Teach 'rebase -i' the command "reword"

Make it easier to edit just the commit message for a commit
using 'git rebase -i' by introducing the "reword" command.

Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -368,14 +368,17 @@ By replacing the command "pick" with the command "edit", you can tell
 the files and/or the commit message, amend the commit, and continue
 rebasing.
 
+If you just want to edit the commit message for a commit, replace the
+command "pick" with the command "reword".
+
 If you want to fold two or more commits into one, replace the command
 "pick" with "squash" for the second and subsequent commit.  If the
 commits had different authors, it will attribute the squashed commit to
 the author of the first commit.
 
-In both cases, or when a "pick" does not succeed (because of merge
-errors), the loop will stop to let you fix things, and you can continue
-the loop with `git rebase --continue`.
+'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--interactive.sh

@@ -340,6 +340,14 @@ do_next () {
 		pick_one $sha1 ||
 			die_with_patch $sha1 "Could not apply $sha1... $rest"
 		;;
+	reword|r)
+		comment_for_reflog reword
+
+		mark_action_done
+		pick_one $sha1 ||
+			die_with_patch $sha1 "Could not apply $sha1... $rest"
+		output git commit --amend
+		;;
 	edit|e)
 		comment_for_reflog edit
 
@@ -752,6 +760,7 @@ first and then run 'git rebase --continue' again."
 #
 # 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
 #

t/lib-rebase.sh

@@ -9,8 +9,8 @@
 #
 #	"[<lineno1>] [<lineno2>]..."
 #
-#   If a line number is prefixed with "squash" or "edit", the respective line's
-#   command will be replaced with the specified one.
+#   If a line number is prefixed with "squash", "edit", or "reword", the
+#   respective line's command will be replaced with the specified one.
 
 set_fake_editor () {
 	echo "#!$SHELL_PATH" >fake-editor.sh
@@ -32,7 +32,7 @@ cat "$1".tmp
 action=pick
 for line in $FAKE_LINES; do
 	case $line in
-	squash|edit)
+	squash|edit|reword)
 		action="$line";;
 	*)
 		echo sed -n "${line}s/^pick/$action/p"

t/t3404-rebase-interactive.sh

@@ -470,4 +470,18 @@ test_expect_success 'avoid unnecessary reset' '
 	test 123456789 = $MTIME
 '
 
+test_expect_success 'reword' '
+	git checkout -b reword-branch master &&
+	FAKE_LINES="1 2 3 reword 4" FAKE_COMMIT_MESSAGE="E changed" git rebase -i A &&
+	git show HEAD | grep "E changed" &&
+	test $(git rev-parse master) != $(git rev-parse HEAD) &&
+	test $(git rev-parse master^) = $(git rev-parse HEAD^) &&
+	FAKE_LINES="1 2 reword 3 4" FAKE_COMMIT_MESSAGE="D changed" git rebase -i A &&
+	git show HEAD^ | grep "D changed" &&
+	FAKE_LINES="reword 1 2 3 4" FAKE_COMMIT_MESSAGE="B changed" git rebase -i A &&
+	git show HEAD~3 | grep "B changed" &&
+	FAKE_LINES="1 reword 2 3 4" FAKE_COMMIT_MESSAGE="C changed" git rebase -i A &&
+	git show HEAD~2 | grep "C changed"
+'
+
 test_done