rebase -i --autosquash: auto-squash commits

Teach a new option, --autosquash, to the interactive rebase.
When the commit log message begins with "!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 come right after the commit to be modified, and change
the action of the moved commit from pick to squash.

Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -308,6 +308,16 @@ which makes little sense.
 	root commits will be rewritten to have <newbase> as parent
 	instead.
 
+--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 quashing come right after the
+	commit to be modified, and change the action of the moved
+	commit from `pick` to `squash` (or `fixup`).
++
+This option is only valid when '--interactive' option is used.
+
 include::merge-strategies.txt[]
 
 NOTES

git-rebase--interactive.sh

@@ -28,6 +28,7 @@ abort              abort rebasing process and restore original branch
 skip               skip current patch and continue rebasing process
 no-verify          override pre-rebase hook from stopping the operation
 root               rebase all reachable commmits up to the root(s)
+autosquash         move commits that begin with squash!/fixup! under -i
 "
 
 . git-sh-setup
@@ -46,6 +47,7 @@ ONTO=
 VERBOSE=
 OK_TO_SKIP_PRE_REBASE=
 REBASE_ROOT=
+AUTOSQUASH=
 
 GIT_CHERRY_PICK_HELP="  After resolving the conflicts,
 mark the corrected paths with 'git add <paths>', and
@@ -519,6 +521,37 @@ get_saved_options () {
 	test -f "$DOTEST"/rebase-root && REBASE_ROOT=t
 }
 
+# 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".
+rearrange_squash () {
+	sed -n -e 's/^pick \([0-9a-f]*\) \(squash\)! /\1 \2 /p' \
+		-e 's/^pick \([0-9a-f]*\) \(fixup\)! /\1 \2 /p' \
+		"$1" >"$1.sq"
+	test -s "$1.sq" || return
+
+	used=
+	while read pick sha1 message
+	do
+		case " $used" in
+		*" $sha1 "*) continue ;;
+		esac
+		echo "$pick $sha1 $message"
+		while read squash action msg
+		do
+			case "$message" in
+			"$msg"*)
+				echo "$action $squash $action! $msg"
+				used="$used$squash "
+				;;
+			esac
+		done <"$1.sq"
+	done >"$1.rearranged" <"$1"
+	cat "$1.rearranged" >"$1"
+	rm -f "$1.sq" "$1.rearranged"
+}
+
 while test $# != 0
 do
 	case "$1" in
@@ -624,6 +657,9 @@ first and then run 'git rebase --continue' again."
 	--root)
 		REBASE_ROOT=t
 		;;
+	--autosquash)
+		AUTOSQUASH=t
+		;;
 	--onto)
 		shift
 		ONTO=$(git rev-parse --verify "$1") ||
@@ -783,6 +819,7 @@ first and then run 'git rebase --continue' again."
 		fi
 
 		test -s "$TODO" || echo noop >> "$TODO"
+		test -n "$AUTOSQUASH" && rearrange_squash "$TODO"
 		cat >> "$TODO" << EOF
 
 # Rebase $SHORTREVISIONS onto $SHORTONTO

t/t3415-rebase-autosquash.sh

@@ -0,0 +1,73 @@
+#!/bin/sh
+
+test_description='auto squash'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo 0 >file0 &&
+	git add . &&
+	test_tick &&
+	git commit -m "initial commit" &&
+	echo 0 >file1 &&
+	echo 2 >file2 &&
+	git add . &&
+	test_tick &&
+	git commit -m "first commit" &&
+	echo 3 >file3 &&
+	git add . &&
+	test_tick &&
+	git commit -m "second commit" &&
+	git tag base
+'
+
+test_expect_success 'auto fixup' '
+	git reset --hard base &&
+	echo 1 >file1 &&
+	git add -u &&
+	test_tick &&
+	git commit -m "fixup! first"
+
+	git tag final-fixup &&
+	test_tick &&
+	git rebase --autosquash -i HEAD^^^ &&
+	git log --oneline >actual &&
+	test 3 = $(wc -l <actual) &&
+	git diff --exit-code final-fixup &&
+	test 1 = "$(git cat-file blob HEAD^:file1)" &&
+	test 1 = $(git cat-file commit HEAD^ | grep first | wc -l)
+'
+
+test_expect_success 'auto squash' '
+	git reset --hard base &&
+	echo 1 >file1 &&
+	git add -u &&
+	test_tick &&
+	git commit -m "squash! first"
+
+	git tag final-squash &&
+	test_tick &&
+	git rebase --autosquash -i HEAD^^^ &&
+	git log --oneline >actual &&
+	test 3 = $(wc -l <actual) &&
+	git diff --exit-code final-squash &&
+	test 1 = "$(git cat-file blob HEAD^:file1)" &&
+	test 2 = $(git cat-file commit HEAD^ | grep first | wc -l)
+'
+
+test_expect_success 'misspelled auto squash' '
+	git reset --hard base &&
+	echo 1 >file1 &&
+	git add -u &&
+	test_tick &&
+	git commit -m "squash! forst"
+	git tag final-missquash &&
+	test_tick &&
+	git rebase --autosquash -i HEAD^^^ &&
+	git log --oneline >actual &&
+	test 4 = $(wc -l <actual) &&
+	git diff --exit-code final-missquash &&
+	test 0 = $(git rev-list final-missquash...HEAD | wc -l)
+'
+
+test_done