Merge branch 'js/rebase-i-final'

The final batch to "git rebase -i" updates to move more code from
the shell script to C.

* js/rebase-i-final:
  rebase -i: rearrange fixup/squash lines using the rebase--helper
  t3415: test fixup with wrapped oneline
  rebase -i: skip unnecessary picks using the rebase--helper
  rebase -i: check for missing commits in the rebase--helper
  t3404: relax rebase.missingCommitsCheck tests
  rebase -i: also expand/collapse the SHA-1s via the rebase--helper
  rebase -i: do not invent onelines when expanding/collapsing SHA-1s
  rebase -i: remove useless indentation
  rebase -i: generate the script via rebase--helper
  t3415: verify that an empty instructionFormat is handled as before

7 files changed, 647 insertions, 360 deletions

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6805a74..3cedfb0 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -430,13 +430,15 @@ without an explicit `--interactive`.
 --autosquash::
 --no-autosquash::
 	When the commit log message begins with "squash! ..." (or
-	"fixup! ..."), and there is a commit whose title begins with
-	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`).  Ignores subsequent
-	"fixup! " or "squash! " after the first, in case you referred to an
-	earlier fixup/squash with `git commit --fixup/--squash`.
+	"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].
 +
 This option is only valid when the `--interactive` option is used.
 +
diff --git a/builtin/rebase--helper.c b/builtin/rebase--helper.c
index c82b4dc..f851936 100644
--- a/builtin/rebase--helper.c
+++ b/builtin/rebase--helper.c
@@ -12,15 +12,30 @@ 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;
+	int keep_empty = 0;
 	enum {
-		CONTINUE = 1, ABORT
+		CONTINUE = 1, ABORT, MAKE_SCRIPT, SHORTEN_SHA1S, EXPAND_SHA1S,
+		CHECK_TODO_LIST, SKIP_UNNECESSARY_PICKS, REARRANGE_SQUASH
 	} command = 0;
 	struct option options[] = {
 		OPT_BOOL(0, "ff", &opts.allow_ff, N_("allow fast-forward")),
+		OPT_BOOL(0, "keep-empty", &keep_empty, N_("keep empty commits")),
 		OPT_CMDMODE(0, "continue", &command, N_("continue rebase"),
 				CONTINUE),
 		OPT_CMDMODE(0, "abort", &command, N_("abort rebase"),
 				ABORT),
+		OPT_CMDMODE(0, "make-script", &command,
+			N_("make rebase script"), MAKE_SCRIPT),
+		OPT_CMDMODE(0, "shorten-ids", &command,
+			N_("shorten SHA-1s in the todo list"), SHORTEN_SHA1S),
+		OPT_CMDMODE(0, "expand-ids", &command,
+			N_("expand SHA-1s in the todo list"), EXPAND_SHA1S),
+		OPT_CMDMODE(0, "check-todo-list", &command,
+			N_("check the todo list"), CHECK_TODO_LIST),
+		OPT_CMDMODE(0, "skip-unnecessary-picks", &command,
+			N_("skip unnecessary picks"), SKIP_UNNECESSARY_PICKS),
+		OPT_CMDMODE(0, "rearrange-squash", &command,
+			N_("rearrange fixup/squash lines"), REARRANGE_SQUASH),
 		OPT_END()
 	};
 
@@ -37,5 +52,17 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		return !!sequencer_continue(&opts);
 	if (command == ABORT && argc == 1)
 		return !!sequencer_remove_state(&opts);
+	if (command == MAKE_SCRIPT && argc > 1)
+		return !!sequencer_make_script(keep_empty, stdout, argc, argv);
+	if (command == SHORTEN_SHA1S && argc == 1)
+		return !!transform_todo_ids(1);
+	if (command == EXPAND_SHA1S && argc == 1)
+		return !!transform_todo_ids(0);
+	if (command == CHECK_TODO_LIST && argc == 1)
+		return !!check_todo_list();
+	if (command == SKIP_UNNECESSARY_PICKS && argc == 1)
+		return !!skip_unnecessary_picks();
+	if (command == REARRANGE_SQUASH && argc == 1)
+		return !!rearrange_squash();
 	usage_with_options(builtin_rebase_helper_usage, options);
 }
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 29b7e88..2563dc5 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -155,13 +155,13 @@ reschedule_last_action () {
 append_todo_help () {
 	gettext "
 Commands:
- p, pick = use commit
- r, reword = use commit, but edit the commit message
- e, edit = use commit, but stop for amending
- s, squash = use commit, but meld into previous commit
- f, fixup = like \"squash\", but discard this commit's log message
- x, exec = run command (the rest of the line) using shell
- d, drop = remove commit
+p, pick = use commit
+r, reword = use commit, but edit the commit message
+e, edit = use commit, but stop for amending
+s, squash = use commit, but meld into previous commit
+f, fixup = like \"squash\", but discard this commit's log message
+x, exec = run command (the rest of the line) using shell
+d, drop = remove commit
 
 These lines can be re-ordered; they are executed from top to bottom.
 " | git stripspace --comment-lines >>"$todo"
@@ -714,154 +714,12 @@ do_rest () {
 	done
 }
 
