Merge branch 'js/rebase-recreate-merge'

"git rebase" learned "--rebase-merges" to transplant the whole
topology of commit graph elsewhere.

* js/rebase-recreate-merge:
  rebase -i --rebase-merges: add a section to the man page
  rebase -i: introduce --rebase-merges=[no-]rebase-cousins
  pull: accept --rebase=merges to recreate the branch topology
  rebase --rebase-merges: avoid "empty merges"
  sequencer: handle post-rewrite for merge commands
  sequencer: make refs generated by the `label` command worktree-local
  rebase --rebase-merges: add test for --keep-empty
  rebase: introduce the --rebase-merges option
  rebase-helper --make-script: introduce a flag to rebase merges
  sequencer: fast-forward `merge` commands, if possible
  sequencer: introduce the `merge` command
  sequencer: introduce new commands to reset the revision
  git-rebase--interactive: clarify arguments
  sequencer: offer helpful advice when a command was rescheduled
  sequencer: refactor how original todo list lines are accessed
  sequencer: make rearrange_squash() a bit more obvious
  sequencer: avoid using errno clobbered by rollback_lock_file()

Documentation/config.txt

@@ -1068,6 +1068,10 @@ branch.<name>.rebase::
 	"git pull" is run. See "pull.rebase" for doing this in a non
 	branch-specific manner.
 +
+When `merges`, pass the `--rebase-merges` option to 'git rebase'
+so that the local merge commits are included in the rebase (see
+linkgit:git-rebase[1] for details).
++
 When preserve, also pass `--preserve-merges` along to 'git rebase'
 so that locally committed merge commits will not be flattened
 by running 'git pull'.
@@ -2669,6 +2673,10 @@ pull.rebase::
 	pull" is run. See "branch.<name>.rebase" for setting this on a
 	per-branch basis.
 +
+When `merges`, pass the `--rebase-merges` option to 'git rebase'
+so that the local merge commits are included in the rebase (see
+linkgit:git-rebase[1] for details).
++
 When preserve, also pass `--preserve-merges` along to 'git rebase'
 so that locally committed merge commits will not be flattened
 by running 'git pull'.

Documentation/git-pull.txt

@@ -101,13 +101,17 @@ Options related to merging
 include::merge-options.txt[]
 
 -r::
---rebase[=false|true|preserve|interactive]::
+--rebase[=false|true|merges|preserve|interactive]::
 	When true, rebase the current branch on top of the upstream
 	branch after fetching. If there is a remote-tracking branch
 	corresponding to the upstream branch and the upstream branch
 	was rebased since last fetched, the rebase uses that information
 	to avoid rebasing non-local changes.
 +
+When set to `merges`, rebase using `git rebase --rebase-merges` so that
+the local merge commits are included in the rebase (see
+linkgit:git-rebase[1] for details).
++
 When set to preserve, rebase with the `--preserve-merges` option passed
 to `git rebase` so that locally created merge commits will not be flattened.
 +

Documentation/git-rebase.txt

@@ -379,6 +379,33 @@ 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.
 
+-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 gitlink: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 `--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 below.
+
 -p::
 --preserve-merges::
 	Recreate merge commits instead of flattening the history by replaying
@@ -776,12 +803,146 @@ 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 isimilar 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 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, 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 `--preserve-merges --interactive` does not
 represent the topology of the revision graph.  Editing commits and
 rewording their commit messages should work fine, but attempts to
-reorder commits tend to produce counterintuitive results.
+reorder commits tend to produce counterintuitive results. Use
+`--rebase-merges` in such scenarios instead.
 
 For example, an attempt to rearrange
 ------------

builtin/pull.c

@@ -27,14 +27,16 @@ enum rebase_type {
 	REBASE_FALSE = 0,
 	REBASE_TRUE,
 	REBASE_PRESERVE,
+	REBASE_MERGES,
 	REBASE_INTERACTIVE
 };
 
 /**
  * Parses the value of --rebase. If value is a false value, returns
  * REBASE_FALSE. If value is a true value, returns REBASE_TRUE. If value is
- * "preserve", returns REBASE_PRESERVE. If value is a invalid value, dies with
+ * "merges", returns REBASE_MERGES. If value is "preserve", returns
- * a fatal error if fatal is true, otherwise returns REBASE_INVALID.
+ * REBASE_PRESERVE. If value is a invalid value, dies with a fatal error if
+ * fatal is true, otherwise returns REBASE_INVALID.
  */
 static enum rebase_type parse_config_rebase(const char *key, const char *value,
 		int fatal)
@@ -47,6 +49,8 @@ static enum rebase_type parse_config_rebase(const char *key, const char *value,
 		return REBASE_TRUE;
 	else if (!strcmp(value, "preserve"))
 		return REBASE_PRESERVE;
+	else if (!strcmp(value, "merges"))
+		return REBASE_MERGES;
 	else if (!strcmp(value, "interactive"))
 		return REBASE_INTERACTIVE;
 
