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diff --git a/third_party/git/Documentation/git-rebase.txt b/third_party/git/Documentation/git-rebase.txt new file mode 100644 index 0000000000..6156609cf7 --- /dev/null +++ b/third_party/git/Documentation/git-rebase.txt @@ -0,0 +1,1053 @@ +git-rebase(1) +============= + +NAME +---- +git-rebase - Reapply commits on top of another base tip + +SYNOPSIS +-------- +[verse] +'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>] + [<upstream> [<branch>]] +'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>] + --root [<branch>] +'git rebase' (--continue | --skip | --abort | --quit | --edit-todo | --show-current-patch) + +DESCRIPTION +----------- +If <branch> is specified, 'git rebase' will perform an automatic +`git switch <branch>` before doing anything else. Otherwise +it remains on the current branch. + +If <upstream> is not specified, the upstream configured in +branch.<name>.remote and branch.<name>.merge options will be used (see +linkgit:git-config[1] for details) and the `--fork-point` option is +assumed. If you are currently not on any branch or if the current +branch does not have a configured upstream, the rebase will abort. + +All changes made by commits in the current branch but that are not +in <upstream> are saved to a temporary area. This is the same set +of commits that would be shown by `git log <upstream>..HEAD`; or by +`git log 'fork_point'..HEAD`, if `--fork-point` is active (see the +description on `--fork-point` below); or by `git log HEAD`, if the +`--root` option is specified. + +The current branch is reset to <upstream>, or <newbase> if the +--onto option was supplied. This has the exact same effect as +`git reset --hard <upstream>` (or <newbase>). ORIG_HEAD is set +to point at the tip of the branch before the reset. + +The commits that were previously saved into the temporary area are +then reapplied to the current branch, one by one, in order. Note that +any commits in HEAD which introduce the same textual changes as a commit +in HEAD..<upstream> are omitted (i.e., a patch already accepted upstream +with a different commit message or timestamp will be skipped). + +It is possible that a merge failure will prevent this process from being +completely automatic. You will have to resolve any such merge failure +and run `git rebase --continue`. Another option is to bypass the commit +that caused the merge failure with `git rebase --skip`. To check out the +original <branch> and remove the .git/rebase-apply working files, use the +command `git rebase --abort` instead. + +Assume the following history exists and the current branch is "topic": + +------------ + A---B---C topic + / + D---E---F---G master +------------ + +From this point, the result of either of the following commands: + + + git rebase master + git rebase master topic + +would be: + +------------ + A'--B'--C' topic + / + D---E---F---G master +------------ + +*NOTE:* The latter form is just a short-hand of `git checkout topic` +followed by `git rebase master`. When rebase exits `topic` will +remain the checked-out branch. + +If the upstream branch already contains a change you have made (e.g., +because you mailed a patch which was applied upstream), then that commit +will be skipped. For example, running `git rebase master` on the +following history (in which `A'` and `A` introduce the same set of changes, +but have different committer information): + +------------ + A---B---C topic + / + D---E---A'---F master +------------ + +will result in: + +------------ + B'---C' topic + / + D---E---A'---F master +------------ + +Here is how you would transplant a topic branch based on one +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, a feature developed in 'topic' depends on some +functionality which is found in 'next'. + +------------ + o---o---o---o---o master + \ + o---o---o---o---o next + \ + o---o---o topic +------------ + +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 + | \ + | o'--o'--o' topic + \ + o---o---o---o---o next +------------ + +We can get this using the following command: + + git rebase --onto master next topic + + +Another example of --onto option is to rebase part of a +branch. If we have the following situation: + +------------ + H---I---J topicB + / + E---F---G topicA + / + A---B---C---D master +------------ + +then the command + + git rebase --onto master topicA topicB + +would result in: + +------------ + H'--I'--J' topicB + / + | E---F---G topicA + |/ + A---B---C---D