[PATCH] merge-tree: sometimes, d/f conflict is not an issue

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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When a merge has a d/f conflict on a path which was not touched
between the merge base(s) and the remote HEAD, and the index and
HEAD contain the same version for that path (even if empty), it
is not really a conflict.

Noticed by Rémi Vanicat, reported to the Git list by Gerrit Pape.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	The only peculiar result is that you can have an entry at
	stage 0 for one path, and stages 1 and 3 for another path
	where the first path is a prefix.

	This can happen now, when you have deleted a directory
	since the branching point, and put a file in the same place, but
	the other side has changed files in that directory.

	This change is reflected in the change to t3030.

	I have no idea if the change is the best there is, but after
	spending some hours trying to get my head around what is written
	in Documentation/technical/trivial-merge.txt, and what is in
	the function threeway_merge(), and still not understanding most of 
	it, there is not much more that I can do.

	Funny note at the side: when I finally got to Gerrit's email again
	today, gmane said _almost_ that it was 3 weeks, 3 days, 3 hours
	and 3 minutes ago...

 t/t3030-merge-recursive.sh |    2 +-
 t/t3502-cherry-pick.sh     |   31 +++++++++++++++++++++++++++++++
 unpack-trees.c             |   14 ++++++++++++++
 3 files changed, 46 insertions(+), 1 deletions(-)
 create mode 100755 t/t3502-cherry-pick.sh

diff --git a/t/t3030-merge-recursive.sh b/t/t3030-merge-recursive.sh
index 607f57f..d413af1 100755
--- a/t/t3030-merge-recursive.sh
+++ b/t/t3030-merge-recursive.sh
@@ -450,7 +450,7 @@ test_expect_success 'merge-recursive d/f conflict result' '
 		echo "100644 $o1 0	a"
 		echo "100644 $o0 0	b"
 		echo "100644 $o0 0	c"
-		echo "100644 $o6 2	d"
+		echo "100644 $o6 0	d"
 		echo "100644 $o0 1	d/e"
 		echo "100644 $o1 3	d/e"
 	) >expected &&
diff --git a/t/t3502-cherry-pick.sh b/t/t3502-cherry-pick.sh
new file mode 100755
index 0000000..da3d26e
--- /dev/null
+++ b/t/t3502-cherry-pick.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+
+test_description='test cherry-pick'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo foo > file &&
+	ln -s dangling link &&
+	git add file link &&
+	test_tick &&
+	git commit -m foo &&
+	git checkout -b branch &&
+	git rm link &&
+	test_tick &&
+	git commit -m "remove link" &&
+	mkdir link &&
+	echo bar > link/file &&
+	git add link/file &&
+	test_tick &&
+	git commit -m "add dir" &&
+	echo bar > file &&
+	git commit -m "change file" file &&
+	git checkout master
+'
+
+test_expect_success 'cherry-pick ignores unrelated dir/symlink conflict' '
+	git cherry-pick branch
+'
+
+test_done
diff --git a/unpack-trees.c b/unpack-trees.c
index cac2411..080b016 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -643,6 +643,20 @@ int threeway_merge(struct cache_entry **stages,
 	index = stages[0];
 	head = stages[o->head_idx];
 
+	/*
+	 * Special case: do not care about a dir/file conflict, when
+	 * the entries have not been touched.
+	 * IOW if the ancestors are identical to the remote, and the
+	 * index is the same as head, just take head.
+	 */
+	if (head && same(index, head)) {
+		for (i = 1; i < o->head_idx; i++)
+			if (!same(stages[i], remote))
+				break;
+		if (i == o->head_idx)
+			return merged_entry(head, index, o);
+	}
+
 	if (head == o->df_conflict_entry) {
 		df_conflict_head = 1;
 		head = NULL;
-- 
1.5.3.rc0.2712.g125b7f