-# skip picking commits whose parents are unchanged
-skip_unnecessary_picks () {
-	fd=3
-	while read -r command rest
-	do
-		# fd=3 means we skip the command
-		case "$fd,$command" in
-		3,pick|3,p)
-			# pick a commit whose parent is current $onto -> skip
-			sha1=${rest%% *}
-			case "$(git rev-parse --verify --quiet "$sha1"^)" in
-			"$onto"*)
-				onto=$sha1
-				;;
-			*)
-				fd=1
-				;;
-			esac
-			;;
-		3,"$comment_char"*|3,)
-			# copy comments
-			;;
-		*)
-			fd=1
-			;;
-		esac
-		printf '%s\n' "$command${rest:+ }$rest" >&$fd
-	done <"$todo" >"$todo.new" 3>>"$done" &&
-	mv -f "$todo".new "$todo" &&
-	case "$(peek_next_command)" in
-	squash|s|fixup|f)
-		record_in_rewritten "$onto"
-		;;
-	esac ||
-		die "$(gettext "Could not skip unnecessary pick commands")"
-}
-
-transform_todo_ids () {
-	while read -r command rest
-	do
-		case "$command" in
-		"$comment_char"* | exec)
-			# Be careful for oddball commands like 'exec'
-			# that do not have a SHA-1 at the beginning of $rest.
-			;;
-		*)
-			sha1=$(git rev-parse --verify --quiet "$@" ${rest%%[	 ]*}) &&
-			rest="$sha1 ${rest#*[	 ]}"
-			;;
-		esac
-		printf '%s\n' "$command${rest:+ }$rest"
-	done <"$todo" >"$todo.new" &&
-	mv -f "$todo.new" "$todo"
-}
-
 expand_todo_ids() {
-	transform_todo_ids
+	git rebase--helper --expand-ids
 }
 
 collapse_todo_ids() {
-	transform_todo_ids --short
-}
-
-# Rearrange the todo list that has both "pick sha1 msg" and
-# "pick sha1 fixup!/squash! msg" appears in it so that the latter
-# comes immediately after the former, and change "pick" to
-# "fixup"/"squash".
-#
-# Note that if the config has specified a custom instruction format
-# each log message will be re-retrieved in order to normalize the
-# autosquash arrangement
-rearrange_squash () {
-	# extract fixup!/squash! lines and resolve any referenced sha1's
-	while read -r pick sha1 message
-	do
-		test -z "${format}" || message=$(git log -n 1 --format="%s" ${sha1})
-		case "$message" in
-		"squash! "*|"fixup! "*)
-			action="${message%%!*}"
-			rest=$message
-			prefix=
-			# skip all squash! or fixup! (but save for later)
-			while :
-			do
-				case "$rest" in
-				"squash! "*|"fixup! "*)
-					prefix="$prefix${rest%%!*},"
-					rest="${rest#*! }"
-					;;
-				*)
-					break
-					;;
-				esac
-			done
-			printf '%s %s %s %s\n' "$sha1" "$action" "$prefix" "$rest"
-			# if it's a single word, try to resolve to a full sha1 and
-			# emit a second copy. This allows us to match on both message
-			# and on sha1 prefix
-			if test "${rest#* }" = "$rest"; then
-				fullsha="$(git rev-parse -q --verify "$rest" 2>/dev/null)"
-				if test -n "$fullsha"; then
-					# prefix the action to uniquely identify this line as
-					# intended for full sha1 match
-					echo "$sha1 +$action $prefix $fullsha"
-				fi
-			fi
-		esac
-	done >"$1.sq" <"$1"
-	test -s "$1.sq" || return
-
-	used=
-	while read -r pick sha1 message
-	do
-		case " $used" in
-		*" $sha1 "*) continue ;;
-		esac
-		printf '%s\n' "$pick $sha1 $message"
-		test -z "${format}" || message=$(git log -n 1 --format="%s" ${sha1})
-		used="$used$sha1 "
-		while read -r squash action msg_prefix msg_content
-		do
-			case " $used" in
-			*" $squash "*) continue ;;
-			esac
-			emit=0
-			case "$action" in
-			+*)
-				action="${action#+}"
-				# full sha1 prefix test
-				case "$msg_content" in "$sha1"*) emit=1;; esac ;;
-			*)
-				# message prefix test
-				case "$message" in "$msg_content"*) emit=1;; esac ;;
-			esac
-			if test $emit = 1; then
-				if test -n "${format}"
-				then
-					msg_content=$(git log -n 1 --format="${format}" ${squash})
-				else
-					msg_content="$(echo "$msg_prefix" | sed "s/,/! /g")$msg_content"
-				fi
-				printf '%s\n' "$action $squash $msg_content"
-				used="$used$squash "
-			fi
-		done <"$1.sq"
-	done >"$1.rearranged" <"$1"
-	cat "$1.rearranged" >"$1"
-	rm -f "$1.sq" "$1.rearranged"
+	git rebase--helper --shorten-ids
 }
 
 # Add commands after a pick or after a squash/fixup serie
@@ -885,96 +743,6 @@ add_exec_commands () {
 	mv "$1.new" "$1"
 }
 