@@ -130,7 +134,7 @@ static struct option pull_options[] = {
 	/* Options passed to git-merge or git-rebase */
 	OPT_GROUP(N_("Options related to merging")),
 	{ OPTION_CALLBACK, 'r', "rebase", &opt_rebase,
-	  "false|true|preserve|interactive",
+	  "false|true|merges|preserve|interactive",
 	  N_("incorporate changes by rebasing rather than merging"),
 	  PARSE_OPT_OPTARG, parse_opt_rebase },
 	OPT_PASSTHRU('n', NULL, &opt_diffstat, NULL,
@@ -800,7 +804,9 @@ static int run_rebase(const struct object_id *curr_head,
 	argv_push_verbosity(&args);
 
 	/* Options passed to git-rebase */
-	if (opt_rebase == REBASE_PRESERVE)
+	if (opt_rebase == REBASE_MERGES)
+		argv_array_push(&args, "--rebase-merges");
+	else if (opt_rebase == REBASE_PRESERVE)
 		argv_array_push(&args, "--preserve-merges");
 	else if (opt_rebase == REBASE_INTERACTIVE)
 		argv_array_push(&args, "--interactive");

builtin/rebase--helper.c

@@ -12,8 +12,8 @@ static const char * const builtin_rebase_helper_usage[] = {
 int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 {
 	struct replay_opts opts = REPLAY_OPTS_INIT;
-	unsigned flags = 0, keep_empty = 0;
+	unsigned flags = 0, keep_empty = 0, rebase_merges = 0;
-	int abbreviate_commands = 0;
+	int abbreviate_commands = 0, rebase_cousins = -1;
 	enum {
 		CONTINUE = 1, ABORT, MAKE_SCRIPT, SHORTEN_OIDS, EXPAND_OIDS,
 		CHECK_TODO_LIST, SKIP_UNNECESSARY_PICKS, REARRANGE_SQUASH,
@@ -24,6 +24,9 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "keep-empty", &keep_empty, N_("keep empty commits")),
 		OPT_BOOL(0, "allow-empty-message", &opts.allow_empty_message,
 			N_("allow commits with empty messages")),
+		OPT_BOOL(0, "rebase-merges", &rebase_merges, N_("rebase merge commits")),
+		OPT_BOOL(0, "rebase-cousins", &rebase_cousins,
+			 N_("keep original branch points of cousins")),
 		OPT_CMDMODE(0, "continue", &command, N_("continue rebase"),
 				CONTINUE),
 		OPT_CMDMODE(0, "abort", &command, N_("abort rebase"),
@@ -57,8 +60,14 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 
 	flags |= keep_empty ? TODO_LIST_KEEP_EMPTY : 0;
 	flags |= abbreviate_commands ? TODO_LIST_ABBREVIATE_CMDS : 0;
+	flags |= rebase_merges ? TODO_LIST_REBASE_MERGES : 0;
+	flags |= rebase_cousins > 0 ? TODO_LIST_REBASE_COUSINS : 0;
 	flags |= command == SHORTEN_OIDS ? TODO_LIST_SHORTEN_IDS : 0;
 
+	if (rebase_cousins >= 0 && !rebase_merges)
+		warning(_("--[no-]rebase-cousins has no effect without "
+			  "--rebase-merges"));
+
 	if (command == CONTINUE && argc == 1)
 		return !!sequencer_continue(&opts);
 	if (command == ABORT && argc == 1)

builtin/remote.c

@@ -245,7 +245,9 @@ static int add(int argc, const char **argv)
 struct branch_info {
 	char *remote_name;
 	struct string_list merge;
-	enum { NO_REBASE, NORMAL_REBASE, INTERACTIVE_REBASE } rebase;
+	enum {
+		NO_REBASE, NORMAL_REBASE, INTERACTIVE_REBASE, REBASE_MERGES
+	} rebase;
 };
 
