merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

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+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