[RFC/PATCH 14/18] Add --index-only support for ff_only merges

[Elijah Newren <newren@gmail.com>]

From: Elijah Newren <newren@palantir.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 builtin/merge.c             | 1 +
 builtin/pull.c              | 4 ++--
 cache.h                     | 1 +
 merge.c                     | 4 +++-
 sequencer.c                 | 2 +-
 t/t6043-merge-index-only.sh | 6 +++---
 6 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index 5f463ad..b791702 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1443,6 +1443,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 		if (checkout_fast_forward(head_commit->object.oid.hash,
 					  commit->object.oid.hash,
+					  index_only,
 					  overwrite_ignore)) {
 			ret = 1;
 			goto done;
diff --git a/builtin/pull.c b/builtin/pull.c
index 10eff03..4f33a89 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -569,7 +569,7 @@ static int pull_into_void(const unsigned char *merge_head,
 	 * index/worktree changes that the user already made on the unborn
 	 * branch.
 	 */
-	if (checkout_fast_forward(EMPTY_TREE_SHA1_BIN, merge_head, 0))
+	if (checkout_fast_forward(EMPTY_TREE_SHA1_BIN, merge_head, 0, 0))
 		return 1;
 
 	if (update_ref("initial pull", "HEAD", merge_head, curr_head, 0, UPDATE_REFS_DIE_ON_ERR))
@@ -871,7 +871,7 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 			"fast-forwarding your working tree from\n"
 			"commit %s."), sha1_to_hex(orig_head));
 
-		if (checkout_fast_forward(orig_head, curr_head, 0))
+		if (checkout_fast_forward(orig_head, curr_head, 0, 0))
 			die(_("Cannot fast-forward your working tree.\n"
 				"After making sure that you saved anything precious from\n"
 				"$ git diff %s\n"
diff --git a/cache.h b/cache.h
index b829410..d51fcbc 100644
--- a/cache.h
+++ b/cache.h
@@ -1785,6 +1785,7 @@ int try_merge_command(const char *strategy, size_t xopts_nr,
 		const char *head_arg, struct commit_list *remotes);
 int checkout_fast_forward(const unsigned char *from,
 			  const unsigned char *to,
+			  int index_only,
 			  int overwrite_ignore);
 
 
diff --git a/merge.c b/merge.c
index 5db7d56..a40307c 100644
--- a/merge.c
+++ b/merge.c
@@ -46,6 +46,7 @@ int try_merge_command(const char *strategy, size_t xopts_nr,
 
 int checkout_fast_forward(const unsigned char *head,
 			  const unsigned char *remote,
+			  int index_only,
 			  int overwrite_ignore)
 {
 	struct tree *trees[MAX_UNPACK_TREES];
@@ -72,7 +73,8 @@ int checkout_fast_forward(const unsigned char *head,
 	opts.head_idx = 1;
 	opts.src_index = &the_index;
 	opts.dst_index = &the_index;
-	opts.update = 1;
+	opts.update = !index_only;
+	opts.index_only = index_only;
 	opts.verbose_update = 1;
 	opts.merge = 1;
 	opts.fn = twoway_merge;
diff --git a/sequencer.c b/sequencer.c
index e66f2fe..1b772fb 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -222,7 +222,7 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 	struct strbuf err = STRBUF_INIT;
 
 	read_cache();
-	if (checkout_fast_forward(from, to, 1))
+	if (checkout_fast_forward(from, to, 0, 1))
 		exit(128); /* the callee should have complained already */
 
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
diff --git a/t/t6043-merge-index-only.sh b/t/t6043-merge-index-only.sh
index f79782c..cb860f2 100755
--- a/t/t6043-merge-index-only.sh
+++ b/t/t6043-merge-index-only.sh
@@ -224,7 +224,7 @@ test_expect_success 'setup simple merges' '
 	test_tick && git commit -m E
 '
 
-test_expect_failure '--index-only ff update, non-bare' '
+test_expect_success '--index-only ff update, non-bare' '
 	git reset --hard &&
 	git checkout A^0 &&
 
@@ -235,7 +235,7 @@ test_expect_failure '--index-only ff update, non-bare' '
 	test ! -d subdir
 '
 
-test_expect_failure '--index-only ff update, bare' '
+test_expect_success '--index-only ff update, bare' '
 	git clone --bare . bare.clone &&
 	(cd bare.clone &&
 
@@ -250,7 +250,7 @@ test_expect_failure '--index-only ff update, bare' '
 	)
 '
 
-test_expect_failure '--index-only ff update, non-bare with uncommitted changes' '
+test_expect_success '--index-only ff update, non-bare with uncommitted changes' '
 	git clean -fdx &&
 	git reset --hard &&
 	git checkout A^0 &&
-- 
2.8.0.18.gc685494