master +------------ + +This is useful when topicB does not depend on topicA. + +A range of commits could also be removed with rebase. If we have +the following situation: + +------------ + E---F---G---H---I---J topicA +------------ + +then the command + + git rebase --onto topicA~5 topicA~3 topicA + +would result in the removal of commits F and G: + +------------ + E---H'---I'---J' topicA +------------ + +This is useful if F and G were flawed in some way, or should not be +part of topicA. Note that the argument to --onto and the <upstream> +parameter can be any valid commit-ish. + +In case of conflict, 'git rebase' will stop at the first problematic commit +and leave conflict markers in the tree. You can use 'git diff' to locate +the markers (<<<<<<) and make edits to resolve the conflict. For each +file you edit, you need to tell Git that the conflict has been resolved, +typically this would be done with + + + git add <filename> + + +After resolving the conflict manually and updating the index with the +desired resolution, you can continue the rebasing process with + + + git rebase --continue + + +Alternatively, you can undo the 'git rebase' with + + + git rebase --abort + +CONFIGURATION +------------- + +include::config/rebase.txt[] + +OPTIONS +------- +--onto <newbase>:: + Starting point at which to create the new commits. If the + --onto option is not specified, the starting point is + <upstream>. May be any valid commit, and not just an + existing branch name. ++ +As a special case, you may use "A\...B" as a shortcut for the +merge base of A and B if there is exactly one merge base. You can +leave out at most one of A and B, in which case it defaults to HEAD. + +<upstream>:: + Upstream branch to compare against. May be any valid commit, + not just an existing branch name. Defaults to the configured + upstream for the current branch. + +<branch>:: + Working branch; defaults to HEAD. + +--continue:: + Restart the rebasing process after having resolved a merge conflict. + +--abort:: + Abort the rebase operation and reset HEAD to the original + branch. If <branch> was provided when the rebase operation was + started, then HEAD will be reset to <branch>. Otherwise HEAD + will be reset to where it was when the rebase operation was + started. + +--quit:: + Abort the rebase operation but HEAD is not reset back to the + original branch. The index and working tree are also left + unchanged as a result. + +--keep-empty:: + Keep the commits that do not change anything from its + parents in the result. ++ +See also INCOMPATIBLE OPTIONS below. + +--allow-empty-message:: + By default, rebasing commits with an empty message will fail. + This option overrides that behavior, allowing commits with empty + messages to be rebased. ++ +See also INCOMPATIBLE OPTIONS below. + +--skip:: + Restart the rebasing process by skipping the current patch. + +--edit-todo:: + Edit the todo list during an interactive rebase. + +--show-current-patch:: + Show the current patch in an interactive rebase or when rebase + is stopped because of conflicts. This is the equivalent of + `git show REBASE_HEAD`. + +-m:: +--merge:: + Use merging strategies to rebase. When the recursive (default) merge + strategy is used, this allows rebase to be aware of renames on the + upstream side. ++ +Note that a rebase merge works by replaying each commit from the working +branch on top of the <upstream> branch. Because of this, when a merge +conflict happens, the side reported as 'ours' is the so-far rebased +series, starting with <upstream>, and 'theirs' is the working branch. In +other words, the sides are swapped. ++ +See also INCOMPATIBLE OPTIONS below. + +-s <strategy>:: +--strategy=<strategy>:: + Use the given merge strategy. + If there is no `-s` option 'git merge-recursive' is used + instead. This implies --merge. ++ +Because 'git rebase' replays each commit from the working branch +on top of the <upstream> branch using the given strategy, using +the 'ours' strategy simply empties all patches from the <branch>, +which makes little sense. ++ +See also INCOMPATIBLE OPTIONS below. + +-X <strategy-option>:: +--strategy-option=<strategy-option>:: + Pass the <strategy-option> through to the merge strategy. + This implies `--merge` and, if no strategy has been + specified, `-s recursive`. Note the reversal of 'ours' and + 'theirs' as noted above for the `-m` option. ++ +See also INCOMPATIBLE OPTIONS below. + +--rerere-autoupdate:: +--no-rerere-autoupdate:: + Allow the rerere