-# Check if the SHA-1 passed as an argument is a
-# correct one, if not then print $2 in "$todo".badsha
-# $1: the SHA-1 to test
-# $2: the line number of the input
-# $3: the input filename
-check_commit_sha () {
-	badsha=0
-	if test -z "$1"
-	then
-		badsha=1
-	else
-		sha1_verif="$(git rev-parse --verify --quiet $1^{commit})"
-		if test -z "$sha1_verif"
-		then
-			badsha=1
-		fi
-	fi
-
-	if test $badsha -ne 0
-	then
-		line="$(sed -n -e "${2}p" "$3")"
-		warn "$(eval_gettext "\
-Warning: the SHA-1 is missing or isn't a commit in the following line:
- - \$line")"
-		warn
-	fi
-
-	return $badsha
-}
-
-# prints the bad commits and bad commands
-# from the todolist in stdin
-check_bad_cmd_and_sha () {
-	retval=0
-	lineno=0
-	while read -r command rest
-	do
-		lineno=$(( $lineno + 1 ))
-		case $command in
-		"$comment_char"*|''|noop|x|exec)
-			# Doesn't expect a SHA-1
-			;;
-		"$cr")
-			# Work around CR left by "read" (e.g. with Git for
-			# Windows' Bash).
-			;;
-		pick|p|drop|d|reword|r|edit|e|squash|s|fixup|f)
-			if ! check_commit_sha "${rest%%[ 	]*}" "$lineno" "$1"
-			then
-				retval=1
-			fi
-			;;
-		*)
-			line="$(sed -n -e "${lineno}p" "$1")"
-			warn "$(eval_gettext "\
-Warning: the command isn't recognized in the following line:
- - \$line")"
-			warn
-			retval=1
-			;;
-		esac
-	done <"$1"
-	return $retval
-}
-
-# Print the list of the SHA-1 of the commits
-# from stdin to stdout
-todo_list_to_sha_list () {
-	git stripspace --strip-comments |
-	while read -r command sha1 rest
-	do
-		case $command in
-		"$comment_char"*|''|noop|x|"exec")
-			;;
-		*)
-			long_sha=$(git rev-list --no-walk "$sha1" 2>/dev/null)
-			printf "%s\n" "$long_sha"
-			;;
-		esac
-	done
-}
-
-# Use warn for each line in stdin
-warn_lines () {
-	while read -r line
-	do
-		warn " - $line"
-	done
-}
-
 # Switch to the branch in $into and notify it in the reflog
 checkout_onto () {
 	GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name"
@@ -989,74 +757,6 @@ get_missing_commit_check_level () {
 	printf '%s' "$check_level" | tr 'A-Z' 'a-z'
 }
 
-# Check if the user dropped some commits by mistake
-# Behaviour determined by rebase.missingCommitsCheck.
-# Check if there is an unrecognized command or a
-# bad SHA-1 in a command.
-check_todo_list () {
-	raise_error=f
-
-	check_level=$(get_missing_commit_check_level)
-
-	case "$check_level" in
-	warn|error)
-		# Get the SHA-1 of the commits
-		todo_list_to_sha_list <"$todo".backup >"$todo".oldsha1
-		todo_list_to_sha_list <"$todo" >"$todo".newsha1
-
-		# Sort the SHA-1 and compare them
-		sort -u "$todo".oldsha1 >"$todo".oldsha1+
-		mv "$todo".oldsha1+ "$todo".oldsha1
-		sort -u "$todo".newsha1 >"$todo".newsha1+
-		mv "$todo".newsha1+ "$todo".newsha1
-		comm -2 -3 "$todo".oldsha1 "$todo".newsha1 >"$todo".miss
-
-		# Warn about missing commits
-		if test -s "$todo".miss
-		then
-			test "$check_level" = error && raise_error=t
-
-			warn "$(gettext "\
-Warning: some commits may have been dropped accidentally.
-Dropped commits (newer to older):")"
-
-			# Make the list user-friendly and display
-			opt="--no-walk=sorted --format=oneline --abbrev-commit --stdin"
-			git rev-list $opt <"$todo".miss | warn_lines
-
-			warn "$(gettext "\
-To avoid this message, use \"drop\" to explicitly remove a commit.
-
-Use 'git config rebase.missingCommitsCheck' to change the level of warnings.
-The possible behaviours are: ignore, warn, error.")"
-			warn
-		fi
-		;;
-	ignore)
-		;;
-	*)
-		warn "$(eval_gettext "Unrecognized setting \$check_level for option rebase.missingCommitsCheck. Ignoring.")"
-		;;
-	esac
-
-	if ! check_bad_cmd_and_sha "$todo"
-	then
-		raise_error=t
-	fi
-
-	if test $raise_error = t
-	then
-		# Checkout before the first commit of the
-		# rebase: this way git rebase --continue
-		# will work correctly as it expects HEAD to be
-		# placed before the commit of the next action
-		checkout_onto
-
-		warn "$(gettext "You can fix this with 'git rebase --edit-todo' and then run 'git rebase --continue'.")"
-		die "$(gettext "Or you can abort the rebase with 'git rebase --abort'.")"
-	fi
-}
-
 # The whole contents of this file is run by dot-sourcing it from
 # inside a shell function.  It used to be that "return"s we see
 # below were not inside any function, and expected to return
@@ -1211,26 +911,27 @@ else
 	revisions=$onto...$orig_head
 	shortrevisions=$shorthead
 fi
-format=$(git config --get rebase.instructionFormat)
-# the 'rev-list .. | sed' requires %m to parse; the instruction requires %H to parse
-git rev-list $merges_option --format="%m%H ${format:-%s}" \
-	--reverse --left-right --topo-order \
-	$revisions ${restrict_revision+^$restrict_revision} | \
-	sed -n "s/^>//p" |
-while read -r sha1 rest
-do
-
-	if test -z "$keep_empty" && is_empty_commit $sha1 && ! is_merge_commit $sha1
-	then
-		comment_out="$comment_char "
-	else
-		comment_out=
-	fi
+if test t != "$preserve_merges"
+then
+	git rebase--helper --make-script ${keep_empty:+--keep-empty} \
+		$revisions ${restrict_revision+^$restrict_revision} >"$todo"
+else
+	format=$(git config --get rebase.instructionFormat)
+	# the 'rev-list .. | sed' requires %m to parse; the instruction requires %H to parse
+	git rev-list $merges_option --format="%m%H ${format:-%s}" \
+		--reverse --left-right --topo-order \
+		$revisions ${restrict_revision+^$restrict_revision} | \
+		sed -n "s/^>//p" |
+	while read -r sha1 rest
+	do
+
+		if test -z "$keep_empty" && is_empty_commit $sha1 && ! is_merge_commit $sha1
+		then
+			comment_out="$comment_char "
+		else
+			comment_out=
+		fi
 