 static struct string_list branch_list = STRING_LIST_INIT_NODUP;
@@ -306,6 +308,8 @@ static int config_read_branches(const char *key, const char *value, void *cb)
 				info->rebase = v;
 			else if (!strcmp(value, "preserve"))
 				info->rebase = NORMAL_REBASE;
+			else if (!strcmp(value, "merges"))
+				info->rebase = REBASE_MERGES;
 			else if (!strcmp(value, "interactive"))
 				info->rebase = INTERACTIVE_REBASE;
 		}
@@ -963,9 +967,15 @@ static int show_local_info_item(struct string_list_item *item, void *cb_data)
 
 	printf("    %-*s ", show_info->width, item->string);
 	if (branch_info->rebase) {
-		printf_ln(branch_info->rebase == INTERACTIVE_REBASE
+		const char *msg;
-			  ? _("rebases interactively onto remote %s")
+		if (branch_info->rebase == INTERACTIVE_REBASE)
-			  : _("rebases onto remote %s"), merge->items[0].string);
+			msg = _("rebases interactively onto remote %s");
+		else if (branch_info->rebase == REBASE_MERGES)
+			msg = _("rebases interactively (with merges) onto "
+				"remote %s");
+		else
+			msg = _("rebases onto remote %s");
+		printf_ln(msg, merge->items[0].string);
 		return 0;
 	} else if (show_info->any_rebase) {
 		printf_ln(_(" merges with remote %s"), merge->items[0].string);

contrib/completion/git-completion.bash

@@ -1949,7 +1949,7 @@ _git_rebase ()
 	--*)
 		__gitcomp "
 			--onto --merge --strategy --interactive
-			--preserve-merges --stat --no-stat
+			--rebase-merges --preserve-merges --stat --no-stat
 			--committer-date-is-author-date --ignore-date
 			--ignore-whitespace --whitespace=
 			--autosquash --no-autosquash
@@ -2120,7 +2120,7 @@ _git_config ()
 		return
 		;;
 	branch.*.rebase)
-		__gitcomp "false true preserve interactive"
+		__gitcomp "false true merges preserve interactive"
 		return
 		;;
 	remote.pushdefault)

git-rebase--interactive.sh

@@ -155,13 +155,19 @@ reschedule_last_action () {
 append_todo_help () {
 	gettext "
 Commands:
-p, pick = use commit
+p, pick <commit> = use commit
-r, reword = use commit, but edit the commit message
+r, reword <commit> = use commit, but edit the commit message
-e, edit = use commit, but stop for amending
+e, edit <commit> = use commit, but stop for amending
-s, squash = use commit, but meld into previous commit
+s, squash <commit> = use commit, but meld into previous commit
-f, fixup = like \"squash\", but discard this commit's log message
+f, fixup <commit> = like \"squash\", but discard this commit's log message
-x, exec = run command (the rest of the line) using shell
+x, exec <commit> = run command (the rest of the line) using shell
-d, drop = remove commit
+d, drop <commit> = remove commit
+l, label <label> = label current HEAD with a name
+t, reset <label> = reset HEAD to a label
+m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
+.       create a merge commit using the original merge commit's
+.       message (or the oneline, if no original merge commit was
+.       specified). Use -c <commit> to reword the commit message.
 
 These lines can be re-ordered; they are executed from top to bottom.
 " | git stripspace --comment-lines >>"$todo"
@@ -964,6 +970,8 @@ git_rebase__interactive () {
 	init_revisions_and_shortrevisions
 
 	git rebase--helper --make-script ${keep_empty:+--keep-empty} \
+		${rebase_merges:+--rebase-merges} \
+		${rebase_cousins:+--rebase-cousins} \
 		$revisions ${restrict_revision+^$restrict_revision} >"$todo" ||
 	die "$(gettext "Could not generate todo list")"
 

git-rebase.sh

@@ -17,6 +17,7 @@ q,quiet!           be quiet. implies --no-stat
 autostash          automatically stash/stash pop before and after
 fork-point         use 'merge-base --fork-point' to refine upstream
 onto=!             rebase onto given branch instead of upstream
+r,rebase-merges?   try to rebase merges instead of skipping them
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
 no-ff!             cherry-pick all commits, even if unchanged
@@ -89,6 +90,8 @@ type=
 state_dir=
 # One of {'', continue, skip, abort}, as parsed from command line
 action=
+rebase_merges=
+rebase_cousins=
 preserve_merges=
 autosquash=
 keep_empty=
@@ -280,6 +283,19 @@ do
 	--no-keep-empty)
 		keep_empty=
 		;;
+	--rebase-merges)
+		rebase_merges=t
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
+	--rebase-merges=*)
+		rebase_merges=t
+		case "${1#*=}" in
+		rebase-cousins) rebase_cousins=t;;
+		no-rebase-cousins) rebase_cousins=;;
+		*) die "Unknown mode: $1";;
+		esac
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
 	--preserve-merges)
 		preserve_merges=t
 		test -z "$interactive_rebase" && interactive_rebase=implied