mechanism to update the index with the + result of auto-conflict resolution if possible. + +-S[<keyid>]:: +--gpg-sign[=<keyid>]:: + GPG-sign commits. The `keyid` argument is optional and + defaults to the committer identity; if specified, it must be + stuck to the option without a space. + +-q:: +--quiet:: + Be quiet. Implies --no-stat. + +-v:: +--verbose:: + Be verbose. Implies --stat. + +--stat:: + Show a diffstat of what changed upstream since the last rebase. The + diffstat is also controlled by the configuration option rebase.stat. + +-n:: +--no-stat:: + Do not show a diffstat as part of the rebase process. + +--no-verify:: + This option bypasses the pre-rebase hook. See also linkgit:githooks[5]. + +--verify:: + Allows the pre-rebase hook to run, which is the default. This option can + be used to override --no-verify. 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 + context exist they all must match. By default no context is + ever ignored. ++ +See also INCOMPATIBLE OPTIONS below. + +--no-ff:: +--force-rebase:: +-f:: + Individually replay all rebased commits instead of fast-forwarding + over the unchanged ones. This ensures that the entire history of + the rebased branch is composed of new commits. ++ +You may find this helpful after reverting a topic branch merge, as this option +recreates the topic branch with fresh commits so it can be remerged +successfully without needing to "revert the reversion" (see the +link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for +details). + +--fork-point:: +--no-fork-point:: + Use reflog to find a better common ancestor between <upstream> + and <branch> when calculating which commits have been + introduced by <branch>. ++ +When --fork-point is active, 'fork_point' will be used instead of +<upstream> to calculate the set of commits to rebase, where +'fork_point' is the result of `git merge-base --fork-point <upstream> +<branch>` command (see linkgit:git-merge-base[1]). If 'fork_point' +ends up being empty, the <upstream> will be used as a fallback. ++ +If either <upstream> or --root is given on the command line, then the +default is `--no-fork-point`, otherwise the default is `--fork-point`. + +--ignore-whitespace:: +--whitespace=<option>:: + These flag are passed to the 'git apply' program + (see linkgit:git-apply[1]) that applies the patch. ++ +See also INCOMPATIBLE OPTIONS below. + +--committer-date-is-author-date:: +--ignore-date:: + These flags are passed to 'git am' to easily change the dates + of the rebased commits (see linkgit:git-am[1]). ++ +See also INCOMPATIBLE OPTIONS below. + +--signoff:: + Add a Signed-off-by: trailer to all the rebased commits. Note + that if `--interactive` is given then only commits marked to be + picked, edited or reworded will have the trailer added. ++ +See also INCOMPATIBLE OPTIONS below. + +-i:: +--interactive:: + Make a list of the commits which are about to be rebased. Let the + user edit that list before rebasing. This mode can also be used to + split commits (see SPLITTING COMMITS below). ++ +The commit list format can be changed by setting the configuration option +rebase.instructionFormat. A customized instruction format will automatically +have the long commit hash prepended to the format. ++ +See also INCOMPATIBLE OPTIONS below. + +-r:: +--rebase-merges[=(rebase-cousins|no-rebase-cousins)]:: + By default, a rebase will simply drop merge commits from the todo + list, and put the rebased commits into a single, linear branch. + With `--rebase-merges`, the rebase will instead try to preserve + the branching structure within the commits that are to be rebased, + by recreating the merge commits. Any resolved merge conflicts or + manual amendments in these merge commits will have to be + resolved/re-applied manually. ++ +By default, or when `no-rebase-cousins` was specified, commits which do not +have `<upstream>` as direct ancestor will keep their original branch point, +i.e. commits that would be excluded by linkgit:git-log[1]'s +`--ancestry-path` option will keep their original ancestry by default. If +the `rebase-cousins` mode is turned on, such commits are instead rebased +onto `<upstream>` (or `<onto>`, if specified). ++ +The `--rebase-merges` mode is similar in spirit to the deprecated +`--preserve-merges`, but in contrast to that option works well in interactive +rebases: commits can be reordered, inserted and dropped at will. ++ +It is currently only possible to recreate the merge commits using the +`recursive` merge strategy; Different merge strategies can be used only via +explicit `exec git merge -s <strategy> [...]