you forked the topic branch from the latter branch, using `rebase --onto`. First let's assume your 'topic' is based on branch 'next'. -For example feature developed in 'topic' depends on some +For example, a feature developed in 'topic' depends on some functionality which is found in 'next'. ------------ @@ -103,9 +103,9 @@ functionality which is found in 'next'. o---o---o topic ------------ -We would want to make 'topic' forked from branch 'master', -for example because the functionality 'topic' branch depend on -got merged into more stable 'master' branch, like this: +We want to make 'topic' forked from branch 'master'; for example, +because the functionality on which 'topic' depends was merged into the +more stable 'master' branch. We want our tree to look like this: ------------ o---o---o---o---o master @@ -232,6 +232,9 @@ OPTIONS --verbose:: Display a diffstat of what changed upstream since the last rebase. +--no-verify:: + This option bypasses the pre-rebase hook. See also linkgit:githooks[5]. + -C<n>:: Ensure at least <n> lines of surrounding context match before and after each change. When fewer lines of surrounding @@ -250,18 +253,16 @@ OPTIONS -p:: --preserve-merges:: - Instead of ignoring merges, try to recreate them. This option - only works in interactive mode. + Instead of ignoring merges, try to recreate them. include::merge-strategies.txt[] NOTES ----- -When you rebase a branch, you are changing its history in a way that -will cause problems for anyone who already has a copy of the branch -in their repository and tries to pull updates from you. You should -understand the implications of using 'git-rebase' on a repository that -you share. + +You should understand the implications of using 'git-rebase' on a +repository that you share. See also RECOVERING FROM UPSTREAM REBASE +below. When the git-rebase command is run, it will first execute a "pre-rebase" hook if one exists. You can use this hook to do sanity checks and @@ -396,6 +397,127 @@ consistent (they compile, pass the testsuite, etc.) you should use after each commit, test, and amend the commit if fixes are necessary. +RECOVERING FROM UPSTREAM REBASE +------------------------------- + +Rebasing (or any other form of rewriting) a branch that others have +based work on is a bad idea: anyone downstream of it is forced to +manually fix their history. This section explains how to do the fix +from the downstream's point of view. The real fix, however, would be +to avoid rebasing the upstream in the first place. + +To illustrate, suppose you are in a situation where someone develops a +'subsystem' branch, and you are working on a 'topic' that is dependent +on this 'subsystem'. You might end up with a history like the +following: + +------------ + o---o---o---o---o---o---o---o---o master + \ + o---o---o---o---o subsystem + \ + *---*---* topic +------------ + +If 'subsystem' is rebased against 'master', the following happens: + +------------ + o---o---o---o---o---o---o---o master + \ \ + o---o---o---o---o o'--o'--o'--o'--o' subsystem + \ + *---*---* topic +------------ + +If you now continue development as usual, and eventually merge 'topic' +to 'subsystem', the commits from 'subsystem' will remain duplicated forever: + +------------ + o---o---o---o---o---o---o---o master + \ \ + o---o---o---o---o o'--o'--o'--o'--o'--M subsystem + \ / + *---*---*-..........-*--* topic +------------ + +Such duplicates are generally frowned upon because they clutter up +history, making it harder to follow. To clean things up, you need to +transplant the commits on 'topic' to the new 'subsystem' tip, i.e., +rebase 'topic'. This becomes a ripple effect: anyone downstream from +'topic' is forced to rebase too, and so on! + +There are two kinds of fixes, discussed in the following subsections: + +Easy case: The changes are literally the same.:: + + This happens if the 'subsystem' rebase was a simple rebase and + had no conflicts. + +Hard case: The changes are not the same.:: + + This happens if the 'subsystem' rebase had conflicts, or used + `\--interactive` to omit, edit, or squash commits; or if the + upstream used one of `commit \--amend`, `reset`, or + `filter-branch`. + + +The easy case +~~~~~~~~~~~~~ + +Only works if the changes (patch IDs based on the diff contents) on +'subsystem' are literally the same before and after the rebase +'subsystem' did. + +In that case, the fix is easy because 'git-rebase' knows to skip +changes that are already present in the new upstream. So if you say +(assuming you're on 'topic') +------------ + $ git rebase subsystem +------------ +you will end up with the fixed history +------------ + o---o---o---o---o---o---o---o master + \ + o'--o'--o'--o'--o' subsystem + \ + *---*---* topic +------------ + + +The hard case +~~~~~~~~~~~~~ + +Things get more complicated if the 'subsystem' changes do not exactly +correspond to the ones before the rebase. + +NOTE: While an "easy case recovery" sometimes appears to be successful + even in the hard case, it may have unintended consequences. For + example, a commit that was removed via `git rebase + \--interactive` will be **resurrected**! + +The idea is to manually tell 'git-rebase' "where the old 'subsystem' +ended and your 'topic' began", that is, what the old merge-base +between them was. You will have to find a way to name the last commit +of the old 'subsystem', for example: + +* With the 'subsystem' reflog: after 'git-fetch', the old tip of + 'subsystem' is at `subsystem@\{1}`. Subsequent fetches will + increase the number. (See linkgit:git-reflog[1].) + +* Relative to the tip of 'topic': knowing that your 'topic' has three + commits, the old tip of 'subsystem' must be `topic~3`. + +You can then transplant the old `subsystem..topic` to the new tip by +saying (for the reflog case, and assuming you are on 'topic' already): +------------ + $ git rebase --onto subsystem subsystem@{1} +------------ + +The ripple effect of a "hard case" recovery is especially bad: +'everyone' downstream from 'topic' will now have to perform a "hard +case" recovery too! + + Authors ------ Written by Junio C Hamano <gitster@pobox.com> and |