refs.c

@@ -615,7 +615,8 @@ int dwim_log(const char *str, int len, struct object_id *oid, char **log)
 static int is_per_worktree_ref(const char *refname)
 {
 	return !strcmp(refname, "HEAD") ||
-		starts_with(refname, "refs/bisect/");
+		starts_with(refname, "refs/bisect/") ||
+		starts_with(refname, "refs/rewritten/");
 }
 
 static int is_pseudoref_syntax(const char *refname)

sequencer.h

@@ -63,6 +63,13 @@ int sequencer_remove_state(struct replay_opts *opts);
 #define TODO_LIST_KEEP_EMPTY (1U << 0)
 #define TODO_LIST_SHORTEN_IDS (1U << 1)
 #define TODO_LIST_ABBREVIATE_CMDS (1U << 2)
+#define TODO_LIST_REBASE_MERGES (1U << 3)
+/*
+ * When rebasing merges, commits that do have the base commit as ancestor
+ * ("cousins") are *not* rebased onto the new base by default. If those
+ * commits should be rebased onto the new base, this flag needs to be passed.
+ */
+#define TODO_LIST_REBASE_COUSINS (1U << 4)
 int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 

t/t3421-rebase-topology-linear.sh

@@ -217,6 +217,7 @@ test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
 test_run_rebase failure -p
+test_run_rebase success --rebase-merges
 