` commands. ++ +See also REBASING MERGES and INCOMPATIBLE OPTIONS below. + +-p:: +--preserve-merges:: + [DEPRECATED: use `--rebase-merges` instead] Recreate merge commits + instead of flattening the history by replaying commits a merge commit + introduces. Merge conflict resolutions or manual amendments to merge + commits are not preserved. ++ +This uses the `--interactive` machinery internally, but combining it +with the `--interactive` option explicitly is generally not a good +idea unless you know what you are doing (see BUGS below). ++ +See also INCOMPATIBLE OPTIONS below. + +-x <cmd>:: +--exec <cmd>:: + Append "exec <cmd>" after each line creating a commit in the + final history. <cmd> will be interpreted as one or more shell + commands. Any command that fails will interrupt the rebase, + with exit code 1. ++ +You may execute several commands by either using one instance of `--exec` +with several commands: ++ + git rebase -i --exec "cmd1 && cmd2 && ..." ++ +or by giving more than one `--exec`: ++ + git rebase -i --exec "cmd1" --exec "cmd2" --exec ... ++ +If `--autosquash` is used, "exec" lines will not be appended for +the intermediate commits, and will only appear at the end of each +squash/fixup series. ++ +This uses the `--interactive` machinery internally, but it can be run +without an explicit `--interactive`. ++ +See also INCOMPATIBLE OPTIONS below. + +--root:: + Rebase all commits reachable from <branch>, instead of + limiting them with an <upstream>. This allows you to rebase + the root commit(s) on a branch. When used with --onto, it + will skip changes already contained in <newbase> (instead of + <upstream>) whereas without --onto it will operate on every change. + When used together with both --onto and --preserve-merges, + 'all' root commits will be rewritten to have <newbase> as parent + instead. ++ +See also INCOMPATIBLE OPTIONS below. + +--autosquash:: +--no-autosquash:: + When the commit log message begins with "squash! ..." (or + "fixup! ..."), and there is already a commit in the todo list that + matches the same `...`, automatically modify the todo list of rebase + -i so that the commit marked for squashing comes right after the + commit to be modified, and change the action of the moved commit + from `pick` to `squash` (or `fixup`). A commit matches the `...` if + the commit subject matches, or if the `...` refers to the commit's + hash. As a fall-back, partial matches of the commit subject work, + too. The recommended way to create fixup/squash commits is by using + the `--fixup`/`--squash` options of linkgit:git-commit[1]. ++ +If the `--autosquash` option is enabled by default using the +configuration variable `rebase.autoSquash`, this option can be +used to override and disable this setting. ++ +See also INCOMPATIBLE OPTIONS below. + +--autostash:: +--no-autostash:: + Automatically create a temporary stash entry before the operation + begins, and apply it after the operation ends. This means + that you can run rebase on a dirty worktree. However, use + with care: the final stash application after a successful + rebase might result in non-trivial conflicts. + +--reschedule-failed-exec:: +--no-reschedule-failed-exec:: + Automatically reschedule `exec` commands that failed. This only makes + sense in interactive mode (or when an `--exec` option was provided). + +INCOMPATIBLE OPTIONS +-------------------- + +The following options: + + * --committer-date-is-author-date + * --ignore-date + * --whitespace + * --ignore-whitespace + * -C + +are incompatible with the following options: + + * --merge + * --strategy + * --strategy-option + * --allow-empty-message + * --[no-]autosquash + * --rebase-merges + * --preserve-merges + * --interactive + * --exec + * --keep-empty + * --edit-todo + * --root when used in combination with --onto + +In addition, the following pairs of options are incompatible: + + * --preserve-merges and --interactive + * --preserve-merges and --signoff + * --preserve-merges and --rebase-merges + * --rebase-merges and --strategy + * --rebase-merges and --strategy-option + +BEHAVIORAL DIFFERENCES +----------------------- + +There are some subtle differences how the backends behave. + +Empty commits +~~~~~~~~~~~~~ + +The am backend drops any "empty" commits, regardless of whether the +commit started empty (had no changes relative to its parent to +start with) or ended empty (all changes were already applied +upstream in other commits). + +The interactive backend drops commits by default that +started empty and halts if it hits a commit that ended up empty. +The `--keep-empty` option exists for the interactive backend to allow +it to keep commits that started empty. + +Directory rename detection +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Directory rename heuristics are enabled in the merge and interactive +backends. Due to the lack of accurate tree information, directory +rename detection is disabled in the am backend. + +include::merge-strategies.txt[] + +NOTES +----- + +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 +reject the rebase if it isn't appropriate. Please see the template +pre-rebase hook script for an example. + +Upon completion, <branch> will be the current branch. + +INTERACTIVE MODE +---------------- + +Rebasing interactively means that you have a chance to edit the commits +which are rebased. You can reorder the commits, and you can +remove them (weeding out bad or otherwise unwanted patches). + +The interactive mode is meant for this type of workflow: + +1. have a wonderful idea +2. hack on the code +3. prepare a series for submission +4. submit + +where point 2. consists of several instances of + +a) regular use + + 1. finish something worthy of a commit + 2. commit + +b) independent fixup + + 1. realize that something does not work + 2. fix that + 3. commit it + +Sometimes the thing fixed in b.2. cannot be amended to the not-quite +perfect commit it fixes, because that commit is buried deeply in a +patch series. That is exactly what interactive rebase is for: use it +after plenty of "a"s and "b"s, by rearranging and editing +commits, and squashing multiple commits into one. + +Start it with the last commit you want to retain as-is: + + git rebase -i <after-this-commit> + +An editor will be fired up with all the commits in your current branch +(ignoring merge commits), which come after the given commit. You can +reorder the commits in this list to your heart's content, and you can +remove them. The list looks more or less like this: + +------------------------------------------- +pick deadbee The oneline of this commit +pick fa1afe1 The oneline of the next commit +... +------------------------------------------- + +The oneline descriptions are purely for your pleasure; 'git rebase' will +not look at them but at the commit names ("deadbee" and "fa1afe1" in this +example), so do not delete or edit the names. + +By replacing the command "pick" with the command "edit", you can tell +'git rebase' to stop after applying that commit, so that you can edit +the files and/or the commit message, amend the commit, and continue +rebasing. + +To interrupt the rebase (just like an "edit" command would do, but without +cherry-picking any commit first), use the "break" command. + +If you just want to edit the commit message for a commit, replace the +command "pick" with the command "reword". + +To drop a commit, replace the command "pick" with "drop", or just +delete the matching line. + +If you want to fold two or more commits into one, replace the command +"pick" for the second and subsequent commits with "squash" or "fixup". +If the commits had different authors, the folded commit will be +attributed to the author of the first commit. The suggested commit +message for the folded commit is the concatenation of the commit +messages of the first commit and of those with the "squash" command, +but omits the commit messages of commits with the "fixup" command. + +'git rebase' will stop when "pick" has been replaced with "edit" or +when a command fails due to merge errors. When you are done editing +and/or resolving conflicts you can continue with `git rebase --continue`. + +For example, if you want to reorder the last 5 commits, such that what +was HEAD~4 becomes the new HEAD. To achieve that, you would call +'git rebase' like this: + +---------------------- +$ git rebase -i HEAD~5 +---------------------- + +And move the first patch to the end of the list. + +You might want to recreate merge commits, e.g. if you have a history +like this: + +------------------ + X + \ + A---M---B + / +---o---O---P---Q +------------------ + +Suppose you want to rebase the side branch starting at "A" to "Q". Make +sure that the current HEAD is "B", and call + +----------------------------- +$ git rebase -i -r --onto Q O +----------------------------- + +Reordering and editing commits usually creates untested intermediate +steps. You