[PATCH v1 02/19] rebase -i: allow rewording an empty commit without complaints

The to-do list command `reword` replays a commit like `pick` but lets
the user also edit the commit's log message. If `--keep-empty` is
passed as option to git-rebase--interactive, empty commits ought to
be replayed without complaints. However, if the users chooses to
reword an empty commit by changing the respective to-do list entry
from

    pick fa1afe1 Empty commit

to

    reword fa1afe1 Empty commit

, then git-rebase--interactive suddenly fails to replay the empty
commit. This is especially counterintuitive because `reword` is
thought of as a `pick` that alters the log message in some way but
nothing more and the unchanged to-do list entry would not fail.

Handle `reword` by cherry-picking the named commit and editing the
log message using

    git commit --allow-empty --amend

instead of

    git commit --amend.

Add test.

Signed-off-by: Fabian Ruch <redacted>
---
 git-rebase--interactive.sh    | 2 +-
 t/t3404-rebase-interactive.sh | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index e733d7f..689400e 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh

@@ -504,7 +504,7 @@ do_next () {
 
 		mark_action_done
 		do_pick $sha1 "$rest"
-		git commit --amend --no-post-rewrite ${gpg_sign_opt:+"$gpg_sign_opt"} || {
+		git commit --allow-empty --amend --no-post-rewrite ${gpg_sign_opt:+"$gpg_sign_opt"} || {
 			warn "Could not amend commit after successfully picking $sha1... $rest"
 			exit_with_patch $sha1 1
 		}

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 8197ed2..9931143 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh

@@ -75,6 +75,14 @@ test_expect_success 'rebase --keep-empty' '
 	test_line_count = 6 actual
 '
 
+test_expect_success 'rebase --keep-empty' '
+	git checkout emptybranch &&
+	set_fake_editor &&
+	FAKE_LINES="1 reword 2" git rebase --keep-empty -i HEAD~2 &&
+	git log --oneline >actual &&
+	test_line_count = 6 actual
+'
+
 test_expect_success 'rebase -i with the exec command' '
 	git checkout master &&
 	(

-- 
2.0.1