-	if test t != "$preserve_merges"
-	then
-		printf '%s\n' "${comment_out}pick $sha1 $rest" >>"$todo"
-	else
 		if test -z "$rebase_root"
 		then
 			preserve=t
@@ -1249,8 +950,8 @@ do
 			touch "$rewritten"/$sha1
 			printf '%s\n' "${comment_out}pick $sha1 $rest" >>"$todo"
 		fi
-	fi
-done
+	done
+fi
 
 # Watch for commits that been dropped by --cherry-pick
 if test t = "$preserve_merges"
@@ -1280,7 +981,7 @@ then
 fi
 
 test -s "$todo" || echo noop >> "$todo"
-test -n "$autosquash" && rearrange_squash "$todo"
+test -z "$autosquash" || git rebase--helper --rearrange-squash || exit
 test -n "$cmd" && add_exec_commands "$todo"
 
 todocount=$(git stripspace --strip-comments <"$todo" | wc -l)
@@ -1316,11 +1017,17 @@ git_sequence_editor "$todo" ||
 has_action "$todo" ||
 	return 2
 
-check_todo_list
+git rebase--helper --check-todo-list || {
+	ret=$?
+	checkout_onto
+	exit $ret
+}
 
 expand_todo_ids
 
-test -d "$rewritten" || test -n "$force_rebase" || skip_unnecessary_picks
+test -d "$rewritten" || test -n "$force_rebase" ||
+onto="$(git rebase--helper --skip-unnecessary-picks)" ||
+die "Could not skip unnecessary pick commands"
 
 checkout_onto
 if test -z "$rebase_root" && test ! -d "$rewritten"
diff --git a/sequencer.c b/sequencer.c
index 60636ce..b8c1e87 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -20,6 +20,7 @@
 #include "trailer.h"
 #include "log-tree.h"
 #include "wt-status.h"
+#include "hashmap.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
@@ -2435,3 +2436,533 @@ void append_signoff(struct strbuf *msgbuf, int ignore_footer, unsigned flag)
 