may want to check that your history editing did not break +anything by running a test, or at least recompiling at intermediate +points in history by using the "exec" command (shortcut "x"). You may +do so by creating a todo list like this one: + +------------------------------------------- +pick deadbee Implement feature XXX +fixup f1a5c00 Fix to feature XXX +exec make +pick c0ffeee The oneline of the next commit +edit deadbab The oneline of the commit after +exec cd subdir; make test +... +------------------------------------------- + +The interactive rebase will stop when a command fails (i.e. exits with +non-0 status) to give you an opportunity to fix the problem. You can +continue with `git rebase --continue`. + +The "exec" command launches the command in a shell (the one specified +in `$SHELL`, or the default shell if `$SHELL` is not set), so you can +use shell features (like "cd", ">", ";" ...). The command is run from +the root of the working tree. + +---------------------------------- +$ git rebase -i --exec "make test" +---------------------------------- + +This command lets you check that intermediate commits are compilable. +The todo list becomes like that: + +-------------------- +pick 5928aea one +exec make test +pick 04d0fda two +exec make test +pick ba46169 three +exec make test +pick f4593f9 four +exec make test +-------------------- + +SPLITTING COMMITS +----------------- + +In interactive mode, you can mark commits with the action "edit". However, +this does not necessarily mean that 'git rebase' expects the result of this +edit to be exactly one commit. Indeed, you can undo the commit, or you can +add other commits. This can be used to split a commit into two: + +- Start an interactive rebase with `git rebase -i <commit>^`, where + <commit> is the commit you want to split. In fact, any commit range + will do, as long as it contains that commit. + +- Mark the commit you want to split with the action "edit". + +- When it comes to editing that commit, execute `git reset HEAD^`. The + effect is that the HEAD is rewound by one, and the index follows suit. + However, the working tree stays the same. + +- Now add the changes to the index that you want to have in the first + commit. You can use `git add` (possibly interactively) or + 'git gui' (or both) to do that. + +- Commit the now-current index with whatever commit message is appropriate + now. + +- Repeat the last two steps until your working tree is clean. + +- Continue the rebase with `git rebase --continue`. + +If you are not absolutely sure that the intermediate revisions are +consistent (they compile, pass the testsuite, etc.) you should use +'git stash' to stash away the not-yet-committed changes +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 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, squash, or fixup 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! + +REBASING MERGES +--------------- + +The interactive rebase command was originally designed to handle +individual patch series. As such, it makes sense to exclude merge +commits from the todo list, as the developer may have merged the +then-current `master` while working on the branch, only to rebase +all the commits onto `master` eventually (skipping the merge +commits). + +However, there are legitimate reasons why a developer may want to +recreate merge commits: to keep the branch structure (or "commit +topology") when working on multiple, inter-related branches. + +In the following example, the developer works on a topic branch that +refactors the way buttons are defined, and on another topic branch +that uses that refactoring to implement a "Report a bug" button. The +output of `git log --graph --format=%s -5` may look like this: + +------------ +* Merge branch 'report-a-bug' +|\ +| * Add the feedback button +* | Merge branch 'refactor-button' +|\ \ +| |/ +| * Use the Button class for all buttons +| * Extract a generic Button class from the DownloadButton one +------------ + +The developer might want to rebase those commits to a newer `master` +while keeping the branch topology, for example when the first topic +branch is expected to be integrated into `master` much earlier than the +second one, say, to resolve merge conflicts with changes to the +DownloadButton class that made it into `master`. + +This rebase can be performed using the `--rebase-merges` option. +It will generate a todo list looking like this: + +------------ +label onto + +# Branch: refactor-button +reset onto +pick 123456 Extract a generic Button class from the DownloadButton one +pick 654321 Use the Button class for all buttons +label refactor-button + +# Branch: report-a-bug +reset refactor-button # Use the Button class for all buttons +pick abcdef Add the feedback button +label report-a-bug + +reset onto +merge -C a1b2c3 refactor-button # Merge 'refactor-button' +merge -C 6f5e4d report-a-bug # Merge 'report-a-bug' +------------ + +In contrast to a regular interactive rebase, there are `label`, `reset` +and `merge` commands in addition to `pick` ones. + +The `label` command associates a label with the current HEAD when that +command is executed. These labels are created as worktree-local refs +(`refs/rewritten/<label>`) that will be deleted when the rebase +finishes. That way, rebase operations in multiple worktrees linked to +the same repository do not interfere with one another. If the `label` +command fails, it is rescheduled immediately, with a helpful message how +to proceed. + +The `reset` command resets the HEAD, index and worktree to the specified +revision. It is similar to an `exec git reset --hard <label>`, but +refuses to overwrite untracked files. If the `reset` command fails, it is +rescheduled immediately, with a helpful message how to edit the todo list +(this typically happens when a `reset` command was inserted into the todo +list manually and contains a typo). + +The `merge` command will merge the specified revision(s) into whatever +is HEAD at that time. With `-C <original-commit>`, the commit message of +the specified merge commit will be used. When the `-C` is changed to +a lower-case `-c`, the message will be opened in an editor after a +successful merge so that the user can edit the message. + +If a `merge` command fails for any reason other than merge conflicts (i.e. +when the merge operation did not even start), it is rescheduled immediately. + +At this time, the `merge` command will *always* use the `recursive` +merge strategy for regular merges, and `octopus` for octopus merges, +with no way to choose a different one. To work around +this, an `exec` command can be used to call `git merge` explicitly, +using the fact that the labels are worktree-local refs (the ref +`refs/rewritten/onto` would correspond to the label `onto`, for example). + +Note: the first command (`label onto`) labels the revision onto which +the commits are rebased; The name `onto` is just a convention, as a nod +to the `--onto` option. + +It is also possible to introduce completely new merge commits from scratch +by adding a command of the form `merge <merge-head>`. This form will +generate a tentative commit message and always open an editor to let the +user edit it. This can be useful e.g. when a topic branch turns out to +address more than a single concern and wants to be split into two or +even more topic branches. Consider this todo list: + +------------ +pick 192837 Switch from GNU Makefiles to CMake +pick 5a6c7e Document the switch to CMake +pick 918273 Fix detection of OpenSSL in CMake +pick afbecd http: add support for TLS v1.3 +pick fdbaec Fix detection of cURL in CMake on Windows +------------ + +The one commit in this list that is not related to CMake may very well +have been motivated by working on fixing all those bugs introduced by +switching to CMake, but it addresses a different concern. To split this +branch into two topic branches, the todo list could be edited like this: + +------------ +label onto + +pick afbecd http: add support for TLS v1.3 +label tlsv1.3 + +reset onto +pick 192837 Switch from GNU Makefiles to CMake +pick 918273 Fix detection of OpenSSL in CMake +pick fdbaec Fix detection of cURL in CMake on Windows +pick 5a6c7e Document the switch to CMake +label cmake + +reset onto +merge tlsv1.3 +merge cmake +------------ + +BUGS +---- +The todo list presented by the deprecated `--preserve-merges --interactive` +does not represent the topology of the revision graph (use `--rebase-merges` +instead). Editing commits and rewording their commit messages should work +fine, but attempts to reorder commits tend to produce counterintuitive results. +Use `--rebase-merges` in such scenarios instead. + +For example, an attempt to rearrange +------------ +1 --- 2 --- 3 --- 4 --- 5 +------------ +to +------------ +1 --- 2 --- 4 --- 3 --- 5 +------------ +by moving the "pick 4" line will result in the following history: +------------ + 3 + / +1 --- 2 --- 4 --- 5 +------------ + +GIT +--- +Part of the linkgit:git[1] suite |