revert: Remove sequencer state when no commits are pending

When cherry-pick or revert is called on a list of commits, and a
conflict encountered somewhere in the middle, the data in
".git/sequencer" is required to continue the operation.  However, when
a conflict is encountered in the very last commit, the user will have
to "continue" after resolving the conflict and committing just so that
the sequencer state is removed.  This is how the current "rebase -i"
script works as well.

  $ git cherry-pick foo..bar
  ... conflict encountered while picking "bar" ...
  $ echo "resolved" >problematicfile
  $ git add problematicfile
  $ git commit
  $ git cherry-pick --continue # This would be a no-op

Change this so that the sequencer state is cleared when a conflict is
encountered in the last commit.  Incidentally, this patch makes sure
that some existing tests don't break when features like "--reset" and
"--continue" are implemented later in the series.

A better way to implement this feature is to get the last "git commit"
to remove the sequencer state.  However, that requires tighter
coupling between "git commit" and the sequencer, a goal that can be
pursued once the sequencer is made more general.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -763,8 +763,18 @@ static int pick_commits(struct commit_list *todo_list, struct replay_opts *opts)
 	for (cur = todo_list; cur; cur = cur->next) {
 		save_todo(cur, opts);
 		res = do_pick_commit(cur->item, opts);
-		if (res)
+		if (res) {
+			if (!cur->next)
+				/*
+				 * An error was encountered while
+				 * picking the last commit; the
+				 * sequencer state is useless now --
+				 * the user simply needs to resolve
+				 * the conflict and commit
+				 */
+				remove_sequencer_state(0);
 			return res;
+		}
 	}
 
 	/*

t/t3510-cherry-pick-sequence.sh

@@ -82,4 +82,28 @@ test_expect_success '--reset cleans up sequencer state' '
 	test_path_is_missing .git/sequencer
 '
 
+test_expect_success 'cherry-pick cleans up sequencer state when one commit is left' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick base..picked &&
+	test_path_is_missing .git/sequencer &&
+	echo "resolved" >foo &&
+	git add foo &&
+	git commit &&
+	{
+		git rev-list HEAD |
+		git diff-tree --root --stdin |
+		sed "s/$_x40/OBJID/g"
+	} >actual &&
+	cat >expect <<-\EOF &&
+	OBJID
+	:100644 100644 OBJID OBJID M	foo
+	OBJID
+	:100644 100644 OBJID OBJID M	unrelated
+	OBJID
+	:000000 100644 OBJID OBJID A	foo
+	:000000 100644 OBJID OBJID A	unrelated
+	EOF
+	test_cmp expect actual
+'
+
 test_done