 	strbuf_release(&sob);
 }
+
+int sequencer_make_script(int keep_empty, FILE *out,
+		int argc, const char **argv)
+{
+	char *format = NULL;
+	struct pretty_print_context pp = {0};
+	struct strbuf buf = STRBUF_INIT;
+	struct rev_info revs;
+	struct commit *commit;
+
+	init_revisions(&revs, NULL);
+	revs.verbose_header = 1;
+	revs.max_parents = 1;
+	revs.cherry_pick = 1;
+	revs.limited = 1;
+	revs.reverse = 1;
+	revs.right_only = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.topo_order = 1;
+
+	revs.pretty_given = 1;
+	git_config_get_string("rebase.instructionFormat", &format);
+	if (!format || !*format) {
+		free(format);
+		format = xstrdup("%s");
+	}
+	get_commit_format(format, &revs);
+	free(format);
+	pp.fmt = revs.commit_format;
+	pp.output_encoding = get_log_output_encoding();
+
+	if (setup_revisions(argc, argv, &revs, NULL) > 1)
+		return error(_("make_script: unhandled options"));
+
+	if (prepare_revision_walk(&revs) < 0)
+		return error(_("make_script: error preparing revisions"));
+
+	while ((commit = get_revision(&revs))) {
+		strbuf_reset(&buf);
+		if (!keep_empty && is_original_commit_empty(commit))
+			strbuf_addf(&buf, "%c ", comment_line_char);
+		strbuf_addf(&buf, "pick %s ", oid_to_hex(&commit->object.oid));
+		pretty_print_commit(&pp, commit, &buf);
+		strbuf_addch(&buf, '\n');
+		fputs(buf.buf, out);
+	}
+	strbuf_release(&buf);
+	return 0;
+}
+
+
+int transform_todo_ids(int shorten_ids)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int fd, res, i;
+	FILE *out;
+
+	strbuf_reset(&todo_list.buf);
+	fd = open(todo_file, O_RDONLY);
+	if (fd < 0)
+		return error_errno(_("could not open '%s'"), todo_file);
+	if (strbuf_read(&todo_list.buf, fd, 0) < 0) {
+		close(fd);
+		return error(_("could not read '%s'."), todo_file);
+	}
+	close(fd);
+
+	res = parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	if (res) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	out = fopen(todo_file, "w");
+	if (!out) {
+		todo_list_release(&todo_list);
+		return error(_("unable to open '%s' for writing"), todo_file);
+	}
+	for (i = 0; i < todo_list.nr; i++) {
+		struct todo_item *item = todo_list.items + i;
+		int bol = item->offset_in_buf;
+		const char *p = todo_list.buf.buf + bol;
+		int eol = i + 1 < todo_list.nr ?
+			todo_list.items[i + 1].offset_in_buf :
+			todo_list.buf.len;
+
+		if (item->command >= TODO_EXEC && item->command != TODO_DROP)
+			fwrite(p, eol - bol, 1, out);
+		else {
+			const char *id = shorten_ids ?
+				short_commit_name(item->commit) :
+				oid_to_hex(&item->commit->object.oid);
+			int len;
+
+			p += strspn(p, " \t"); /* left-trim command */
+			len = strcspn(p, " \t"); /* length of command */
+
+			fprintf(out, "%.*s %s %.*s\n",
+				len, p, id, item->arg_len, item->arg);
+		}
+	}
+	fclose(out);
+	todo_list_release(&todo_list);
+	return 0;
+}
+
+enum check_level {
+	CHECK_IGNORE = 0, CHECK_WARN, CHECK_ERROR
+};
+
+static enum check_level get_missing_commit_check_level(void)
+{
+	const char *value;
+
+	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
+			!strcasecmp("ignore", value))
+		return CHECK_IGNORE;
+	if (!strcasecmp("warn", value))
+		return CHECK_WARN;
+	if (!strcasecmp("error", value))
+		return CHECK_ERROR;
+	warning(_("unrecognized setting %s for option"
+		  "rebase.missingCommitsCheck. Ignoring."), value);
+	return CHECK_IGNORE;
+}
+
+/*
+ * Check if the user dropped some commits by mistake
+ * Behaviour determined by rebase.missingCommitsCheck.
+ * Check if there is an unrecognized command or a
+ * bad SHA-1 in a command.
+ */
+int check_todo_list(void)
+{
+	enum check_level check_level = get_missing_commit_check_level();
+	struct strbuf todo_file = STRBUF_INIT;
+	struct todo_list todo_list = TODO_LIST_INIT;
+	struct strbuf missing = STRBUF_INIT;
+	int advise_to_edit_todo = 0, res = 0, fd, i;
+
+	strbuf_addstr(&todo_file, rebase_path_todo());
+	fd = open(todo_file.buf, O_RDONLY);
+	if (fd < 0) {
+		res = error_errno(_("could not open '%s'"), todo_file.buf);
+		goto leave_check;
+	}
+	if (strbuf_read(&todo_list.buf, fd, 0) < 0) {
+		close(fd);
+		res = error(_("could not read '%s'."), todo_file.buf);
+		goto leave_check;
+	}
+	close(fd);
+	advise_to_edit_todo = res =
+		parse_insn_buffer(todo_list.buf.buf, &todo_list);
+
+	if (res || check_level == CHECK_IGNORE)
+		goto leave_check;
+
+	/* Mark the commits in git-rebase-todo as seen */
+	for (i = 0; i < todo_list.nr; i++) {
+		struct commit *commit = todo_list.items[i].commit;
+		if (commit)
+			commit->util = (void *)1;
+	}
+
+	todo_list_release(&todo_list);
+	strbuf_addstr(&todo_file, ".backup");
+	fd = open(todo_file.buf, O_RDONLY);
+	if (fd < 0) {
+		res = error_errno(_("could not open '%s'"), todo_file.buf);
+		goto leave_check;
+	}
+	if (strbuf_read(&todo_list.buf, fd, 0) < 0) {
+		close(fd);
+		res = error(_("could not read '%s'."), todo_file.buf);
+		goto leave_check;
+	}
+	close(fd);
+	strbuf_release(&todo_file);
+	res = !!parse_insn_buffer(todo_list.buf.buf, &todo_list);
+
+	/* Find commits in git-rebase-todo.backup yet unseen */
