[PATCH v2] sequencer: do not squash 'reword' commits when we hit conflicts

[Elijah Newren <newren@gmail.com>]

Ever since commit 18633e1a22 ("rebase -i: use the rebase--helper builtin",
2017-02-09), when a commit marked as 'reword' in an interactive rebase
has conflicts and fails to apply, when the rebase is resumed that commit
will be squashed into its parent with its commit message taken.

The issue can be understood better by looking at commit 56dc3ab04b
("sequencer (rebase -i): implement the 'edit' command", 2017-01-02), which
introduced error_with_patch() for the edit command.  For the edit command,
it needs to stop the rebase whether or not the patch applies cleanly.  If
the patch does apply cleanly, then when it resumes it knows it needs to
amend all changes into the previous commit.  If it does not apply cleanly,
then the changes should not be amended.  Thus, it passes !res (success of
applying the 'edit' commit) to error_with_patch() for the to_amend flag.

The problematic line of code actually came from commit 04efc8b57c
("sequencer (rebase -i): implement the 'reword' command", 2017-01-02).
Note that to get to this point in the code:
  * !!res (i.e. patch application failed)
  * item->command < TODO_SQUASH
  * item->command != TODO_EDIT
  * !is_fixup(item->command) [i.e. not squash or fixup]
So that means this can only be a failed patch application that is either a
pick, revert, or reword.  For any of those cases we want a new commit, so
we should not set the to_amend flag.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
Differences since v1 (Thanks to Eric Sunshine for the suggestions):
  * Add test_when_finished "reset_rebase" calls
  * Remove unnecessary word from description of test

 sequencer.c              |  2 +-
 t/t3423-rebase-reword.sh | 48 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100755 t/t3423-rebase-reword.sh

diff --git a/sequencer.c b/sequencer.c
index cca968043e..9e6d1ee368 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3217,7 +3217,7 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 			} else if (res && is_rebase_i(opts) && item->commit)
 				return res | error_with_patch(item->commit,
 					item->arg, item->arg_len, opts, res,
-					item->command == TODO_REWORD);
+					0);
 		} else if (item->command == TODO_EXEC) {
 			char *end_of_arg = (char *)(item->arg + item->arg_len);
 			int saved = *end_of_arg;
diff --git a/t/t3423-rebase-reword.sh b/t/t3423-rebase-reword.sh
new file mode 100755
index 0000000000..6963750794
--- /dev/null
+++ b/t/t3423-rebase-reword.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+
+test_description='git rebase interactive with rewording'
+
+. ./test-lib.sh
+
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+test_expect_success 'setup' '
+	test_commit master file-1 test &&
+
+	git checkout -b stuff &&
+
+	test_commit feature_a file-2 aaa &&
+	test_commit feature_b file-2 ddd
+'
+
+test_expect_success 'reword without issues functions as intended' '
+	test_when_finished "reset_rebase" &&
+
+	git checkout stuff^0 &&
+
+	set_fake_editor &&
+	FAKE_LINES="pick 1 reword 2" FAKE_COMMIT_MESSAGE="feature_b_reworded" \
+		git rebase -i -v master &&
+
+	test "$(git log -1 --format=%B)" = "feature_b_reworded" &&
+	test $(git rev-list --count HEAD) = 3
+'
+
+test_expect_success 'reword after a conflict preserves commit' '
+	test_when_finished "reset_rebase" &&
+
+	git checkout stuff^0 &&
+
+	set_fake_editor &&
+	test_must_fail env FAKE_LINES="reword 2" \
+		git rebase -i -v master &&
+
+	git checkout --theirs file-2 &&
+	git add file-2 &&
+	FAKE_COMMIT_MESSAGE="feature_b_reworded" git rebase --continue &&
+
+	test "$(git log -1 --format=%B)" = "feature_b_reworded" &&
+	test $(git rev-list --count HEAD) = 2
+'
+
+test_done
-- 
2.18.0.rc2.1.g5453d3f70b.dirty