[PATCH V2] git-apply: silence errors for success cases

[Jerry Zhang <jerry@skydio.com>]

Certain invocations of "git apply --3way"
will print error messages even though git
is able to fall back on apply_fragments and
apply the patch successfully with a return
value of 0. To fix, return early from
try_threeway() in the following cases:

When the patch is a rename and no lines have
changed. In this case, "git diff" doesn't
record the blob info, so 3way is neither
possible nor necessary.

When the patch is an addition and there is
no add/add conflict, i.e. direct_to_threeway
is false. In this case, threeway will fail
since the preimage is not in cache, but isn't
necessary anyway since there is no conflict.

Only error messaging is affected and other
behavior does not change.

Signed-off-by: Jerry Zhang <jerry@skydio.com>
---
V1->V2: rebase onto master and rerun tests

I think I addressed previous comments. What
are the next steps for this patch?

 apply.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/apply.c b/apply.c
index 44bc31d6eb..fb321c707b 100644
--- a/apply.c
+++ b/apply.c
@@ -3560,7 +3560,9 @@ static int try_threeway(struct apply_state *state,
 
 	/* No point falling back to 3-way merge in these cases */
 	if (patch->is_delete ||
-	    S_ISGITLINK(patch->old_mode) || S_ISGITLINK(patch->new_mode))
+	    S_ISGITLINK(patch->old_mode) || S_ISGITLINK(patch->new_mode) ||
+	    (patch->is_new && !patch->direct_to_threeway) ||
+	    (patch->is_rename && !patch->lines_added && !patch->lines_deleted))
 		return -1;
 
 	/* Preimage the patch was prepared for */
-- 
2.32.0.1314.g6ed4fcc4cc