+	for (i = todo_list.nr - 1; i >= 0; i--) {
+		struct todo_item *item = todo_list.items + i;
+		struct commit *commit = item->commit;
+		if (commit && !commit->util) {
+			strbuf_addf(&missing, " - %s %.*s\n",
+				    short_commit_name(commit),
+				    item->arg_len, item->arg);
+			commit->util = (void *)1;
+		}
+	}
+
+	/* Warn about missing commits */
+	if (!missing.len)
+		goto leave_check;
+
+	if (check_level == CHECK_ERROR)
+		advise_to_edit_todo = res = 1;
+
+	fprintf(stderr,
+		_("Warning: some commits may have been dropped accidentally.\n"
+		"Dropped commits (newer to older):\n"));
+
+	/* Make the list user-friendly and display */
+	fputs(missing.buf, stderr);
+	strbuf_release(&missing);
+
+	fprintf(stderr, _("To avoid this message, use \"drop\" to "
+		"explicitly remove a commit.\n\n"
+		"Use 'git config rebase.missingCommitsCheck' to change "
+		"the level of warnings.\n"
+		"The possible behaviours are: ignore, warn, error.\n\n"));
+
+leave_check:
+	strbuf_release(&todo_file);
+	todo_list_release(&todo_list);
+
+	if (advise_to_edit_todo)
+		fprintf(stderr,
+			_("You can fix this with 'git rebase --edit-todo' "
+			  "and then run 'git rebase --continue'.\n"
+			  "Or you can abort the rebase with 'git rebase"
+			  " --abort'.\n"));
+
+	return res;
+}
+
+/* skip picking commits whose parents are unchanged */
+int skip_unnecessary_picks(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct strbuf buf = STRBUF_INIT;
+	struct todo_list todo_list = TODO_LIST_INIT;
+	struct object_id onto_oid, *oid = &onto_oid, *parent_oid;
+	int fd, i;
+
+	if (!read_oneliner(&buf, rebase_path_onto(), 0))
+		return error(_("could not read 'onto'"));
+	if (get_oid(buf.buf, &onto_oid)) {
+		strbuf_release(&buf);
+		return error(_("need a HEAD to fixup"));
+	}
+	strbuf_release(&buf);
+
+	fd = open(todo_file, O_RDONLY);
+	if (fd < 0) {
+		return error_errno(_("could not open '%s'"), todo_file);
+	}
+	if (strbuf_read(&todo_list.buf, fd, 0) < 0) {
+		close(fd);
+		return error(_("could not read '%s'."), todo_file);
+	}
+	close(fd);
+	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+		todo_list_release(&todo_list);
+		return -1;
+	}
+
+	for (i = 0; i < todo_list.nr; i++) {
+		struct todo_item *item = todo_list.items + i;
+
+		if (item->command >= TODO_NOOP)
+			continue;
+		if (item->command != TODO_PICK)
+			break;
+		if (parse_commit(item->commit)) {
+			todo_list_release(&todo_list);
+			return error(_("could not parse commit '%s'"),
+				oid_to_hex(&item->commit->object.oid));
+		}
+		if (!item->commit->parents)
+			break; /* root commit */
+		if (item->commit->parents->next)
+			break; /* merge commit */
+		parent_oid = &item->commit->parents->item->object.oid;
+		if (hashcmp(parent_oid->hash, oid->hash))
+			break;
+		oid = &item->commit->object.oid;
+	}
+	if (i > 0) {
+		int offset = i < todo_list.nr ?
+			todo_list.items[i].offset_in_buf : todo_list.buf.len;
+		const char *done_path = rebase_path_done();
+
+		fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
+		if (fd < 0) {
+			error_errno(_("could not open '%s' for writing"),
+				    done_path);
+			todo_list_release(&todo_list);
+			return -1;
+		}
+		if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
+			error_errno(_("could not write to '%s'"), done_path);
+			todo_list_release(&todo_list);
+			close(fd);
+			return -1;
+		}
+		close(fd);
+
+		fd = open(rebase_path_todo(), O_WRONLY, 0666);
+		if (fd < 0) {
+			error_errno(_("could not open '%s' for writing"),
+				    rebase_path_todo());
+			todo_list_release(&todo_list);
+			return -1;
+		}
+		if (write_in_full(fd, todo_list.buf.buf + offset,
+				todo_list.buf.len - offset) < 0) {
+			error_errno(_("could not write to '%s'"),
+				    rebase_path_todo());
+			close(fd);
+			todo_list_release(&todo_list);
+			return -1;
+		}
+		if (ftruncate(fd, todo_list.buf.len - offset) < 0) {
+			error_errno(_("could not truncate '%s'"),
+				    rebase_path_todo());
+			todo_list_release(&todo_list);
+			close(fd);
+			return -1;
+		}
+		close(fd);
+
+		todo_list.current = i;
+		if (is_fixup(peek_command(&todo_list, 0)))
+			record_in_rewritten(oid, peek_command(&todo_list, 0));
+	}
+
+	todo_list_release(&todo_list);
+	printf("%s\n", oid_to_hex(oid));
+
+	return 0;
+}
+
+struct subject2item_entry {
+	struct hashmap_entry entry;
+	int i;
+	char subject[FLEX_ARRAY];
+};
+
+static int subject2item_cmp(const void *fndata,
+			    const struct subject2item_entry *a,
+			    const struct subject2item_entry *b, const void *key)
+{
+	return key ? strcmp(a->subject, key) : strcmp(a->subject, b->subject);
+}
+
+/*
+ * Rearrange the todo list that has both "pick commit-id msg" and "pick
+ * commit-id fixup!/squash! msg" in it so that the latter is put immediately
+ * after the former, and change "pick" to "fixup"/"squash".
+ *
+ * Note that if the config has specified a custom instruction format, each log
+ * message will have to be retrieved from the commit (as the oneline in the
+ * script cannot be trusted) in order to normalize the autosquash arrangement.