 #       m
 #      /

t/t3430-rebase-merges.sh

@@ -0,0 +1,244 @@
+#!/bin/sh
+#
+# Copyright (c) 2018 Johannes E. Schindelin
+#
+
+test_description='git rebase -i --rebase-merges
+
+This test runs git rebase "interactively", retaining the branch structure by
+recreating merge commits.
+
+Initial setup:
+
+    -- B --                   (first)
+   /       \
+ A - C - D - E - H            (master)
+       \       /
+         F - G                (second)
+'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+test_cmp_graph () {
+	cat >expect &&
+	git log --graph --boundary --format=%s "$@" >output &&
+	sed "s/ *$//" <output >output.trimmed &&
+	test_cmp expect output.trimmed
+}
+
+test_expect_success 'setup' '
+	write_script replace-editor.sh <<-\EOF &&
+	mv "$1" "$(git rev-parse --git-path ORIGINAL-TODO)"
+	cp script-from-scratch "$1"
+	EOF
+
+	test_commit A &&
+	git checkout -b first &&
+	test_commit B &&
+	git checkout master &&
+	test_commit C &&
+	test_commit D &&
+	git merge --no-commit B &&
+	test_tick &&
+	git commit -m E &&
+	git tag -m E E &&
+	git checkout -b second C &&
+	test_commit F &&
+	test_commit G &&
+	git checkout master &&
+	git merge --no-commit G &&
+	test_tick &&
+	git commit -m H &&
+	git tag -m H H
+'
+
+test_expect_success 'create completely different structure' '
+	cat >script-from-scratch <<-\EOF &&
+	label onto
+
+	# onebranch
+	pick G
+	pick D
+	label onebranch
+
+	# second
+	reset onto
+	pick B
+	label second
+
+	reset onto
+	merge -C H second
+	merge onebranch # Merge the topic branch '\''onebranch'\''
+	EOF
+	test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
+	test_tick &&
+	git rebase -i -r A &&
+	test_cmp_graph <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	* |   H
+	|\ \
+	| |/
+	|/|
+	| * B
+	|/
+	* A
+	EOF
+'
+
+test_expect_success 'generate correct todo list' '
+	cat >expect <<-\EOF &&
+	label onto
+
+	reset onto
+	pick d9df450 B
+	label E
+
+	reset onto
+	pick 5dee784 C
+	label branch-point
+	pick ca2c861 F
+	pick 088b00a G
+	label H
+
+	reset branch-point # C
+	pick 12bd07b D
+	merge -C 2051b56 E # E
+	merge -C 233d48a H # H
+
+	EOF
+
+	grep -v "^#" <.git/ORIGINAL-TODO >output &&
+	test_cmp expect output
+'
+
+test_expect_success '`reset` refuses to overwrite untracked files' '
+	git checkout -b refuse-to-reset &&
+	test_commit dont-overwrite-untracked &&
+	git checkout @{-1} &&
+	: >dont-overwrite-untracked.t &&
+	echo "reset refs/tags/dont-overwrite-untracked" >script-from-scratch &&
+	test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
+	test_must_fail git rebase -r HEAD &&
+	git rebase --abort
+'
+
+test_expect_success 'failed `merge` writes patch (may be rescheduled, too)' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout -b conflicting-merge A &&
+
+	: fail because of conflicting untracked file &&
+	>G.t &&
+	echo "merge -C H G" >script-from-scratch &&
+	test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
+	test_tick &&
+	test_must_fail git rebase -ir HEAD &&
+	grep "^merge -C .* G$" .git/rebase-merge/done &&
+	grep "^merge -C .* G$" .git/rebase-merge/git-rebase-todo &&
+	test_path_is_file .git/rebase-merge/patch &&
+
+	: fail because of merge conflict &&
+	rm G.t .git/rebase-merge/patch &&
+	git reset --hard &&
+	test_commit conflicting-G G.t not-G conflicting-G &&
+	test_must_fail git rebase --continue &&
+	! grep "^merge -C .* G$" .git/rebase-merge/git-rebase-todo &&
+	test_path_is_file .git/rebase-merge/patch
+'
+
+test_expect_success 'with a branch tip that was cherry-picked already' '
+	git checkout -b already-upstream master &&
+	base="$(git rev-parse --verify HEAD)" &&
+
+	test_commit A1 &&
+	test_commit A2 &&
+	git reset --hard $base &&
+	test_commit B1 &&
+	test_tick &&
+	git merge -m "Merge branch A" A2 &&
+
+	git checkout -b upstream-with-a2 $base &&
+	test_tick &&
+	git cherry-pick A2 &&
+
+	git checkout already-upstream &&
+	test_tick &&
+	git rebase -i -r upstream-with-a2 &&
+	test_cmp_graph upstream-with-a2.. <<-\EOF
+	*   Merge branch A
+	|\
+	| * A1
+	* | B1
+	|/
+	o A2
+	EOF
+'
+
+test_expect_success 'do not rebase cousins unless asked for' '
+	git checkout -b cousins master &&
+	before="$(git rev-parse --verify HEAD)" &&
+	test_tick &&
+	git rebase -r HEAD^ &&
+	test_cmp_rev HEAD $before &&
+	test_tick &&
+	git rebase --rebase-merges=rebase-cousins HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge the topic branch '\''onebranch'\''
+	|\
+	| * D
+	| * G
+	|/
+	o H
+	EOF
+'
+
+test_expect_success 'refs/rewritten/* is worktree-local' '
+	git worktree add wt &&
+	cat >wt/script-from-scratch <<-\EOF &&
+	label xyz
+	exec GIT_DIR=../.git git rev-parse --verify refs/rewritten/xyz >a || :
+	exec git rev-parse --verify refs/rewritten/xyz >b
+	EOF
+
+	test_config -C wt sequence.editor \""$PWD"/replace-editor.sh\" &&
+	git -C wt rebase -i HEAD &&
+	test_must_be_empty wt/a &&
+	test_cmp_rev HEAD "$(cat wt/b)"
+'
+
+test_expect_success 'post-rewrite hook and fixups work for merges' '
+	git checkout -b post-rewrite &&
+	test_commit same1 &&
+	git reset --hard HEAD^ &&
+	test_commit same2 &&
+	git merge -m "to fix up" same1 &&
+	echo same old same old >same2.t &&
+	test_tick &&
+	git commit --fixup HEAD same2.t &&
+	fixup="$(git rev-parse HEAD)" &&
+
+	mkdir -p .git/hooks &&
+	test_when_finished "rm .git/hooks/post-rewrite" &&
+	echo "cat >actual" | write_script .git/hooks/post-rewrite &&
+
+	test_tick &&
+	git rebase -i --autosquash -r HEAD^^^ &&
+	printf "%s %s\n%s %s\n%s %s\n%s %s\n" >expect $(git rev-parse \
+		$fixup^^2 HEAD^2 \
+		$fixup^^ HEAD^ \
+		$fixup^ HEAD \
+		$fixup HEAD) &&
+	test_cmp expect actual
+'
+
+test_expect_success 'refuse to merge ancestors of HEAD' '
+	echo "merge HEAD^" >script-from-scratch &&
+	test_config -C wt sequence.editor \""$PWD"/replace-editor.sh\" &&
+	before="$(git rev-parse HEAD)" &&
+	git rebase -i HEAD &&
+	test_cmp_rev HEAD $before
+'
+
+test_done