+ */
+int rearrange_squash(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	struct hashmap subject2item;
+	int res = 0, rearranged = 0, *next, *tail, fd, i;
+	char **subjects;
+
+	fd = open(todo_file, O_RDONLY);
+	if (fd < 0)
+		return error_errno(_("could not open '%s'"), todo_file);
+	if (strbuf_read(&todo_list.buf, fd, 0) < 0) {
+		close(fd);
+		return error(_("could not read '%s'."), todo_file);
+	}
+	close(fd);
+	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+		todo_list_release(&todo_list);
+		return -1;
+	}
+
+	/*
+	 * The hashmap maps onelines to the respective todo list index.
+	 *
+	 * If any items need to be rearranged, the next[i] value will indicate
+	 * which item was moved directly after the i'th.
+	 *
+	 * In that case, last[i] will indicate the index of the latest item to
+	 * be moved to appear after the i'th.
+	 */
+	hashmap_init(&subject2item, (hashmap_cmp_fn) subject2item_cmp,
+		     NULL, todo_list.nr);
+	ALLOC_ARRAY(next, todo_list.nr);
+	ALLOC_ARRAY(tail, todo_list.nr);
+	ALLOC_ARRAY(subjects, todo_list.nr);
+	for (i = 0; i < todo_list.nr; i++) {
+		struct strbuf buf = STRBUF_INIT;
+		struct todo_item *item = todo_list.items + i;
+		const char *commit_buffer, *subject, *p;
+		size_t subject_len;
+		int i2 = -1;
+		struct subject2item_entry *entry;
+
+		next[i] = tail[i] = -1;
+		if (item->command >= TODO_EXEC) {
+			subjects[i] = NULL;
+			continue;
+		}
+
+		if (is_fixup(item->command)) {
+			todo_list_release(&todo_list);
+			return error(_("the script was already rearranged."));
+		}
+
+		item->commit->util = item;
+
+		parse_commit(item->commit);
+		commit_buffer = get_commit_buffer(item->commit, NULL);
+		find_commit_subject(commit_buffer, &subject);
+		format_subject(&buf, subject, " ");
+		subject = subjects[i] = strbuf_detach(&buf, &subject_len);
+		unuse_commit_buffer(item->commit, commit_buffer);
+		if ((skip_prefix(subject, "fixup! ", &p) ||
+		     skip_prefix(subject, "squash! ", &p))) {
+			struct commit *commit2;
+
+			for (;;) {
+				while (isspace(*p))
+					p++;
+				if (!skip_prefix(p, "fixup! ", &p) &&
+				    !skip_prefix(p, "squash! ", &p))
+					break;
+			}
+
+			if ((entry = hashmap_get_from_hash(&subject2item,
+							   strhash(p), p)))
+				/* found by title */
+				i2 = entry->i;
+			else if (!strchr(p, ' ') &&
+				 (commit2 =
+				  lookup_commit_reference_by_name(p)) &&
+				 commit2->util)
+				/* found by commit name */
+				i2 = (struct todo_item *)commit2->util
+					- todo_list.items;
+			else {
+				/* copy can be a prefix of the commit subject */
+				for (i2 = 0; i2 < i; i2++)
+					if (subjects[i2] &&
+					    starts_with(subjects[i2], p))
+						break;
+				if (i2 == i)
+					i2 = -1;
+			}
+		}
+		if (i2 >= 0) {
+			rearranged = 1;
+			todo_list.items[i].command =
+				starts_with(subject, "fixup!") ?
+				TODO_FIXUP : TODO_SQUASH;
+			if (next[i2] < 0)
+				next[i2] = i;
+			else
+				next[tail[i2]] = i;
+			tail[i2] = i;
+		} else if (!hashmap_get_from_hash(&subject2item,
+						strhash(subject), subject)) {
+			FLEX_ALLOC_MEM(entry, subject, subject, subject_len);
+			entry->i = i;
+			hashmap_entry_init(entry, strhash(entry->subject));
+			hashmap_put(&subject2item, entry);
+		}
+	}
+
+	if (rearranged) {
+		struct strbuf buf = STRBUF_INIT;
+
+		for (i = 0; i < todo_list.nr; i++) {
+			enum todo_command command = todo_list.items[i].command;
+			int cur = i;
+
+			/*
+			 * Initially, all commands are 'pick's. If it is a
+			 * fixup or a squash now, we have rearranged it.
+			 */
+			if (is_fixup(command))
+				continue;
+
+			while (cur >= 0) {
+				int offset = todo_list.items[cur].offset_in_buf;
+				int end_offset = cur + 1 < todo_list.nr ?
+					todo_list.items[cur + 1].offset_in_buf :
+					todo_list.buf.len;
+				char *bol = todo_list.buf.buf + offset;
+				char *eol = todo_list.buf.buf + end_offset;
+
+				/* replace 'pick', by 'fixup' or 'squash' */
+				command = todo_list.items[cur].command;
+				if (is_fixup(command)) {
+					strbuf_addstr(&buf,
+						todo_command_info[command].str);
+					bol += strcspn(bol, " \t");
+				}
+
+				strbuf_add(&buf, bol, eol - bol);
+
+				cur = next[cur];
+			}
+		}
+
+		fd = open(todo_file, O_WRONLY);
+		if (fd < 0)
+			res = error_errno(_("could not open '%s'"), todo_file);
+		else if (write(fd, buf.buf, buf.len) < 0)
+			res = error_errno(_("could not read '%s'."), todo_file);
+		else if (ftruncate(fd, buf.len) < 0)
+			res = error_errno(_("could not finish '%s'"),
+					   todo_file);
+		close(fd);
+		strbuf_release(&buf);
+	}
+
+	free(next);
+	free(tail);
+	for (i = 0; i < todo_list.nr; i++)
+		free(subjects[i]);
+	free(subjects);
+	hashmap_free(&subject2item, 1);
+	todo_list_release(&todo_list);
+
+	return res;
+}
diff --git a/sequencer.h b/sequencer.h
index f885b68..6f3d3df 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -45,6 +45,14 @@ int sequencer_continue(struct replay_opts *opts);
 int sequencer_rollback(struct replay_opts *opts);
 int sequencer_remove_state(struct replay_opts *opts);
 
+int sequencer_make_script(int keep_empty, FILE *out,
+		int argc, const char **argv);
+
+int transform_todo_ids(int shorten_ids);
+int check_todo_list(void);
+int skip_unnecessary_picks(void);
+int rearrange_squash(void);
+
 extern const char sign_off_header[];
 
 void append_signoff(struct strbuf *msgbuf, int ignore_footer, unsigned flag);
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 37821d2..3704dbb 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1249,20 +1249,13 @@ test_expect_success 'rebase -i respects rebase.missingCommitsCheck = error' '
 	test B = $(git cat-file commit HEAD^ | sed -ne \$p)
 '
 
-cat >expect <<EOF
-Warning: the command isn't recognized in the following line:
- - badcmd $(git rev-list --oneline -1 master~1)
-
-You can fix this with 'git rebase --edit-todo' and then run 'git rebase --continue'.
-Or you can abort the rebase with 'git rebase --abort'.
-EOF
-
 test_expect_success 'static check of bad command' '
 	rebase_setup_and_clean bad-cmd &&
 	set_fake_editor &&
 	test_must_fail env FAKE_LINES="1 2 3 bad 4 5" \
 		git rebase -i --root 2>actual &&
-	test_i18ncmp expect actual &&
+	test_i18ngrep "badcmd $(git rev-list --oneline -1 master~1)" actual &&
+	test_i18ngrep "You can fix this with .git rebase --edit-todo.." actual &&
 	FAKE_LINES="1 2 3 drop 4 5" git rebase --edit-todo &&
 	git rebase --continue &&
 	test E = $(git cat-file commit HEAD | sed -ne \$p) &&
@@ -1284,20 +1277,13 @@ test_expect_success 'tabs and spaces are accepted in the todolist' '
 	test E = $(git cat-file commit HEAD | sed -ne \$p)
 '
 
-cat >expect <<EOF
-Warning: the SHA-1 is missing or isn't a commit in the following line:
- - edit XXXXXXX False commit
-
-You can fix this with 'git rebase --edit-todo' and then run 'git rebase --continue'.
-Or you can abort the rebase with 'git rebase --abort'.
-EOF
-
 test_expect_success 'static check of bad SHA-1' '
 	rebase_setup_and_clean bad-sha &&
 	set_fake_editor &&
 	test_must_fail env FAKE_LINES="1 2 edit fakesha 3 4 5 #" \
 		git rebase -i --root 2>actual &&
-	test_i18ncmp expect actual &&
+	test_i18ngrep "edit XXXXXXX False commit" actual &&
+	test_i18ngrep "You can fix this with .git rebase --edit-todo.." actual &&
 	FAKE_LINES="1 2 4 5 6" git rebase --edit-todo &&
 	git rebase --continue &&
 	test E = $(git cat-file commit HEAD | sed -ne \$p)
diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index 5848949..e364c12 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -271,6 +271,18 @@ test_expect_success C_LOCALE_OUTPUT 'autosquash with custom inst format' '
 	test 2 = $(git cat-file commit HEAD^ | grep squash | wc -l)
 '
 
+test_expect_success 'autosquash with empty custom instructionFormat' '
+	git reset --hard base &&
+	test_commit empty-instructionFormat-test &&
+	(
+		set_cat_todo_editor &&
+		test_must_fail git -c rebase.instructionFormat= \
+			rebase --autosquash  --force -i HEAD^ >actual &&
+		git log -1 --format="pick %h %s" >expect &&
+		test_cmp expect actual
+	)
+'
+
 set_backup_editor () {
 	write_script backup-editor.sh <<-\EOF
 	cp "$1" .git/backup-"$(basename "$1")"
@@ -278,7 +290,7 @@ set_backup_editor () {
 	test_set_editor "$PWD/backup-editor.sh"
 }
 
-test_expect_failure 'autosquash with multiple empty patches' '
+test_expect_success 'autosquash with multiple empty patches' '
 	test_tick &&
 	git commit --allow-empty -m "empty" &&
 	test_tick &&
@@ -304,4 +316,18 @@ test_expect_success 'extra spaces after fixup!' '
 	test $base = $parent
 '
 
+test_expect_success 'wrapped original subject' '
+	if test -d .git/rebase-merge; then git rebase --abort; fi &&
+	base=$(git rev-parse HEAD) &&
+	echo "wrapped subject" >wrapped &&
+	git add wrapped &&
+	test_tick &&
+	git commit --allow-empty -m "$(printf "To\nfixup")" &&
+	test_tick &&
+	git commit --allow-empty -m "fixup! To fixup" &&
+	git rebase -i --autosquash --keep-empty HEAD~2 &&
+	parent=$(git rev-parse HEAD^) &&
+	test $base = $parent
+'
+
 test_done